Showing posts with label Reculver. Show all posts
Showing posts with label Reculver. Show all posts
Saturday, 4 November 2017
Tuesday, 8 November 2016
Reculver getting chilly
8 female Common Scoter, Melanitta nigra, were initially pointed out to me flying and then mixing with Wigeon. You can spot them quite easily from a distance by picking out their pale faces, which Velvet and Surf just don't have. I rather thought that they had slightly paler bellies as well, which might, or might not, indicate that they might have been first winter birds.
I hadn't realised that a few Common Scoter actually breed in Scotland and Ireland, on inland lakes as indeed they do elsewhere. In Scotland it tends to be quite variably sized lochs in the North and West, particularly in the Flow Country in Caithness and Sutherland. It is possible that they didn't breed in Scotland much before the mid 1800s. In 1995 there were about 100 pairs in Ireland and 100 pairs in Scotland, down slightly from the 70s. However, the main breeding range of the nominate race, nigra, is across the Arctic Ocean coastlands of Northern Europe and Russia, with the other, americana, race further to the east, and across towards Alaska. It is quite possible of course that subspecies americana is actually a separate species, recognisable by differences in call/song - some US research is treating it as such, and the division has been accepted by the BOU since the mid-noughties.
Threats might include eutrophication, competition for food, or predation by mink (encouraged by conifer planting in Scotland perhaps). A study in Scotland, triggered by a post-1995 more than halving of the population, indicated that lakes with shallow water around the edges, containing larger invertebrates, with more Three-Spined Sticklebacks but fewer Brown Trout, held significantly more birds. It was suggested that the water levels in hydro-electric lakes could be lowered, and also that perhaps more fishing in trout lakes could be encouraged! Many small trout might be worse than a few large ones.
Age of first breeding is 2 - 3 years. There is a monogamous pair-bond for the season, which may start in the winter flocks, with increasing pairing on the breeding grounds. The nests are usually built by the female, concealed close to the water's edge. It is hollow, lined with grass, moss, lichen and down. The male tends to defend the female wherever she may be. Egg-laying date is determined by timing of the arctic thaw, 6 - 8 eggs laid at 1-2 day intervals. Incubation is for almost exactly a month, with the eggs covered by down if the female leaves the nest. Hatching is quite synchronous. However, the male often deserts the female soon after the start of incubation, and the female then tends the young until they fledge - broods may sometimes be amalgamated. The young are nidifugous and precocial. They are generally self-feeding, but cared for and brooded at night by the female while still young. They fledge after roughly 45 - 50 days.
Common Scoters tend to over-winter in large flocks, hundreds or even thousands. Around the UK the winter population is about 100,000 with main concentrations in Carmarthen and Cardigan Bays, the Moray Firth and the North Norfolk coast. A previously unknown concentration on Shell Flat in the Irish Sea off the NorthWest coast was discovered by aerial survey in preparation for proposed windfarms. Most of the over-wintering birds generally stay between October and March. Males tend to concentrate more in the north, females and immatures apparently have to fly further south. After breeding, the birds move to moulting areas, for example Northern European and Russian birds moving into the Baltic. Then they move on to the over-wintering areas, for example the North Sea and the coasts of Britain. Numbers in the Waddensee appear to have dropped from about 40,000 in the 1960s, to about 1,000 now - but could this be due to migration shortening? The East Siberian/American race by contrast over-winters along the coasts of North America. The return journey was also studied in Surf Scoters on the west coast of North America. Data from birds tracked over 2 years indicated strong migration route fidelity, but altered chronology and stopover locations between years. Departure date varied by wintering site, but arrival and apparent settling dates were synchronous, suggesting individuals adjusted migration timing to meet an optimized reproductive schedule. Canadian research showed a positive correlation between longer snow cover and population size in Scoter species, indicating that climatic warming might reduce survival - but how were populations measured?
The Common Scoter feeds on shellfish obtained by diving, generally in daylight, from smaller groups, occasionally group-diving. Other birds or even fish such as introduced Perch on inland waters may compete with the Scoters for food. They may loaf from time to time during the day, and roost at night. A wide range of molluscs are taken such as mussels, cockles, clams, whelks, etc. Also some crustacea and tube-worms. There was strong evidence (Bangor University) that the maximum observed biomass of bivalves occurred at a mean depth of c. 14 m off the Lancashire coast and at c. 8 m off the north Wales coast. This coincided well with the distribution of Common Scoter at Shell Flat, but less well with the distribution of birds off North Wales. In Holland, research indicated that a decline in the bivalve Spisula was perhaps linked to the long-term decline in Common Scoter.
There is a lot of data on the Common Scoters in the Solway Firth - in British Birds here.
Foraging behaviour can be varied. One Canadian paper stated that the distribution of predators is widely recognized to be intimately linked to the distribution of their prey. Foraging theory suggests that predators will modify their behaviors, including movements, to optimize net energy intake when faced with variation in prey attributes or abundance. While many studies have documented changes in movement patterns of animals in response to temporal changes in food, very few have contrasted movements of a single predator species naturally occurring in dramatically different prey landscapes. We documented variation in the winter movements, foraging range size, site fidelity, and distribution patterns of a molluscivorous sea duck, the Surf Scoter (Melanitta perspicillata), in two areas of coastal British Columbia with very different shellfish prey features. Baynes Sound has extensive tidal flats with abundant clams, which are high-quality and temporally stable prey for Scoters. Malaspina Inlet is a rocky fjord-like inlet where Scoters consume mussels that are superabundant and easily accessible in some patches but are heavily depleted over the course of winter. We used radio telemetry to track surf scoter movements in both areas and found that in the clam habitats of Baynes Sound, Surf Scoters exhibited limited movement, small winter ranges, strong foraging site fidelity, and very consistent distribution patterns. By contrast, in mussel habitats in the Malaspina Inlet, Surf Scoters displayed more movement, larger ranges, little fidelity to specific foraging sites, and more variable distribution patterns. We conclude that features associated with the different prey types, particularly the higher depletion rates of mussels, strongly influenced seasonal space use patterns. These findings are consistent with foraging theory and confirm that predator behavior, specifically movements, is environmentally mediated.
Heavy shipping appeared to negatively impact on Scoter distribution in Canadian research. Off-shore wind-farms could perhaps impact either positively or negatively. On the other hand tanker spills definitely have impact: After the Sea Empress oil spill in Carmarthen Bay, numbers crashed for the next three years, but then recovered to the level of the previous population. The NAO appeared to impact upon distribution of Scoters of the east coast of North America. On the other hand, off-bottom oyster culture structures offered opportunities for mussels to settle in large numbers, and thereby increase feeding opportunities for Scoters, and its benefits have been demonstrated to increase habitat choice off British Columbia.
In a study of Surf Scoter diving activity in Canada, variation in both hourly and daily foraging efforts was best explained by date only, as opposed to substrate nature. Effort per hour was lowest in early December (presumably owing to very high prey abundance), increased until mid-February as prey declined, and then decreased again in March (probably owing to increased daylight time for foraging). Foraging effort estimated over a full day increased steadily from December to March as prey were depleted. Temporal patterns of effort did not vary by habitat (commercial mussel beds with easy to access shellfish, rapidly depleted upon harvest) after accounting for seasonal effects. Instead of increasing foraging effort in habitats with strong depletion, Surf Scoters redistributed to habitats with lower degrees of prey reduction as the season progressed. We suggest that Surf Scoters respond to variation in prey by adjusting both foraging effort and habitat selection as the prey landscape changes.
The duckling diet is quite varied, including insects and seeds. Looking at correlates of distribution of other species of Boreal waterbirds such as White-winged Scoter, Scaup and a Grebe, the presence of amphipods in larger lakes (>25 Ha) appeared to be the main interaction promoting occupancy and nest building.
It is thought that gluco-corticoids may influence weight gain, activity and breeding status. But what controls the gluco-corticoids?
Aggressive behaviour: Males may dash at each other (skating) with neck outstretched. Actual violent combat rare.
There is also a head-shake.
Several groups of Dark-bellied Brent Geese, including about 65 in one larger group gathered just off-shore in the gloom as I walked back.
I hadn't realised that a few Common Scoter actually breed in Scotland and Ireland, on inland lakes as indeed they do elsewhere. In Scotland it tends to be quite variably sized lochs in the North and West, particularly in the Flow Country in Caithness and Sutherland. It is possible that they didn't breed in Scotland much before the mid 1800s. In 1995 there were about 100 pairs in Ireland and 100 pairs in Scotland, down slightly from the 70s. However, the main breeding range of the nominate race, nigra, is across the Arctic Ocean coastlands of Northern Europe and Russia, with the other, americana, race further to the east, and across towards Alaska. It is quite possible of course that subspecies americana is actually a separate species, recognisable by differences in call/song - some US research is treating it as such, and the division has been accepted by the BOU since the mid-noughties.
Threats might include eutrophication, competition for food, or predation by mink (encouraged by conifer planting in Scotland perhaps). A study in Scotland, triggered by a post-1995 more than halving of the population, indicated that lakes with shallow water around the edges, containing larger invertebrates, with more Three-Spined Sticklebacks but fewer Brown Trout, held significantly more birds. It was suggested that the water levels in hydro-electric lakes could be lowered, and also that perhaps more fishing in trout lakes could be encouraged! Many small trout might be worse than a few large ones.
Age of first breeding is 2 - 3 years. There is a monogamous pair-bond for the season, which may start in the winter flocks, with increasing pairing on the breeding grounds. The nests are usually built by the female, concealed close to the water's edge. It is hollow, lined with grass, moss, lichen and down. The male tends to defend the female wherever she may be. Egg-laying date is determined by timing of the arctic thaw, 6 - 8 eggs laid at 1-2 day intervals. Incubation is for almost exactly a month, with the eggs covered by down if the female leaves the nest. Hatching is quite synchronous. However, the male often deserts the female soon after the start of incubation, and the female then tends the young until they fledge - broods may sometimes be amalgamated. The young are nidifugous and precocial. They are generally self-feeding, but cared for and brooded at night by the female while still young. They fledge after roughly 45 - 50 days.
Common Scoters tend to over-winter in large flocks, hundreds or even thousands. Around the UK the winter population is about 100,000 with main concentrations in Carmarthen and Cardigan Bays, the Moray Firth and the North Norfolk coast. A previously unknown concentration on Shell Flat in the Irish Sea off the NorthWest coast was discovered by aerial survey in preparation for proposed windfarms. Most of the over-wintering birds generally stay between October and March. Males tend to concentrate more in the north, females and immatures apparently have to fly further south. After breeding, the birds move to moulting areas, for example Northern European and Russian birds moving into the Baltic. Then they move on to the over-wintering areas, for example the North Sea and the coasts of Britain. Numbers in the Waddensee appear to have dropped from about 40,000 in the 1960s, to about 1,000 now - but could this be due to migration shortening? The East Siberian/American race by contrast over-winters along the coasts of North America. The return journey was also studied in Surf Scoters on the west coast of North America. Data from birds tracked over 2 years indicated strong migration route fidelity, but altered chronology and stopover locations between years. Departure date varied by wintering site, but arrival and apparent settling dates were synchronous, suggesting individuals adjusted migration timing to meet an optimized reproductive schedule. Canadian research showed a positive correlation between longer snow cover and population size in Scoter species, indicating that climatic warming might reduce survival - but how were populations measured?
The Common Scoter feeds on shellfish obtained by diving, generally in daylight, from smaller groups, occasionally group-diving. Other birds or even fish such as introduced Perch on inland waters may compete with the Scoters for food. They may loaf from time to time during the day, and roost at night. A wide range of molluscs are taken such as mussels, cockles, clams, whelks, etc. Also some crustacea and tube-worms. There was strong evidence (Bangor University) that the maximum observed biomass of bivalves occurred at a mean depth of c. 14 m off the Lancashire coast and at c. 8 m off the north Wales coast. This coincided well with the distribution of Common Scoter at Shell Flat, but less well with the distribution of birds off North Wales. In Holland, research indicated that a decline in the bivalve Spisula was perhaps linked to the long-term decline in Common Scoter.
There is a lot of data on the Common Scoters in the Solway Firth - in British Birds here.
Foraging behaviour can be varied. One Canadian paper stated that the distribution of predators is widely recognized to be intimately linked to the distribution of their prey. Foraging theory suggests that predators will modify their behaviors, including movements, to optimize net energy intake when faced with variation in prey attributes or abundance. While many studies have documented changes in movement patterns of animals in response to temporal changes in food, very few have contrasted movements of a single predator species naturally occurring in dramatically different prey landscapes. We documented variation in the winter movements, foraging range size, site fidelity, and distribution patterns of a molluscivorous sea duck, the Surf Scoter (Melanitta perspicillata), in two areas of coastal British Columbia with very different shellfish prey features. Baynes Sound has extensive tidal flats with abundant clams, which are high-quality and temporally stable prey for Scoters. Malaspina Inlet is a rocky fjord-like inlet where Scoters consume mussels that are superabundant and easily accessible in some patches but are heavily depleted over the course of winter. We used radio telemetry to track surf scoter movements in both areas and found that in the clam habitats of Baynes Sound, Surf Scoters exhibited limited movement, small winter ranges, strong foraging site fidelity, and very consistent distribution patterns. By contrast, in mussel habitats in the Malaspina Inlet, Surf Scoters displayed more movement, larger ranges, little fidelity to specific foraging sites, and more variable distribution patterns. We conclude that features associated with the different prey types, particularly the higher depletion rates of mussels, strongly influenced seasonal space use patterns. These findings are consistent with foraging theory and confirm that predator behavior, specifically movements, is environmentally mediated.
Heavy shipping appeared to negatively impact on Scoter distribution in Canadian research. Off-shore wind-farms could perhaps impact either positively or negatively. On the other hand tanker spills definitely have impact: After the Sea Empress oil spill in Carmarthen Bay, numbers crashed for the next three years, but then recovered to the level of the previous population. The NAO appeared to impact upon distribution of Scoters of the east coast of North America. On the other hand, off-bottom oyster culture structures offered opportunities for mussels to settle in large numbers, and thereby increase feeding opportunities for Scoters, and its benefits have been demonstrated to increase habitat choice off British Columbia.
In a study of Surf Scoter diving activity in Canada, variation in both hourly and daily foraging efforts was best explained by date only, as opposed to substrate nature. Effort per hour was lowest in early December (presumably owing to very high prey abundance), increased until mid-February as prey declined, and then decreased again in March (probably owing to increased daylight time for foraging). Foraging effort estimated over a full day increased steadily from December to March as prey were depleted. Temporal patterns of effort did not vary by habitat (commercial mussel beds with easy to access shellfish, rapidly depleted upon harvest) after accounting for seasonal effects. Instead of increasing foraging effort in habitats with strong depletion, Surf Scoters redistributed to habitats with lower degrees of prey reduction as the season progressed. We suggest that Surf Scoters respond to variation in prey by adjusting both foraging effort and habitat selection as the prey landscape changes.
The duckling diet is quite varied, including insects and seeds. Looking at correlates of distribution of other species of Boreal waterbirds such as White-winged Scoter, Scaup and a Grebe, the presence of amphipods in larger lakes (>25 Ha) appeared to be the main interaction promoting occupancy and nest building.
It is thought that gluco-corticoids may influence weight gain, activity and breeding status. But what controls the gluco-corticoids?
Aggressive behaviour: Males may dash at each other (skating) with neck outstretched. Actual violent combat rare.
There is also a head-shake.
Several groups of Dark-bellied Brent Geese, including about 65 in one larger group gathered just off-shore in the gloom as I walked back.
Sunday, 16 October 2016
Robin on the rocks at Reculver
As usual there were House Sparrows to be found at the car park and around the Towers.
There was a Robin on the rocks just beyond the Towers as I went East and I saw it again when I returned, presumably the same one.
Five or more Pied Wagtails on the grass, counted no return.
Six or more Meadow Pipit in a small flock.
Flock of Turnstones and a few Ringed Plover on the way out, and counted about twenty Turnstone but only two Ringed Plover by one of the groynes on return. The waders were joined by a Grey Plover when last seen.
Seven plus Little Egret, up to five in view at any one time on the "paddle-wheels", and then one roosting on the larger conifer by the seafood farm as I returned.
Eight Redshank on the of the farm pools on the way out, with two more at Coldharbour Lagoon.
Overall hundreds of Black-headed Gulls around today, on the sea, in the fields or up in the air, together with many Herring Gulls and several Common Gulls, Larus canus.
Three or more cormorants, diving on the sea or flyovers.
At least one, probably two Stock Doves in the stubble with the Gulls.
Four Mute Swans, in two pairs, on fields and flying.
Ninety three or more Wigeon in one large raft on the sea, over a score of Mallard at Colharbour, and on the sea.
One Marsh Harrier being mobbed by the Carrion Crows, and then one female Kestrel along the seawall ditch, hunting briefly, on the way back.
A passing lady cyclist reported a possible Short-Eared Owl being harried by crows and going down at the seafood farm.
There was a Robin on the rocks just beyond the Towers as I went East and I saw it again when I returned, presumably the same one.
Five or more Pied Wagtails on the grass, counted no return.
Six or more Meadow Pipit in a small flock.
Flock of Turnstones and a few Ringed Plover on the way out, and counted about twenty Turnstone but only two Ringed Plover by one of the groynes on return. The waders were joined by a Grey Plover when last seen.
Seven plus Little Egret, up to five in view at any one time on the "paddle-wheels", and then one roosting on the larger conifer by the seafood farm as I returned.
Eight Redshank on the of the farm pools on the way out, with two more at Coldharbour Lagoon.
Overall hundreds of Black-headed Gulls around today, on the sea, in the fields or up in the air, together with many Herring Gulls and several Common Gulls, Larus canus.
Three or more cormorants, diving on the sea or flyovers.
At least one, probably two Stock Doves in the stubble with the Gulls.
Four Mute Swans, in two pairs, on fields and flying.
Ninety three or more Wigeon in one large raft on the sea, over a score of Mallard at Colharbour, and on the sea.
One Marsh Harrier being mobbed by the Carrion Crows, and then one female Kestrel along the seawall ditch, hunting briefly, on the way back.
A passing lady cyclist reported a possible Short-Eared Owl being harried by crows and going down at the seafood farm.
Friday, 23 September 2016
Reculver
Two Wheatears, three Mute Swans, half a dozen Redshank, Black-headed Gulls, Herring Gulls, three Little Egret, a juvenile Pied Wagtail, a Meadow Pipit, several Reed Buntings, and I also found at least one very neat Common Sandpiper at the lagoon.
On the sea was a raft of Mallard, a pair of Gadwall and a few Teal.
There were a few Golden Plover, one Dunlin and a few Ringed Plover with about 35 gorgeous Sanderling on the shore on the return walk. This one still has a couple of summer feathers showing.
This one is slightly further back in the moult process.
Saturday, 30 April 2016
Wryneck weirdness!
Had a lovely walk down to Reculver Marshes this afternoon - slow and concentrating on bird ID. over the railway line a kindly birder walked me back to where the Wreyneck was - its so easy when someone points a bird out to you!
The Wryneck is a really weird looking bird. Its colouration is all odd - the spots and streaks remind me of dazzle camouflage from WW I.
House Sparrows. Pied Wagtail. 10+ Swallows flying out to sea and along the coast. Also 14 Turnstone, some in breeding plumage, 7 Cormorants, Herring Gulls, 1 Black-headed Gull, 5 Oystercatchers. 7 Sedge Warblers, 2 or more Reed Warblers, 3+ Whitethroats, 5 Blackbirds, 3 Robins. 1 Little Egret, 2 Redshanks, 17 Mute Swan. most in one group.
The Wryneck is a really weird looking bird. Its colouration is all odd - the spots and streaks remind me of dazzle camouflage from WW I.
House Sparrows. Pied Wagtail. 10+ Swallows flying out to sea and along the coast. Also 14 Turnstone, some in breeding plumage, 7 Cormorants, Herring Gulls, 1 Black-headed Gull, 5 Oystercatchers. 7 Sedge Warblers, 2 or more Reed Warblers, 3+ Whitethroats, 5 Blackbirds, 3 Robins. 1 Little Egret, 2 Redshanks, 17 Mute Swan. most in one group.
Monday, 4 April 2016
Reculver
Wonderful afternoon, starting with a Black Redstart, followed by Swallows, a Knot and finally a couple of beautiful male Wheatears.
This is the Knot, the first time I have been really sure of seeing one. Nice combination of a shortish black bill and greenish (although I would have said yellowish-greenish) very grey overall, with the barred rump visible between the wings (rather more marked than I had imagined). The wing feathers were not scalloped as in a juvenile, but maybe there are no juvenile plumages left by this time of year anyway. The eye-stripe was obvious through the telescope. The breast markings were small elongated spots, with a few chevron marking below the wings towards the rear.
Why was this bird on its own? It was feeding by dipping its bill into the water very rapidly, quite close to the shore. This is described in BWP as pecking, "to be found 2 hours either side of high tide on sand on the upper shore" and is much more rapid (about once a second) than the normal probing down on the estuary mud.
Sunday, 20 December 2015
Reculver, warm but breezy with a little windchill
It was nice to get back to Reculver today and we were blessed with an open sky and drier conditions. Great to see a Grey Plover, Pluvialis squatarola, together with Oystercatchers and Gulls on the rocky foreshore by Coldharbour.
I identified it as a Grey Plover by its eyespot, overall bulkiness, lack of colour, and the fact that it was solitary - I have only seen Golden Plovers in large flocks over the winter, and never seen birds on their own. The Grey Plovers have travelled further to get to these wintering grounds, generally nesting up towards the Arctic Circle, on tundra beyond the tree limit. A nearly cosmopolitan bird it is known as the black-bellied plover in America. Russian birds get as far as Australia and South Africa, Alaskan birds get as far as Central America.
In winter feeds as much by night as by day, perhaps defending feeding territories and maybe not the most highly mobile wader species on its wintering grounds.
The adults generally leave the breeding grounds, generally non-coastal wet tundra from July to September, and the juveniles follow September to mid-October. When they arrive they tend to end up on beaches by the winter - although I have seen them at Cliffe and Oare Marshes in good numbers earlier in the autumn, presumably birds still moving through on passage. Northward return passage peaks in May and breeding should start in May and June. In Europe this appears to be primarily coastal, with few birds crossing continental Russia, but in America migration may be more continental as birds appear to be able to use the Mississippi Valley as one return route. Young birds however may stay southerly for the first year, presumably moulting into breeding plumage.
There was an interesting piece of research from the Sivash lagoons near the Black Sea indicating that waders may be more limited in feeding opportunities by salinity, wind speed, direction and tide state than might initially appear to the human researchers. The organisms accessibility is often limited by their vertical distribution in the sediments themselves, the worms being highly mobile.
Australian summaries indicated that during the non-breeding season, Grey Plovers mostly eat molluscs (especially gastropods), insects and their larvae, crustaceans (especially crabs) and polychaete worms. Vegetation is very occasionally found in their stomachs. During the breeding season, they eat mostly insects, but may occasionally eat vegetation. The Grey Plover usually forages during the day, but sometimes also feeds at night, when up to 40% of food may be obtained. They usually locate prey by sight, with cues used including movement of water, sand or casts from the burrows of polychaete worms. They feed with a running, stopping and pecking action typical of many species of plovers, gleaning and probing the substrate. Bivalves are seized by the siphon and torn from the shell, while crabs are pecked apart. Main prey in French research on wintering grounds indicated main prey items of benthic worms such as Nereis diversicolor or Nepthys hombergii. However I often see them just standing about, and not appearing to feed very much at all, so maybe they are not all that desperate? This was true of the half dozen birds I saw on the 30th December at Reculver last Christmas. However, maybe I need to look more closely as well!
Prey items include Fiddler Crabs, Uca spp. In one study of feeding on these in Argentina this species fed in a similar way to American Golden Plovers, but waiting longer than that species until they ran at the crabs. Several times they waited until crabs surfaced, capturing crabs very close to their standing position (n = 15). Crabs were always eaten entirely. The selectivity index showed that females were the preferred prey, while unidentified items and males were attacked at much lower proportion than their availablity. This species was the only species that defended its territories by singing displays and chasing other conspecifics or American golden plovers when their feeding area was approached. American golden plover had a cyclical use of the crab bed and the nearby intertidal, spending a variable time (range: 3-9 rain) in the Uca bed, moving to the lower intertidal, and then returning to the Uca bed "after a similar amount of time (range: 6-10 rain). It was unclear from the paper whether the Grey Plover shared this habit.
I identified it as a Grey Plover by its eyespot, overall bulkiness, lack of colour, and the fact that it was solitary - I have only seen Golden Plovers in large flocks over the winter, and never seen birds on their own. The Grey Plovers have travelled further to get to these wintering grounds, generally nesting up towards the Arctic Circle, on tundra beyond the tree limit. A nearly cosmopolitan bird it is known as the black-bellied plover in America. Russian birds get as far as Australia and South Africa, Alaskan birds get as far as Central America.
In winter feeds as much by night as by day, perhaps defending feeding territories and maybe not the most highly mobile wader species on its wintering grounds.
The adults generally leave the breeding grounds, generally non-coastal wet tundra from July to September, and the juveniles follow September to mid-October. When they arrive they tend to end up on beaches by the winter - although I have seen them at Cliffe and Oare Marshes in good numbers earlier in the autumn, presumably birds still moving through on passage. Northward return passage peaks in May and breeding should start in May and June. In Europe this appears to be primarily coastal, with few birds crossing continental Russia, but in America migration may be more continental as birds appear to be able to use the Mississippi Valley as one return route. Young birds however may stay southerly for the first year, presumably moulting into breeding plumage.
There was an interesting piece of research from the Sivash lagoons near the Black Sea indicating that waders may be more limited in feeding opportunities by salinity, wind speed, direction and tide state than might initially appear to the human researchers. The organisms accessibility is often limited by their vertical distribution in the sediments themselves, the worms being highly mobile.
Australian summaries indicated that during the non-breeding season, Grey Plovers mostly eat molluscs (especially gastropods), insects and their larvae, crustaceans (especially crabs) and polychaete worms. Vegetation is very occasionally found in their stomachs. During the breeding season, they eat mostly insects, but may occasionally eat vegetation. The Grey Plover usually forages during the day, but sometimes also feeds at night, when up to 40% of food may be obtained. They usually locate prey by sight, with cues used including movement of water, sand or casts from the burrows of polychaete worms. They feed with a running, stopping and pecking action typical of many species of plovers, gleaning and probing the substrate. Bivalves are seized by the siphon and torn from the shell, while crabs are pecked apart. Main prey in French research on wintering grounds indicated main prey items of benthic worms such as Nereis diversicolor or Nepthys hombergii. However I often see them just standing about, and not appearing to feed very much at all, so maybe they are not all that desperate? This was true of the half dozen birds I saw on the 30th December at Reculver last Christmas. However, maybe I need to look more closely as well!
Prey items include Fiddler Crabs, Uca spp. In one study of feeding on these in Argentina this species fed in a similar way to American Golden Plovers, but waiting longer than that species until they ran at the crabs. Several times they waited until crabs surfaced, capturing crabs very close to their standing position (n = 15). Crabs were always eaten entirely. The selectivity index showed that females were the preferred prey, while unidentified items and males were attacked at much lower proportion than their availablity. This species was the only species that defended its territories by singing displays and chasing other conspecifics or American golden plovers when their feeding area was approached. American golden plover had a cyclical use of the crab bed and the nearby intertidal, spending a variable time (range: 3-9 rain) in the Uca bed, moving to the lower intertidal, and then returning to the Uca bed "after a similar amount of time (range: 6-10 rain). It was unclear from the paper whether the Grey Plover shared this habit.
Saturday, 24 January 2015
Reculver in a Force Five
Great sight of the Dark-bellied Brents flying past out to sea, they are such wonderful animals.
The second bird here MIGHT be a first year, just getting a white v-shaped collar, but still (maybe) with the whitish barring on the flanks.
Here is a link to an excellent video of a juvenile bird, taken in October 2011, before the white collar develops in mid winter. The white edges to the greater coverts seem very visible, and the generally browner tinges to the dark upper parts. https://www.youtube.com/watch?v=KhILLrcXo_w
Saturday, 17 January 2015
Icy Reculver and a Short-eared Owl
Definitely a frigid day at Reculver at the end of the afternoon (I only got back to the car just after 5 pm, proper dark), with a bit of a go with the 500 mm lens and the EOS350. Both Monty and I hoping to get back to our longer walks from now on - but will I get the marking done if I lose my marking focus??
A Short-eared Owl, Asio flammeus, flushed across the oyster marsh channels, was beautiful, very long-winged and ghostly. I saw the large pale grey-brown bird, with very long wings in comparison with its body, floating over the channels and banks, Maybe the second bird I have seen, I remember seeing Short-eared (I think) Owls with Phil down at Rye Harbour, many years ago.
In the first picture you can easily see the pale belly and underside behind the dark "head" region, one of the main characters that separates Short-eared from Long-eared (description applies to the nominate Eurasian race). Long-eared Owls have a dark belly, that continues on from the head, and contrasts clearly with the pale underside of the wings. There is also a hint of the possible yellow rather than orange eyes, but this is the one character that in the end I couldn't be at all sure of. In this picture the light caught the colour of the bird, turning it a warm biscuit colour.
In this next photo the colour is much less picked up by the last of the evening light. The barring of the tail is seen very clearly, and although this feature is found in both Short-eared and Long-eared Owls, it is more distinct in Short-Eared, as I think can be seen here. In this photo the dark tips to the wings are more or less as clear as the carpal marks, which should be right for Short-eared. In Long-eared the carpal marks are very clear and far more obvious than the wing-tips, which are also fairly clearly barred in Long-Eared, rather than dark-tipped, so to say.
The other thing you can see is the white trailing edge to the wing, which is another of the clear characters separating the two species. Also Long-tailed would be rare, although not impossible sight!
The distribution of the species is fairly world-wide, including Eurasia, North Africa, North and South America, various Caribbean Islands and even the Falklands and the Hawaiian Islands. Its apparently quite a wanderer, one of the most widely distributed birds in the world, although it hasn't reached Australia! It is Least Concern worldwide.
We don't really know how Short-eared Owls are doing as a breeding bird in the UK, but from BTO surveys there are thought to be maybe quite a few hundred or perhaps a few thousand pairs in Scotland and other areas where there is mixed moorland or young forestry plantations. Latest figures suggest about 600 - 2000 pairs. In Europe most observers seem to think that numbers are well down on previous decades and it is graded as Amber status. However it is a very difficult bird to estimate populations of, and there is a lot of uncertainty about the counts. This uncertainty is compounded by its very variable and irruptive population status, apparently very dependent upon vole numbers.
The migratory tendency may be linked to the population size in any particular year. Movements of up to 2000 km have been recorded, but UK birds are less migratory than their continental cousins.
The highest densities are found in areas of mixed rough grasslands and heather moors (marginal hill ground or ‘white moor’). A typical home range is around 200 hectares (~300 football pitches) and it seems that a variety of grassland types and heights within range is beneficial. However, territory sizes vary considerably, ranging from 40 to 875 hectares. Resident owls will defend winter territories of about 6 hectares. Winter communal roosts, occasionally of many birds, may occur.
Young conifer plantations can also be important habitats, though second and later rotation plantings may be less frequently used. (did this cause the apparent increase through to the 70s and subsequent decline? Lowland rough grassland, marshes and coastal sand dunes are also sometimes used for breeding though their use of these areas can be erratic (except on some of the western islands and Orkney). In Norfolk they tend to focus on Brown Rats. European birds use more agricultural habitats, and probably prey upon a different range of mammals.
Sexual maturity is attained within one year. It is a generally monogamous bird, with the males hovering and then swooping down (sky-dancing), perhaps wing-clapping, in front of a female in a courtship dance. Because it is a nomadic bird, site and mate fidelity from one year to another is likely to be low. Courtship may begin as early as February, but is later in higher latitudes.
The nest is on the ground, lined and camouflaged, with normally about 5 - 7(12) eggs. This makes the species unusual, as most owls nest up in trees, and generally do not make their own nests, taking over the nests made by others. Normally the females incubate, and are fed by the males. Chicks scatter from the nest 12-17 days after hatching to hide in the undergrowth, but cannot fly until 25 days or older. There is one brood a year (although replacement clutches are laid following predation) and the young fledge after about 4 weeks in total.
Hunting is mainly at night but often seen during the evening and the rest of the day, often low looking for voles and other small mammals. In the UK typical prey could be predominantly short-tailed vole, but these are absent on Orkney, so there the SEOs have adapted to eating the Common Vole. They will also predate upon birds, particularly waders and gulls/terns by the coast, passerines inland.
Using radio-telemetry, short-term cycles of activity, with a period of about 3 h, were detected in Orkney voles Microtus arvalis orcadensis and in one short-eared owl Asio flammeus, their principal predator. Visual observations showed that owls from four adjacent nests had similar activity patterns. These cycles tended to be synchronous both within and between the two species. Short-eared owls thus appeared to be foraging optimally by timing their hunting to coincide with peaks in vole activity, i.e. at times of maximum potential yield. The extent of diurnal activity in short-eared owls varied seasonally. Daytime activity was conspicuous for only a short period in spring and early summer. Otherwise owls were almost exclusively nocturnal. These seasonal changes in activity were probably a response to variations in vole diurnality, vole population size and daylength. Harassment and kleptoparasitism may have been additional influences that interacted with these seasonal factors to determine the extent of preferred nocturnal hunting. In addition, it is possible that the energetic constraints of breeding may force owls to hunt during daylight. Were males only to hunt at night then they may not be able to provide enough food for their mate and young at a time when nights are short and vole populations are only starting to increase.
They tend to be silent on the wintering grounds, but with occassional scratchy barking calls during the breeding season.
There are some wonderful videos on the BBC site, http://www.bbc.co.uk/nature/life/Short-eared_Owl#p0039c4y
There were a lot of Black-headed Gulls and Herring Gulls on the beach, exploring the wide sand exposed by the low tide.
Cormorants overflew regularly:
Tuesday, 30 December 2014
A very still but chilly Reculver
Half a dozen mute Swan, about 600 Dark-bellied Brent Geese, 2 little Grebe, 1 little Egret, about 50 Common (?) Gulls, a dozen Herring Gulls, a score of Black-headed Gulls, one Great Black-backed Gull, about 30 Cormorant, 6 Grey Plover, 2 Ringed Plover, 30+ Redshank, 2 Curlew, half a dozen Turnstone, a score of Oystercatchers, a score of Carrion Crows, a Magpie, a pair of Stonechat, 3 Blackbirds.
It was so nice the see the pair of Stonechat, with good views, I do always like to see "monogamous" birds. The male is perhaps the same one as I saw here on the 27th, 3 days ago, in a howling gale along the seawall but quite a bit further to the West. Plumage features for this male were all OK for hibernans, with a deep russet and widely-spread chest patch, not too extensive a white collar, and a fairly buffy rump. I could see white wing bars when either bird flew, but more obviously in the male. The pair were on the grassy islands and seaward borders of the Coldharbour Lagoon, and I saw the male first, mainly perching, occasionally descending to the ground and back again. The female was generally quite close, once only a few metres away. It was possibly using lower perches on average than the male, and I couldn't keep track of it as well as the male.
Then a few minutes later either the same pair or a new one were on the beach between the Coldharbour Lagoon and the Outfall, causing me some considerable confusion! I think the male was on a seaweedy breakwater first, then on the beach with the female, then on a line of boulders.
Saturday, 27 December 2014
Reculver in a howling gale - my first Stonechat there!
Very difficult to see anything in the high winds and driving spray off the sea.
One Kestrel hunting along the beach, half a dozen Turnstone off the waters edge, one Stonechat on the sea wall, half a dozen Redshank on the Oyster Farm pools and ditches, about a hundred Dark-bellied Brent Geese overhead, landing on the field just to the west of the Coldharbour Lagoon. Many Herring and Black-headed Gulls, several Common Gulls, Larus canus, one Great Black-backed Gull, four Shelduck on the sea.
Tuesday, 16 December 2014
Reculver on another lovely day, with Brent Geese
Black-headed and Herring Gulls, and one Oystercatcher with the Geese, with Cormorants out to sea. A Pied Wagtail and a Blackbird by St Mary's. I thought there was a Pipit along the wall by the Oyster Farm. At least a score of Linnets by Coldharbour, feeding on the bank by the bunded pools, together with half a dozen Redshank, both seen and heard, and two Black-headed Gulls.
I was moving fairly quickly, but thought I might also have seen a Stonechat behind Coldharbour, just from an impression of a shape, coupled with a perch high on a bush - weak evidence I know!
About 540 Dark-bellied Brent Geese on the fields and commuting to and from a gravel bank on the beach, lovely to see, and hear! Their almost grunting (the BBC suggests "gobbling") calls are surprisingly attractive and restful. BWP has them characteristically noisier on water, and indeed it was while they were on the sea, or flying from the sea that I heard them calling (BWP = hronk, hronk)! I also thought I saw one Pale-bellied Brent Goose, as regularly reported here, but it was difficult to be really sure. The birds were quite mobile, first disturbed from the field, and then moving in smaller groups backwards and forwards from the shingle bank by the Coldharbour outfall into the fields, including the one by the Green Bank. It was noteworthy that they flew quite low and in loose "brunches" or long "lines" rather than V-shaped skeins.
They lead lives that are so close to the edge. Average annual winter mortality in the UK is estimated to be about 15%, although a typical life span may be as long as 11 years, and the current BTO record being over 28 years old. On their long migration it is essential that they arrive on the breeding grounds in as good a condition as possible. On the breeding grounds they may first eat mosses and lichens, then turning to grass as it becomes more available. They need to have nutritional reserves to see them through problems such as any remaining snow and ice. It seems that individual birds that have better access to food within the flock, and therefore build up heavier body masses on the spring staging areas show better reproductive success. The females seem to get about half their energy for incubation from stored endogenous sources, the other half from intensive feeding episodes the length of which depend on the threat from weather, etc (Inger et al, 2008). It is suggested that an increase of body mass of one sixth on migration may lead to raising breeding success from 8% to 65%. However I think birds should not be too heavy before long distance flights, or they will have potential problems migrating.
Marine habitats seem to be greatly preferred by Brent Geese over terrestrial food sources for quality. Best food sources are Zostera spp., Eelgrass, Ulva sp, Sea Lettuce and Enteromorpha spp, The rationale is that these algae are easier to digest than the fibre-rich grass, particularly important in geese, which have rather inefficient digestive systems.
Increasingly as the migratory populations have grown over the years from the nadir of the '30s, (10 fold perhaps?), Brents are apparently being forced onto (or are turning to) farmland rather than the Zostera or Enteromorpha rich intertidal zone. This may in the longer run have impacts on the average reproductive success of the populations. I wasn't paying proper attention today or I would have been surer of their detailed behaviour. The little I did see suggested that the Brents at Reculver were perhaps feeding a bit while they were on the autumn sown cereal (wheat?) and definitely often interacting aggressively. While they were on the seashore, they didn't seem to be feeding, or indeed showing too much aggression to each other, but I should have been actively checking. The flock was fairly densely packed on the sea and I wouldn't have thought there was anything for them to eat where they were anyway, perhaps a little Enteromorpha. They seemed more to be having a bit of a "little seaside break".
Normal food sources start off with Zostera, Eel Grass. In early winter the Zostera spp. beds are relatively intact and the rhizome, in particular, provides an important food resource (Mathers et al. 1998). In late winter, however, the availability of Zostera spp. declines, as a result of foraging and senescence, and it is more patchily distributed. Presumably there is Zostera, Ulva or Enteromorpha somewhere around off Reculver or Minnis Bay?? Perhaps they spend most of their feeding time on the fields?
At this time of year the flocks may consist of mixed ages, including the yearlings, if any are present - again I didn't really look at the time! The first winter birds are similar to the adults, although the white neck markings are less conspicuous, the white tipped coverts of the juveniles are largely retained and there is rather less white edging to the flanks. In retrospect I think I did see the white-tipped coverts indicating first winter birds in a number of cases.
The social inequities will mean that the higher-ranked individuals get the better resources in a feeding flock. It seems that in the winter period at least, families with any number of juveniles dominate pairs, pairs dominate singletons, and males dominate females. Several of these characters correlate with breeding success, and may be difficult to disentangle. Another paper suggested that large families do control more feeding resources than small ones, leading to less cost to the increased parental investment, so that things balance out. However by springtime arrival on the breeding grounds, the yearlings will apparently have been excluded from the family and the more mature birds will have settled into their pairbonds again. The pairings give advantages to the females of the pair, as the males protect them from aggressive behaviour from the other birds, allowing the females longer to feed up. BWP also notes that the birds are monogamous and pair for life!
The behaviour of the birds on the Arctic breeding grounds is extremely interesting. Laying is quite synchronous over a wide area - but do young birds lay later than experienced ones? The sites chosen will generally be on the drier hummocks to avoid melt flooding, perhaps on islands. The nests shaped like shallow bowls are about 30 cm. across, the internal bowl about 6 cm deep, of about 20 cm. diameter. They may be roughly 25 m. apart. Both sexes build the nest, using nearby materials, lining the nest with moss and grass, and covering with a fair amount of down. Incubation starts when the last egg is laid, leading to synchronous hatching. The nests may be re-used from year to year. Breeding success ranges are the most variable of all Arctic Geese, as calculated by the numbers of yearlings in winter flocks in the UK ranging from 1% to 45%. Up to 4 eggs are laid, generally only in one batch.
Like most, but not all, Arctic geese, the females have to eat as well as incubate. They cover the eggs with down and then move off the nest to feed, pecking virtually continuously and quite close to the nest, thus maximising food intake. The males do not incubate, but take on a protective role, against predators and conspecifics, being relatively more alert while the female is feeding, and feeding relatively more while the female is incubating. Once the chicks are hatched, both parents remain protective, although they do not need to feed the young as the chicks are precocial, nidifugous and self-feeding.
They tend to have two brood attempts, and then moult all in a narrow time window, before migrating, quite a challenge!?
The recorded numbers of these geese at Reculver do seem to fluctuate considerably. Chris Hindle's blog suggests that numbers in November 2014 were up to a thousand or so, but they seem to be down to 400 - 500 now in December 2014. They may disperse quite widely, moving onto other areas according to the weather, or food resources. They may perhaps move to Chichester or Harbour on the South Coast, or the French coast at Morbihan for example.
Boorman and Ranwell (1977) summarised much of information held about Brent Geese at that time, in their ITE paper scoping the possible environmental impact of the construction of Maplin Airport on the East Coast, never implemented in the end thank goodness. They showed that at least 20% of the world's population of Brent Geese (40% of the UK population) used the area over at least part of the winter, normally the first part.
In the 1930s the Eelgrass Zostera species had been hit by a disease that greatly lowered their populations, particularly Z. marina. Anecdotal accounts suggested that the Brent Geese had been hit as well, but the reduction cannot now be quantified. Between the 1950s and 1970s populations increased to about 25,000 - 30,000, contemporaneously with the introduction of shooting bans in the 1950s in the main European countries used as migration routes. It was thought that the population increases were being, or would be, limited by land reclamations in various European countries, particularly the Netherlands. However between 1968 and 1973 the world population more than doubled, shooting up to about 68,000 birds, while at the same time they started using farmland sources of winter food!
In the Maplin study, in the first half of winter, September to January, over half the Essex population fed on the Zostera beds of Foulness and Leigh, then moving on to the Enteromorpha beds of the other estuaries. In January/February '72-3, with peak counts double the previous year, about 30% of the birds turned to farmland, a behaviour only previously noted in the freezing winter of '62-3. In 1973-74, at very high populations, weight losses in birds averaging about 9% were noted. These losses could significantly impact upon reproductive success. By contrast in '62-63 in Denmark, with about a third of the 73-74 populations, despite the terrible weather, no weight losses were found.
ITE then organised some ground-breaking netting and ringing to try to understand the movements of the geese. Cannon netting had to be used on the open flats, based on siting the cannon nets in advance, hoping to guess where the geese might be. Only about 16 individual Brent Geese had ever been ringed before, so little was known of their winter distribution changes. In this exercise one family was noted to move North to the Blackwater, then South to Chichester Harbour, and then finally on to the Waddensee within 24 hours of leaving Chichester - interesting to see how they stuck together. Of course such familial cohesion is essential. Juveniles feed for up to 95% of their time presumably being partly watched over by their parents, who feed for about 75% of their time early in the winter, although this trends to 95% later in the year, as food quantity and quality decreases. The ringing demonstrated that at least some birds remained relatively faithful to their sites on particular estuaries at least for some time.
Brent geese have very variable breeding results according to the weather and predation. In the year 1977 it was estimated that successful breeding had occurred in only 8 of the previous 15 years. No other goose species has such a variable breeding success leading to unbalanced age class structures
in the population from year to year, likely to affect social behaviour. In years with success, the family groups migrate together, adults with that year's juveniles. In unsuccessful years the (non)breeding adults migrated before the two year old birds.
The approximate age composition of the British population of Dark-bellied Brent geese was calculated for 1973-74 by the ITE. The total population was estimated then at roughly 41,000, with about 15,400 first-winter birds, 7,600 breeding adults and 18,000 full grown birds without young (from the estimated mean brood size of 4.0 and the estimated percentage of first winter birds as 37.5). The full grown birds without young were probably mostly in their second winter, for Brent geese do not usually breed until their third or fourth summer.
It is worth noting that the latest BTO population estimate is in the region of 95,000 Dark-bellied birds wintering in the UK! There are also about 27,000 Canadian Light-bellied Brent Geese and 3,400 Svalbard Light-bellied Brent Geese. The main concentrations of Dark-bellied birds are in the Wash, the North Norfolk coastal marshes, Essex estuaries, the Thames Estuary and Chichester and Langstone Harbours.
The ITE trials demonstrated that disturbance by humans or light aircraft caused the geese to stop feeding or fly, reducing their feeding success by 3 - 4 percent, which might seem low, although any reduction may be very significant. Using a nightscope it was established that the Brent Geese did feed at night throughout the winter, sometimes in cloudy weather, as well as during the day, and in some cases on quite sparse Enteromorpha. However, Brent geese appeared not to feed so intensely at night as during the day, and were almost exclusively confined to the tide edge.
Clearly the farm cereals and grasses are not going to be anywhere near as nutritional as Zostera, and the balance between energy expanded, and energy gained while feeding may be greatly narrowed. It is also worth remembering that extended periods of frost may mean that the farmland resources become completely unavailable for a period! I wonder how the Reculver Geese did over the severe winters of 2011/2012 and 2012/13. The impact of switching to farm resources on individual fitness is certainly of some potential concern.
The amount of Zostera, or Enteromorpha, likely to be available in future years is not necessarily predictable. Particular species appear to have very finely attuned requirements for drainage/drying out of the substrate, and the balance between accretion and erosion. These factors may be affected by other changes along the coast, and climate. Zostera noltii of the intertidal zone appears to be the currently preferred species for Brent Geese, with the role of the subtidal Z. marina var. angustifolia now less well understood. Coastal squeeze and shore steepening may impact on Zostera beds as well as salt marsh availability.
These are monthly peak counts for Brents at Reculver. 2008/09 was a relatively poor year across North Kent, but not too bad at Reculver. Interestingly the winter of 2011/12 gave high numbers, but the significantly colder winter of 2012/13 (at least in the East and Southeast) gave only the "normal" moderate numbers.
Bibliography:
Boorman, L.A. and Ranwell, D.S. (1977) The ecology of Maplin Sands and the coastal zones of
Suffolk, Essex and North Kent. Institute of Terrestrial Ecology, Cambridge.
Birds of the Western Palaearctic (BWP).
I was moving fairly quickly, but thought I might also have seen a Stonechat behind Coldharbour, just from an impression of a shape, coupled with a perch high on a bush - weak evidence I know!
About 540 Dark-bellied Brent Geese on the fields and commuting to and from a gravel bank on the beach, lovely to see, and hear! Their almost grunting (the BBC suggests "gobbling") calls are surprisingly attractive and restful. BWP has them characteristically noisier on water, and indeed it was while they were on the sea, or flying from the sea that I heard them calling (BWP = hronk, hronk)! I also thought I saw one Pale-bellied Brent Goose, as regularly reported here, but it was difficult to be really sure. The birds were quite mobile, first disturbed from the field, and then moving in smaller groups backwards and forwards from the shingle bank by the Coldharbour outfall into the fields, including the one by the Green Bank. It was noteworthy that they flew quite low and in loose "brunches" or long "lines" rather than V-shaped skeins.
They lead lives that are so close to the edge. Average annual winter mortality in the UK is estimated to be about 15%, although a typical life span may be as long as 11 years, and the current BTO record being over 28 years old. On their long migration it is essential that they arrive on the breeding grounds in as good a condition as possible. On the breeding grounds they may first eat mosses and lichens, then turning to grass as it becomes more available. They need to have nutritional reserves to see them through problems such as any remaining snow and ice. It seems that individual birds that have better access to food within the flock, and therefore build up heavier body masses on the spring staging areas show better reproductive success. The females seem to get about half their energy for incubation from stored endogenous sources, the other half from intensive feeding episodes the length of which depend on the threat from weather, etc (Inger et al, 2008). It is suggested that an increase of body mass of one sixth on migration may lead to raising breeding success from 8% to 65%. However I think birds should not be too heavy before long distance flights, or they will have potential problems migrating.
Marine habitats seem to be greatly preferred by Brent Geese over terrestrial food sources for quality. Best food sources are Zostera spp., Eelgrass, Ulva sp, Sea Lettuce and Enteromorpha spp, The rationale is that these algae are easier to digest than the fibre-rich grass, particularly important in geese, which have rather inefficient digestive systems.
Increasingly as the migratory populations have grown over the years from the nadir of the '30s, (10 fold perhaps?), Brents are apparently being forced onto (or are turning to) farmland rather than the Zostera or Enteromorpha rich intertidal zone. This may in the longer run have impacts on the average reproductive success of the populations. I wasn't paying proper attention today or I would have been surer of their detailed behaviour. The little I did see suggested that the Brents at Reculver were perhaps feeding a bit while they were on the autumn sown cereal (wheat?) and definitely often interacting aggressively. While they were on the seashore, they didn't seem to be feeding, or indeed showing too much aggression to each other, but I should have been actively checking. The flock was fairly densely packed on the sea and I wouldn't have thought there was anything for them to eat where they were anyway, perhaps a little Enteromorpha. They seemed more to be having a bit of a "little seaside break".
Normal food sources start off with Zostera, Eel Grass. In early winter the Zostera spp. beds are relatively intact and the rhizome, in particular, provides an important food resource (Mathers et al. 1998). In late winter, however, the availability of Zostera spp. declines, as a result of foraging and senescence, and it is more patchily distributed. Presumably there is Zostera, Ulva or Enteromorpha somewhere around off Reculver or Minnis Bay?? Perhaps they spend most of their feeding time on the fields?
At this time of year the flocks may consist of mixed ages, including the yearlings, if any are present - again I didn't really look at the time! The first winter birds are similar to the adults, although the white neck markings are less conspicuous, the white tipped coverts of the juveniles are largely retained and there is rather less white edging to the flanks. In retrospect I think I did see the white-tipped coverts indicating first winter birds in a number of cases.
The social inequities will mean that the higher-ranked individuals get the better resources in a feeding flock. It seems that in the winter period at least, families with any number of juveniles dominate pairs, pairs dominate singletons, and males dominate females. Several of these characters correlate with breeding success, and may be difficult to disentangle. Another paper suggested that large families do control more feeding resources than small ones, leading to less cost to the increased parental investment, so that things balance out. However by springtime arrival on the breeding grounds, the yearlings will apparently have been excluded from the family and the more mature birds will have settled into their pairbonds again. The pairings give advantages to the females of the pair, as the males protect them from aggressive behaviour from the other birds, allowing the females longer to feed up. BWP also notes that the birds are monogamous and pair for life!
The behaviour of the birds on the Arctic breeding grounds is extremely interesting. Laying is quite synchronous over a wide area - but do young birds lay later than experienced ones? The sites chosen will generally be on the drier hummocks to avoid melt flooding, perhaps on islands. The nests shaped like shallow bowls are about 30 cm. across, the internal bowl about 6 cm deep, of about 20 cm. diameter. They may be roughly 25 m. apart. Both sexes build the nest, using nearby materials, lining the nest with moss and grass, and covering with a fair amount of down. Incubation starts when the last egg is laid, leading to synchronous hatching. The nests may be re-used from year to year. Breeding success ranges are the most variable of all Arctic Geese, as calculated by the numbers of yearlings in winter flocks in the UK ranging from 1% to 45%. Up to 4 eggs are laid, generally only in one batch.
Like most, but not all, Arctic geese, the females have to eat as well as incubate. They cover the eggs with down and then move off the nest to feed, pecking virtually continuously and quite close to the nest, thus maximising food intake. The males do not incubate, but take on a protective role, against predators and conspecifics, being relatively more alert while the female is feeding, and feeding relatively more while the female is incubating. Once the chicks are hatched, both parents remain protective, although they do not need to feed the young as the chicks are precocial, nidifugous and self-feeding.
They tend to have two brood attempts, and then moult all in a narrow time window, before migrating, quite a challenge!?
The recorded numbers of these geese at Reculver do seem to fluctuate considerably. Chris Hindle's blog suggests that numbers in November 2014 were up to a thousand or so, but they seem to be down to 400 - 500 now in December 2014. They may disperse quite widely, moving onto other areas according to the weather, or food resources. They may perhaps move to Chichester or Harbour on the South Coast, or the French coast at Morbihan for example.
Boorman and Ranwell (1977) summarised much of information held about Brent Geese at that time, in their ITE paper scoping the possible environmental impact of the construction of Maplin Airport on the East Coast, never implemented in the end thank goodness. They showed that at least 20% of the world's population of Brent Geese (40% of the UK population) used the area over at least part of the winter, normally the first part.
In the 1930s the Eelgrass Zostera species had been hit by a disease that greatly lowered their populations, particularly Z. marina. Anecdotal accounts suggested that the Brent Geese had been hit as well, but the reduction cannot now be quantified. Between the 1950s and 1970s populations increased to about 25,000 - 30,000, contemporaneously with the introduction of shooting bans in the 1950s in the main European countries used as migration routes. It was thought that the population increases were being, or would be, limited by land reclamations in various European countries, particularly the Netherlands. However between 1968 and 1973 the world population more than doubled, shooting up to about 68,000 birds, while at the same time they started using farmland sources of winter food!
In the Maplin study, in the first half of winter, September to January, over half the Essex population fed on the Zostera beds of Foulness and Leigh, then moving on to the Enteromorpha beds of the other estuaries. In January/February '72-3, with peak counts double the previous year, about 30% of the birds turned to farmland, a behaviour only previously noted in the freezing winter of '62-3. In 1973-74, at very high populations, weight losses in birds averaging about 9% were noted. These losses could significantly impact upon reproductive success. By contrast in '62-63 in Denmark, with about a third of the 73-74 populations, despite the terrible weather, no weight losses were found.
ITE then organised some ground-breaking netting and ringing to try to understand the movements of the geese. Cannon netting had to be used on the open flats, based on siting the cannon nets in advance, hoping to guess where the geese might be. Only about 16 individual Brent Geese had ever been ringed before, so little was known of their winter distribution changes. In this exercise one family was noted to move North to the Blackwater, then South to Chichester Harbour, and then finally on to the Waddensee within 24 hours of leaving Chichester - interesting to see how they stuck together. Of course such familial cohesion is essential. Juveniles feed for up to 95% of their time presumably being partly watched over by their parents, who feed for about 75% of their time early in the winter, although this trends to 95% later in the year, as food quantity and quality decreases. The ringing demonstrated that at least some birds remained relatively faithful to their sites on particular estuaries at least for some time.
Brent geese have very variable breeding results according to the weather and predation. In the year 1977 it was estimated that successful breeding had occurred in only 8 of the previous 15 years. No other goose species has such a variable breeding success leading to unbalanced age class structures
in the population from year to year, likely to affect social behaviour. In years with success, the family groups migrate together, adults with that year's juveniles. In unsuccessful years the (non)breeding adults migrated before the two year old birds.
The approximate age composition of the British population of Dark-bellied Brent geese was calculated for 1973-74 by the ITE. The total population was estimated then at roughly 41,000, with about 15,400 first-winter birds, 7,600 breeding adults and 18,000 full grown birds without young (from the estimated mean brood size of 4.0 and the estimated percentage of first winter birds as 37.5). The full grown birds without young were probably mostly in their second winter, for Brent geese do not usually breed until their third or fourth summer.
It is worth noting that the latest BTO population estimate is in the region of 95,000 Dark-bellied birds wintering in the UK! There are also about 27,000 Canadian Light-bellied Brent Geese and 3,400 Svalbard Light-bellied Brent Geese. The main concentrations of Dark-bellied birds are in the Wash, the North Norfolk coastal marshes, Essex estuaries, the Thames Estuary and Chichester and Langstone Harbours.
The ITE trials demonstrated that disturbance by humans or light aircraft caused the geese to stop feeding or fly, reducing their feeding success by 3 - 4 percent, which might seem low, although any reduction may be very significant. Using a nightscope it was established that the Brent Geese did feed at night throughout the winter, sometimes in cloudy weather, as well as during the day, and in some cases on quite sparse Enteromorpha. However, Brent geese appeared not to feed so intensely at night as during the day, and were almost exclusively confined to the tide edge.
Clearly the farm cereals and grasses are not going to be anywhere near as nutritional as Zostera, and the balance between energy expanded, and energy gained while feeding may be greatly narrowed. It is also worth remembering that extended periods of frost may mean that the farmland resources become completely unavailable for a period! I wonder how the Reculver Geese did over the severe winters of 2011/2012 and 2012/13. The impact of switching to farm resources on individual fitness is certainly of some potential concern.
The amount of Zostera, or Enteromorpha, likely to be available in future years is not necessarily predictable. Particular species appear to have very finely attuned requirements for drainage/drying out of the substrate, and the balance between accretion and erosion. These factors may be affected by other changes along the coast, and climate. Zostera noltii of the intertidal zone appears to be the currently preferred species for Brent Geese, with the role of the subtidal Z. marina var. angustifolia now less well understood. Coastal squeeze and shore steepening may impact on Zostera beds as well as salt marsh availability.
These are monthly peak counts for Brents at Reculver. 2008/09 was a relatively poor year across North Kent, but not too bad at Reculver. Interestingly the winter of 2011/12 gave high numbers, but the significantly colder winter of 2012/13 (at least in the East and Southeast) gave only the "normal" moderate numbers.
Bibliography:
Boorman, L.A. and Ranwell, D.S. (1977) The ecology of Maplin Sands and the coastal zones of
Suffolk, Essex and North Kent. Institute of Terrestrial Ecology, Cambridge.
Birds of the Western Palaearctic (BWP).
Saturday, 13 December 2014
Reculver
An inspirational afternoon trip out to Reculver by the Wantsum Channel, on a cold but beautifully sunny day.
About half a dozen Turnstones, a dozen Redshanks, and a score of dark-bellied Brent Geese, Branta bernicla bernicla, over. Several Reed Buntings, one Little Grebe, a dozen Black Headed Gulls with at least one Common Gull, Larus canus. A score of Linnets (one might have had a white flash on its wings), half a dozen Cormorants, one Great Crested Grebe, four Shelduck, one Great Black-backed Gull, half a dozen Herring Gulls.
This is the view across the reclaimed marshland of the Wantsum Channel towards the railway line, and the glasshouses. One of the birders said that he saw a Marsh Marrier in the distance there:
Monty picked up a fish on the path back, and made fairly short work of it, including the head and tail. No ill effects so far.
About half a dozen Turnstones, a dozen Redshanks, and a score of dark-bellied Brent Geese, Branta bernicla bernicla, over. Several Reed Buntings, one Little Grebe, a dozen Black Headed Gulls with at least one Common Gull, Larus canus. A score of Linnets (one might have had a white flash on its wings), half a dozen Cormorants, one Great Crested Grebe, four Shelduck, one Great Black-backed Gull, half a dozen Herring Gulls.
This is the view across the reclaimed marshland of the Wantsum Channel towards the railway line, and the glasshouses. One of the birders said that he saw a Marsh Marrier in the distance there:
Monty picked up a fish on the path back, and made fairly short work of it, including the head and tail. No ill effects so far.
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