Oare Marshes thinking of Golden Plover again

The Golden Plover at Oare 

Eurasian Golden Plover, Pluvialis apricaria (Gravenhorst, 1820), (Desvignes, 1856). An interesting bird that seems to have declined in its UK breeding population steadily over the last few decades, perhaps due to changes including reductions in keepering on upland moorland, consequent increased carrion crow predation, reduction in moorland burning, possibly increased raptor numbers, or many other factors.

The much larger overwintering Golden Plover population from northern Europe, Russia and Iceland does also seem to have shifted its wintering distribution in the UK away from pastures in the West towards (particularly) arable land on the eastern side of the country since the 1980s. The Kent birds might seem to prefer grassland still but I well remember seeing birds on ploughed fields in Yorkshire on one journey up to see or pick up Simon.

In the early part of the winter in Kent, large numbers can be seen in the Swale and specifically at Oare Marshes. Today there must have been getting on for a thousand birds here at Oare today.  It is one of the twenty two sites listed in the non-breeding SPA for this species, each site being a multispecies SPA.

The plumages of the birds are quite variable in detail. This might be a juvenile or first winter bird on the left - underside more speckled further down the flanks and belly, and ONLY IN MY PERSONAL VIEW, a little warmer in the face and the supercilium thereby a bit less contrasty.

I checked for slender (long-legged?) birds with somewhat clearer supercilia and long wings projecting beyond their tails - but no possible American Golden Plovers as far as I could see!

The overall ecology of the bird is very interesting:

Moorland Breeding

In the small and declining UK population the birds nest on moorland, although during the incubation period the adults really like to feed on neighbouring farmland pastures on worms and cranefly larvae, etc, while their partners are incubating the eggs. During the day the males incubate and the females feed, and during the night the females incubate and the males feed. Tipulids are a key feature of both the later adult and the chick diet. Pearce-Higgins and Yalden showed in one of their South Pennines studies (2003) that the particular arable, improved and pasture fields chosen by the off-duty birds for foraging in were those with appropriate pasture sward heights, appropriate moisture levels and good numbers of earthworms and particularly cranefly (Tipulid) larvae. Over time, sheep stocking density has increased in UK uplands, which might be helpful, but is also associated with agricultural intensification such as drainage, which would probably reduce Tipulid numbers.

According to Whittingham et al., working on moorland in Northern England in 2001, chicks on the moorland tend to use mosaics of dwarf shrubs such as willow, crowberry and bilberry, and more open areas of cotton-grass and bare peat. Again Tipulids and Beetle larvae do tend to be very important in the diet. Rotational strip-burning or careful manipulation of grazing management systems could be used to help maintain these mosaics.

Later in 2011 Pearce-Higgins did some very interesting theoretical modelling on the extent of the impact of expected climate change on this population on the southern edge of its range, and suggested that the impacts would greatly reduce Tipulid numbers, and chick survivability, and proposed equivalent increased management activity to help maintain the population, either environmental management to increase Tipulid food sources by 80%, or by reducing nest and egg predation by 35%.

There are birds in Sweden that also breed in the uplands, like the UK breeding population, although the habitat there is referred to as Fennoscandian arctic tundra. Machin et al in 2017 showed that the chicks in this habitat in Sweden feed on a more diverse diet of beetle larvae, cranefly larvae and St Marks Fly (Bibionids) larvae, and breeding success appears to be at least in part linked to Bibionid population fluctuations from year to year. The Bibionids are found more in willow scrub, and the chicks may move into this habitat as they grow in part according to prey availability, but also in part in order to gain increased protection from predator attack.

Over-wintering

After the young have fledged, the adults and young migrate to lowland farmland and coastal habitats for the autumn and the winter. According to Gillings et al., in 2007, in recent decades winter populations of both Golden Plover and Lapwings appear to have switched from using pastures in the west of the country to using arable land for much of the winter - October - February (harrowed fields for winter cereal initially, then sugar beet and then other crops). Large open fields which had been manured were particularly favoured, and it is perhaps to be hoped that both manuring and sugar beet growing will continue into the future for these large numbers of birds over-wintering in the UK. However the reasons underlying the move and whether the pastures have become less attractive, or the arable more attractive, or both or neither remains a bit of a mystery. Could climate change have impacted on the relative attractiveness of these two types of habitats? In France research reported in 2007 indicated that cereal fields were the preferred wintering habitat in that country.

As for field size, Leitão and Peris working in Portugal in the late 90s concluded that Golden Plovers avoided fields less than 10 Ha, and preferred fields larger than 20 Ha, and preferred pastures in this particular environment.

Birds migrating from further North and East in Europe and Russia use arable fields in southern Sweden as autumn staging posts, where Lindstrm et al. showed in 2010 that numbers tend to be quite high and they are able to both moult and then also (critically) put on weight after their moult for the next stages of their journey, perhaps to the UK. The adults and young follow more or less the same pattern although the young do follow the adults after a little delay. The length of stay on these fields is about three months, August to November, indicating the importance of this habitat to this population of migrating birds.

Research reported by Piersma et al in 2003 into birds over-wintering in the Netherlands showed some fascinating patterns. The birds put on weight in the autumn (September - November) and their weights peak in late November and December as they (presumably) put on fat to sustain themselves in bad times. They then lose weight again - I imagine as they use up their reserves, perhaps with somewhat poorer food availability. Then in the spring they start to put on weight again, perhaps as food becomes more available again, in preparation for their spring migration and the breeding season to come.

However between the 80s and 90s, the December peak mass decreased as the weight gain stopped earlier, although the rate of increase during the shorter period of weight gain remained the same. As weather conditions remained similar, this was interpreted as a response to increased raptor numbers, such as Peregrines and Goshawks - possibly leading to slimmer fitter birds more adapted to raptor evasion. However this seems to me to be a rather over-optimistic view of the ability of these birds to plan ahead, and to control their weight!

Machin et al reported in 2015 on individual winter movements of birds from a breeding population in Swedish Lapland, showing that some started their winters in NW Europe in areas such as northern France, and shifted south to Spain or Africa in cold spells, giving a degree of flexibility to their over-wintering, while others sometimes didn't move further and stuck out the cold spells where they were. Cold weather movements were noticeably long and fast, real escape movements.

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.

Cliffe in mild weather

160 Golden Plover, over a thousand Lapwing, several Redshank, Great Black-backed Gulls, one Lesser Black-backed Gull, Herring Gulls, Black-headed Gulls, Coot, Shoveller, Teal, Mallard, Wigeon, Pochard, Tufted Duck, Great Crested Grebe, Little Grebe, one Cormorant, two Grey Heron, four Marsh Harrier, two or three Fieldfares, two Black-tailed Godwits, two Curlew, one Little Egret, one Cetti's Warbler heard.

The weather held throughout the visit, from 12:30 until about 4 pm, although we lost the sun about 2 pm.

It was lovely to see the Golden Plover, Pluvialis apricaria (Linnaeus, 1758), in good numbers at Cliffe. The last time I saw them in numbers was on Horse Sands in the Swale on the "predators day" with Tony Swandale. 

Back at Cliffe with a possible Little Stint, thinking of Golden Plover

Made it to Cliffe about an hour before high tide, just in time to see many of the waders arrive off the Thames.

Great numbers of Avocet, Dunlin, Black-tailed Godwit, Redshank, Little Egret, Great Crested Grebe, Little Grebe, Black-headed Gull, Black-backed Gull, Herring Gull, Shoveller, Teal, Shelduck, Mallard, some Pintail.

One possible Little Stint actively feeding on the drier sand behind a large group of Dunlin.

Woodpigeon, Stock Dove, Woodpigeon, Robin, Blue Tit, Long-tailed Tit. Some warblers seen, possibly an autumn call of a Chiff-chaff.

It was very nice to see the Golden Plover on the edges of the pools. There were a number of the Grey Plover as well, looking tougher as they so often do, with their heavier bills. However the Golden Plover, Pluvialis apricaria, were my main interest today. These may be breeding in Northern Europe or Russia, but they could be from the uplands of the UK as well. The breeding in the UK might be regarded as somewhat on the edge of its range, and also slightly artificial as upland moorland is largely created by historic land management, but there has been quite a lot of research on the breeding ecology of these gorgeous birds. The UK population could be regarded as at the southern edges of its breeding range and particularly subject to potential warming and drying climate change, which could reduce food sources such as cranefly (Tipulid) larvae. In order to preserve this potentially threatened population, 9Pearce-Higgins, 2011) suggested thart efforts could be made to improve habitat, and thus breeding success, and reduce predation on the other hand.

One very interesting and unexpected feature - the males and females split incubation period in an interesting way: the males incubate during the day, while the females incubate at night.

The research has shown some rather odd features of this species' breeding ecology. When not incubating their eggs on moorland, the adults can often be found on neighbouring agricultural pasture fields rather than moorland, where they are likely to be feeding (perhaps) or resting for about half their time.  This is however less true for the males. The average distance moved to the fields was about 2.7 km in the Sunderland study, with females flying further than males. Individual flocks of birds tended to show fairly strong faithfulness to their individual favourite fields, both within a year, and from year to year. Relatively few of the available fields were used for feeding, with those used tending to be large, old, with some cover of rushes Juncus spp., and grazed by sheep. Leatherjackets were possibly the favoured prey.

Although field size did not seem to determine whether fields were occupied or not, field size was correlated with the numbers of birds in an occupied field. Having wet flushes did seem to increase the popularity of a field being chosen, as did the sward kept short by sheep. The nature of the boundary did not seem to have much of an effect, although this might have been expected to have affected ease of predation. The number of molehills, as a proxy for earthworm numbers, was a good indicator of field attractiveness, (according to Whittingham et al, 2000).

Once the eggs hatch, the behaviour of the adults changes, and then they spend much motre time foraging on moorland.

It was estimated that there were about 2,000 pairs breeding in Caithness, of which about half would have been nesting in the Special Protection Area (declared because of the importance of this area for the total breeding population. The fields used while incubating need to be managed appropriately: Management of areas of pasture to maintain their suitability for feeding golden plovers should, in general, avoid ‘improvement’ in the sense typified by agricultural intensification (Wilson et al., 2005). Specifically, the following practices should be avoided: Draining; Application of pesticides to control tipulid larvae (cranefly larvae = leatherjackets); Ploughing and re-seeding with single palatable grass species; Application of inorganic fertilisers; Removal of grazing; Conversion to silage or hay crop.

Based on the apparent preferences of golden plovers, the following characteristics of fields should be maintained: Field size (although enlargement through removal of fences between fields should not have an adverse effect); Poor drainage (as revealed by at least some coverage of Juncus rushes); Multi-species grass community; Grazing regime to maintain a short sward less than 5 cm

Tipulid larvae abundance is also enhanced by the presence of a taller sward during the adult tipulid emergence period ( July – September); this is thought to be because taller grass prevents airborne laying females being blown away by the wind and hence encourages them to lay their eggs in a small area around their emergence site (McCracken et al., 1995; Bignal et al., 1996). Thus a grazing regime whereby livestock is put on to fields in late winter (to create a short sward) but is removed shortly before the adult tipulid emergence period begins in July (to allow a taller sward to develop and retain laying female tipulids) should create favourable conditions for feeding golden plover. In this context, fields used as ‘lambing parks’, especially where ewes and lambs (or other livestock after lambing has finished) are held until mid-June before being hefted to other areas, are likely to be favoured by golden plovers, assuming other field characteristics are compatible.

Clearly these practices should be targeted at those fields already known to be used by plovers, although, as noted earlier, identification and maintenance of suitable ‘alternative’ fields nearby should also be desirable. The proportions of all fields which are used by golden plover are so small (about 3% overall) that it should be feasible to strike a balance between maintaining sufficient suitable fields whilst still being compatible with any intensification deemed as necessary by farmers, although in some holdings the proportion of ‘plover fields’ may be locally greater. Maintenance of fields which are potentially or known to be suitable for golden plover should also benefit several other wader species which appear to have similar preferences.

The chicks obviously feed closer to the nest, and appear in NorthEast England to like patches of mixed heather and grasses, as well as wet areas. Mixed grazing of appropriate intensity to create the vegetation mosaic, as well as stopping up drains to create the wet areas, might therefore be very helpful in aiding their feeding, possibly primarily in Tipulids (according to Whittingham et al, 2001). In Swedish Lapland the pattern differed somewhat according to (Machin et al, 2001), where the chicks fed largely on Coleoptera but also  first on Tipulids on more open areas, then switched (as these ran out (?)) to Bibionids in Willow Scrub a bit later, which might also have helped to protect them from predators.