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.