Wintering Golden Plovers and Lapwings

Nocturnality

When did you last see a flock of Golden Plovers or Lapwings? Were they feeding, or just sitting around, loafing or roosting in the middle of a field? Quite often it will be the latter. We usually think of winter as a hard time of year for most bird species, so how can plovers afford to sit around rather than feed? The answer is that both species often feed at night. Actually it is not just owls that are active after dark - many wader species also feed at night. For estuarine waders the chance of low tide falling during the short winter's day is low meaning that opportunities for feeding are limited and many must supplement their intake at night. It may also be the case that there are fewer predators at night, habitats are less disturbed, or different prey are available at night.

Surely though it must be harder to feed at night? For probing species like dunlin, feeding in darkness makes little difference to their efficiency since they feed by tactile cues. For waders that use visual cues to locate their prey we might expect efficiency to be lower at night. As a consequence, some species that are visual hunters by day switch to using tactile cues at night (e.g. stilts, yellowlegs). However plovers have specially adapted eyes that give them superior vision in poor light conditions and they can continue using visual cues irrespective of light levels.

Given the potential differences in prey, predators, competitors and disturbance between day and night, we might logically expect that birds will chose to feed in completely different places between day and night. Indeed if birds have been feeding all day in one location, it may pay to move if they have temporarily depleted that patch. This is not just an academic question because if we hope to adequately protect the habitat and places a species requires, we cannot hope to do this by only looking at where the species lives during the day. We must also look to their nocturnal requirements. This is something that Simon Gillings and Rob Fuller have been looking into for Golden Plovers and Lapwings on the arable farmland of East Anglia, and their findings are soon to be published in the journal Auk.

They found that whereas during the day both species mixed in very large flocks, at night they tended to segregate and occur in small flocks or even individually (something very rarely seen by day). This meant that they also occupied a far greater proportion of fields at night than during the day. This fact alone means that if one relied only on daytime surveys one might conclude that these species could be adequately protected by effectively managing just a handful of fields, whereas in fact they require many more when nocturnal feeding is taken into account. Given that plovers are able to capture larger earthworms at night (which are not stolen by kleptoparasitic gulls), they can actually achieve a higher intake rate at night than they can by day. Therefore arguably, nocturnal feeding could be considered even more important than diurnal feeding and understanding night time habitat and space use are doubly important. More of these results can be seen here.

These observations are also relevant to the locating of wind turbines. The very fact that plovers (and other wader species) are active after dark and potentially moving between feeding and roosting areas at night means that they more than many species could be susceptible to collision with wind turbines.