Changes in the foraging pattern of plovers in relation to environmental factors

Abstract

The effects of environmental conditions on the foraging behaviour of ringed and grey plovers ( Charadrius hiaticula and Pluvialis squatarola) were investigated at Lindisfarne National Nature Reserve, Northumberland. Plovers forage by an apparently visual searching technique, scanning an area while standing still, before running to peck at prey. Plovers appeared to select large prey, in suitable conditions, by not responding to cues of small prey at the start of each waiting period. Within a waiting period, they became progressively more ready to take smaller prey, before eventually giving up and moving to a new waiting site. Giving-up time was adjusted to different conditions, resulting in the selection of larger prey when prey availability was high, notably at high temperatures. The birds tended to concentrate their activity on clumps of high density of available prey, by moving less far after taking large prey than after taking small or no prey. When no prey was taken after a wait, the bird moved on sufficiently far to scan a new area, or further in areas of low-density, highly clumped prey. In addition to feeding by day, plovers also forage at night. Night observations of foraging behaviour and performance are presented, and discussed in relation to visual foraging and the increased activity of some intertidal invertebrates at night. Although plovers apparently use visual searching, for which the prey detection ranges are probably shorter at night, they were able to maintain fairly high pecking rates at night, partly because of higher surface activity levels of prey.