Use of Perches as Vantage Points During Foraging By Male and Female Stonechats Saxicola Torquata

Abstract

AbstractThe behaviour of individual stonechats (Saxicola torquata) foraging in heathland habitats was studied, to reveal possible influences of the height of the perches used as vantage points on feeding efficiency. Feeding rates, methods of prey capture, time spent on perches, and perching heights were quantified for male and female birds in a pre-breeding, and breeding periods; in addition, the integration of foraging with pre-breeding male song behaviour was examined. Rates of prey capture were highly variable, showing no clear seasonal trends or sex differences. Perching heights averaged 1.0 m in spring, and 1.6 m in summer, and although sex differences were small, males tended to perch higher, and closer to the top of the vegetation, in spring. Comparison with randomly encountered perches showed that birds selected higher perches than the average available. Of three principal prey-capture techniques, only diving to the ground was used in spring, but flycatching, and snatching prey off foliage, were also employed in summer. The change correlated with the appearance of new prey types on the foliage of birch and bracken. Visits to perches were short, averaging 25 s, and showed no clear sex or seasonal differences, but tended to be longer on higher perches, up to 2 min. These data were combined to assess the profitabilty for foraging of different perching heights. For feeding by diving to the ground, the lowest heights provided the greatest capture rates, but for flycatching and snatching, very high perches were more successful. The birds' observed preferences for perches in spring corresponded to those allowing the highest chance of capture per visit, rather than per unit time. In summer, there was no correspondence. Birds departed from perches when their prospects of capture were still high, and thus the lengths of unsuccessful visits cannot be regarded as 'giving-up' times. In spring, the frequencies of foraging attempts and song-phrases were inversely related in short observation periods, and incompatibility of the activities was suggested by the different heights chosen (averaging 0.9 m for foraging, 1.8 m for singing). The lack of differences in the spring foraging behaviour of males and females (who do not sing) suggests that males separated their foraging and singing into discrete bouts. This was apparently accomplished by tactical allocation of time in stable conditions, rather than relegation of singing to times when foraging conditions were poor.