WHY DOES THE LESSER GREY SHRIKE (LANIUS MINOR) SELDOM STORE FOOD? DETERMINANTS OF IMPALING IN AN UNCOMMON STORING SPECIES

Abstract

AbstractHoarding behaviour in birds is well known, but some aspects, like variation in hoarding among closely related species, have received little attention. To explain this variation would help understand the evolution of hoarding and ecological aspects related to prey storing. Shrike species are ideal for this purpose, because hoarding is widespread in them but apparently varies too. Here we analyse impaling in one of these species, the lesser grey shrike, and try to unravel experimentally factors triggering and constraining such behaviour. Field data show that the lesser grey shrike seldom stores food under natural conditions. Longterm food surplus of valuable prey did not stimulate food storing. Hoarding was induced experimentally by offering birds a transient, spatially clumped food surplus. Repeated exposure of birds to experimental food surplus significantly increased the impaling rate. This suggests that low caching rates may be partly caused by lack of experience. Foraging successfully competed with hoarding, which was more frequent after satiation. Males also preferred to feed the female rather than to store food. We conclude that lesser grey shrikes hoard when the immediate food needs are satisfied as a result of a transient high prey availability, which probably occurs seldom in nature. This variable and a likely limitation on suitable places for impaling may result in few stimuli for shrikes to cache, and may thus constrain the birds' learning process. This may also result in the lesser grey shrike's low hoarding propensity compared to other shrike species.