The function of food storing in shrikes: the importance of larders for the condition of females and during inclement weather

Abstract

Food storing is a well-known phenomenon among birds, described in shrikes Laniidae. The preferred explanation suggests that its function is to signify male quality to females and to mark territorial borders during the mating period. The importance of food storing must vary among different species, however, because in the Red-backed Shrike Lanius collurio, this behaviour takes place during the nestling care period. The aim of this study was to evaluate the significance of food storing by male Red-backed Shrikes. We did not find any differences in the breeding parameters between pairs in which the males did or did not store food. There was, however, a significant tendency for the number of stored prey items to increase when the atmospheric pressure was falling prior to the onset of rain. The mates of males that did store food had a larger body mass than those females whose partners did not do so. This study showed that food storage have a variety of functions, including different ones compared with those described for the best-known shrike species. Differences in food storing phenology in various shrike species are probably due to the period when they start nesting: Red-backed Shrikes start their breeding season in late spring, when food is plentiful. Our study demonstrates that the abundance of food in territories and one’s own condition, as expressed by the number of prey items stored when food is readily available, is not really so relevant. The food store of a Red-backed Shrike thus functions as a larder, which the female makes use of when her energy requirements are the highest, i.e. when caring for her young. Larders are thus essential if females are to remain in good bodily condition: this could be significant if a clutch is lost and a replacement one has to be laid.