Time Budgeting and Feeding Efficiency

Abstract

Our treatment of diet selection by lapwings and golden plovers has so far been taken across birds feeding in very different types of flock. It is well known, however, that the size and species composition of a flock can influence individual foraging behaviour and feeding efficiency (see Chapters 1 and 5). Effects of flock size and composition may be another reason why plovers did not follow the predictions of our simple optimal-diet model exactly. We have seen that, in lapwings and golden plovers, both characteristics of flocks may correlate with feeding efficiency because of their relationship with the spatial and temporal availability of food (for instance, flocks tend to be bigger and denser where the density of earthworms is greatest). Flocking can also influence individual feeding efficiency by allowing birds to devote more time to foraging activities. The various anti-predator effects of flocking may allow birds to spend less time scanning for predators and thus more time doing other things. The relationship between flocking and time budgeting has been especially well studied in single-species flocks (e.g. Lazarus 1972, 1978, Powell 1974, Caraco 1979a,b, Caraco et al. 1980a,b, Barnard 1980a, Draulans 1981). In mixed flocks, however, attention has tended to focus on the form of interspecific association and interaction (e.g. Morse 1970, 1978, Rubenstein et al 1977, Greig-Smith 1978, Balph and Balph 1979, Powell 1980) rather than on time budgeting and, except for a few studies (e.g. Barnard and Stephens 1983,.Waite 1983, Sullivan 1984), the effect of mixed flocking on time allocation has been ignored.