Fat Reserves of an Opportunist and of a Specialist Species in the Negev Desert

Abstract

We extracted fat from samples of two sympatric lark species resident in the Negev Desert of Israel. The Crested Lark (Galerida cristata), which fed on a wide range of seed sizes, exhibited within-day but not seasonal fluctuations in fat content and carried on average 12.9% fat (of lean dry mass). The Desert Lark (Ammomanes deserti), which fed on a narrower range of seed sizes, exhibited smaller within-day fluctuations in the amount of fat, and carried on average 8.9% fat. We propose that although the two larks occupy the same environment and are of the same feeding guild, these differences are adaptive. When food becomes periodically scarce, feeding specializations of the Desert Lark may often suffice to overcome shortage, but their absence in the generalist Crested Lark may make it more dependable on fat reserves.