Potential influence of egg location on synchrony of hatching of precocial birds

Abstract

Although the onset of incubation prior to completion of the clutch leads to developmental asynchrony of the embryos, waterfowl eggs tend to hatch synchronously (within 3-24 hr). The mechanisms waterfowl use to synchronize development of embryos and allow for synchronous hatching are still not well understood. A variety of mechanisms have been proposed, including vocalization by embryos, egg size, egg constituents, and developmental asynchrony at hatching. Empirical evidence for any of these mechanisms, however, is limited for species that lay large clutches (>6 eggs). We hypothesize that the eggs' position within the clutch may synchronize development of embryos of dabbling ducks that lay clutches large enough that central and peripheral eggs may be distinguished. We tested this hypothesis by comparing the developmental stage of central and peripheral eggs and testing for a relationship between the order in which an egg was laid and its position (central or peripheral) within the clutch. We found that eggs laid later were central more often than expected if their distribution were random and that during the first 12 days of incubation central eggs tended to be less developed than peripheral eggs. © 2010 The Cooper Ornithological Society.