Initial Size Hierarchy in Broods of the Shag: Relative Significance of Egg Size and Hatching Asynchrony

Abstract

Wsetu diedt he relative importanceo f hatchinga synchronya nd intraclutch egg-sizev ariationi n the establishmenot f a sizeh ierarchyi n broodso f the Shag( Phalacrocorax aristotelisI)n. 3-egg clutches( 87%o f all clutches),t he seconde gg averaged3 .0% larger than the first and 2.3% larger than the third. Mean hatching intervals were 11.7 h between the first and second chicks, and 48.3 h between the second and third chicks. In broods of three, the first chick weighed on average 1.9 times more than the last chick at the time the last one hatched.T his differencew as almoste ntirely a result of hatchinga synchronyF. or the last two chicks, hatching asynchrony accounted for 95% of mass difference and the variation in egg size for the remaining 5%. We conclude that variation in egg size has little influence in determining the initial size differences within broods. This applies to several other bird speciesH. atchinga synchronya nd variationi n eggs izes eemt o resultf rom selectionp ressures other than those connectedw ith size differencesb etween nestlings