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Position in the Sequence of Laying, Embryonic Metabolic Rate, and Consequences for Hatching Synchrony and Offspring Survival in Canada Geese

Abstract. Waterfowl lay large clutches of eggs over many days, yet the offspring hatch synchronously, indicating regulatory mechanisms must aid in minimizing developmental differences among offspring. Understanding how embryos' metabolic rates vary with the sequence in which the egg is laid can provide insight into intrinsic mechanisms regulating the synchrony of hatching. Furthermore, developmental rates differing among offspring within a clutch likely have post-hatching consequences for offspring performance. We characterized variation in developmental rates within a clutch and the consequences for offspring performance in the Canada Goose (Branta canadensis maxima). We measured embryonic metabolic rates every 2 to 3 days, examined goslings' yolk reserves immediately after hatching, and conducted a cross-fostering experiment to assess plasticity in hatching synchrony and gosling survival in the 2 weeks after hatching. We found that embryonic O2 consumption rates increased with age in an S-shaped pattern, as in other birds with precocial young. Embryos in eggs laid later in the sequence had higher metabolic rates than those in eggs laid earlier in the sequence. Yolk reserves at hatching were also lower in goslings hatched from eggs laid later in the sequence. We altered the incubation period by 1–2 days, with no effect on gosling survival in the 2 weeks after hatching. Embryos in eggs laid later consume O2 at a higher rate and develop faster, reducing yolk reserves available at hatching. Reduced yolk reserves did not have immediate consequences for gosling survival. We hypothesize that maternal influences regulate the synchrony of hatching.