Egg-Capping and Eggshell Removal by Western and Semipalmated Sandpipers

Abstract

Parents of birds with nidicolous young that remain in the nest after hatching generally remove eggshells from the nest after the chicks emerge from the eggs. In contrast, birds with nidifugous young usually leave eggshells and unhatched eggs in the nest when the brood departs on the day of hatching. Shorebirds (Suborder Charadrii) are a curious exception to this pattern. Despite having well-developed precocial young that leave the nest soon after hatching, many shorebirds will remove the shells of hatched eggs from the nest (e.g., Red Knot Calidris canutus, Whitfield and Brade 1991; White-rumped Sandpiper C.fuscicollis, Parmelee 1992; Buff-breasted Sandpiper Tryngites subruficollis, Lanctot and Laredo 1994; Black-necked Stilt Himantopus mexicanus, American Avocet Recurvirostra americana, Sordahl 1994). Tinbergen et al. (1962) suggested five reasons that parents might remove eggshells: (1) if sharp shell edges injure chicks, (2) if shells from hatched eggs interfere with brooding, (3) if material on remaining shells increases the risk of bacterial infection, (4) if the white linings of eggshells from hatched eggs increase the conspicuousness of the nest to a predator (here called the predation hypothesis), or (5) if the shells from a hatched egg become affixed to a later-hatching egg, forming a double shell layer that a pipping chick cannot break through (here called the egg-capping hypothesis, Derrickson and Warkentin 1991, Arnold 1992). The first three explanations seem unlikely for shorebirds because the young do not remain long in the nest. In this note, I evaluate the predation and egg-capping hypotheses as explanations for parental removal of eggshells at hatching by Western Sandpipers (Calidris mauri) and Semipalmated Sandpipers (C. pusilla).