How small is too small? Incubation of large eggs by a small host

摘要

The Yellow Warbler (Setophaga petechia (L., 1766)) is among the putative hosts of the Black-billed Cuckoo (Coccyzus erythropthalmus (Wilson, 1811)), which is hypothesized to have once been an obligate brood parasite. Most parasites lay a small egg relative to their body size, possibly to prevent hosts from discriminating against the larger egg and to facilitate incubation. We tested whether warblers, which lay eggs -17% of the volume of cuckoo eggs, could have potentially been suitable hosts of Coccyzus cuckoos by determining whether they accept and successfully incubate cuckoo-sized eggs. Warblers accepted 63% (n = 54) of cuckoo-sized eggs added into their nests and successfully incubated eggs as large as cuckoo eggs (surrogate American Robin (Turdus migratorius L., 1766) eggs). This suggests that the lower limit to host size is not just related to egg size. Warblers are not ideal hosts because they rejected a high frequency of experimental eggs (37%). Nests from which eggs were rejected tended tohave smaller volumes than nests at which eggs were accepted. The nest cups of warblers are oval, which may promote egg crowding more than round cups. Factors such as nest size, not host size, influence acceptance or rejection of large eggs by Yellow Warblers.