Examining incubation behavior during laying and that behavior's consequences on patterns of hatching can help discriminate among hypotheses competing to explain the evolution of asynchronous hatching. Consequently, I documented nest attentiveness and patterns of hatching of American Coots (Fulica americana) nesting in southwestern Manitoba from 1986 to 1991. Coots gradually increased their nest attentiveness from laying of the first to the sixth egg, and attentiveness to late-season clutches peaked earlier during laying, but it was unaffected by clutch size, first vs. replacement nest, or supplemental food. Nest attentiveness during laying was effective at initiating embryo development, as evidenced by a strong positive correlation between the order of laying of eggs and order of hatching of chicks. These results are most consistent with hypotheses that nest attentiveness during laying evolved to protect eggs or maintain viability of embryos. Clutch-initiation date had the most pronounced effect on patterns of hatching, with late-laid clutches hatching sooner and more asynchronously. Very large clutches took longer to hatch, whereas renesting and supplementally fed coots hatched early-sequence eggs more quickly. Despite large clutches and pronounced asynchrony, there was no evidence that neglect of last-laid eggs delayed their hatching. Observed variation in patterns of hatching provided little support for hypotheses that asynchrony of hatching has evolved to produce a hierarchy within a brood (e.g., brood reduction, reduction of peak loads) but strongly supported hypotheses that hatching asynchrony serves to minimize risks to unincubated eggs (e.g., egg viability, nest protection, and nest failure).
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Vol. 113 • No. 1