Sibling Competition, Hatching Asynchrony, Incubation Period, and Lifespan in Altricial Birds

Abstract

This article addresses the relationship between two unresolved problems in avian biology—the significance of variation among taxa in incubation period and the significance of variation in synchrony of hatching—and their implications for other aspects of the life history. Among bird species of similar size and developmental state of the neonate, incubation periods vary over a threefold range (Rahn and Ar, 1974). Long incubation periods have puzzled avian biologists because they convey no evident advantage (Boersma, 1982; Ricklefs, 1984a; Nol, 1986). Time-dependent mortality, energetic efficiency of embryonic growth, sibling competition, and cost of parental investment all favor rapid development and short incubation periods. Significant roles for other factors, such as egg temperature, egg neglect, and pleiotropic coupling of embryonic and postnatal growth rates have been ruled out (Ricklefs, 1984a). In contrast to the situation with incubation period, explanations for variation in hatching synchrony invoke many factors and plausible causes (Clark and Wilson, 1981; Slagsvold, 1986; Slagsvold and Lifjeld, 1989; Slagsvold, 1990; Magrath, 1990; Mock and Schwagmeyer, 1990). None of the hypotheses, however, has strong empirical or experimental support as a single comprehensive explanation.