The Optimization of Growth Rate in Altricial Birds

Abstract

I have developed models relating the rate of growth of altricial bird~ to annual product! on of fledglings, a measure of evolutionary fitness. In the models, growth rate mfluence_s production through its effects on the power requirements of the nestling and the length of the nestmg cycle; the latter in turn affects probability of survival to fledging and number of broods reared per year. The models were evaluated to determine whether empirically reasonable estimates of power reqmrements and nesting mortality resulted in predicted optimum growth rates within the range of observed values. By and large the models were successful. They do not adequately explain the reduced growth rates of tropical altricial species compared to their temperate-zone counterparts. Moreover, th~y do not address the phenomenon of slow growth in self-feeding, precocial species. Bu~ the con?rmatJ~m .of t~e model for many altricial birds suggests that it may be possible to understand .mterspec1fic vanat10~ m .~owth rates as the result of adaptations to levels of predation and the reqmrement for, and avaliab1hty of, energy to the nestling.

Avian Life History Evolution in Relation to Nest Sites, Nest Predation, and Food

“…4), reducing the vulnerable period and allowing more attempts per season (Figs. 2 and 5), providing broad support for relationships suggested previously (see Lack 1948, Case 1978, Ricklefs 1984, Westmoreland et al 1986, Zaias and Breitwisch 1989, Major 1991, Rowley et al 1991, Sieving 1992. In contrast, Lack (1948Lack ( , 1968 argued that longer nestling periods under reduced predation allow larger clutch sizes, but clutch size was not correlated with nestling period when phylogenetic effects were controlled, providing little support for this hypothesis (also see Ricklefs 1968).…”

“…2 and 5), providing broad support for relationships suggested previously (see Lack 1948, Case 1978, Ricklefs 1984, Westmoreland et al 1986, Zaias and Breitwisch 1989, Major 1991, Rowley et al 1991, Sieving 1992. In contrast, Lack (1948Lack ( , 1968 argued that longer nestling periods under reduced predation allow larger clutch sizes, but clutch size was not correlated with nestling period when phylogenetic effects were controlled, providing little support for this hypothesis (also see Ricklefs 1968). Instead, increased nest predation may favor increased iteroparity to spread risk (bet-hedging; Slatkin 1974, Bulmer 1984 which may be manifested as reduced clutch size to save energy for renesting attempts following failure, or more broods following success (Foster 1974, Slagsvold 1982, Linden 1988.…”

“…Nest predation may vary negatively with latitude (e.g., Ricklefs 1969, Kulesza 1990, so latitude was included as a covariate in analyses of nest predation. However, latitude was not a significant covariate of nest predation for the data examined here (Table 1).…”

“…in other situations. Yet, nest predation is the primary source of nesting mortality (Ricklefs 1969, Martin 1992a, 1993a and can potentially affect life history traits in several ways, while also acting together with food limitation (see Martin 1992b). For example, greater nest predation may favor smaller clutch size, allowing more energy for renesting attempts following failure (Foster 1974, Slatkin 1974, Slagsvold 1982, Bulmer 1984.…”

Sibling Competition and the Evolution of Brood Size and Development Rate in Birds

“…Due to the basic asymmetry of genetic relationships among siblings (Trivers 1974), nestlings and their parents may come into conflict with respect to such nestling adaptations as growth rate and such parental adaptations as brood size and responsiveness to solicitation. Rapid growth benefits nestlings directly by reducing time-dependent mortality, which may be high during the period of nestling development (Ricklefs 1969(Ricklefs , 1984Trivers 1974;Bosque & Bosque 1995;Martin 1995). Moreover, rapid growth may improve the competitive position of a nestling within the brood when it achieves large size at an early age (Magrath 1990;Stouffer & Power 1990).…”