Current Ornithology Volume 6, 1989, pp 1-50

Mortality Patterns, Sex Ratios, and Parental Investment in Monogamous Birds

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Abstract

A subject of great interest to students of animal mating systems over the past 15 years has been parental investment, a concept that includes parental care and the cost of gametes. Parental care in birds (and other animals) had been studied for many years prior to Trivers’s (1972) seminal paper, but Trivers’s contribution was of major importance because he placed parental care in a theoretical framework. Specifically, he attempted to link parental care to mortality patterns and sex ratios, and thereby account for the varying strength of sexual selection in a diversity of mating systems. Parental investment (PI) is defined as “any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring” (Trivers, 1972). This definition has been modified to apply to clutches or broods of offspring (Wittenberger, 1981).