A NEW EQUATION FOR CALCULATING REPRODUCTIVE SUCCESS OF CLUTCHES AS A FUNCTION OF THE DAY ON WHICH INCUBATION STARTS: SOME IMPLICATIONS.

Many species of birds start incubation before the last egg of a clutch is laid, which often results in asynchronous hatching and fledging. The incubation pattern favored by natural selection should lead to greater reproductive success than alternative patterns. Equations for calculating the reproductive success of a clutch as a function of the start of incubation have been proposed by Clark and Wilson (1981) and Hussell (1985). Both equations predicted a greater frequency of an earlier start of incubation than occurs in nature. Here, I present a new equation in which the relevant parameters determining reproductive success as a function of the start of incubation are (1) the probability of any young leaving a nest and (2) the post-first-fledging daily survival rates of the remaining nestlings. This equation is universally applicable and accounts for the greater frequency of incubation starting later, rather than earlier, in the laying sequence of most birds. I use the equation to evaluate various hypotheses regarding the evolution of incubation patterns. [ABSTRACT FROM AUTHOR]