Offspring Desertion in the Magnificent Frigatebird: Are Males Facing a Trade-Off between Current and Future Reproduction?

Abstract

Timing of offspring desertion is expected to be the outcome of the trade-off between current and future reproductive benefits for deserters. I investigated this idea by analysing the timing of male desertion in the Magnificent Frigatebird Fregata magnificens. I recorded parental attendance, male desertion and chick survival from an average of 39 days old (+ 2.7 S.E. days) to fledging (181.2 + 3.4 days old, n = 24) at 42 nests, and checked the presence and breeding state of marked males (red gular pouch) at the colony the following breeding season. All male parents deserted their nest when their only chick was between 19 and 160 days old (77.1 + 5.0 days). Male desertion was influenced by settling and deserting dates: settling date correlated negatively with the age of the chick at the time of male desertion. Late-settling males deserted later during the year than males settling early, the condition of their chick (at the time of male desertion) was lower and their chick fledged late during the year. In spite of the obligate and apparently date-constrained desertion, chicks deserted when very young died more frequently than those deserted when older, and successful males deserting late during the year (after the average desertion date) were marginally less likely to be seen in reproductive state the following breeding season than those deserting early. The inter-individual variation is consistent with the idea that male frigatebirds may face a trade-off between current and future reproductive expectations: early-settled individuals began breeding before 16 October, deserted before the average deserting date, stayed with the chick for 92 days, their chicks survived well (84%) and 75% of these males were seen in reproductive state the following breeding season. Late-settled individuals began to breed around 19 December, deserted when their chick was 55 days old, chicks survived well (64%) but still only 50% of males were seen in breeding state the following breeding season. Some early-settled individuals who remained longer attending the chick (120 days) and whose chick survived, deserted after the average desertion date (20 April), but only 50% of them were seen in breeding state the following season.