Egg losses and nest desertion in Greater Rheas Rhea americana

Abstract

Avian nest desertion should occur when the cost of attending the nest results in a reduction of parental fitness. In Greater Rheas Rhea americana, the male incubates the eggs so that the decision to desert the nest is made exclusively by him. Because of constraints, the timing of desertion may affect the possibility of renesting. We estimated nest desertion rates through the breeding season and at different stages of the nesting cycle (laying and early, mid- and late incubation). We also analysed the effect of egg losses at different stages of the nesting cycle on the probability of deserting the nest. Nest desertion rates decline throughout the breeding season. The probability of deserting the nest was higher during the laying stage and decreased through incubation. For all stages, egg losses were higher in nests that were deserted than in nests that were still active at the end of the corresponding stage. Egg losses were less likely to elicit nest desertion as incubation advanced. Egg losses in experimental (unattended) nests were not random. We postulate that egg losses during the first stages of the nesting cycle would be a good predictor of future egg losses and risk of nest failure. As females remain associated with the male during egg-laying and because incebation in rheas is an energetically costly activity that may affect renesting attempts, early nest desertion could increase a male's ability to remate and renest.