Egg losses and nest desertion in Greater Rheas Rhea americana

Avian nest desertion should occur when the cost of attending the nest resul ts 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 ex clusively by him. Because of constraints, the timing of desertion may affec t the possibility of renesting. We estimated nest desertion rates through t he breeding season and at different stages of the nesting cycle (laying and early, mid- and late incubation). We also analysed the effect of egg losse s 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 de creased 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 a s incubation advanced. Egg losses in experimental (unattended) nests were n ot random. We postulate that egg losses during the first stages of the nest ing cycle would be a good predictor of future egg losses and risk of nest f ailure. As females remain associated with the male during egg-laying and be cause incubation in rheas is an energetically costly activity that may affe ct renesting attempts, early nest desertion could increase a male's ability to remate and renest.