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Abstract

We examined how different facets of guira cuckoo sociality influence reproductive investment in eggs (mass, volume, albumen, yolk, shell weight and thickness). The highly variable egg size in this species suggests the possibility of reproductive manipulation by females. Our data support the hypothesis that investment in eggs and clutches reflects a social context. The lowest egg ejection probabilities occurred in very small communal clutches where there were fewer laying females. Eggs retained in the nest had larger yolks than those ejected, a possible mechanism for minimizing energy expenditure in eggs with high chances of failure. Results showed that eggs laid in smaller communal clutches had, on average, less investment in all nutrient measures, except yolk, compared with eggs from larger communal clutches. It may be important for eggs to be of high quality in larger communal clutches, where competition between hatchlings will most likely be intense. Larger guira cuckoo eggs in this study produced heavier chicks. We found that chicks that were smaller and lighter at hatching were victimized by infanticide significantly more than chicks that were heavier and bigger at hatching. (C) 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.