Parental care in Sula leucogaster (Boddaert) (Aves, Pelecaniformes, Sulidae) on the Currais Islands, Paraná, Brazil

In Sula leucogaster (Boddaert, 1783) it happens a brood reduction from two to one egg. The eggs hatch asynchronously and it is rare for the second chick to survive for long. A quantify parental investment is proposed and the differences between males and females of Sula leucogaster is verified for to help to understand the brood reduction. The studies were conducted on Ilhas dos Currais, Paraná, Brazil, where a total of 140 nests were studied. Males and females shared the breeding care period. However, females invested about 8% more on incubation than males (c² = 7,37; c² critic = 3,842). Time of absence in the nest for females was larger than for males (c² = 13,9; c² critic = 3,842). This is probably a function of females bringing food to chicks more frequently (61%, n = 120) than males (c² = 5,63; c² critic = 3,842). The main parental investment during the phases with eggs and/or hatchings was protection, and during the postfledging period was to provide feeding. The brood reduction in S. leucogaster is due to the high cost of rearing two chicks during the same breeding attempt. This could be a disadvantage to the future survival and/or the reproduction of both parents and chicks