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eJacanas represent the extreme in avian sex-role reversal. We studied the division of labour between the two sexes in parental care of the eggs and chicks in wattled jacanas, Jacana jacana, in the Republic of Panama. Males were the sole incubators of the eggs (515 clutches). Males were also the sole caretakers of chicks for 97 % of broods (NZ 252). Caretaking activities included continuous close association with the young, leading them to foraging locations, brooding them during cold temperatures and rain, and maintaining nearly constant vigilance against threats of predation. Although females were also observed to perform all of these direct chick care behaviours, they did so very rarely (3 % of broods) and only when the male was unavailable to provide such care himself. This happened either when females laid new clutches for males that were still tending dependent chicks, or when predators killed males, leaving broods defenceless and untended. The only regular contribution to chick care by females was providing defence against predators. The male was usually the first parent to detect a predator, but he recruited the female to join him in confronting threats that he could not deter alone. We conclude that, although males perform the overwhelming majority of parental care in wattled jacanas, females provide critical backup support. By displaying parental behaviours facultatively, only when the male is unable to provide them adequately himself, female wattled jacanas are able to enhance the survival of their eggs and young while typically expending only minutes per day in such efforts. 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. Parental investment refers to anything done for an off-spring that increases its chance of survival while de-creasing the parents ’ ability to produce additional offspring (Trivers 1972). It includes the cost of producing the gamete plus any additional time or effort expended on behalf of the offspring until it becomes independent. In the vast majority of animal species, parental investment by females exceeds that by males. In birds, for example, females produce extremely large and costly eggs, and when there is an asymmetry in egg care behaviour by the two sexes, it is usually the female that performs the majority (or all) of the incubation (Lack 1968; Clutton