SHARED AND UNSHARED PARENTAL INVESTMENT IN THE PRECOCIAL GOLDENEYE (AVES, ANATIDAE)

Lazarus & Inglis (Anim. Behav., 1986, 34, 1791-1804) introduced a mode l of the influence of brood size on the optimal level of parental inve stment and parent-offspring conflict and drew a distinction between sh ared and unshared types of parental investment. With respect to this d ivision, we measured the parental costs in the goldeneye, Bucephala cl angula, a precocial species with uniparental female care, in terms of time spent in vigilance and intraspecific aggression. We also compared levels of anti-predator vigilance and intraspecific aggression betwee n females with and without broods. Females with broods spent considera bly more time on both vigilance and intraspecific aggression, but anti -predator vigilance was independent of brood size. Furthermore, female behaviour was unaffected by brood reduction. Both these observations support the 'fixed-loss' model of unshared care, where the level of pa rental investment is predicted to be independent of brood size, since the predator is likely to take only a single offspring. In contrast, i ntraspecific aggression, mainly associated with defence of the brood's feeding area, increased with brood size. This supports the 'shared ca re' model where the level of parental investment increases with brood size, a type of care usually associated with altricial species. (C) 19 98 The Association for the Study of Animal Behaviour.