Incompatibility between antipredatory vigilance and scrounger tactic in nutmeg mannikins, Lonchura punctulata

Most social foragers must search for food while avoiding predators. Group-foraging nutmeg mannikins engaged in a producer-scrounger game search for their own food (play producer) by hopping with the head down and search for others' food discoveries (play scrounger) by hopping with the head up. If the scrounger tactic is compatible with antipredatory vigilance, then an increase in antipredatory vigilance should lead to the detection of more joining opportunities, and hence to more joining by foragers. We tested this prediction as well as the extent to which stationary birds use head up exclusively for antipredatory purposes and hopping birds use head up for foraging purposes only. We observed three flocks of nutmeg mannikins searching for hidden clumps of food in an indoor aviary. We used a 2 x 2 factorial design in which both the distance to a safe refuge and the food distribution were manipulated. The use of head up by stationary and eating birds increased significantly with increased distance to cover. Distance to cover, however, had no effect on the use of the scrounger tactic or on the level of joining. We found no evidence of compatibility between the scrounger tactic and antipredatory vigilance. Our results provide the first unambiguous evidence for the existence of two distinct and incompatible patterns of vigilance for predators and for conspecifics. (C) 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.