Head position as an indicator of producer and scrounger tactics in a ground-feeding bird

The benefits of group foraging depend on the frequency of feeding from food uncovered by companions (joining) versus self-discovered food (finding). Information-sharing (IS) and; producer-scrounger (PS) games predict different joining frequencies because they make distinct assumptions about food searching. IS games assume individuals can search concurrently for finding and joining opportunities while PS games assume incompatible search modes; individuals search either as a producer, detecting only finding opportunities, or as a scrounger, detecting only joining opportunities; To determine the search assumption for flocks of ground-feeding granivores we studied the behaviour of spice finches, Lonchura punctulata, foraging in indoor aviaries for clumps of hidden millet seed. We looked for behaviour patterns preceding finding and joining events. An analysis of covariance showed that the frequencies of hopping with the head pointing up and down were statistically associated with the frequencies of a bird's joining and finding, respectively. When the expected stable frequency of the scrounger tactic was altered by changing the seed distribution, the birds' relative frequency of hopping with the head up changed accordingly When the seed distribution made any use of the scrounger tactic unprofitable, the frequency of hopping with the head up declined to zero. Consequently, in ground-feeding birds such as spice finches, finding and joining behaviour conform more closely to the assumptions of a PS rather than an IS game. (C) 2001 The Association for the Study Animal Behaviour.