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). I nformation-sharing (TS) and; producer-scrounger (PS) games predict differen t joining frequencies because they make distinct assumptions about food sea rching. IS games assume individuals can search concurrently for finding and joining opportunities while PS games assume incompatible search modes; ind ividuals 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 be haviour of spice finches, Lonchura punctulata, foraging in indoor aviaries for clumps of hidden millet seed. We looked:for behaviour patterns precedin g finding and joining events. An analysis of covariance showed that the fre quencies of hopping with the head pointing up and down were statistically a ssociated with the frequencies of a bird's joining and finding, respectivel y. When the expected stable frequency of the scrounger tactic was altered b y changing the seed distribution, the birds' relative frequency of hopping with the head up changed accordingly When the seed distribution made any us e f the scrounger tactic unprofitable, the frequency of hopping with the he ad up declined to zero. Consequently, in ground-feeding birds such as spice finches, finding and joining behaviour conform more closely to the assumpt ions of a PS rather than an IS game. (C) 2001 The Association for the Study Animal Behaviour.