Scrounging prevents cultural transmission of food-finding behaviour in pigeons

Living in groups should promote the cultural transmission of a novel behaviour because opportunities for observing knowledgeable individuals are likely to be more numerous in this condition. However, in this study pigeons who shared the food discoveries of others (scroungers) did not learn the food-finding technique used by the discoverers (producers). Individually-caged pigeons prevented from scrounging easily learned the technique from a conspecific tutor. When caged pigeons obtained food from the tutor's performance, most nai've observers failed to learn. In a flock, scroungers selectively followed producers. In individual cages, scrounging during the tutor's demonstration was equivalent to getting no demonstration at all. This effect of scrounging did not interfere with subsequent acquisition of the foodfinding behaviour when scrounging was no longer possible. Many animals are known to adopt a novel behaviour as a result of observing others performing it (see Galef 1976; Bonner 1980; Mainardi 1981 for reviews). This type of learning has been variously labelled cultural transmission, social learning, imitation, observational learning, etc. One consequence of such learning is the potentially rapid spread of behavioural innovations within populations. All other things being equal, cultural transmission should be very rapid in group-living animals, since the rate of diffusion of the innovation increases with the frequency of contact between knowledgeable and naive individuals (Cavalli-Sforza & Feldman 1981). When animals forage in groups, however, occasions arise in which some individuals (scroungers) may parasitize the food discoveries of other individuals (producers; Barnard & Sibly 1981; Barnard 1984). Pigeons, Columba livia, exhibit these producer and scrounger behaviours (Giraldeau & Lefebvre 1986), but they do so in a flexible way: different individuals become producers in different contexts, leading to what Giraldeau (1984) calls a skill pool, a system of exchangeable producerscrounger roles. Feral pigeons are highly opportunistic flock feeders (Murton & Westwood 1966; Murton et al. 1972) and are thus prime candidates for cultural learning. Palameta & Lefebvre (1985) have shown that individually-caged pigeons can adopt a novel food-finding behaviour via observational learning and local enhancement. Yet when pigeons are tested in a group, the same behaviour that is easily learned by caged individuals spreads to only a few birds within the flock (Giraldeau & Lefebvre 1986: Lefebvre, in press). The scrounging that occurs in a group thus appears to be associated with a blockage of learning. In this paper, we test the hypothesis that scrounging blocks cultural learning. We first examine producing and scrounging in a group context and determine whether dominance and competition for opportunities to produce can account for the producer-scrounger relationship. We then test whether scrounging is sufficient to block observational learning in individually-caged birds. Finally, we investigate whether scrounging blocks learning (1) by interfering with the reception of information during observation of the producing skill, (2) by blocking only performance, despite acquisition of information about the producing skill, or (3) by long-term interference with learning of the skill. F L O C K E X P E R I M E N T S