Does father know best? Social learning from kin and non-kin in juvenile ringdoves

Abstract

Parent-offspring transmission is usually thought to be the major route for cultural learning. We tested this assumption in ringdoves (Streptopelia risoria), a flock feeding Columbid that is easily raised in captivity. An aviary study first determined the foraging associations of juveniles placed with their sibling, their parents and a pair of non-kin adults. Juveniles foraged more often with kin than with non-kin and joined food discoveries in proportion to these foraging associations; aggression was relatively rare and came more often from unrelated adults than from parents. Two cage experiments showed that parents were not copied more often than unrelated adults when the two tutor types provided different, but equally productive, solutions to a feeding problem. Neither the ingestion of unfamiliar food (two seed types the juveniles had never encountered) nor the learning of a new food searching skill (opening a box containing seed) showed a differential effect of father versus non-kin tutors. Animals that scramble compete for food may thus acquire social information from whatever knowledgeable individuals are present, whether these are kin, unrelated conspecifics or heterospecifics.

Introduction

One of the major pathways for cultural (or social) learning is commonly throught to be parent-offspring transmission. Mathematical models routinely underline the importance of this mode of transmission (termed `vertical transmission'; Cavalli-Sforza and Feldman, 1981, Pulliam, 1983), while experiments on laboratory-raised rodents have brought to light maternal influences on offspring diet (Galef, 1977, Valsecchi et al., 1993). Numerous field studies describe adult-juvenile associations that are indirectly presumed to promote learning (Davies, 1976, Skutch, 1976, Diamond, 1987), but those specifically testing for parent-offspring transmission are rare. Descriptive reports on chimpanzees suggest that juveniles learn to fish for termites by observing adults (Goodall, 1973). In oystercatchers, cross-fostering experiments have shown that offspring may learn mussel-opening techniques by copying the variant used by their parent (Norton-Griffiths, 1968). More recently, (Aisner and Terkel, 1992) have reported that black rats learn to open pine cones through exposure to partially-opened ones stripped by their mothers.

In all of these cases, the relative importance of parents versus non-parents as tutors is not specifically addressed. In a laboratory study, (Chesler, 1969) has examined preferential social learning in kittens and found that learning from the mother is more rapid than learning from an unfamiliar, unrelated adult. These results are intriguing, but the design used by Chesler unfortunately confounds familiarity with kinship, a problem that may be difficult to avoid in a nongregarious species. In a group-living animal, juveniles will routinely be exposed to kin and nonkin as potential informers. The young of territorial species may also show frequent learning from their parents, but in the absence of any alternative source of information (non-parents are chased from the territory), it is impossible to argue for preferential learning. The most stringent test of parent-offspring transmission thus lies in group-living animals, where the efficiency of parent versus non-parent tutors for juvenile social learning can be directly compared.

Ringdoves (Streptopelia risoria) are a good candidate to study preferential learning from the parent in captive experiments, since they are not only gregarious, but are also easy to breed. The ringdove is a domesticated descendant of African collared doves, S. roseogrisea (Irwin, 1959, Goodwin, 1983), which are known to forage in small flocks in West Africa (Morel, 1983). Although ringdoves are for the most part a domesticated species, feral colonies have been established in a few localities of the southern USA (Goodwin, 1983). In this paper, we test for preferential social learning from the parent by giving laboratory-raised juvenile ringdoves the choice between copying their father or a familiar, unrelated flock member. We look at two key components of foraging behaviour: the learning of new searching and handling techniques and the ingestion of novel food types. To derive predictions for these learning experiments, we first examine foraging interactions between juvenile rindgdoves, their parents and unrelated adults housed together in free-flight aviaries. In the field, foraging interactions have proven to be an excellent predictor of preferential social learning in an opportunistic avian guild: three populations of Zenaida doves (Zenaida aurita) and one population of Carib grackles (Quiscalus lugubris) in Barbados show a striking relationship between intra-and interspecific use of scramble (unaggressive) feeding competiton and social learning (Lefebvre, 1996). Territorial Z. aurita from St-James are extremely aggressive against conspecific intruders, but forage unaggressively with grackles; in captive learning experiments, territorial doves learn very poorly from conspecific tutors, but very well from grackles (Lefebvre et al., 1996, Dolman et al., 1996). In contrast, group living Zenaida doves from the Barbados Deep Water Harbour feed in homospecific flocks, but rarely forage with grackles; they learn readily from a dove tutor, but not from a grackle (Dolman et al., 1996). Zenaida doves from a site adjacent to the harbour, Brandon's Beach, show an intermediate social foraging pattern and encounter both small flocks of conspecifics and grackles in high density food conditions: they learn as readily from conspecific and grackle tutors (Carlier and Lefebvre, in press). Finally, grackles use scramble competition against both conspecifics and Zenaida doves; they learn as readily from either tutor type (Lefebvre et al., in pressRusson et al., in press).

We use this comparative ecological framework to link foraging interactions with social learning in juvenile S. risoria and show that ringdoves learn as readily from their father as they do from a familiar non-kin adult, consistent with the unaggressive scramble competiton they show against both types of birds.