Benefits of cooperative food search in the maintenance of group living in ocellated antbirds

Johel Chaves, Purdue University

Abstract

I studied ocellated antbirds (Phaenostictus mcleannani : Thamnophilidae) in Costa Rica to identify the mechanisms that favor sociality in this species. Ocellated antbirds aggregate to capture fleeing prey at swarms of nomadic army ants. I used radio telemetry to record bird movements, and developed novel molecular markers to estimate genetic relatedness. My results show that ocellated antbirds do not live in family groups. Each mated pair has its own roosting area and adjacent roosting neighbors were generally unrelated. Most feeding aggregations included unrelated individuals; these birds do not usually feed with relatives. The birds often traveled in cohesive groups from one ant colony to another, and individuals without information on ant colony location sometimes followed informed ones to ant colonies. Travel groups were composed of close relatives more often than expected, suggesting they can gain indirect components of fitness by leading relatives to swarms. Travel groups were also composed of adjacent roosting neighbors more often than expected. When birds aggregated to feed at a swarm located in the roosting area of one of the birds present, that bird obtained priority access to prey. Priority access to prey was only shared with adjacent roosting neighbors; other birds present in the aggregation obtained lower prey-intake rates. This suggests that ocellated antbirds gain direct components of fitness by leading adjacent neighbors to swarms because they can later follow them to other swarms close to their roosting areas (where they obtain higher prey intake). Overall, the results show that group feeding in animals can be maintained by the direct and indirect components of fitness obtained by leading/following and tolerating particular individuals.

Degree

Ph.D.

Advisors

Rabenold, Purdue University.

Subject Area

Ecology

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