SENTINEL BEHAVIOR, SEASONALITY, ANO THE STRUCTUREOF BIRO FLOCKS IN A BRAZlLIAN SAVANNA

Suiriri Flycatcher (Suiriri suiriri) Science Article 1

abstract

We investigated composition, annual cycle, site fidelity; foraging behavior of birds in mixed-species flocks, and the importance of sentinel behavior by the White-banded Tanager, Neothraupis fasciata, in a cerrado (savanna) near Brasilia, Brazil. Mixed-species flocks, comprising up to twenty-five resident, migratory, and transitory species, occurred in all months of the year, and were most frequent during the dry season, compared to the rainy season when breeding occurred and most species were absent or occasional in the flocks. The nuclear species were Whitebanded Tanager and Suiriri Flycatcher (Suiriri suirin), both residents with permanent territories. White-banded Tanagers showed sentinel behavior, performed by males and females usually one at a time. The intensity of the tanagers’ sentinel behavior was significantly lower in mixed-species flocks compared to conspecific associations. This is consistent with the prediction that enhanced protection by other species resulted in lower requirements for vigilance by White-banded Tanagers. Sentinel behavior did not depend on group size, flock size or time of year. Most species were insectivorous. There was no evidence of convergence in foraging height or tactics amongthe three most frequent species. We suggest that protection from predation is a major factor in the formation of mixed species flocks in cerrada.

Maria Alice S. Alves & Roberto S. Cavalcanti, ORNITOLOGIA NEOTROPICAL 7: 43-51, 1996

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