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Seasonal shift in the foraging niche of a tropical avian resident: resource competition at work?

Published online by Cambridge University Press:  10 July 2006

Julie A. Jedlicka ,
Russell Greenberg ,
Ivette Perfecto ,
Stacy M. Philpott  and
Thomas V. Dietsch
Julie A. Jedlicka
Affiliation:
Department of Ecology and Evolutionary Biology, University of Michigan, 830 N. University Ave., Ann Arbor, MI 48104, USA
Russell Greenberg
Affiliation:
Smithsonian Migratory Bird Center, National Zoological Park, 3001 Connecticut Ave NW, Washington DC 20008, USA
Ivette Perfecto
Affiliation:
School of Natural Resources and the Environment, University of Michigan, 430 E. University, Ann Arbor, MI 48109, USA
Stacy M. Philpott
Affiliation:
Department of Ecology and Evolutionary Biology, University of Michigan, 830 N. University Ave., Ann Arbor, MI 48104, USA
Thomas V. Dietsch
Affiliation:
School of Natural Resources and the Environment, University of Michigan, 430 E. University, Ann Arbor, MI 48109, USA Center for Tropical Research, University of California, La Kretz Hall, Suite 300, Box 951496, Los Angeles, CA 90095-1496, USA
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Abstract

This study examined the foraging behaviour of a resident bird species, the rufous-capped warbler (RCWA, Basileuterus rufifrons), in a shaded-coffee farm in Chiapas, Mexico. Unlike many resident species that use shaded-coffee agroecosystems seasonally, RCWAs do not move to other habitats when migrants are present. RCWA foraging was compared when migrant birds were present (dry season) and absent (wet season). It was hypothesized that RCWAs would exhibit a seasonal foraging niche shift because of resource competition with migrants. Observations from both the canopy and coffee understorey show that RCWAs foraged almost equally in both vegetative layers during the wet season although they were more successful foraging in the canopy. In the dry season, migrants foraged primarily in the canopy and RCWAs shifted so that 80% of RCWA foraging manoeuvres were in the understorey. At that time RCWAs foraged less successfully in both vegetative layers. Avian predation in the dry season was found to reduce densities of arthropods by 47–79% in the canopy, as opposed to 4–5% in the understorey. In the canopy, availability of large (>5 mm in length) arthropods decreased by 58% from the wet to dry season. Such resource reductions could have caused the RCWA foraging niche shift yet other alternative or additional hypotheses are discussed. Shifts in foraging niche may be a widespread mechanism for some small insectivorous residents to avoid seasonal competition with abundant migrant species.

Keywords

avian insectivorybirdsbreeding demandChiapasMexicocoffee agroecosystemdirect interferenceforagingindirect competitionmigrant–resident interactionresource competitionrufous-capped warblersexual segregationshaded coffee
Type
Research Article
Information
Journal of Tropical Ecology , Volume 22 , Issue 4 , July 2006 , pp. 385 - 395
Copyright
2006 Cambridge University Press

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