Yellow warblers are small insect-eating songbirds that breed in North America and migrate to the tropics for the winter. Scientists studied them at a wintering area in a sun coffee plantation in Guatemala.
A sun coffee plantation consists of coffee planted in rows, much like a field of corn or soybeans. Coffee can also be grown under a canopy of shade trees.
Sun coffee plantations are not particularly attractive to birds, but the scattered trees interspersed within the coffee shrubs provide some bugs for birds to eat.
Only the male yellow warblers occupied the plantation. The females were in other habitats. The males defended territories about half a hectare in size.
Much like a neighborhood bully, the yellow warblers were selective in who they chased away, mostly birds smaller than themselves (such as magnolia and Tennessee warblers) that eat the same food items.
Most wintering migratory birds hang out in small flocks together and do not defend territories (except for birds defending nectar or fruit sources) so the behavior of these yellow warblers is somewhat unusual. Perhaps insect food is so scarce in sun coffee plantations that this aggression is necessary.
This article summarizes the information in this scientific paper:
Greenberg, Russell S., Reitsma, R. and Cruz, A. 1996. Interspecific aggression by yellow warblers in a sun coffee plantation. The Condor, 98: 640-643.
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