Crowding Affects Black-throated Blue Warbler Foraging Behavior

January 1, 2007 by Gregory Gough

small white bird with black throat and blue upperparts

In the forests of the White Mountains of New Hampshire, black-throated blue warbler pairs set up territories in crowded neighborhoods. Typically, they are surrounded by 4 to 6 couples.

Scientists wondered how this concentration of birds might affect their ability to forage for insects. Lots of neighbors could mean smaller territories with less food, and more time spent defending the territory from the encroachments of neighbors.

To answer the question scientists established control plots in sparsely populated areas to compare with the densely populated plots. In the control plots the pairs would likely have larger territories, more food, and need to spend less time in defence.

To see if there were differences between the plots scientists took 3 measurements: how often birds caught insects, how quickly they ate, and how often they hunted aerially versus hopping among branches. Aerial feeding occurs when the warbler flies out from a perch to catch prey.

The results showed that the parents ate and caught prey at the same rates in both the control and experimental plots. However, there was a difference in the type of foraging—those in the control plots spent more time gleaning insects from the foliage as opposed to flying out to catch insects.

It is likely that lesser availability of food in the crowded plots forced the birds to fly out to catch different prey items (flying bugs, for example). This comes at a cost as it is easier to hop among branches to catch prey than to fly out and try to catch it.

This study continues a series of experiments on what happens when an animal's population increases and what subsequently caused the population to stabilize or reduce.

This article summarizes the information in this scientific paper:

Dobbs, Robert C., Sillett, Terence Scott, Rodenhouse, Nicholas L. and Holmes, Richard T. 2007. Population density affects foraging behavior of male Black-throated Blue Warblers during the breeding season. Journal of Field Ornithology, 78(2): 133-139.

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