Thursday, May 8, 2014

Tree Swallow

Tree Swallows, with their aggressive defense of artificial nesting boxes, are not always the favorite bird of bluebird enthusiasts. These swallows are, nevertheless, gorgeous birds, with their fresh plumage glistening in the sun. The pair is one of my first in 2014. One consequence of their use of nesting boxes is that Tree Swallows are among the best-studied birds in North America (Winkler et al. 2011).
The two birds here perched near a “bluebird” box. The two birds chattered and gaped at each other. Earlier I posted that one reason for swallow yawns is to strengthen their jaw muscles. Another possibility is that these are appeasement displays to calm this swallow’s aggressive nature. Throughout the breeding season, Tree Swallows are on a constant defense of their nesting sites. Substantial numbers of non-breeding males and females (non-breeding floaters) constantly attempt to take over occupied sites. The territory holders drive the intruders away. Perhaps this gaping behavior reduces aggression to one’s proper mate.

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