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David Sibley explains how to use nesting behavior to help identify birds

TREE SWALLOWS: Among swallows, only Tree and Violet-green nest in cavities. If you observe a pair investigating a nest box, you have enough information to rule out other species. Art by David Sibley.
TREE SWALLOWS: Among swallows, only Tree and Violet-green nest in cavities. If you observe a pair investigating a nest box, you have enough information to rule out other species. Art by David Sibley.

In most of North America, nesting behavior is common any time between April and July. You may not think of it as a field mark, but it can be helpful in the identification process, since it narrows the possibilities.

You can start by noticing the signs of nesting. Almost any bird holding food or nesting material is likely to have a nest nearby. A bird showing extreme agitation, such as a distraction display, is likely to be defending a nest. A bird carrying a fecal sac or an eggshell as it flies from a nest, and courtship feeding, raptors perched side by side, or other evidence of pair bonds can also suggest nesting.

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David Sibley

David Sibley

David Sibley writes the column “ID Toolkit” in every issue of BirdWatching. He published the Sibley Guide to Birds in 2000, the Sibley Guide to Bird Life and Behavior in 2001, and Sibley’s Birding Basics in 2002. He is also the author of the Sibley Guide to Trees (2009), the Sibley Guide to Birds-Second Edition (2014), and guides to birds of eastern and western North America (2016). He is the recipient of the American Birding Association’s Roger Tory Peterson Award for lifetime achievement in promoting the cause of birding and a recognition award from the National Wildlife Refuge System for his support of bird conservation.

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