|A family of Northern Rough-winged Swallows, 19 July 2011, Forest Grove, Oregon by Greg Gillson.|
You see, the first set of juvenile feathers on Tree Swallows are brown. Then these 3 or 4 month old swallows go through another complete "preformative" molt in fall--basically into an adult-like plumage. However, many of the first-year females have a dull brown plumage. They keep these feathers until the next autumn, so some first-year females arrive on the breeding grounds in spring a rather drab brown color. Thus, at any time of year you may encounter brown Tree Swallows.
Northern Rough-winged Swallow
Rather evenly brown above. The throat and upper chest are pale brownish merging into white belly. Long winged and graceful languid flight. Call is a rough flatulent-like sound "pbbbt." Nest in single or small groups of burrows in sandy or muddy bank.
|Northern Rough-winged Swallow, 9 August 2010, Forest Grove, Oregon by Greg Gillson.|
Brown back with contrastingly darker wings. Underparts, including throat, white. Dark, full brown neck collar, sometimes with a central "spike" going down the belly. A small swallow; wings shorter and more triangular. Flight more direct with rapid wing beats. Call is a rough buzz like electric line, "bzzzt," or "prit-prit." Nest in large colonies of burrows in sandy bank or cliff.
|Bank Swallow, 29 May 2013, Malheur NWR, Oregon by Greg Gillson|
|Bank Swallow, 28 May 2013, Hines, Oregon by Greg Gillson.|
Adult males have metallic steel-blue back and wing coverts, black mask, gleaming white underparts. Females are duller. Some first-year females are brownish rather than blue, but usually have some blue feathers on the bend of the wing, at least. Juveniles are brownish with white throat and an indistinct (usually) grayish breast band. In flight the breast band can be conspicuous, but not as strong as Bank Swallows. Rather long wings and graceful flight. Calls are a liquid twittering. Nest in tree cavity or nest box.
|Tree Swallow, juvenile showing Bank Swallow-like breast band, 10 July 2013, Hillsboro, Oregon by Greg Gillson.|
|Tree Swallow, first year female, 17 April 2004, Forest Grove, Oregon by Greg Gillson.|
|Tree Swallow, male, 16 April 2010, Forest Grove, Oregon by Greg Gillson.|
In 2008 Don Roberson wrote an article, Identification of brown swallows, on his Monterrey, California birding pages that provides additional ID tips.