[cobirds] Swallows

I was having trouble accessing my Birds of North American (BNA) account this morning when I first posted about swallows.  Apparently the reference I quoted in lieu of BNA (Erlich's Birder's Handbook) about Cliff Swallows sometimes having "2-3 broods per year" is in error.  The Birds of North America account by Brown, which is heavily based on studies of this species in Nebraska, states Cliff Swallow is single brooded.  Evidence of late summer nesting is usually the result of nest failures earlier in the summer.  This is also stated in the BBA I account authored by David Pantle (which heavily references Bailey and Niedrach's Birds of Colorado).   Thus, part of my question was answered once I straightened myself out on this brood business.  Barn Swallow is the only regularly double-brooded swallow species in CO.  Apparently Bank Swallow is the only other swallow species that is sometimes double-brooded in N.A. but that usually (always?) occurs in areas outside CO.  It stands to reason, then, that in our state Barn Swallows would require a longer summer stay to accomplish their breeding tasks.

I appreciate the comments about the post, most of them observations of Barn Swallows and Cliff Swallows seen of late.  The more I think about this, the more questions come to mind.  It still seems like Barn Swallows are the lone representatives of the swallow clan for a longer period of time at the end of the breeding season than they used to be (that is, either they are staying longer and/or the other 5 species are leaving earlier).  Why is a seemingly semi-hardy species like Tree Swallow (which often is the first to show up in spring) among the set of swallows that leaves toward the end of July-early August?  Why do most of the swallows leave rather abruptly after their broods fledge, when the majority of other passerine species stick around until times get tough?

Dave Leatherman
Fort Collins