[cobirds] Re: Swallow departures from northern Front Range in 2013

I observed scores of both Cliff and Barn Swallows nesting under three different bridges-over-ditches on the Federal Center (6th & Kipling) all summer.  The majority left sometime between August 27 and Sept 12.

On Thursday, September 26, 2013 10:29:57 AM UTC-6, Dave Leatherman wrote:

So, is it just me or does it seem like Barn Swallows have been the last swallow species standing for much longer this late summer-autumn than usual? 

In the way of example, in the northwest corner of Grandview Cemetery in Fort Collins there is a bridge over a ditch that hosts nesting by both Cliff and Barn Swallows.  It appears to me the Cliff Swallows were single-brooded this year and the Barns did their normal double nesting.  Last Cliff was seen there, or anywhere else for that matter, on 4 August.  Birder's Handbook by Erlich et al says Cliff Swallows "usually have 1 brood, sometimes 2-3."  I guess the weather this year, particularly the late spring storms and a resultant late start to nesting, determined 2013 as a single brood year for the Cliffs.  I just don't recall a year when for essentially all of August and September if one sees a swallow, one could assume the overwhelming possibility was Barn.  Given the explosion of aerial insects of late, it seems ironic that a major group (excepting Barn) of insect-eaters is no where to be seen.  The analogy that comes to mind are sports fans who leave the game early, only to hear during their drive home that the home team pulled off a record-setting comeback.  Just what is the environmental clue that dominates the decision of a species to refrain from, or go for, an additional brood?  Ditto for migration south.  Is it day-length, nighttime temps, an assessment of available food resources now and into the near future, something else?

I'd be interested in the observations of others about Cliff, or any other swallow species for that matter, departing earlier this year compared to a "normal" year, if there is such a thing in CO? 

Dave Leatherman
Fort Collins  

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