[cobirds] Bay-breasted Warbler in Estes Park on 3Nov2021

I was curious about the situation with the Bay-breasted Warbler at Lake Estes and its involvement with Russian-olive.  On the spur of the moment, with visions of getting a photo of this warbler gripping a fat olive in its beak, I headed up there this afternoon.  Upon arrival at 2:45 I turned s off US36 toward the Fairground on Community, parked at the Dog Park, went n under 36 via the pedestrian/bike tunnel and immediately found the bird just n of the tunnel in the biggest, lush Russian-olive between the bike trail and Lake Estes.

I was surprised, but probably shouldn't have been, to see the bird very actively eating aphids, NOT olives.  The classic book by Miriam Palmer Aphids of Colorado lists two aphid species in the genus Capitophorus on Russian-olive, C. shepherdiae and C. braggii.  I believe the more common of the two and the one we see the most along the Front Range and in a place like Estes is C. braggii, the so-called "OleasterThistle Aphid".  From the beginning up until 4:45 when I left, the bird was nitpicking aphids at the rate of about 1/second from leaves mostly, but also from twigs and bigger branches.  An earlier post from another observer mentioned seeing it on the ground.  I saw it from a distance on the ground briefly but could not really tell what it was doing.  It was probably getting winged male aphids which are much more mobile than other life stages, but I suppose it could have been pecking pulp from fallen olives, the pulp being a favorite of other warblers, especially Yellow-rumps.

      

Interestingly, the aphid pics above were taken just this morning at Sheldon Lake in Fort Collins City Park.  I believe this is the same exact aphid favored, also today, by the very fat Bay-breast.  The Fort Collins host was also Russian-olive and hundreds were being consumed by a ravenous flock of about 20 Bushtits.  The left photo shows an adult male; the middle photo illustrates the diverse life stages typical of most aphids and features a male mating with a female in the upper left; the right photo shows a group of three females discussing the shameless mating pair.

In the cropped shot of the Bay-breast at Lake Estes below, note the aphid on its lower mandible.

  

If you recall the Bay-breast present in Boulder at this same time of year in 2013, it was eating a different species of aphid (genus Schizolachnus) on Austrian pine. 

Thanks to Glen for finding the Bay-breast, to Marc for his faithful monitoring of the entire Lake Estes area, and for the updates about this bird by many folks to eBird and COBIRDS.

Dave Leatherman

Fort Collins