Sunday, 22 November 2015

[cobirds] Tennessee Warbler continues at CSU (Larimer)

The first fall female Tennessee Warbler initially discovered at the Plant Environmental Research Center (PERC) in the southwest corner of the Fort Collins campus of Colorado State University on 19November continued today thru at least 3pm in the exact same general area and trees (mostly in the European Beech (Fagus sylvatica) plot up on the hill in the southwestern part of the property) thru at least 3pm on 11/22.  PERC is north of W. Lake Street about a half mile e of Shields Street.  The warbler was seen today by CSU's Team BrachyRAMphus, Janet Hardin, Joe Mammoser, Adam Vesely, Cheri Phillips, Jessie Casias, the Pughs, me, and maybe others.

The area it likes is FULL of aphids.  This little bird, so fat it now has cleavage, has been gleaning aphids, from the undersides of leaves mostly, in European Beech, various oaks, and viburnum shrubs.  It also spends a good bit of time on the ground getting aphids and perhaps other arthropod morsels like collembola.  I should point out that almost all of the plants at PERC have metal or plastic tags on them.  Usually these are on a low branch on the north side of the plant.   The warblers absolute favorite tree is the 'Red Obelisk" European Beech, which is a 30 foot tall columnar specimen full of aphids, and which still has most of its leaves.  If the bird doesn't fly south tonight and is there tomorrow, and maybe even longer, if you check tags and find the 'Red Obelisk' beech, I can almost guarantee it will appear in that tree at least once an hour.  This tree is about 10 feet south of where Andy Bankert made a pile of sticks at the base of the rather large, leafy 'Atropurpurea' European Beech.  Andy's creation looks like something that only lacks kindling and a spark to keep you warm.  The bird tends to hang with either juncos or bushtits, but does so loosely.  I have seen it by itself quite a bit.  But if you hear other birds coming (to these same aphid-laden beeches, oaks, and viburnums), pay attention to every individual and one of them might well be the very greenish Tennessee Warbler.  I have heard the bird make a very few vocalizations, usually when it leaves one tree for another, but would say sound is not really of much help in finding her.  And, as stated, do not ignore watching the ground.

Dave Leatherman
Fort Collins


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