E. J. Raynor found a nice treat on Halloween at Grandview Cemetery late yesterday, a beautiful black-throated green warbler. He first found it in a honeylocust in the northeast corner of the portion w of the ditch (Section B). I was in another portion of the cemetery and he kindly called me. We searched, didn't find it, split up, he refound it, recalled me, and we enjoyed seeing it forage in two bur oak trees that occur on either side of the road that divides the Soldier Monument Section S from Section F. This area is in the center of the cemetery due w of the entrance. It was not particularly associated with other birds during the time I watched this individual. I think it is a female of undetermined age. Its throat was mottled black and the flank stripes were not as black as I remember males having.
The bird in a cotoneaster shrub which is out in the open n of the oaks just nne of the Soldier Monument in Section S. The bird was giving its distinctive metallic chip note, which is similar to Townsend's and other close relatives (hermit and golden-cheeked). While the bird left the oaks briefly multiple times and went to Colorado blue spruce, Norway maple, Rocky Mountain juniper and a particular cotoneaster shrub, it definitely favored the oaks. One of the oaks has a good compliment of green leaves, the other is mostly leafless. I think the attraction in these two oaks might well be adult cynipid wasps which form at least two types of galls on these oaks. One of these small stingless wasps, the rough bullet gall maker, emerges from galls at this exact time of year. Obviously, their trick to being successful emergers at this time of year is they are loaded up with antifreeze type chemicals. This was also a good year for a particular aphid on oak, Myzocallis alhambra, which could have been another attraction for the warbler, either live adults or cadavers.
Many thanks to E. J. for his skillful detection of this warbler and for recognizing my car at the entrance and calling me.
From now thru early December has been a productive time in Colorado over the last several years for late-migrating eastern warblers. After what I would characterize as a pathetic autumn migration for marquis landbirds, maybe there is still hope. A chestnut-sided in Denver, bay-breasted in Estes Park, who knows what else is out there? Warblers mostly eat insects, plus a little bit of fruit and suet. The only insects present in numbers from here on out until next spring are midges near open water, aphids (both living adults loaded with glycols) or cadavers, scale insects, lacewings and maybe a late-emerging gall insect like mentioned above. Clusters of pines with aphids and scale insects in historically good spots like parks and neighborhoods with mature landscaping have been the most productive in late October thru early December in the past.
Dave Leatherman
Fort Collins
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