So we know the Centennial Park Prothonotary Warbler's version of "cranberries"
consists of European Buckthorn berries.
As for meat, excellent photos shared with me by Kris Petersen show a hairless
caterpiller in the beak of the Prothonotary. The bird found this morsel at the
base of plants/rocks along the little outlet "stream" w of the gazebo. I
thought it looked like a "cutworm". My friend Dr. Boris Kondratieff at CSU
concurred. Dr. Paul Opler, expert birder, author of the Peterson Guide to
Western Butterflies, and moth guru refined this to the Large Yellow Underwing
(Noctua pronuba), a European cutworm introduced into eastern Canada in 1979 and
recently spread to CO (where it is now common).
Mark Chavez shared with me a photo taken by his friend Daren OBrien which shows
a biggish spider in the Prothonotary's beak. I sent this to Dr. Paula Cushing,
spider queen at the Denver Museum of Nature & Science. She said the photo did
not show enough detail for a positive ID, but that "it is most likely some type
of wolf spider".
Several people talked about the Prothonotary going into Russian-olives and at
least two of them proved this with photos. No fruit on these trees that I saw,
so that's apparently not the attraction. Russian-olive hosts a couple aphid
species, but a cursory inspection last Sunday did not reveal any. I did find a
few arthropods within wilted leaves hanging limp on one tree: a midge cadaver
and a spider egg sac. Thus, like is the case with many warblers, the
Prothonotary is probably finding dead-leaf searching to be productive.
No doubt many other living (and perhaps dead) arthropods are being found by
this bird when it is not eating berries. During the 5 hours I watched it, I'd
estimate berry-eating to only consume about 10-15% of its time.
Lastly, in the way of drink, twice after a berry session I saw the Prothonotary
go to the ground and appear to eat snow. Perhaps it is diluting the fruit of a
tree with the species name cathartica as a form of antidote.
I give thanks to all the contributors who helped construct this partial
Thanksgiving diet account.
Dave Leatherman
Fort Collins
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