Date: 10/28/19 11:03 am
From: Janet Justice-Waddington <jjustwaddington...>
Subject: Re: [cobirds] Boulder Wood Thrush and warbler food
I have a Pine Siskin at a black-oiled sunflower seed feeder. I do not have
a thistle feeder, and it does not go to ground where a mix including
smaller seeds is located. I do know a neighbor found 3 dead siskins. Could
a siskin, with it's tiny bill, feed on sunflower seeds?

On Mon, Oct 28, 2019 at 11:12 AM DAVID A LEATHERMAN <daleatherman...>

> I visited the Boulder site of the recent rare bird complex to try and see
> the birds, of course, but also to try and figure out the "why" part of it.
> The block north of Baseline between 29th and 30th certainly has
> understandable bird attractions in the form of a flowing creek with rich
> riparian vegetation in both the understory and overstory, plus landscaped
> deciduous and coniferous trees. That said, I could not really figure out
> anything obvious about why the warblers are there other than the usual late
> fall-early winter situation with pines that harbor a few species of aphid
> that have been the focus of late-moving insectivores in the past. I
> checked the pines, and also the big crack/golden willows along that creek
> near the red shed in which the warblers have been reported, and did NOT see
> any aphids. They are probably there, mostly in the upper pine crowns,
> maybe settled down into the base of needle bundles. They were not visible
> on lower branches out on the needles as has been the case in the past at
> Pueblo City Park, Denver West, Longmont Meadowbrook neighborhood, and other
> such "hotspot" sites at this time of year on forward into early December.
> It wasn't too many years ago when we had 10 species of warblers on the
> Colorado RBA in early December, all concentrated in the same sort of
> pines-with-aphids sites, but also including buckthorn berries (Lakewood
> Prothonotary at Centennial Park). On my visit to Boulder on 24October I
> did not come across any of the special warblers but I notice they have been
> seen since, so something is holding them at that site. Please, somebody
> figure it out. The only thing I noticed was on willow branches with
> leaves attached: fairly significant defoliation damage by one of the willow
> leaf beetles (*Chrysomela knabi*). Not sure which stage of this insect
> might be available at this time of year for birds to eat but maybe adults
> (look somewhat like ladybird beetles in terms of size and color pattern,
> yellow or orange with black spots, see below), or maybe larval cadavers.
> Adult willow leaf beetle (Chrysomela knabi), actual size about 3/8 inch
> long. Damage is ragged chewing (adults), shotholes (larvae).
> As for the Wood Thrush, it has lots of options from the berry aisle. I
> have looked at images accompanying all the eBird Wood Thrush checklists
> from Boulder of late and two things keep showing up in narratives and
> images: crabapples and mountain-ash berries. The crabapples are what I saw
> it going after repeatedly on the north side of the creek just w of the
> footbridge w of 30th. Gwen Moore had photos on her checklist of it eyeing
> mountain-ash berries, also just w of the footbridge just w of the
> aforementioned crabapple on the north side of the creek. Photos of both
> are below. I also saw plenty of common buckthorns in the area loaded with
> dark blackish-purple fruits, a favorite of thrushes. Last Friday up here
> in Fort Collins just e of Grandview Cemetery I had a late Swainson's Thrush
> feeding on honeysuckle berries and a prominent buckthorn grew right next to
> the honeysuckle which I would wager got sampled, also. A Hermit Thrush has
> been along the ditch in the cemetery in a large buckthorn for the last two
> weeks.
> Would be interesting to see how long the rare bird complex persists in
> Boulder. Insects loaded with anti-freeze chemicals that suppress their
> freezing temperature, and fruits, should still be available to sustain the
> birds, as would cadavers of insects killed by the snow and cold. Figuring
> out food habits is often easier when weather conditions are bad because the
> birds are in desperado mode and place food acquisition ahead of worrying
> about potential threats like approaching birders to the extent they would
> when not so stressed from a nutrition standpoint. Priorities!
> Mountain-ash berry
> clusters (left), small fruited variety of crabapple (right)
> Dave Leatherman
> Fort Collins
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