Perhaps the alternating position maximizes body area in direct contact, minimizing heat loss. Just a guess.
Rolf Hertenstein, Lyons, Boulder County On Wednesday, December 2, 2020 at 4:00:25 PM UTC-7 [email protected] wrote: > Dave's post reminded me of an excellent book on this -- Bernd Heinrich's > *Winter > World: The Ingenuity of Animal Survival*. The book is largely written > about northeastern species, but briefly addresses our poorwill's torpor. > Heinrich makes a star of Maine's Golden-crowned Kinglets in the book. > > Among the most memorable and darling cold weather behaviors of our metro > area birds has to be the lines of Bushtit that pack in together to stay > warm. I don't know if they're consistent with their poses -- but in most > lines (usually during cold, cold mornings) I see, the birds alternate: one > looking forward, one looking backward, one looking forward, etc. So it's > tail, head, tail, head facing you. Is it to keep an eye on all directions? > Balance? I have some photos of this, but the new Google groups interface > doesn't seem to allow embedded photos anymore... > > - Jared Del Rosso > Centennial, CO > > > > On Wednesday, December 2, 2020 at 2:49:57 PM UTC-7 Dave Leatherman wrote: > >> I almost responded to this issue yesterday when Gregg brought it up, and >> I will now. >> >> Sub-freezing temperatures are rarely an issue for birds unless they are >> extreme, take away the availability of free water or coincide with >> conditions that got a bird's feathers wet. When feathers are dry the >> literature says they can result in as much as an 80-degree difference in >> air temp compared to that under the feathers next to the skin. In other >> words, it could be -20 outside and 60 right next to the skin. That data >> comes from the famous ecologist Ernst Mayer's work in Maine with >> thermistors and a golden-crowned kinglet. Cute little birds get counted >> every year on the Nome, Alaska CBC. Ducks move on not because the water is >> cold but because the surface freezes and takes away their ability to tip or >> dive and obtain food. >> >> As Brian said, the biggest issue with birds and the onset of >> significantly colder weather is generally decreased food availability (and >> the issue of liquid water). A lot of the birds we get excited about seeing >> in early winter are neotropical migrants that for whatever reason are still >> passing thru or even lingering. These late insectivores still rely on >> insects, especially insect types with chemistry that suppresses their >> freezing temperature (usually involving glycols) and insect cadavers. >> Also, most neotropical migrants also have dietary flexibility that allows >> exploiting fruits. and when all else fails, can lower their standards and >> engage in desperate measures like scavenging and stealing. *Midges*, >> such as what the Bay-breasted Warbler at the Fountain sewage plant must be >> getting, or *aphids and scales* (Tennessee, Black-throated Green, Pine, >> Northern Parula and Black-throated Blue lately along the middle Front >> Range) make up the bulk of what cold weather insectivores can still find >> and rely on. But we also have species of grasshoppers that overwinter as >> adults, and even certain moths and butterflies, flies, ichneumonid wasps, >> leafhoppers, etc. can be active in temps as low as 45 degrees. Then there >> are always back-up foods like the contents of galls, cocoons, spider webs >> and egg sacs, feeders with suet, etc. Birds are simply amazing in >> coping, of course, within the limits all life forms have. >> >> It was this time of year in 2013 when we had 10 species of warblers on >> the Colorado RBA. One of them was a Northern Parula in Boulder that along >> with the famous Bay-breasted and some yellow-rumps was sustaining itself on >> aphids from one particular Austrian Pine. I took pics of it on >> 16November2013 but believe it made it into early December. Apparently none >> of us entered this individual into eBird if Gregg says there are no records >> from the Denver to FC area for early December. That brings up another >> misconception, that being the notion eBird is a complete record of all that >> is known. Far from it, but I'll leave it at that. >> >> Anybody checking the Denver West Office Park? Interlocken? 28th e of >> Baseline in Boulder? Bow Mar apartment complex in Littleton? Longmont >> neighborhood e of Hover s of Nelson? No doubt many other aphid-scale-midge >> "food courts" like the one Joey just found near Chatfield exist out there. >> >> Dave Leatherman >> Fort Collins >> ------------------------------ >> *From:* [email protected] <[email protected]> on behalf of >> Bryan Guarente <[email protected]> >> *Sent:* Wednesday, December 2, 2020 7:57 AM >> *To:* Brandon <[email protected]> >> *Cc:* Cobirds <[email protected]> >> *Subject:* Re: [cobirds] Re: Northern Parula in December >> >> Gregg and others, >> I would love to hear whether the Parula and Pine Warbler stuck around >> after the cold frontal passage last night. I doubt the temperatures would >> be the problem. The snow could cause food gathering issues. The winds are >> appropriate for migration southward, but I don't know whether the "need" to >> migrate is still there. Hormonally, There must be a point in every bird >> that they don't feel like they need to migrate anymore. These birds will >> be interesting case studies from both the perspective of Dave Leatherman >> and from Bryan "Weatherman". Bad joke... moving on. >> >> Keep us informed. >> >> Thanks, >> Bryan >> >> Bryan Guarente >> Meteorologist/Instructional Designer >> UCAR/The COMET Program >> Boulder, CO >> >> >> On Wed, Dec 2, 2020 at 2:04 AM Brandon <[email protected]> wrote: >> >> Pueblo County is up to 17 species of warblers now thst have been seen >> during December to February. Pretty amazing total. Most have been since >> the 1990s. >> >> Brandon K. Percival >> Pueblo West, CO >> >> Sent from my Android >> >> On Tue, Dec 1, 2020, 6:44 PM Gregg Goodrich <[email protected]> wrote: >> >> There are no previous December eBird records of Northern Parula in the >> Denver/Fort Collins area until today December 1st, 2020. The Chatfield bird >> was seen and photographed today. The Springs, Pueblo, Pitkin Cnty and >> Garfield Cnty have had December records. It will get down to around 20 >> degrees tonight with chance of snow. 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