To add to this discussion, a Yellow-throated and Cassin's Vireo were amongst a mixed flock of YRWA gleaning in low trees and shrubs along the Poudre River at Watson Fish Hatchery in Larimer County this morning. It does seem like whatever is on the menu, nearby water sources are a common thread the past few days.
https://ebird.org/checklist/S134626358 Brendan Beers Fort Collins On Sat, Apr 22, 2023 at 11:47 AM Peter Burke <[email protected]> wrote: > COBirders, > Just to add to this wonderful discussion, I ventured down to the creek on > Thursday late morning and found the Northern Parula feeding with a pair of > Audubon's Yellow-rumpeds high in a leafless tree. I stuck around hoping to > see the Yellow-throated and was fortunate to see it briefly feeding among > the rocks right along the stream. It was then I noticed what a hot spot > this section was, per Nathan's description. > > I was hoping to photograph the Yellow-throated Warbler, so I took a seat > and waited. Over the next hour or so I watched the Parula, two Audubon's > and one Myrtle Yellow-rump, American Goldfinch, Pink-sided and Oregon > Dark-eyed Juncos, House Finch, White-crowned Sparrow, American Crow, > Chipping Sparrow, American Robin, White-breasted Nuthatch and European > Starling all scouring this one area. As Nathan noted, the Parula and > Yellow-rumped Warblers were doing some flycatching, but for the most part > all the birds were gleaning from the rocks and branches quite close to the > water. This would support Dave's hypothesis for a localized insect hatch as > aquatic insects tend to pause after emerging from their pupal(?) skins to > allow their wings to unfold and dry. > > Of course the Yellow-throated Warbler never returned while I was there, > but that's how it often goes... > > Best, > > Peter Burke > Boulder > > > > On Sat, Apr 22, 2023 at 10:29 AM DAVID A LEATHERMAN <[email protected]> > wrote: > >> I intended this to go to everyone, not just Nathan. Sorry. >> Dave >> ------------------------------ >> *From:* DAVID A LEATHERMAN <[email protected]> >> *Sent:* Saturday, April 22, 2023 10:23 AM >> *To:* Nathan Pieplow <[email protected]> >> *Subject:* Re: [cobirds] Rare warbler diets >> >> Nathan et al, >> Short answer is "I don't know". >> >> Long guess is as follows. >> >> When multiple species of birds are foraging on multiple types of plants >> in multiple styles, and the situation is near water, my default guess is >> always an aquatic insect hatch. And the most likely aquatic insect group >> is chironomid midges. We have several species, some of which are quite >> small. The nymphs feed on organic plant and animal matter in the water and >> emerge from the surface as flying, mosquito-like adults. As adults they >> often form swarms, especially in the evening. Adults also sit around on >> all manner of vegetation and are not particular about which kind. We have >> had real pulses of midge emergence over the last few weeks. Flying midges >> and sitting midges could account for the two types of foraging (flycatching >> and standard twig gleaning). >> >> Why just one stretch of the creek? Perhaps it has just the right organic >> matter, or the flow rate is just right. Or the lighting in general along >> this stretch is such that birds can more easily spot flying/perched prey >> than stretches on either side of it. Hard to say. The same way one 9 >> cubic foot section of air has a swarm of midges, it's easy to imagine a >> clumped distribution of ideal larval development conditions in the creek >> bed. It's a clumpy world out there. >> >> Staying with the guess of aquatic insects, I suppose the next most likely >> prey suspect is one of the caddisflies, but they would be darker/bigger and >> more conspicuous than some of the smallest midges. If it was caddisflies, >> Nathan's sharp eye would have seen them. >> >> About the only way to confirm any of this is to be present with a net and >> sweep it thru the air in the area with birds and the nearby inactive areas, >> and see if there's a difference in the catch. I did some of that in >> November 2021 when "the pond" on the north side of the CU campus had the >> magnolia warbler. Lots of aphids of many types in the air and on foliage, >> but the pond and creek had plenty of midges, too. Late fall is more likely >> to be when flying adult aphids compete with midges for the crown of best >> staple for migrating passerines. In early spring, 1) midges; 2) small >> flies, bees and weevil larvae attracted to, or in, willow/cottonwood >> flowers; 3) overwintering scale insect nymphs (especially elm); 4) >> gall-making adult psyllids emerging from hackberry trunk bark or other >> types of tree bark near hackberries - these are consistent common >> denominators in many spring rare bird events. Aphids not so much. >> >> The only thing more fun than observing the mysteries is solving the >> mysteries. I must say it's a great comfort to know this task will never >> end. >> >> Thanks, Nathan, for your efforts and questions. >> >> Dave Leatherman >> Fort Collins >> ------------------------------ >> *From:* [email protected] <[email protected]> on behalf of >> Nathan Pieplow <[email protected]> >> *Sent:* Friday, April 21, 2023 10:29 PM >> *To:* cobirds <[email protected]> >> *Subject:* [cobirds] Rare warbler diets >> >> On Wednesday afternoon, Curtis Beimborn discovered a Yellow-throated >> Warbler and a Northern Parula along a section of Boulder Creek just below >> the university, about 100 yards east of 17th Street in Boulder. Both birds >> were still present this evening at about 6:00 PM. With the exception of a >> 24-hour disappearance by the Yellow-throated, both birds have been >> consistently sticking to the same 50-yard stretch of creek. >> >> This same stretch of creek has also been the center of activity for >> juncos, goldfinches, nuthatches, Ruby-crowned Kinglets, and Yellow-rumped >> Warblers. But if you walk more than a few dozen yards away from this spot >> in either direction, bird numbers drop precipitously. This situation has >> remained stable for the past three days, and so, Dave Leatherman-style, I >> decided that the birdy spot must have some kind of food that is keeping all >> these birds around. >> >> I tried this evening to observe food habits. Interestingly, the two rare >> warblers are engaging almost exclusively in flycatching -- especially the >> parula, which sallies constantly. The Yellow-throated's sallies are less >> frequent and possibly less successful, and it also gleaned some branches >> while I was there. Whatever they are catching is too small for me to see in >> the air. And most of the other birds present seem to be following more >> typical foraging strategies for their species -- i.e. few of them are >> flycatching. >> >> The rare warblers are frequenting some dead branches over the creek as >> well as some barely leafed-out elms, cottonwoods, and buckthorns. Dave, >> what do you think they are going for? Flying adult aphids? >> >> Why would the flying insects be so faithful to this one short stretch of >> creek? And how long might this situation last? Can we expect other migrants >> to join the fun in the coming days? >> >> Nathan Pieplow >> Boulder >> >> -- >> -- >> You received this message because you are subscribed to the Google >> Groups "Colorado Birds" group. >> To post to this group, send email to [email protected] >> For more options, visit this group at >> http://groups.google.com/group/cobirds?hl=en?hl=en >> * All posts should be signed with the poster's full name and city. >> Include bird species and location in the subject line when appropriate >> * Join Colorado Field Ornithologists https://cobirds.org/CFO/Membership/ >> --- >> You received this message because you are subscribed to the Google Groups >> "Colorado Birds" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/cobirds/CAFhaDVJbPxdcHcvaRHfEBkdKGZVqKhw2JT1kcBKj%3Dk7n%2Bm03cw%40mail.gmail.com >> <https://groups.google.com/d/msgid/cobirds/CAFhaDVJbPxdcHcvaRHfEBkdKGZVqKhw2JT1kcBKj%3Dk7n%2Bm03cw%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> -- >> -- >> You received this message because you are subscribed to the Google >> Groups "Colorado Birds" group. >> To post to this group, send email to [email protected] >> For more options, visit this group at >> http://groups.google.com/group/cobirds?hl=en?hl=en >> * All posts should be signed with the poster's full name and city. >> Include bird species and location in the subject line when appropriate >> * Join Colorado Field Ornithologists https://cobirds.org/CFO/Membership/ >> --- >> You received this message because you are subscribed to the Google Groups >> "Colorado Birds" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/cobirds/PH7PR12MB73541FD22448D7200EA3898EC1619%40PH7PR12MB7354.namprd12.prod.outlook.com >> <https://groups.google.com/d/msgid/cobirds/PH7PR12MB73541FD22448D7200EA3898EC1619%40PH7PR12MB7354.namprd12.prod.outlook.com?utm_medium=email&utm_source=footer> >> . >> > -- > -- > You received this message because you are subscribed to the Google > Groups "Colorado Birds" group. > To post to this group, send email to [email protected] > For more options, visit this group at > http://groups.google.com/group/cobirds?hl=en?hl=en > * All posts should be signed with the poster's full name and city. 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