Re: Fw: [cobirds] Rare warbler diets

2023-04-22 Thread Brendan Beers
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  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 
> wrote:
>
>> I intended this to go to everyone, not just Nathan.  Sorry.
>> Dave
>> --
>> *From:* DAVID A LEATHERMAN 
>> *Sent:* Saturday, April 22, 2023 10:23 AM
>> *To:* Nathan Pieplow 
>> *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 

Re: Fw: [cobirds] Rare warbler diets

2023-04-22 Thread Peter Burke
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 
wrote:

> I intended this to go to everyone, not just Nathan.  Sorry.
> Dave
> --
> *From:* DAVID A LEATHERMAN 
> *Sent:* Saturday, April 22, 2023 10:23 AM
> *To:* Nathan Pieplow 
> *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:* cobirds@googlegroups.com  on behalf of
> Nathan Pieplow 
> *Sent:* Friday, April 21, 2023 10:29 PM
> *To:* cobirds 
> *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 

Fw: [cobirds] Rare warbler diets

2023-04-22 Thread DAVID A LEATHERMAN
I intended this to go to everyone, not just Nathan.  Sorry.
Dave

From: DAVID A LEATHERMAN 
Sent: Saturday, April 22, 2023 10:23 AM
To: Nathan Pieplow 
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: cobirds@googlegroups.com  on behalf of Nathan 
Pieplow 
Sent: Friday, April 21, 2023 10:29 PM
To: cobirds 
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?