Date: 10/17/18 8:46 am
From: Sandra Laursen <salaursen...>
Subject: Re: [cobirds] Yesterday's golden-plover event--and a question for Bryan Guarente
thanks for this analysis. One lesson I have absorbed from you in the past
is that it's not the surface-level winds that are important, but the wind
up a bit higher where the birds are migrating. Why do you focus on surface
winds this time?

- Sandra Laursen

On Monday, October 15, 2018 at 10:40:25 PM UTC-6, Bryan Guarente wrote:
> Cobirders,
> when Ted beckons... you get a really long email...
> So the question is:
> 1. Why did this situation bring more birds to the Front Range?
> *TL;DR* (Too long; didn't read) -- Super-short snarky answer just for
> Ted: it was the wind! The weather had a lot to do with it and which end of
> the cold front Colorado ended up on helped dictate that flow of migrants.
> Based on percentage of the total flow area behind the cold front compared
> to the overall flow, it looked like a 30-40% chance that birds would end up
> in the Front Range due to funneling or convergence.
> *Full version:*
> - *Why did this weather situation bring more birds to the Front Range?*
> Let's look through the computer models because it is sexier, and makes it
> easier for everyone to understand because I can give you data everywhere on
> the globe. One could also do this with satellite imagery, but it is harder
> to get you to see what I want to see, so I will work with the easier
> option.
> -
> That animation of a single time gives you the idea of what is going on
> that made Colorado a hotspot for any migrants yesterday. Any bird trying
> to make its way to the southeast from Canada may have started out with good
> intentions, but depending on which side of the flow it started from or
> ended up in over time, it had a strong chance of ending up heading toward
> the Front Range. The cold front itself is the "blue" area with no wind
> that curves from Lake Nipigon down through Iowa, Nebraska, then curving
> into Colorado. All of the airflow behind that cold front (to the north and
> west) is what we want to focus on. The flow had multiple possible end
> points at that time: near Lake Nipigon, along the cold front just south of
> Lake Superior, along the cold front in Iowa, or into the Colorado Front
> Range.
> The highest likelihood location for the birds to end up was actually along
> the Front Range. The percentage of the total area of that flow behind the
> cold front that was showing a distinct convergence into the Front Range was
> about 30-40% (guesstimated). So any birds within that 30-40 percentage of
> the total area had a strong likelihood of ending up in Colorado's Front
> Range. That means that birds ranging from Alberta through Montana, North
> Dakota, Minnesota, and western Iowa and then everywhere southwest of that
> behind the cold front, had a strong chance of ending up in the Colorado
> Front Range. The door was wide open so to speak. The flow was broad
> initially, then came crashing in on itself converging into a small area
> (Colorado Front Range). So think of this as your funnel for bird
> convergence. On the broad end, you put in any birds you'd like, then on
> the other end, you get a stronger concentration of birds because the winds
> they like to follow are forcing them together more over time. Other places
> are getting lower concentrations of migrants due to the divergence of the
> birds from their area into our area.
> This was only one snapshot of the winds at the surface though. For a
> period of about 12 hours, this was still the case around this. Earlier it
> was less convergent into the Front Range, but picked up, then maximized
> around the time I showed you earlier, then tapered off a little.
> Importantly though, the time I linked you to was right around sunset when
> the snow started to pick up all along the Front Range. This was a bonus
> for birders, hindrance for the birds. Both the sunset and the snowfall
> made this more important for the birds to get to the ground, and then they
> likely stayed the night to try their luck at adding some munchies in the
> morning.
> This is the time for American Golden-Plover migration. It also happens
> that the location this storm started from had a good chance of grabbing
> some of those migrant AGPLs trying to make their way through the Central
> Plains like they normally do. However, as luck would have it, they ended
> up on the wrong side of the flow behind that cold front. They got stuck on
> the Colorado Front Range side, and then we got lucky to see them here. The
> number of AGPLs that migrate through this corridor in a short period of
> time is HUGE. That also gives us a higher chance of getting them here in
> CO. I remember from my days in Illinois that this time of year would
> produce fields upon fields of AGPLs numbering in the thousands easily.
> They would take off in huge flocks and migrate quite broadly through the
> area during the day. You could easily go a day with seeing 20-40 flocks
> numbering 500-1000 birds a piece. It is kind of surprising that there
> weren't more AGPL found along the Front Range when you think of it that
> way.
> Yes, you may say as a counterargument to my arguments about the wind that
> birds have wings, and they don't have to follow the winds. True. They
> don't have to follow the winds. If you ended up on the wrong side of that
> flow though (the west side closer to Montana or Alberta), the chances of
> you covering enough ground to not end up in Colorado was pretty slim
> without a LOT of extra effort to cross the flow. Ask your pilot friends
> which way they spend more fuel with a tail wind or with a cross wind and
> you will get some idea of why they ended up here instead of Iowa like they
> were "supposed" to.
> Hope that helps. This was my quick response. If you want to hear more,
> just ask and I will see what I can do to respond. If you get to this email
> soon after I sent it, you can see the same type of wind pattern play out in
> the satellite imagery here:
> This is real-time data though, so you won't be able to watch that loop for
> too much longer as it purges the old stuff.
> Hope that helps, Ted. And I hope others gleaned some knowledge from this
> as well. It was a fun situation to analyze and even more fun to bird.
> Bryan Guarente
> Meteorologist/Instructional Designer
> UCAR/The COMET Program
> Boulder, CO
> On Mon, Oct 15, 2018 at 10:42 AM Ted Floyd <tedfl......>
> <javascript:>> wrote:
>> Hey, everybody.
>> American Golden-Plovers were reported from eleven (11) sites in Colorado
>> yesterday, Sunday, Oct. 14. To put that in perspective, there were two (2)
>> previous reports for Colorado in 2018: one (1) in Washington County, Sept.
>> 4-8, and one (1) in Kiowa County, Sept. 18.
>> The previous analysis is based on eBird data-mining.
>> When one ponders such matters, one's thoughts turn instantly to Bryan
>> Guarente. Bryan, what caused this? The snow, obviously. But why this
>> particular snowfall? And why this particular species?
>> Ted Floyd
>> Lafayette, Boulder County
>> P.s. Other than an American Golden-Plover, goodies yesterday in the
>> general vicinity of Waneka Lake, Boulder County, included an Eastern
>> Bluebird, hundreds of southbound Sandhill Cranes, two Hermit Thrushes, FOS
>> Gray-headed and Pink-sided juncos, FOS Townsend's Solitaire, a Long-billed
>> Dowitcher, Wilson's and Orange-crowned warblers, a getting-latish flock of
>> 15 Lesser Goldfinches, and a Wood Duck.
>> P.p.s. This Monday morning, Oct. 15, a quick stop at the Legion Park
>> overlook revealed the Valmont Reservoir complex to be very birdy, harboring
>> a Sanderling, a Semipalmated Plover, a couple dozen Mountain Bluebirds, and
>> distant gulls, geese, and grebes galore. It would be very much worth the
>> effort, I suspect, to walk in from Red Deer Drive and watch from the Open
>> Space tract beyond the end of the road.
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