Interesting observations by David, Ira and Tammy, Scott and Rachel. Ira and Tammy's, and Rachel's buteos were most likely Broadwings (or Swainson's if they were longer-winged) since these are the only species which migrate in groups.
This information helps complement our fall observations at the Mount Zion Hawk Watch.
Broad-winged Hawk and Swainson's Hawk are known to migrate on a broad front using thermals - they do not need ridges to fly south.
Beginning in August from the Mount Zion Hawk Watch we would see migrant raptors around the easternmost of the two tall antennae on Lookout Mountain, but look as we might we could never find any migrant raptors north of and leading to Lookout Mountain. In fact we had very few migrants flying above the horizon. We theorized that they were flying low over Golden or Denver, getting a ridge lift/ orographic lift off the SE face of Lookout Mountain, as we did not see any ascending the 3 ‘feet’/bases of that mountain running NE we could see from the watch.
In September the migration was different in that we could see migrants above the horizon going south over Green Mountain or in the gap between that mountain and Lookout Mountain, but we would still see many migrants for the first time around the two antennae, indicating that these were still flying low before reaching Lookout Mountain.
One observation we had made when we last counted here in 2024 was that raptors that flew over North, then South Table Mountain, when they left the latter and went over Lakewood, they would lose lift and drop very low and we would often lose them against the trees and houses, which are not conducive to thermal formation. This year we know better and we anticipate and look to the northern flank of Green Mountain where we often find them again.
In one notable instance I found a Turkey Vulture over Denver which I was able to find in my scope before it dropped below the horizon and follow it all the way going over the same trees and houses, it went up to the two antennae on Lookout Mountain, gained a lot of height through ridge lift, going straight up as if in an invisible escalator (i.e. without going in circles as in a thermal), and migrated to the South.
The Mount Zion Hawk Watch is at 7165 feet. We are looking down on Golden and Denver. Trying to find a raptor flying over the trees and houses all around Denver is very difficult, and when we find raptors over the Eastern horizon and they drop below the horizon it's very difficult to continue following them with our binoculars, they are lost to us unless they fly above the horizon again.
Looking from the watch we can see how many trees there are around Denver, so there's not much lift available to raptors on migration south. Thermal formation requires hard surfaces like huge parking lots or highways, or rocky surfaces which can absorb the sun's heat and radiate them out as thermals. Perfect examples of these are the two Table Mountains made of lava flows, and the foothills of the Rockies which are made of granite.
So all the hawks that you folk have described flying over various parts of Denver, you have been fortunate seeing them because of a lack of lift. Given time they would all find thermals to rise up on.
The Soaring Forecast of the National Weather Service predicted lift at 12 feet per second, though the height of thermals was only 7474 ft above ground level provided the trigger temperature of 65.4°F /18.5°C was achieved, which was expected to be reached around 12:30 MDT, so the height of the thermals would be lower in the morning, accounting for the lower buteo observations.
Here at the watch, most of the raptors are found by binocular scanning and very few found without binoculars.
Ajit I Antony
Central Park, Denver
***I mean US 85 and I-25 lol sorry
Rachel Leggett
--On Thu, Oct 1, 2026 at 12:15 PM Rachel <leggett.rachel@gmail.com> wrote:
I saw a kettle of about 16-18 raptors, looked like mixed turkey vultures and buteos, over Castle Rock between 85 and US25 here in DougCo on Tuesday. I was driving so I unfortunately couldn't pause to ID, but it was exciting!
Rachel Leggett
On Thu, Oct 1, 2026 at 12:04 PM Scott Somershoe <ssomershoe@gmail.com> wrote:
After seeing Ira's post, and being a mile away, I went for a walk. I had 2 Broad-winged up high with a kettle of turkey vultures. I saw mostly vultures. Sky watching sure beats doing work. This was on the fed center in Lakewood, JeffCo.
Scott SomershoeLittleton CO
--On Thu, Oct 1, 2026 at 11:57 AM David Suddjian <dsuddjian@gmail.com> wrote:
On the theme of kettling Buteos . . .Yesterday in the late afternoon I spotted a flock of 6 Broad-winged Hawks pass right over my Ken Caryl (JeffCo) home, heading south. And this morning a kettle of 15 Broad-wingeds was moving south at Chatfield SP (Douglas) along the Platte south of Kingfisher Bridge. Prior to these observations, all of my occasional fall BWHA sightings in CO have been of singletons (all from September).
David SuddjianLittleton CO
--On Thu, Oct 1, 2026 at 10:22 AM zroadrunner14 <zroadrunner14@gmail.com> wrote:
--Birders,At 10 am we were N bound on Kipling S of Alameda and Tammy spotted a kettle of at least 70 - 80 hawks just E of Kipling. 2 min later there was another of about 15 birds. She spotted a couple of TV's but the rest were buteos.Too far east for Ajit to get them.I've never seen that in Colorado before.
Ira SandersTrinidad, COTemporarily in Lakewood"
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