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
On Thu, Oct 1, 2026, 12:18 PM Rachel <leggett.rachel...> wrote:
> ***I mean US 85 and I-25 lol sorry
>
> Rachel Leggett
>
>
> On Thu, Oct 1, 2026 at 12:15 PM Rachel <leggett.rachel...> 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...>
>> 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 Somershoe
>>> Littleton CO
>>>
>>> On Thu, Oct 1, 2026 at 11:57 AM David Suddjian <dsuddjian...>
>>> 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 Suddjian
>>>> Littleton CO
>>>>
>>>> On Thu, Oct 1, 2026 at 10:22 AM zroadrunner14 <zroadrunner14...>
>>>> 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 Sanders
>>>>> Trinidad, CO
>>>>> Temporarily in Lakewood
>>>>> "
>>>>>
>>>>>
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