Evaluation of the experimental fall2025 hawk watch at Dinosaur Ridge

[AJIT ANTONY]

When we visited Denver for an extended stay in 2016, we thought we would help at the local hawk watch, and to our surprise there were no hawk counts in fall in Colorado. We helped in most spring hawk counts since, both with volunteer counters, as well as after Emma Riley came on board.

I have been a volunteer hawk counter in New York State, starting with Mount Peter in 1986. Liza began helping me once she retired in 2015. Hook Mountain had only a fall count, where Liza and I proved that it had excellent spring counts as well, creating a few eastern flyway records between 2020 and 2022; I-84 Overlook in 2021 where we had a record 27 GE for the fall season with 8 on one day alone!

After we moved to Denver in July2022, I suggested to Carol Cwiklinski who was then in charge of the hawk watch at Dinosaur Ridge, that Liza and I do an exploratory fall count in 2022 at Dinosaur Ridge, but our total count was only 78 with 115.75 hours, counts starting with a few days in August, more select days in September and October,and only a few days in November and December when we had no migrants. This seemed to be enough proof that those who decided initially not to have a fall migrant count at this site were correct.

Carol Cwiklinski, who counted at Dinosaur with Steve Small, had given us some observations she and Steve had had, both from Dinosaur Ridge as well as from Mount Vernon, across the valley to the west from Dinosaur Ridge, and they had good numbers in fall between 2018- 2020.
Because of this we went across the valley from Dinosaur Ridge on 9/8/24 to the Mount Vernon Cemetery and in 3.5 hours saw 25 migrants including 6 Swainson’s Hawk! This rekindled our interest in the fall migration, and looking for sites which could give us a better view north than Dinosaur Ridge, we found Mount Zion fitted the bill.

Liza and I did an exploratory count in fall 2024 at Mount Zion, which is immediately north of Lookout Mountain and4 miles northwest of the Dinosaur Ridge Hawk Watch. Part of the reason for this count was that we were wondering whether any raptors migrated west of the ‘westernridge’ that we could see from Dinosaur Ridge in spring at that location and whether we were missing any raptors in spring which would not be visible from Dinosaur Ridge. We had a reasonable seasonal count with a total of 576migrating raptors which averages 9.1 raptors per hour.
The raptors seen from Mount Zion were seen around the easternmost of the 3 antennae on Lookout Mountain, and further east over North and South Table Mountains. A number of kestrels came immediately East of the watch, below us, flying in the valley between the watch and Lookout Mountain, eventually flying over the middle of Lookout Mountain. We called it the Kestrel Channel.
Lookout Mountain is about 1.6 miles long measured from east to west. Only a few raptors flew directly over us and flew over the middle of Lookout Mountain, and extremely rare raptors flew to the west of Mount Zion, so it did not look as if raptors were flying to the West of the ‘western ridge’ which would correspond to the West end of Lookout Mountain.
We would see raptors flying over North and South Table Mountains, and once they went south of that area with the area full of trees and houses, they would lose lift completely, which meant that they ought to fly in the valley to the east of Dinosaur Ridge between it and Green Mountain, or west of Dinosaur Ridge.
This suggested to us that the main flyway for this area in fall is East of Lookout Mountain i.e. visible from Dinosaur Ridge.

We had also done an experimental count at Mount Zion in spring 2025 to see if we could match Dinosaur Ridge or see raptors not seen by them. By March it was evident that Dinosaur Ridge had far many more raptors counted than we did, 573 counting every day of the month at DR versus 65 at MZ, presumably because the raptors were flying far to the east of Mount Zion and difficult to find from there, so we abandoned MZ for the spring, and came and helped Emma and Audrey at DR.

I’ve found that Dinosaur Ridge is the most difficult watch to count at, in that the majority of the raptors are binocular-birds with very few showing up easily visible to the naked-eye.
You may have seen the images in Jerry Liguori’s book ‘Hawks at a Distance.’ I sometimes wish that we could see raptors as ‘close’ as depicted in his book, at the Dinosaur Ridge hawk watch.

When we conducted a fall exploratory count at Dinosaur Ridge Hawk Watch in 2022, we had just moved here from New York, where the best winds for big flights were the day after a cold front had gone through with NW winds, and we assumed that the same would pertain here not knowing any better, and looking at our data in Hawkcount.org , there was a definite emphasis on NW/W, which could explain why we had such a paltry count of 78 raptors for the fall season 2022.
Over the past 3years we've learned that NW and West winds in spring are the worst winds for Dinosaur Ridge.
In addition, we learned over the last 3 years of helping the spring count that most of the migrants fly very far over the western ridge requiring systematic binocular scanning to find, with a few going to the east or in the valleys to the east and west of the site itself.

Because of our fall Mount Zion 2024experience which suggested that raptors may be moving over Dinosaur Ridge in fall, we wondered whether we had done an adequate count in 2022 fall, especially because in New York at the sites I had volunteer-counted at, the raptors came in quite low, easily visible to the naked eye, and easily with binoculars;while at Dinosaur Ridge the raptors were extremely far away, but when we helped with the spring watch for the past three years at Dinosaur Ridge we got used to the distance we had to scan with binoculars and were be able to find migrant raptors, so being more adept, we decided to do another experimental count at Dinosaur Ridge in fall 2025, approved by Natalie Uschner- Arroyo the Chairman of the Hawk Watch Committee, and Emma Riley.
We started at the end of July and continued through September, by which time we had realized that we were not going to get a good count compared to the year before in fall at Mount Zion, so we didn’t count in October. We counted 237 migrant raptors (only half of what we counted the previous fall at the nearby Mount Zion Hawk Watch counted by the same two counters Liza and myself, at both sites, so we eliminated one variable) of which an astounding 68 were Swainson’s Hawk (29%)

To put this into perspective, before we had professional paid counters beginning in 2022, we had volunteer counters who would count on only some days a month, and on the day they counted, they did until the migration seemed to have stopped for the day, so only for a few hours each day that they went up, similar to our efforts. For the past 5years going back from 2021 they counted 14, 17, 10, 15 and 15 SW respectively for the entire spring seasons.
Emma Riley has been our Project Lead and primary counter since 2022 and starting that year until 2025 the number of SW counted in the spring season were 54,77,48 and 46respectively, staying a full 8 hours each day.
Janet Peters made the suggestion to calculate the number of raptors per hour, and in the spring season 2025 the total number of raptors amounts to 6.4 hawks/hour, while in fall it is 1.7hawks/hour.
Specifically for Swainson's Hawk in spring 2025 the number per hour was 0.09. For 2025 fall the number of SW found per hour of count is 0.5!

It would appear that more Swainson's Hawk are using ridge lift to fly south in fall, compared to flying north in spring, possibly because the urgency to breed, they're possibly going as fast as possible to their breeding grounds in the prairies of eastern Colorado and states to the north, and they don't necessarily need ridges to fly (they usually migrate on along a broad front).

The discrepancy between the 36 Swainson’s Hawk we counted at Mount Zion in 2024 and the 68 at Dinosaur Ridge in 2025 is likely because we did not count at all in August at Mount Zion. We know better now, that Swainson’s Hawk begin their fall migration quite early.

Almost all the migrant raptors we counted in fall at Dinosaur Ridge flew far to the west between Lookout Mountain to the western ridge to south of Mount Morrison. Some flew directly overhead,high.
We searched to the east in the valley and as well as over Green Mountain, looking over South Table Mountain as well, and did not find many migrant raptors.

The daily Soaring Forecast of the National Weather Service really meant for gliders, was usually very helpful as it gave the meters/feet of lift per second, and the height of thermals above ground level, provided a stated trigger temperature is reached, suggesting how high the raptors may be migrating at. Most days the lift was very good from2.4 to 5 meters per second with the maximum height of thermals anywhere from6500 to 12,000 feet and more. When you think about it that’s over two miles high. It’s very difficult to find raptor migrants that high in the sky,especially against a blue sky without clouds.
On one of the days I counted, I remember there were fine cirrus clouds overhead and to the north, and I tried using them to be able to find birds against, and to my surprise I was able to find migrant raptors at the limit of binocular ID straight up in the sky, but only because of the backdrop of the cirrus clouds. Most days we have perfectly blue skies, developing some clouds in the afternoon.
Most of the days we had migrant raptors between 9 and 10 AM, and then presumably because of high thermals and raptors flying much higher, few thereafter.

I know that raptors are migrating in fall past Dinosaur Ridge as they are flying past the Mount Zion Hawk Watch, but I suspect that perhaps they catch a good ridge lift off Lookout Mountain and fly really high, too high to be seen even with binoculars at DR.

So, our conclusion at the end of two seasons of fall migrant hawk counting at the Dinosaur Ridge Hawk Watch is that this is not a productive spot to count in fall.

Almost every day, the wind at the watch which can be from any direction early in the morning eventually changes to from the E to the NE, this being caused by local factors such as the area around Denver being warmer, and the wind ascending the ridge. The wind direction here is not really predictive of a good flight in fall, compared to when I volunteer counted in New York state at 3 different hawk watches, the day after a cold front with NW wind was always predictive for a good count.

You can find every year’s result at Dinosaur Ridge, Mount Zion, as well as any other hawk count in North, Central and South America at Hawkcount.org

We will continue counting in fall regularly at Mount Zion Hawk Watch, which is only the second hawk watch in Colorado, and the only one active in fall!

Ajit and Liza Antony
Central Park, Denver, Colorado