Evaluation and observations of the exploratory hawk watch at Dinosaur Ridge in 2025, to the end of August

[AJIT ANTONY]

To know why we are counting at Dinosaur Ridge this fall, read: https://tinyurl.com/6m6n43fu

When we did an exploratory count in 2022, we did what we did in New York which is look naked-eye for raptors, and scanning with binoculars for distant ones.
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.
Some of you may have seen the images in Jerry Liguori’s book ‘Hawks at a Distance.’ I sometimes wish that we could see birds as ‘close’ as depicted in his book!

In addition, we learned over the last 3 years of helping the spring count that most of the migrants fly far over the western ridge requiring binoculars to find, with a few going to the east, or in the valleys to the east and west of the site itself.

This fall, we counted107 migrant raptors, of which an astounding 56 were Swainson’s Hawk, and the peak migration time for the species is the at end of September and the beginning of October.
See https://tinyurl.com/yx5t5k6bfor details of species and individuals.
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 days they counted, they did until the migration seemed to have stopped for the day,resulting in variable hours counted, and for the past 5 years going back from2021 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 it amounts to 6.4 hawks/hour, while in fall it is 2.13 hawks/hour though we haven’t really got into the time of getting good numbers of raptors yet.
Specifically for Swainson's Hawk in spring 2025 the number of SW per hour was 0.093. For 2025 fall, until the end of August the number of SW found per hour of count is 1.11.

It would appears 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 going as fast as possible to their breeding grounds in the prairies of eastern Colorado,and they don't necessarily need ridges to fly (they migrate on along a broad front).

Almost all the migrant raptors flew far to the west between Lookout Mountain to the western ridge to south of Mount Morrison.
Of course, we were looking more to the West because that's where we saw most of the birds but it may be a self-proving fulfilling prophecy, and we may be missing raptors to the east.
Liza reminded me when we were counting last fall at Mount Zion hawk watch that we would see raptors flying over North and South Table Mountains and once they went south of that area with an area full of trees and houses they would lose lift completely which means that they should fly in the valley to the east of Dinosaur Ridge between it and Green Mountain, so we have resolved to take turns sitting and looking for raptors to the east as well, though to date we haven’t found a single migrant there. This illustrates the importance of having multiple observers if at all possible, to get a better count.

The first migrant raptor of the day is often found around 9:30 a.m. MDT.

Kestrels seem to fly between in the valley to the west of the watch, so far.

The Soaring Forecast of the National Weather Service really meant for gliders, is usually very helpful as it gives 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.

Almost every day,the wind at the watch comes 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, compared to when I volunteer counted in New York state at 3 different hawk watches, the day after a cold front with NW winds were always predictive of good counts.

Earth.nullschool.net could be more predictive. I am recording it daily using the 700 hPa air pressure which corresponds to up to 1 mile above ground level in Denver, giving us a better idea which winds aloft help or hinder a good flight.

Someone emailed me privately after a previous post asking whether we allow visitors to the hawk watch. Of course! It's well established that the greater the number of observers at any hawk watch, the greater are the number of raptors found.
We plan to be at the watch every day starting at 9:00 AM through November, or until the migration ceases. The peak for SW is the end of September to the beginning of October.
We can see up to17 different species at the watch, there are two of them goshawk and Rough-legged Hawk are quite rare, though I did see one of the former in August, though not a migrant.

Ajit and Liza Antony
Central Park, Colorado