December Winter Raptor Survey, and sighting of a mystery buteo

[aiant...@gmail.com]

December Winter Raptor Survey of Rocky Mountain Arsenal NWR and DIA Raptor Alley, with sighting of a mystery buteo

This is our 2^nd season doing volunteer Winter Raptor Surveys (WRS) for the Hawk Migration Association of North America (HMANA) since moving to Denver in July 2022. Prior to moving we did 4 WRS in New York State in the Hudson Valley area since 2016.

Last winter season we did 3 surveys here – 1 in Denver and 2 in Boulder in December 2022, and January and February 2023 for each route, following it exactly, and roughly in the same week each month.

This year we added another WRS in the area between Bennett and Jackson Lake SP. We did that route a week ago with nothing special to report. It may improve as winter progresses.

Yesterday we completed the Rocky Mountain Arsenal to Barr Lake, and west of Denver International Airport route for December 2023.

We saw and identified 78 Raptors, including

Ferruginous Hawk          5, all adult

Prairie Falcon                 1, which attacked a Red-tailed Hawk as well as a Northern Harrier

Bald Eagle                      25

Northern Harrier             10

American Kestrel            5

Red-tailed Hawk            25, including 2 dark morph RT on Piccadilly Road at Barr Lake, one perched and both in flight together. Spectacular.

In addition we had a mystery buteo at 1^st Creek at DEN Open Space perched in a tree next to Peña Boulevard at 10:15 AM. When we finished our survey and on the way back we could still see it (presumably the same buteo) at the same location at 4:30 PM while driving south on Peña Boulevard.

Our eBird checklist for that location with images is:

https://ebird.org/checklist/S156663182

My notes written during the observation were: The tail was reddish with multiple equal width bands, no sub-terminal band, with more reddish distally than proximally, as well the left side of the tail was slightly more red than the right side of the tail which was less red. There was a thin eyeline on an otherwise white head with a black blob in the malar area, no belly band but a few speckles in the flank area, white scapulars and coverts. 

 

Liza fancied a Krider's Hawk looking at the Raptor ID  app. Looking at Brian Wheeler's Raptors of Western North America at the time, I felt it could be a juvenile light morph Harlan's Hawk, except today reading more about it in his Birds of Prey of the East and looking at the pictures, the back is not stark black and white as his images show.

I sent the images to the WRS coordinator for expert opinions. So far one opinion is that it could be a Krider’s Hawk or an intergrade between Krider’s and an Eastern borealis Red-tailed Hawk.

Any learned expert opinions with detailed reasons for your ID would be most welcome.

I have to admit that neither of us have ever seen any of these possible species! Our ID speculations are book/image-based only.

You can see what we found on our previous WRSs along the same and other routes at

https://wrs.hmana.org/public_html/index.php as well as the 1 other route developed in the past winter season in Colorado – the Nunn Raptor Alley route conducted by Robert Beauchamp. Go to the website to the left sidebar and click on Survey Map and enlarge it to Colorado, you can click on individual surveys and using the drop-down menu, find previous survey results.

Anyone can develop their own survey route. It is open to all. You can get more information at:

https://www.hmana.org/winter-raptor-survey/

If you like raptors and know of an area with raptors you can develop your own route, as long as it doesn’t overlap an established one. Just follow the guidelines on the website. If you want any questions answered you can email the WRS coordinator Janice Sweet. I can also be of help if you want someone local.

Ajit & Liza Antony

Central Park, CO (which used to be called Stapleton)

 

[KevyG...@aol.com]

Perhaps the mystery buteo is a leucistic Red-tailed Hawk?

Kevin Corwin

Centennial, Arapahoe County

[Ajit Antony]

Hi Kevin and everyone else.

I looked up Brian K Wheeler's 'Birds of Prey of the East' ( this is the first of his 2 books that came out, and I bought it when I was living in New York).

He has a plate devoted to 'Albinos and other Variants,' Plate 34 where he shows albinos and lucistic RTHA,  where he says in a picture of a Eastern partial albino that "Albinism affects wings and dorsal body surface more commonly than ventral body surface and tail." 

A few weeks ago we were at East 126th Avenue doing a raptor survey and we did see a leucistic RTHA which had large splotchy white patches on its dorsum as it flew, correctly IDd by Liza my wife and partner in the winter raptor surveys that we do.

Ajit Antony

Central Park, Colorado

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[cogoshawk]

In 2012, Dick Schottler and I found a leucistic RTHA during the Denver CBC. It so happens that we found this bird in my neighborhood, which is on the western edge of the count circle.  I was fortunate enough to watch this bird, likely a female (she was bigger than any other RTHA that tried to consort with her) up through 2020 when she disappeared. One thing I noticed over time was that she became whiter and whiter, although her red tail feathers remained distinct.  I have a couple of photos if anyone is interested, but I have to say when I saw Ajit and Lisa's photos, my first thought was "wow, another leucistic red tail!" I also remember sometime back in the last year or two someone reporting on finding a leucistic RTHA corpse.  All of which suggests that leucism is a bit more common than we may tend to think.

Ed Furlong

Evergreen, CO

[aiant...@gmail.com]

The very beautiful Red-tailed Hawk we described on 12/17/23 was still there at the 1st Creek at DEN Open Space this afternoon. I could easily see it from the  parking lot with the naked eye because of its gleaming white breast and belly.

Any raptor enthusiasts with good camera equipment could take better pictures than Liza and I could with using a cell phone and spotting scope, such images could be posted/sent to raptor experts for ID.

So far our working hypothesis is that it could be an Eastern Red-tail x Krider's intergrade.

I found an excellent article from Birding March 2010 called "A study of Krider's Red-tailed Hawk" by Jerry Liguori and Brian L Sullivan which also discusses and depicts intergrades.

http://tinyurl.com/4upszd8d

An additional feature I saw when it flew from one tree to another was that it had very large white prominent rectangular patches just within the wingtips dorsally, as shown in figure 11b in the article.

My eBird checklist from this afternoon:

https://ebird.org/checklist/S156820852

Ajit Antony

Central Park, Colorado