After months of waiting, our birds Kansas 01 and 02 have started their fall migration back to their wintering areas in Kansas. We now know where each bird breeds, and we can tell a bit about each just from this knowledge.

Surprisingly, both birds breed in an area of northern British Columbia, in a glacial valley on the western side of the front range. To me, this is perhaps the most surprising part of the story. Both birds follow a very east/west migration path that includes a flight over the mountains, rather than tracing ridge lines in a more north/south direction. Very peculiar, but enlightening!

The birds appeared to have nested, and it looks like our birds are one male and one female. Check out the image below that indicates that within reason, both did indeed breed, because of the central orientation of the movements. For both images, I filtered the dates for the locations to include 6 June to 6 July, and cropped each at the same dimensions and altitude, so they represent approximately the same coverage of geographic area. Focus on the dots, and ignore the lines and you can tell the clustering is quite different for the two during this time period.

These clusters suggest that KAHA 01 (red) is likely a male, while KAHA 02 (purple) is likely a female. From the distribution of the spread during particular times, we can tell that KAHA 02 was probably incubating, and the breadth of the movements of KAHA 01 suggest it was making foraging movements quite regularly throughout the summer. We do have blood samples from each so we have the ability to check for certain if these are a male and a female.

What subspecies are these birds? Does this answer the question of whether or not the subspecies abieticola has a dark morph? The short answer is that it is complicated, and at the moment it does not answer the question of polymorphism in abieticola. This is for two reasons – the first being that this region is a contact zone between as many as four taxa – calurus, harlani, abieticola, and borealis. Thus, the genetic work will be crucial for figuring out where these two birds fit in these categories, if they fit at all!

To solve the subspecies question, we need to put out more transmitters!

Special thanks to the organizations that made this work possible: Burroughs Audubon Society, Kansas Ornithological Society, and the Hawk Migration Association of North America (HMANA).

The question of whether or not Western Red-tailed Hawks winter on the great plains has been debated for years. Below I detail an anecdote that shows that at least one bird does…

We were surprised to catch the bird below in eastern Kansas last winter. It’s a rufous bird that as far as I can tell, is a Western Red-tailed Hawk (ssp. calurus). Take a look, and compare the bird to the photos of a bird I caught near Boise, Idaho, in July.

Eastern Kansas – February 2020

Southwestern Idaho – July 2020

Westerns, or nearly pure Westerns, do breed east of the rockies in New Mexico, Colorado, Wyoming, etc. The hybrid zone from calurus into borealis hasn’t been properly characterized, but through eBird and the Macaulay Library we are beginning to get a broad picture of this cline. Consider the pattern at the Colorado contact zone. We know that borealis breed to the front range in Colorado (with influence likely entering the range in some areas), and interbreed with calurus throughout the region. One the other end, Kansas is yet to have a clearly documented breeding calurus in the state, although Luke may change that, but that is his story. The point is, calurus influence largely fades out before the border between Colorado and Kansas.

Could the rufous bird we caught come from an area like the Colorado contact zone? Could it have originated from intermountain region? Or could it come from further north within the distribution of calurus in British Columbia?

At the moment, we don’t have the answers for these questions, but we can find out by scaling up our transmitter effort!

In February 2020, we trapped a very interesting dark bird north of Atchison, Kansas. We were targeting dark non-harlani for our transmitter effort to track these birds to their breeding grounds as a first step for understanding if the subspecies abieticola is polymorphic.

At first pass this bird looked like our target, but when we extracted it we immediately saw the multiple harlani traits throughout the birds plumage. After later successfully trapping our targets, I came back to photos of this bird for comparison and recognized the similarities in traits, which led me to the conclusion that this interesting dark bird is likely an intergrade between harlani and the dark birds that we outfitted with transmitters (we are calling these abieticola, which might be an oversimplification, but we’re working on it!)

Below I’ve included a figure that compares a dark harlani (top) that I trapped with Neil Paprocki, Caitlin Davis, and Johnna Eilers in Northern Idaho in November 2019, the interesting intergrade (middle), and one of our transmitter birds (bottom). I also included photos of the tails of each to allow more detailed comparison between the three.

On April 25, a friend, Sylvain Bourdages, found one of our birds, Kansas 02 (purple track below), near Grand Prairie, Alberta, Canada. Although the bird was far from the road, Sylvain was able to take a few photos. We thought it would be a nice thing to share along with an update on where we last heard from both birds.

Both of our birds ended up going through this migration rich region of Alberta. We last heard from them on 1 May. Because these transmitters depend on cellular service to transmit data, this indicates that the birds have moved out of cell range somewhere in Canada or Alaska, and we likely won’t find out where they breed until they return south this coming fall.

Thanks for the photos Sylvain!

In late February 2020, Bryce, Luke, and Mark teamed up in eastern Kansas to trap two dark morph, non-harlani Red-tailed Hawks. The objective was to deploy GSM transmitters to better understand where this phenotype breeds, and along with blood and feather samples thus discover their proper subspecies designation. In the past, this type was considered to belong to calurus, but given the status of light calurus in the eastern plains and the current understanding of winter distributions of abieticola, Jerry Liguori and Brain Sullivan suggested that these dark birds may represent the previously undescribed dark morph abieticola. Because of some evidence of where this phenotype ends up during migration and the breeding season, this idea held some favor. So, we decided to organize and attempt to discover the proper subspecies designation for this subtly unique type.

On 1 March, after ten days of trapping we successfully outfitted two dark non-harlani birds with GSM units. Below are photos of each bird, as well as a summary of their movements up to 20 April 2020.

Kansas 01, Transmitter 67

Kansas 02, Transmitter 97

These birds are still moving, and we are yet to receive indication on where they will settle to breed. As expected, each is headed into the northern boreal forests. The GSM transmitters depend on the cellular network to transmit data, so we may not hear from either bird until they come back into cell reception next fall.

In the future, we will be adding more birds to this dark morph abieticola effort, as well as birds of other migratory subspecies. You can find a full list and photos of our current birds on the Movement Ecology page.

A special thanks to John Bolin and Dave Rintoul for their help in Kansas!