We have breeding locations!

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).