Monday, September 17, 2007

Hawk Migration Conference

I’ve spent the last four days at a raptor conference sponsored by the Hawk Migration Association of North America (HMANA). Scientists, researchers, biologists and citizen scientists gathered to hear about the decline of the American Kestrel and the new statistical model for determining continent-wide raptor populations from migration counts. I’m sure this last sounds boring, but it’s really very exciting and marks the first time that hawkwatch site counts gathered from many previous seasons has been used to help keep track of the populations of our raptor species in a scientifically rigorous method. As the editor of HMANA’s journal, Hawk Migration Studies, I got to attend too, and was able to hang out with some of this continent’s most well known raptor experts.

So first off, I attended the Kestrel symposium and heard several presentations on the decline of our smallest falcon. I wasn’t able to attend all of this symposium but the research I did hear was fascinating. The decline of the kestrel is real and appears to be worst in the east, though signs of it declining in the west are beginning.

What is causing the decline? No one yet knows for sure but some of the latest information is pointing the direction for more research. One bander has data from the past 20 years of banding in Connecticut and has been showing a steady decline of the birds’ weights over that time. The birds leave their summer breeding grounds much lighter than when they arrive in the spring. This man speculates that many birds simply aren’t surviving migration. Each year the spring arrival weights and especially the weights of the birds migrating south in the fall are lighter than the previous year.

Other information points to loss of habitat (grassland) along their migration routes, meaning that the birds must fly much further each day to find open grassland where they can refuel and continue their flight north. Some may simply starve before they reach their summer or their wintering grounds. A corollary to this is that the kestrel’s main source of food—grasshoppers—are declining from habitat loss and pesticide use.

The second symposium I attended was on the state of North American Birds of Prey. The newly unveiled raptor population index (RPI) received perhaps the most attention. It is a very complicated (to me at least!) statistical model that uses hawkwatch count information from selected sites across the hemisphere to determine if specific species of raptors are increasing or decreasing. Overall, to no one’s surprise, the bald eagle, golden eagle, turkey vulture and black vulture are increasing. However, the most recent trends suggest that many species that were increasing through the 80’s and 90’s are now stabilizing or even decreasing. Merlin and Cooper’s Hawk are two species that are doing pretty well. Populations of Broad-winged Hawk seem pretty stable, too. The kestrel is declining.

I won’t bore you with more conference minutiae, so tomorrow I’ll be back posting my more typical ruminations on what’s going on around the cabin. The temperature is dropping, and fall is knocking at the door.

In the meantime, let me leave you with a link to the annual winter finch forecast. This man reports on finch food in the north to determine if and which of those irruptive little darlings will show up in the south this year. Keep those bird feeders filled this winter! The report looks like good news for those of us in the south.
Today's photo is a simple one--morning light on the long grasses around one of Roundtop's ponds. It was a beautiful morning.


Cicero Sings said...

Oops, the link didn't work.

Carolyn H said...


Thanks! The link is fixed now (I hope).

Carolyn H.