Friday, July 02, 2010

Eagle predation on pronghorn fawns

On July 1, as I drove down a two-tract road on the sheep allotment, I came upon two golden eagles on the ground. The raptors rose heavily into the air, weighed down by a recent meal. I drove straight to the spot in the sagebrush where the eagles had been grounded, and discovered the fresh remains of a pronghorn antelope fawn. This predation event was about three and one-half miles from a similar occurrence I witnessed on June 21. That earlier event also involved two golden eagles, and I’ve every reason to assume it was the same two. I photographed the eagles and the remains of the fawns in both events. If these two eagles are keying on pronghorn fawns, imagine the success they could have in this vast sagebrush steppe.

I wondered what the impact of eagle predation on fawns is in areas with abundant eagle populations. Sheep producers in eastern Wyoming have told us that golden eagles sometimes take a big toll on their lamb crops, until pronghorn fawning begins and the eagles switch to fawns. I see golden eagles frequently on the sheep allotment, even perched on hillsides above the sheep, but am thankful to report we haven’t had any problems with them. I think the fact that our guardian dogs don't like big birds has something to do with it.


Steve Bodio said...

According to Byers' pretty recent monograph on the pronghorn the eagle is one of the most significant predators on baby antelope.

But they are perfectly capable of taking adults as well! Some think they only take big prey like roe deer when trained (search Lauren in the blog window for Czech meet stuff). But it is simply not true.

In old Wyoming archaeologist George Frison's Survival By Hunting he includes a painting by a trusted friend, a rancher and guide, of two Goldens teaming up to kill an adult pronghorn. And a friend of mine, a biologist AND a falconer who trains eagles, watched a single female take one on a harsh winter day in the Red Desert. "It was like", he said of her expertise, "she did it every day!"

As a matter of fact, my own Socorro County is the one place they proved (a single pair of) eagles killed calves, in the 1970's.

Don't believe it? The Audubon Society filmed it.

I'd say your dogs are doing their job.

Josh said...

I recently posted a comment at Phillip's "Hog Blog", with a reference to a study on golden eagle predation of foxes on the Channel Islands. It seems that the only reason enough of them are around to impact the fox population is because they are so successfully hunting wild piglets.

They are powerful creatures.

Lauren said...

I certainly believe it - great post.

Interestingly, in the soum where I've primarily been flying eagles (southern Bayan-Olgii near the Chinese border)there is one of the largest populations of Argali sheep. The local belief is that Golden Eagles predate heavily on the lambs. When discussing unusual catches with a neighboring eaglehunter, I was told that a grizzled old female he flew (trapped at four years old) took an Argali lamb once while he was looking for foxes.