RVRI Research Update 03-27-13

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RVRI Research Update 03-27-13

March 29, 2013

Adam Shreading and Rob Domenench share a research update about golden eagle, and osprey, tracking.

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Five of the six adult Golden Eagles outfitted with GPS satellite transmitters on the MPG Ranch are well on their way towards their summer ranges.

This adult male spent his second winter entirely in the Bitterroot Valley, with the exception of a long loop through Idaho.

This adult female’s wintering movements were very similar to that of last year, including a trip east of the Continental Divide in mid-February.

We were beginning to think he would reside there, when he headed back west along the Clark Fork and I-90. He passed Missoula and, like 110270, went up the Ninemile Valley, continuing north into Canada. Currently he is in north British Columbia and still moving north. So far both he and 110270 have followed nearly identical routes through British Columbia along the Rocky Mountain Trench.We were surprised when this adult male left the Bitterroot Valley less than a week after capture, and spent more than a month between Anaconda and Butte.

The healthy eye shows the marbled, uniquely patterned iris indicative of an older Golden Eagle

This adult male has done several laps from the Bitterroot Valley out to the foothills of the Front Range west of Conrad, Montana.

This adult female hung around the ranch for a few days after capture before flying to an area north of Ovando in the Blackfoot Valley. Towards the end of February, she left the Blackfoot valley and headed up the Swan Range. North of Glacier National Park, she cut over to the Rocky Mountain Front and headed up the Golden Eagle highway. Currently she is just north of the Wrangell Mountains, just south of the Alaska Range.

We captured what we believed to be a resident adult female near Whaley Draw after setting our bait and getting into position under the cover of darkness. Everything appeared fine the first few days after capture, but locations for the eagle began stacking up on the back (east) side of Baldy Mountain. We attributed this to three possible scenarios: 1) the eagle was incubating on a previously undiscovered nest, 2) the eagle had managed to get the transmitter off via the “breakaway” on the harness and the unit was on the hillside, or 3) the eagle was dead with the unit still attached. Fearing the worst, we headed out the following day to investigate.

After a long trek over rugged, snow-covered terrain, we arrived on the steep, south-facing slope that was the transmitter’s last recorded location. After a bit of searching, we were able to locate the transmitter, and were relieved to find that the harness had simply broken away. We do not want to saddle these incredible birds with a device that will never drop off, so we design their harness to break away after a bit of work from the eagle’s beak.

This photo shows the transmitter as it was when located. Despite having the accuracy of a handheld GPS unit, the transmitter’s small size and the ruggedness of the area made it extremely difficult to find.

We expect the adult MPG Ranch Osprey to make a northern move for the ranch any day now. Currently, each Osprey is still on their wintering territories. We are checking on them daily and will put out an immediate update when they leave.

This adult male from the Ranch Entrance Nest is still sticking tight to his winter territory along the Bay of California on mainland Mexico. He appears to be doing well, fishing the mangrove islands and coastal estuaries.

The adult female from the Ranch Entrance Nest is still on her wintering ground along the Pacific coast of Nicaragua. We expect the females to stay on wintering territories a little longer than the males, who generally return first and secure the nest sites.

The adult male from the North Center Pivot Nest is along the Gulf Coast and coastal plain of Mexico. He spends all of his time near a small inland lake, bordered by a small aircraft runway. He is approximately 30 miles from the Caribbean Coast, 200 miles north of Veracruz, near the small farming village of Santa Rosa.

The sole survivor of the MPG Ranch youngsters has found refuge near Galveston Island. Recently it has been spending more time away from the barrier islands habitat; perhaps resident adult Ospreys occupy this prime real estate. Most young Ospreys stay on their wintering grounds until they reach sexual maturity. It is unclear whether this bird will return to its natal grounds; hopefully both the young and its transmitter survive long enough to provide us with an answer.

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