10-03-13 Field Note

10-03-13 Field Note

October 3, 2013

Eric Rasmussen's Field Note shows Cooper's hawks, Osprey satellite tracking, and a fall songbird banding update.

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Broad-winged hawks typically fly high overhead. This hawk gave us a close look at the white undersides, black on the trailing edge of the wing, and a strong terminal band on the tail.

A strong low-pressure system engulfed the northern Rockies this week. The day before the weather system arrived, we had our biggest day up to that point. 125 turkey vultures helped to bring that daily total to 178. Two consecutive days, 9/24 and 9/25, we had steady drizzle with gusty winds and zero migrants. On 9/26, moisture and low clouds covered the region, except the Bitterroot valley north to the Mission valley. What occurred was a monumental migration event. We counted 665 raptors in 5 hours! Turkey vultures represented over half the total. We saw the first Swainson’s and ferruginous hawks of the season. The broadwinged hawk total is now our highest at 31. 62 American kestrels doubled the previous daily high count.

900 1367 Raptor Migration Update Raptor Counts: 9/20/13-9/26/13 A strong low-pressure system engulfed the northern Rockies this week. The day before the weather system arrived, we had our biggest day up to that point. 125 turkey vultures helped to bring that daily total to 178. Two consecutive days, 9/24 and 9/25, we had steady drizzle with gusty winds and zero migrants. On 9/26, moisture and low clouds covered the region, except the Bitterroot valley north to the Mission valley. What occurred was a monumental migration event. We counted 665 raptors in 5 hours! Turkey vultures represented over half the total. We saw the first Swainson’s and ferruginous hawks of the season. The broadwinged hawk total is now our highest at 31. 62 American kestrels doubled the previous daily high count. A kettle of raptors formed in the distance. This group had over 30 birds of 4 species; turkey vulture, red-tailed hawk, broad-winged hawk, and Cooper’s hawk.

We captured 15 raptors of three different species this week. Precipitation and heavy cloud cover prevented trapping two days this week and limited the hours we were able to work on two other days. As we predicted, based on anecdotal observations from previous seasons, the lower trapping blind was more productive than our higher site on West Baldy Ridge. With less thermal lift available, migrating raptors tend to travel at lower altitudes. Fourteen of the 15 raptors banded this week were Accipiters; the last week of September and first week of October are the peak period of Accipiter migration.

The long tail in proportion to short, broad wings of this adult Cooper’s hawk is a definitive characteristic of Accipiters.

This photo shows the difference in size between the smaller Sharp-shinned hawk and larger Cooper’s hawk and also exhibits the difference in juvenile (left) and adult (right) plumage patterns of the two species.

The tail of this hatch-year Red-tailed hawk will not turn red until its second year.

Three of the five Osprey outfitted with satellite transmitters have left the Bitterroot Valley for their wintering grounds. As expected the adult female Ospreys left first, followed by the young. As of September 27, both adult males were still on the ranch. We expect the males to start moving any day; last year they started their southern journeys on September 27 and September 30.

The adult female Osprey from the Ranch Entrance nest left the Bitterroot Valley August 30. This was one day earlier than the previous year. By September 26, she had flown to the Pacific coast of central Nicaragua, just north of where she spent the winter last year.

The adult female Osprey from the North Center Pivot Nest left the area on September 13 and covered the distance to Corpus Christi, Texas in just ten days.

The young Osprey from the North Center Pivot Nest left the ranch on September 20. After eight days of traveling, it was in eastern New Mexico following a path similar to that of its mother.

Ruby-crowned kinglet captures increased on the floodplain. Cedar waxwings continue to search for berries along the floodplain in numbers slightly higher than the previous week. Insect dependent birds like flycatchers, decreased this week due to colder temperatures. Vesper sparrows were absent at banding stations and the shrubby draw surveys.

Thursday, September 19th, was the biggest day this fall. We caught 128 birds throughout the morning. Two new species for this season include the Clark’s nutcracker (above) and Cassin’s finch (bottom, right). Male downy woodpeckers (bottom, left) show a red patch on the head.

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