News From The Field

February 2011

Female ferruginous hawk 80631 from north-central Oregon.
Adult ferruginous hawk 47839 "Charlie".
(Photo Robin Nieto, USFS).
Two hawks from the grasslands continue to provide movement data in early 2011. Both hawks were captured in New Mexico in 2007. During the past year several hawks died or disappeared. The most notable was hawk 47839 from North Dakota that provided more information than any other study bird, and nested every season. "Charlie" was shot on his territory in June, 2010. More recently, in January 2011 adult female 47840 was recovered by biologist Daryl Fisher, a biologist with Kansas Wildlife and Parks. This hawk was emaciated and had a green anal discharge suggestive of poisoning (potentially lead) but necropsy results are pending.

Adult ferruginous hawk 47839 "Charlie" (image right) was shot and killed on his territory in July, 2010. He provided over 17,000 GPS locations during the time he was monitored.

March 2010

We continue to monitor eight hawks in spring, 2010, in addition to hawks telemetered as part of windpower studies in Washington and Oregon. The winter of 2010 was interesting in that all but one of the eight hawks wintered in the southern grasslands, primarily Kansas, Colorado, and Oklahoma. One hawk, 39421, wintered again in our Mexican study area of La Soledad and as of this update had not started his spring migration back to his nest territory in the Thunder Basin, Wyoming. Of the other adults, hawk 47839 ("Charlie") is returning to the Dakota Prairie Grasslands in North Dakota from Kansas where he will be monitored for his 5th breeding season. Adult female 47840 (Thunder Basin, WY) has returned to nest from eastern Colorado, and New Mexico female 55373 (Kiowa National Grassland) should return from her wintering area in eastern Colorado to nest soon.

The other four hawks were telemetered as nestlings and will begin their third and fourth years after hatching this summer. We hope that one or two of these birds may nest in 2010, although the transmitter signal for male 35576, captured in 2007 in Oklahoma, became stationary in early March, 2010 about 13 miles from his natal territory. Game Warden Rusty Menefee, of the Oklahoma Department of Wildlife Conservation, volunteered to search for the PTT but was unable to it due to deep snow, and the signal disappeared after that time. The fate of that bird is unknown.

May 2009

Female ferruginous hawk 80631 from north-central Oregon.
Female Ferruginous Hawk 80631 from
north-central Oregon.
We continue to monitor 11 hawks in spring, 2009. Noteworthy is the fact that none of the five adult hawks that returned to Wyoming in spring, 2009 appear to be nesting based on location information. Perhaps not coincidentally, the rabbit population on the Thunder Basin has decreased markedly from two or three years ago. We continue to monitor bird 47839, the male hawk dubbed “Charlie”, which appears to be nesting again for the 4th straight year in North Dakota. He and female 55375, which was radioed in Wyoming in 2005, are the longest radio-monitored hawks in the study. In addition to monitoring hawks marked as juveniles in Wyoming, Oklahoma, and New Mexico, we are following an interesting female telemetered in Oregon in 2008 (photo). Her movements have taken her from Oregon to the northern plains down to Mexico last fall, to a wintering area near Lubbock, Texas. She recently began moving northward through the Great Plains (View Migration Maps).

Even though we don’t plan any further deployments in the grasslands, we will continue to telemeter hawks in Oregon and Washington as part of work associated with Wind Turbine development.

November 2008

In October two telemetered juvenile hawks died leaving two of ten juveniles that we telemetered in 2008 still active. One of the hawks (55380) was probably killed by a golden eagle in Wyoming, and the other hawk (85884) disappeared abruptly in northwestern New Mexico. One of the active juveniles, 80631, which hatched in Oregon, spent the fall in southern Saskatchewan, and flew through the Janos, Mexico study area in October. She spent several days west of Chihuahua before moving north again and is now near Lubbock, Texas.

Another interesting movement in October was by adult male hawk (55374) from the Thunder Basin, Wyoming. He arrived to winter near La Soledad, Mexico on the Mexican study area and joined hawk 39421, also from the Thunder Basin. This is the third breeding male from Wyoming to winter near La Soledad. The first hawk (39426) was captured in Mexico and track to the Thunder Basin in 2005.

August 2008

Telemetered hawks began to move by early August but also experienced mortality. Two of four juvenile hawks in the Dakotas did not survive to disperse from their natal territories, and signals on the two other birds were lost and were presumed mortalities. The signal from one of the Oregon juveniles and the New Mexico fledgling were lost in late July and they were also presumed mortalities. On the bright side, the three Wyoming juveniles left their territories in August and two of them have migrated northward, one into Alberta. Additionally, one Oregon juvenile is in southern Saskatchewan. One of the adult male hawks in Wyoming (35644) died unexpectedly on his territory in late July after raising 2 young. There were no obvious causes of death. Finally, the two adult females radioed in the Dakotas this past spring shredded their harnesses and removed their PTTs as have at least 2 other adult females in this study.

July 2008

Ferruginous Hawk 55372 and siblings in North Dakota, July 2008.
Ferruginous Hawk 55372 and
siblings in North Dakota, July 2008.

It was another interesting field season with nesting delayed by a couple weeks in the Dakotas. As of late July, three recently telemetered juvenile hawks had already died and two of these birds were recovered in the Dakotas. This was not unexpected as there is a mortality bottleneck for recently fledged ferruginous hawks from starvation in the first few weeks post-fledging, and again during early winter. We are hopeful that a few of the remaining juveniles will survive the initial challenge of learning to hunt for themselves.

During spring, 2008, we completed deployment of PTTs in the final year of field work in the grasslands that included four adults and 11 juveniles in North and South Dakota, Wyoming, and New Mexico. In addition, we deployed two PTTs on adults, and two PTTs on juveniles as part of windpower studies in Oregon and Washington. In total, 56 adult hawks and 44 juvenile hawks have been monitored during the study.

December 2007

Ferruginous Hawk Carcass at Badger Hole
Location of carcass of 47845

During winter, 2007, two of our telemetered hawks went off the air. Adult female 47838, captured in Colorado in 2005, stopped broadcasting in November and we believe her PTT battery expired. Juvenile hawk 47845, telemetered in North Dakota in 2007, died in southwest Nebraska in late November. Chad Taylor and Jeff Hoffman, biologists with the Nebraska Game and Parks Commission, checked the GPS location and found only feathers. After searching the area they discovered a fresh badger dig at a prairie dog burrow and several additional feathers (photo). They successfully excavated the intact PTT without the badger making an appearance. Thanks Chad and Jeff!

The carcass of 47845 was too scavenged to confirm cause of death, but the period at the onset of winter appears to be another mortality bottleneck for juvenile ferruginous hawks, presumably related to the scarcity of small mammals during colder weather and resulting starvation.

November 2007

The two adult male hawks that we telemetered on the Thunder Basin in Wyoming in 2007 (35644 and 39421) migrated abruptly southward in October. 35644 seems to have settled near Roswell NM, for now, but 39421 continued southward and has since settled on our Mexican study area near La Soledad! This is important information since another adult male we radioed in Mexico in 2004 (39426) migrated to the Thunder Basin to nest in the spring.

October 2007

The migration season was characterized by expected mortality of some juvenile hawks but successful migration of others to fall hunting grounds. Mortality of juveniles was especially high in Canada (3) and the Dakotas (2). Four juveniles in Wyoming, Oklahoma, and New Mexico survived the post-fledging period and were active as of early October. Movement of Wyoming hawks has been local, whereas hawks in the southern plains moved northward from nesting areas.

Unfortunately, one of the adult hawks from North Dakota died on the fall range in Saskachewan; circumstances suggest she was predated by another raptor. Additionally, a second-year bird from North Dakota, telemetered in 2006, died near Cheyenne, Wyoming in September. She was badly emaciated and we suspect there were underlying causes related to her death (lead poisoning or West Nile Virus). Tests will be forthcoming. An adult hawk in Oklahoma also removed her backpack by shredding the attachment ribbon. This is an unusual occurrence in our study, but because we have been able to recover all PTTs that use GPS technology we can redeploy these PTTs in the future.

July 2007

Ferruginous Hawk with Telemetry Device
Dan Svingen prepares to release
hawk 75619 on the North Dakota

It was a busy spring and summer in the field. Field teams captured six adult birds in the Great Plains to gather additional information on adult movements especially in the Dakotas and southern Grasslands. The Canadian field team deployed three PTTs on juveniles in southern Alberta, and juveniles were also telemetered in the Dakotas (3), Wyoming (2), New Mexico (1), and Oklahoma (1).

Nesting chronology was unusual this season with some northern birds completing nesting well before their southern counterparts. Wet conditions in the grasslands of the Dakotas and Wyoming are still providing abundant prey, especially rabbits, for nesting hawks. Only one hawk captured in Wyoming last season migrated from the area during the winter, and the remaining hawks (including one adult, 55375) stayed in the Thunder Basin where they hatched.