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

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.