By Jeff Smith, Science Director

During fall 2000, our satellite-tracking program grew to include four new Northern Goshawks, a new Red-tailed Hawk, and a new Golden Eagle. The adult Red-tailed Hawk outfitted in the Manzano Mountains, New Mexico, and the first-year Golden Eagle outfitted in the Goshute Mountains, Nevada, are both alive and well. Unfortunately, the news concerning the four goshawks (three from the Goshutes, one from the Manzanos) is not so positive.

Red-tailed Hawks

Our newest Red-tailed Hawk (Hong Wei Ying, adopted by Jon and Emilee Reynolds) is wintering about 1,450 km (910 mi) south-southwest of the Manzanos in west-central Durango, Mexico, where it arrived by mid-November. Thus, unlike the young red-tail we outfitted in fall 2000, which ended up on the southwest coast of Mexico, our new red-tail has remained within the central portion of the Rocky Mountain Flyway.

Besides the new Manzano red-tail, we continued to receive good data into early winter from the three adult Red-tailed Hawks we outfitted during fall 1999 in the Goshute Mountains. All three birds returned to the exact same wintering locations they used during winter 1999/2000—one in southern Baja California, one in the Nayarit province of southern Mexico, and one in northern Chihuahua, Mexico! This may be the last we hear from these birds due to expected battery expiration, but we are hoping to get at least some spring 2001 migration data.

Golden Eagles

Our newest Golden Eagle (Walbridge II, adopted by Mr. George Perkins, Jr.) is wintering approximately 100 km (63 mi) west of the Goshutes in the foothills of the Ruby Mountains just south of Elko, Nevada. In our focus on young eagles, we expected to regional residents dispersing from natal territories and relatively long-distance migrants from northern latitudes. However, recent satellite-tracking data for Golden Eagles fledged in interior Alaska have identified wintering areas in several western states that are almost entirely east of the Continental Divide (study by Carole McIntyre, National Park Service, AK). Moreover, the few birds that traveled west of the Divide remained north of Nevada and Utah. With only limited data on spring and summer movements, we cannot be confident of the origins of our tagged eagles. However, it appears that the first two birds we outfitted in the Goshutes in 1999 may have been regional residents, and thus far the limited movements of our newest eagle also suggest local origins. While the sample is small and the data set incomplete, the results to date, coupled with results from Alaska, suggest that Goshute migration counts could be a useful tool for monitoring regional Golden Eagle productivity and population trends.

Northern Goshawks

It now appears that all four of the young Northern Goshawks that we outfitted during fall 2000 have died. The first goshawk (adopted by Margaret and Harry Ritchie), outfitted in the Goshutes on 4 October, first moved southwest through the Cherry Creek Range, but then reversed course and moved northeast more than 150 km (94 mi), eventually ending up north of the Goshute Mountains in the Delano and Pilot ranges. Unfortunately, the sensor data indicated that the bird died on about 14 November. We subsequently recovered the intact carcass and PTT within the pinon–juniper foothills on the western flanks of the Pilot Range. The outward appearance and mass of the bird indicated mortality due to starvation, with no obvious problems caused by the transmitter and harness. We are seeking to have a full autopsy done on the bird to conclusively determine the cause of mortality.

The second goshawk, outfitted in the Goshutes on 17 October, died only two days later in the pinon–juniper foothills on the eastern flanks of the Goshute Mountains. Only scattered feathers and bone fragments remained by the time we recovered the PTT, leaving the cause of mortality unknown. However, the short time between banding and mortality suggests that the bird succumbed to a fatal accident or predation. We found fox tracks and scat around the carcass, but they may have been scavengers.

The third goshawk, outfitted in the Goshutes on 25 October, moved about 12 km west of the Goshutes to the northern end of the Dolly Varden Range before it died around 1 November. Only feathers remained by the time we arrived on the scene, but the pattern of plucked feathers and the presence of a couple of eagle feathers indicated probable Golden Eagle predation and later scavenging by a large mammal. The PTT was not in the immediate vicinity of the carcass on our first visit, but hope to recover it on our next visit to the area.

We received considerably more data from the young goshawk outfitted in the Manzano Mountains on 18 October 2000 (Tarquin, adopted by Katharine Richardson). By mid-December, this bird had made extensive movements, moving as much as 100 km west of the original tagging location to near Grants, NM, then nearly 300 km northeast to the Sangre de Cristo Range north of Santa Fe. The bird then returned to a location just north of the Manzanos and continued south, making a direct flight into Chihuahua, Mexico, approximately 100 km south of the U.S.–Mexico border. Unfortunately, the sensor data again indicated probable mortality in late December. In early February, we will travel to Mexico to attempt to recover the PTT and discover the cause of mortality.

The limited goshawk data we have collected thus far support the hypothesis that immature goshawks moving through the Goshutes are, at most, short-distance migrants and may only be making exploratory movements as part of natal dispersal. Several recaptures of previously banded birds, including one in fall 2000, indicate natal origins in the Independence Mountains of northern Nevada. Location data from subsequent spring and fall migration seasons will be necessary to confirm whether the localized pattern of movement is sustained following the birds’ first fall migration or dispersal event. Unfortunately, poor survival of Goshute tagged goshawks has thus far precluded collection of such data. Continued indication of local origins for Goshute goshawks would support the hypothesis that Goshute migration counts are a useful tool for monitoring regional goshawk productivity and population trends.

The preliminary results from the Manzano goshawk were unexpected and highlight the importance of gathering more data. Although initial movements suggested post-fledging dispersal and not true migration, consistent with our hypothesis of local origins, movements into Mexico were not expected. This movement raises important questions concerning wintering goshawk habitat availability and use, particularly for juvenile birds. Almost nothing is currently known concerning the dispersal of juvenile goshawks or their winter habitat requirements, and satellite locations should help us learn more about this critical life cycle stage.

The 100% mortality rate of our tagged goshawks raises the possibility that carrying a PTT of this weight (32 grams) and/or design adversely affects survival of juvenile goshawks. First-winter mortality of raptors, including goshawks, is always high, frequently averaging 60–70%. Nevertheless, in the future we will take a more conservative approach by outfitting additional birds with either lighter PTTs or PTTs with an improved aerodynamic design that should help decrease any potential negative effects.

We are also hoping to augment our understanding of goshawk movements and the potential impact of the PTTs by following the movements of six more immature goshawks, which we outfitted with conventional tail-mounted radio transmitters in the Goshutes this last fall. Our plan is to survey the region within about a 300 km radius of the Goshute site several times during the 6–9 months following the fall migration season when the transmitters should still be attached and transmitting. Our first flight in early December revealed no birds, however, despite an extensive search. This may mean that all six birds traveled relatively long distances out of the region, which would be unexpected given the relatively local movements of the first five satellite-tagged birds. Subsequent surveys this winter will determine whether this pattern holds. If it does, it may provide additional support for the notion that the PTTs may be adversely affecting the young birds.

Future Plans

Currently, we have four goshawk/red-tail transmitters, and we hope to recover and refurbish two more in the next few weeks. Depending on staff availability, we may attempt to deploy one or two of these transmitters on red-tails this spring at our Sandia Mountains field site in New Mexico. Otherwise, we will deploy any remaining transmitters next fall. We currently have several grant proposals pending to purchase and deploy additional units in fall 2001 in Nevada, New Mexico, and Washington.