Philip F. Schempf

Bald eagle survival and population dynamics in Alaska after the Exxon Valdez oil spill

We investigated age-specific annual survival rates for 159 bald eagles (Haliaeetus Leucocephalus) radiotagged from 1989 to 1992 in Prince William Sound (PWS), Alaska. We monitored radio-tagged eagles for {le}3 years beginning 4 months after the Exxon Valdez oil spill. There was no difference (P > 0.10) in survival rates between eagles radiotagged in oiled areas and eagles radiotagged in unoiled areas of PWS. Pooled annual survival rates were 71% for first-year eagles, 95% for subadults, and 88% for adult bald eagles. Most deaths occurred from March to May. We found no indication that survival of bald eagles radiotagged >4 months after the oil spill in PWS was directly influenced by the spill and concluded that any effect of the spill on survival occurred before eagles were radiotagged. A deterministic life table model suggests that the PWS bald eagle population has an annual finite growth rate of 2%. Given the cumulative effects of direct mortality and reduced productivity caused by the oil spill, we predicted that the bald eagle population would return to its pre-spill size by 1992. 27 refs., 2 figs., 2 tabs.

Bald eagle population in Prince William Sound after the Exxon Valdez oil spill

We initiated studies to determine whether the Exxon Valdez oil spill influenced bald eagle (Haliaeetus leucocephalus) demography in Prince William Sound (PWS), Alaska. Using fixed-wing aircraft, we surveyed bald eagle populations within random plots once each year and censused nearly all islands in PWS in 1989-91 and 1995 to estimate population size. We calculated population indices (uncorrected for birds not seen) of 2,199; 1,935; 2,116; and 2,641 adult eagles for the 4 years studied. Subsequent to the 1989 oil spill, the eagle population returned to its estimated pre-spill size by 1995. The PWS bald eagle population has increased at an average annual rate of 3.7% from 1982 to 1995. The proportion of immatures in the population averaged 29% and did not vary significantly among years.

Detection Probability of Cliff-Nesting Raptors During Helicopter and Fixed-Wing Aircraft Surveys in Western Alaska

Abstract We conducted repeated aerial surveys for breeding cliff-nesting raptors on the Yukon Delta National Wildlife Refuge (YDNWR) in western Alaska to estimate detection probabilities of Gyrfalcons (Falco rusticolus), Golden Eagles (Aquila chrysaetos), Rough-legged Hawks (Buteo lagopus), and also Common Ravens (Corvus corax). Using the program PRESENCE, we modeled detection histories of each species based on single species occupancy modeling. We used different observers during four helicopter replicate surveys in the Kilbuck Mountains and five fixed-wing replicate surveys in the Ingakslugwat Hills near Bethel, AK. During helicopter surveys, Gyrfalcons had the highest detection probability estimate (;  =  0.79; SE 0.05), followed by Golden Eagles (  =  0.68; SE 0.05), Common Ravens (  =  0.45; SE 0.17), and Rough-legged Hawks (  =  0.10; SE 0.11). Detection probabilities from fixed-wing aircraft in the Ingakslugwat Hills were similar to those from the helicopter in the Kilbuck Mountains for Gyrfalcons and Golden Eagles, but were higher for Common Ravens (  =  0.85; SE 0.06) and Rough-legged Hawks (  =  0.42; SE 0.07). Fixed-wing aircraft provided detection probability estimates and SEs in the Ingakslugwat Hills similar to or better than those from helicopter surveys in the Kilbucks and should be considered for future cliff-nesting raptor surveys where safe, low-altitude flight is possible. Overall, detection probability varied by observer experience and in some cases, by study area/aircraft type.

Nest-Site Fidelity and Dispersal of Gyrfalcons Estimated by Noninvasive Genetic Sampling

Abstract. We used feathers from adult Gyrfalcons (Falco rusticolus) molted in breeding territories and blood samples from nestlings to document nest-site fidelity and dispersal of breeding adults and juveniles at three areas 100– 350 km apart in Yukon Delta National Wildlife Refuge, Alaska, 2003–2007. We used genotypes from seven polymorphic microsatellite loci that provided a mean probability of identity of 0.91 × 10-5. Breeding Gyrfalcons were highly faithful to study area and territory; we documented no dispersals of breeding birds among study areas and only one dispersal between territories. But their fidelity to nest sites was low; 22% of birds returned to the same nest site the following year. Distance among alternate nests within a territory averaged 750 m and was similar for both sexes. Mean tenure in a territory was 2.8 years, similar for both sexes, and distributed bimodally with peaks at 1 and 4 years. Mean annual turnover rate at the Ingakslugwat Hills (Volcanoes) study area was 20%. We detected three young that established breeding territories at distances ranging from 0 to 254 km from their natal territory, representing 2.5% apparent recruitment. Gyrfalcons in the Askinuk Mountains study area were slightly but statistically significantly differentiated genetically from those in the Volcanoes and Kilbuck Mountain study areas. These data are the first published on the nest-site fidelity, breeding dispersal, and natal dispersal of the Gyrfalcon in North America and demonstrate the utility of noninvasive genetic sampling to greatly improve our understanding of avian dispersal and its underlying mechanisms.

Preening Behavior of Adult Gyrfalcons Tagged with Backpack Transmitters

Comportamiento de Acicalamiento de Halcones Falco rusticolus Adultos Marcados Con Transmisores de Mochila Realizamos observaciones continuas o muestreos de observacion instantanea para documentar el comportamiento de acicalamiento de dos hembras adultas reproductivas de Falco rusticolus con transmisores satelitales de 30 g y de sus companeros libres de transmisores en el Refugio Delta Yukon de Vida Silvestre, en Alaska, (61.5°N, 164°W) a partir del 20 de mayo hasta el 6 de julio de 2005. Los transmisores fueron fijados a las aves usando arneses tipo mochila hechos de una cinta de nylon de 5 mm recubierta por teflon, siguiendo las recomendaciones publicadas para halcones. Los transmisores pesaron menos de 2% de la masa corporal de cada ave y se colocaron en las aves durante el final del periodo de incubacion o a principios del periodo de polluelos. El tiempo dedicado a acicalarse oscilo entre 0% y 50% del tiempo total observado durante las observaciones de las hembras con transmisores y de 0% a 8% en las o...