Michael N. Kochert
United States Geological Survey
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Featured researches published by Michael N. Kochert.
Journal of Animal Ecology | 1997
Karen Steenhof; Michael N. Kochert; Trent L. McDonald
1. The reproduction of the golden eagle Aquila chrysaetos was studied in southwestern Idaho for 23 years, and the relationship between eagle reproduction and jackrabbit Lepus californicus abundance, weather factors, and their interactions, was modelled using general linear models. Backward elimination procedures were used to arrive at parsimonious models. 2. The number of golden eagle pairs occupying nesting territories each year showed a significant decline through time that was unrelated to either annual rabbit abundance or winter severity. However, eagle hatching dates were significantly related to both winter severity and jackrabbit abundance. Eagles hatched earlier when jackrabbits were abundant, and they hatched later after severe winters. 3. Jackrabbit abundance influenced the proportion of pairs that laid eggs, the proportion of pairs that were successful, mean brood size at fledging, and the number of young fledged per pair. Weather interacted with prey to influence eagle reproductive rates. 4. Both jackrabbit abundance and winter severity were important in predicting the percentage of eagle pairs that laid eggs. Percentage laying was related positively to jackrabbit abundance and inversely related to winter severity. 5. The variables most useful in predicting percentage of laying pairs successful were rabbit abundance and the number of extremely hot days during brood-rearing. The number of hot days and rabbit abundance were also significant in a model predicting eagle brood size at fledging. Both success and brood size were positively related to jackrabbit abundance and inversely related to the frequency of hot days in spring. 6. Eagle reproduction was limited by rabbit abundance during approximately two-thirds of the years studied. Weather influenced how severely eagle reproduction declined in those years. 7. This study demonstrates that prey and weather can interact to limit a large raptor populations productivity. Smaller raptors could be affected more strongly, especially in colder or wetter climates.
Journal of Wildlife Management | 1993
Karen Steenhof; Michael N. Kochert; Jerry A. Roppe
Raptors and common ravens (Corvus corax) (hereafter called ravens) began nesting on towers along a 596-km segment of a 500-kV transmission line in southern Idaho and Oregon within 1 year of its construction. We began monitoring these nesting populations in 1981 to assess the effectiveness of artificial structures in attracting nesting raptors and to provide guidelines for enhancing raptor nesting opportunities on transmission lines. Within 10 years, 133 pairs of raptors and ravens were nesting along the 500-kV line. Rapid colonization of towers along the line probably was due to lack of other nesting substrate in the transmission line corridor, and the proximity of existing nesting populations in the nearby Snake River Canyon
Oikos | 1993
Carl D. Marti; Karen Steenhof; Michael N. Kochert; Jeffrey S. Marks
We examined trophic structure in an assemblage of 17 vertebrate predators - two snakes (Pituophis catenifer and Crotalus viridis), six hawks (Circus cyaneus, Buteo jamaicensis, B. regalis, Aquila chrysaetos, Falco sparverius, and F. mexicanus), six owls (Tyto alba, Otus kennicottii, Bubo virginianus, Speotyto cunicularia, Asio otus, and Aegolius acadicus), one passerine (Corvus corax), and two mammals (Canis latrans and Taxidea taxus). These predators fed collectively on prey in nine taxonomic classes. Mammalian prey were numerically most important in 15 diets and contributed the most biomass to all 17 diets. Mean prey mass ranged from 2.2 to 711 g, and correlated with predator mass. No significant differences were apparent in food-niche breadth or mean prey mass between diurnal and nocturnal predators, but dietary overlap among predators with the same diel activity was significantly greater than that among asynchronously-active predators. Mean diet overlap was significantly greater among nocturnal predators than among diurnal predators. Four feeding guilds were defined by dietary similarity. A ground squirrel-eating guild contained one snake, three hawks, and a mammal. A jackrabbit-eating guild consisted of a hawk and a mammal. An arthropod/mammal-eating guild was composed of an owl and the raven. Four owls, one hawk, and one snake formed a small-rodent guild. One owl and one hawk were not members of guilds. Mass ratios of adjacent-sized predators were greatest within guilds.
Wildlife Society Bulletin | 2006
Karen Steenhof; Kirk K. Bates; Mark R. Fuller; Michael N. Kochert; James O. McKinley; Paul M. Lukacs
Abstract From 1999–2002, we attached satellite-received platform transmitter terminals (PTTs) to 40 adult female prairie falcons (Falco mexicanus) on their nesting grounds in the Snake River Birds of Prey National Conservation Area (NCA) in southwest Idaho. We used 3 variations of a backpack harness design that had been used previously on raptors. Each radiomarked falcon also received a color leg band with a unique alphanumeric code. We monitored survival of birds using radiotelemetry and searched for marked birds on their nesting grounds during breeding seasons after marking. Because 6 falcons removed their harnesses during the first year, we were able to compare survival rates of birds that shed PTTs with those that retained them. We describe a harness design that failed prematurely as well as designs that proved successful for long-term PTT attachment. We resighted 21 marked individuals on nesting areas 1–5 years after they were radiomarked and documented 13 mortalities of satellite-tracked falcons. We used a Cormack-Jolly-Seber model to estimate apparent survival probability based on band resighting and telemetry data. Platform transmitter terminals had no short-term effects on falcons or their nesting success during the nesting season they were marked, but birds that shed their transmitters increased their probability of survival. Estimated annual survival for birds that shed their transmitters was 87% compared to 49% for birds wearing transmitters. We discuss possible reasons for differences in apparent survival rates and offer recommendations for future marking of falcons.
The Condor | 1999
Karen Steenhof; Michael N. Kochert; Leslie B. Carpenter; Robert N. Lehman
We studied a nesting population of Prairie Falcons (Falco mexicanus) in the Snake River Birds of Prey National Conservation Area (NCA) from 1974-1997 to identify factors that influence abundance and reproduction. Our sampling period included two major droughts and associated crashes in Townsends ground squirrel (Spermophilus townsendii) populations. The number of Prairie Falcon pairs found on long-term survey segments de- clined significantly from 1976-1997. Early declines were most severe at the eastern end of the NCA, where fires and agriculture have changed native shrubsteppe habitat. More recent declines occurred in the portion of canyon near the Orchard Training Area (OTA), where the Idaho Army National Guard conducts artillery firing and tank maneuvers. Overall Prairie Falcon reproductive rates were tied closely to annual indexes of ground squirrel abundance, but precipitation before and during the breeding season was related inversely to some mea- sures of reproduction. Most reproductive parameters showed no significant trends over time, but during the 1990s, nesting success and productivity were lower in the stretch of canyon near the OTA than in adjacent areas. Extensive shrub loss, by itself, did not explain the pattern of declines in abundance and reproduction that we observed. Recent military training activities likely have interacted with fire and livestock grazing to create less than favorable foraging opportunities for Prairie Falcons in a large part of the NCA. To maintain Prairie Falcon populations in the NCA, managers should suppress wildfires, restore native plant communities, and regulate potentially incompatible land uses.
Journal of Wildlife Management | 1999
Michael N. Kochert; Karen Steenhof; Leslie B. Carpenter; John M. Marzluff
We examined effects of fire on golden eagle (Aquila chrysaetos) territory occupancy and reproductive success in southwestern Idaho because wildfires since 1980 have resulted in large-scale losses of shrub habitat in the Snake River Plain. Success (percentage of pairs that raised young) at burned territories declined after major fires (P = 0.004). Pairs in burned areas that could expand into adjacent vacant territories were as successful as pairs in unburned territories and more successful than pairs in burned territories that could not expand. Success at extensively burned territories was lowest 4-6 years after burning but increased 4-5 years later. The incidence and extent of fires did not help predict territories that would have low occupancy and success rates in postburn years. The presence of a vacant neighboring territory and the amount of agriculture and proportion of shrubs within 3 km of the nesting centroid best predicted probability of territory occupancy. Nesting success during preburn years best predicted the probability of a territory being successful in postburn years. Burned territories with high success rates during preburn years continued to have high success rates during postburn years, and those with low success in prebum years continued to be less successful after burning. In areas where much shrub habitat has been lost to fire, management for golden eagles should include active fire suppression and rehabilitation of burned areas.
The Condor | 2005
Karen Steenhof; Mark R. Fuller; Michael N. Kochert; Kirk K. Bates
Abstract From 1999–2003, we tracked movements of adult female Prairie Falcons (Falco mexicanus) using satellite telemetry to characterize long-range movement patterns and breeding dispersal. We radio marked 40 falcons from April–May on their nesting grounds in the Snake River Birds of Prey National Conservation Area in southwest Idaho. All falcons with functioning transmitters left the Snake River Canyon from late June through mid-July. Most headed northeast across the Continental Divide to summering areas in Montana, Alberta, Saskatchewan, and the Dakotas. Prairie Falcons stayed at their northern summer areas for 1–4 months before heading to the southern Great Plains or to southwest Idaho. The Great Plains was a key migration pathway. Important wintering areas included the Texas Panhandle and southwest Idaho. Most falcons completed their seasonal migrations within 2 weeks. Use of widely separated nesting, summering, and wintering areas appears to be a strategy to exploit seasonally abundant prey resources. Most falcons had three or fewer use areas during the nonbreeding season, and falcons showed a high degree of fidelity to their use areas during each season. At least 21 falcons returned to nest within 2.5 km of where they nested in the previous year, but one falcon moved to a new nesting area 124 km south of her previous breeding area. Prairie Falcon movements suggest large-scale connectivity of grassland and shrubsteppe landscapes throughout western North America. Conservation of Prairie Falcons must be an international effort that considers habitats used during both nesting and non-nesting seasons. Movimientos de Largo Alcance y Dispersión Reproductiva de Falco mexicanus del Sudoeste de Idaho Resumen. Entre los años 1999 y 2003, seguimos los movimientos de hembras adultas de Falco mexicanus utilizando telemetría satelital para caracterizar los patrones de movimiento de largo alcance y la dispersión reproductiva. Marcamos con radios a 40 halcones desde abril hasta mayo en sus sitios de nidificación en el Área de Conservación Nacional de Aves de Presa Snake River en el sudoeste de Idaho. Todos los halcones con transmisores funcionando dejaron el cañón de Snake River desde fines de junio hasta mediados de julio. La mayoría se dirigió hacia el noreste a lo largo de la línea de división continental rumbo a las áreas de veraneo en Montana, Alberta, Saskatchewan y Dakotas. F. mexicanus permaneció en sus áreas de veraneo del norte durante 1 a 4 meses antes de dirigirse hacia las Great Plains del sur o hacia el sudoeste de Idaho. Las Great Plains representaron una ruta migratoria clave. Las áreas de invernada importantes incluyeron al Texas Panhandle y el sudoeste de Idaho. La mayoría de los halcones completaron su migración estacional en menos de dos semanas. El uso de áreas de nidificación, de veraneo e de invernada ampliamente separadas entre sí parece ser una estrategia para explotar presas estacionalmente abundantes. La mayoría de los halcones tuvo tres o menos áreas de uso durante la estación no reproductiva y los halcones mostraron un alto nivel de fidelidad a sus áreas de uso durante cada estación. Al menos 21 halcones regresaron a nidificar a menos de 2.5 km de donde nidificaron el año previo, pero un halcón se desplazó a una nueva área de nidificación ubicada a 124 km al sur de su área previa de cría. Los movimientos de F. mexicanus sugieren la existencia de una conectividad a gran escala de los paisajes de pastizal y la estepa arbustiva a través del oeste de América del Norte. La conservación de F. mexicanus debe ser un esfuerzo internacional que considere los ambientes usados durante las estaciones reproductivas y no reproductivas.
Journal of Raptor Research | 2012
Michael N. Kochert; Karen Steenhof
Abstract We studied nest use by Golden Eagles (Aquila chrysaetos) from 1966 to 2011 to assess nest reuse within territories, ascertain the length of time that elapses between uses of nests, and test the hypotheses that reproductive success and adult turnover influence nest switching. Golden Eagles used 454 nests in 66 territories and used individual nests 1 to 26 times during 45 continuous years of observation. Time between reuse ranged from 1 to 39 yr. Distances between nearest adjacent alternative nests within territories ranged between <1 and 1822 m, and distances between 90% of adjacent nests were <500 m. Of all nests used, 21% fell or disintegrated, and 31% were newly constructed during the study. Nest switching was not associated with the previous years nesting success, but eagles tended to change nests after turnover of at least one member of the pair. Five of 42 nests used in 1971 and monitored continuously through 2011 were used only once and 21 were used >5 times. Two nests were unused for 21 and 27 yr after 1971 before being used every 1 to 3 yr thereafter. Eagles used 43% of the nests in series of consecutive years (range 3 to 20 consecutive nestings). Protecting unused nests for a proposed 10 yr after the last known use would not have protected 34% of all 300 nests that were reused during the study and 49% of 37 reused nests monitored consistently for 41 yr. The 102 nests that would not have received protection were in 56 of the 66 territories. FRECUENCIA DEL USO DE NIDOS DE AQUILA CHRYSAETOS EN EL SUDOESTE DE IDAHO Estudiamos el uso de nidos por parte de Aquila chrysaetos desde 1966 hasta 2011 para evaluar la reutilización de nidos dentro de territorios, determinar el lapso de tiempo que transcurre entre la utilización de nidos y probar la hipótesis de que el éxito reproductivo y el recambio de adultos influencian el cambio del nido. Las águilas utilizaron 454 nidos en 66 territorios y utilizaron nidos individuales de 1 a 26 veces durante 45 años continuos de observación. El tiempo transcurrido entre reutilizaciones varió de 1 a 39 años. Las distancias entre los nidos alternativos adyacentes más cercanos dentro de los territorios osciló entre <1 y 1822 m, y las distancias entre el 90% de los nidos adyacentes fueron de <500 m. De todos los nidos utilizados, el 21% se cayó o desintegró, mientras que el 31% fue construido desde cero durante el estudio. El cambio del nido no estuvo asociado con el éxito de nidificación del año anterior, pero las águilas tendieron a cambiar de nido después de un recambio de al menos uno de los miembros de la pareja. Cinco de 42 nidos utilizados en 1971 y monitoreados continuamente hasta el 2011 fueron ocupados sólo una vez y 21 fueron utilizados >5 veces. Dos nidos no fueron utilizados por 21 y 27 años después de 1971 para ser luego ocupados cada uno a tres años a partir de entonces. Las águilas utilizaron el 43% de los nidos en series de años consecutivos (rango de 3 a 20 nidadas consecutivas). La protección de nidos sin utilizar durante 10 años posteriores al último uso conocido no hubiera alcanzado un 34% del total de los 300 nidos que fueron reutilizados durante el estudio y 49% de los 37 nidos reutilizados monitoreados constantemente durante 41 años. Los 102 nidos que no hubieran recibido protección se ubicaron en 56 de los 66 territorios.
The Condor | 2011
Michael N. Kochert; Mark R. Fuller; Linda S. Schueck; Laura Bond; Marc J. Bechard; Brian Woodbridge; Geoff L. Holroyd; Mark S. Martell; Ursula Banasch
Abstract. From 1995 to 1998, we tracked movements of adult Swainsons Hawks (Buteo swainsoni), using satellite telemetry to characterize migration, important stopover areas, and movements in the austral summer. We tagged 46 hawks from July to September on their nesting grounds in seven U.S. states and two Canadian provinces. Swainsons Hawks followed three basic routes south on a broad front, converged along the east coast of central Mexico, and followed a concentrated corridor to a communal area in central Argentina for the austral summer. North of 20° N, southward and northward tracks differed little for individuals from east of the continental divide but differed greatly (up to 1700 km) for individuals from west of the continental divide. Hawks left the breeding grounds mid-August to mid-October; departure dates did not differ by location, year, or sex. Southbound migration lasted 42 to 98 days, northbound migration 51 to 82 days. Southbound, 36% of the Swainsons Hawks departed the nesting grounds nearly 3 weeks earlier than the other radio-marked hawks and made stopovers 9.0–26.0 days long in seven separate areas, mainly in the southern Great Plains, southern Arizona and New Mexico, and north-central Mexico. The birds stayed in their nonbreeding range for 76 to 128 days. All used a core area in central Argentina within 23% of the 738 800-km2 austral summer range, where they frequently moved long distances (up to 1600 km). Conservation of Swainsons Hawks must be an international effort that considers habitats used during nesting and non-nesting seasons, including migration stopovers.
Western North American Naturalist | 2006
Karen Steenhof; Eric Yensen; Michael N. Kochert; Kenneth L. Gage
Abstract Piute ground squirrels (Spermophilus mollis idahoensis) are normally above ground from late January until late June or early July in the Snake River Birds of Prey National Conservation Area in southwestern Idaho. In 2002 they were rarely seen above ground after early May. Because of the ecological importance of ground squirrels for nesting raptors and other species, we sought to determine the reasons for their early disappearance. We sampled 12 sites from January 2003 through March 2003 to determine if a population crash had occurred in 2002. Tests indicated that Piute ground squirrels had not been exposed to plague within the past year. The presence of yearlings in the population indicated that squirrels reproduced in 2002 and that at least some yearlings survived the winter. Both yearling and adult squirrels appeared to be reproducing at or above normal rates in 2003. The most plausible explanation for the early disappearance of Piute ground squirrels in 2002 is that squirrels entered seasonal torpor early in response to a late spring drought. In addition, the breeding chronology of squirrels may have shifted during the past 2 decades in response to climate change and/or habitat alteration. Shrub habitats provide a more favorable and stable environment for squirrels than grass habitats. Squirrel abundance was higher on live-trapping grids with sagebrush than on grids dominated by grass, and squirrel masses were higher at sites dominated by shrubs and Sandberg bluegrass (Poa secunda). Densities in big sagebrush (Artemisia tridentata) were within the ranges reported for earlier years, but densities in grass were lower than previously reported. Low densities at grassland sites in 2003 support other findings that drought affects squirrels in altered grass communities more than those in native shrub habitats. Long-term shifts in ground squirrel breeding chronology may have implications for raptors that depend on them for food.