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Geology topics

Michael N. Kochert

Publications and source records attributed to Michael N. Kochert.

At least 19 recordsLinked to original sources
USGS2025

Landscape changes and declines in Aquila chrysaetos (Golden Eagle) territory occupancy in southwestern Idaho

Rapid loss of native shrubs and expansion of invasive annual plants like cheatgrass ( Bromus tectorum ) have altered North American shrub-steppe systems across extensive areas. Predators, like Aquila chrysaetos (Golden Eagle) that forage on shrub-reliant prey, may abandon historically occupied territories or increase their territory size to cope with degraded habitat. We used a multiseason Bayesian occupancy model that accounted for imperfect detection to investigate the associations between landscape cover, fire history, conspecific neighbor density, and occupancy of 36 A. chrysaetos territories in southwestern Idaho and the Morley Nelson Snake River Birds of Prey National Conservation Area, USA from 1986 to 2022. The probability of A. chrysaetos occupancy at historically occupied territories decreased 25% from 1986 to 2022 (0.83–0.58). Once territories became vacant for 5 yr, they tended to remain vacant, suggesting that they were no longer suitable for eagles, or that no new eagles were recruiting into the population. Territory occupancy was positively associated with shrub cover ( β : 0.90, 95% CrI: 0.12 to 1.71) and negatively (albeit weakly) associated with annual herbaceous cover ( β : –0.63, 95% CrI: –1.32 to 0.05). Territories closer to other occupied territories had a lower probability of occupancy than territories with distant neighbors ( β : –3.89, 95% CrI: –4.61 to –3.14), likely because eagles compensated for degraded habitat by expanding their territories. Years since the territory last burned had a slightly positive effect on occupancy with high uncertainty and a credible interval that overlapped 0 ( β : 0.28, 95% CrI: –0.26 to 0.87). The probability of detecting eagles in an occupied territory was high (0.90) and improved in surveys conducted earlier in the day and later in the breeding season. Shrub conversion to invasive grasslands has negative bottom-up consequences on A. chrysaetos territory occupancy, which may decrease the local carrying capacity for eagles in this area.

Idaho↗
USGS2025

Prairie Falcon (Falco mexicanus) abundance in a National Conservation Area in Idaho has increased since the 1970s–1990s

The Morley Nelson Snake River Birds of Prey National Conservation Area (NCA), in southwestern Idaho, USA supports a large population of breeding Prairie Falcons ( Falco mexicanus ). Abundance of Prairie Falcons in the NCA was previously monitored in 1976–1978 and 1990–1994. That research indicated maximum counts for each period in 1976 and 1992 and a possible population decline across that time span. We assessed the abundance and nesting success of Prairie Falcons in the NCA in 2002–2003 and 2019–2021, and we compared results to data from before 2000 to assess possible population change. Number of nesting pairs increased over 45 years from peak counts of 206, 193, and 217 in the 1970s, 1990s, and early 2000s, respectively, to 257 in 2021. Increases were not concentrated in one region, but widely distributed across the study area. Rates of nesting success in 2002–2003 and 2019–2021 averaged 57 ± 11.8% (SD) at 49.8 ± 3.3 nests observed each year and did not differ from pre-2000 rates. Finally, our analysis showed that in all 10 years in which a full census was conducted, a sampling approach to surveys would have been effective at estimating the number of falcons nesting within the NCA. Prairie Falcons are of conservation concern because of possible population declines in parts of their range. These results illustrate an area with apparently increasing numbers of this important species and highlight the importance of long-term surveys for tracking population fluctuations and the value of a national conservation area for providing raptor breeding habitat.

Idaho↗
USGS2021

Golden Eagle dietary shifts following wildfire and shrub loss have negative consequences for nestling survivorship

Wildfires and invasive species have caused widespread changes in western North America’s shrub-steppe landscapes. The bottom–up consequences of degraded shrublands on predator ecology and demography remain poorly understood. We used a before–after paired design to study whether Golden Eagle ( Aquila chrysaetos ) diet and nestling survivorship changed following wildfires in southwestern Idaho, USA. We assessed burn extents from 1981 to 2013 and vegetation changes between 1979 (pre-burn) and 2014 (post-burn) within 3 km of Golden Eagle nesting centroids. We measured the frequency and biomass of individual prey, calculated diet diversity indexes, and monitored nestling survivorship at 15 territories in 1971–1981 and 2014–2015. On average, 0.70 of the area within 3 km of nesting centroids burned between 1981 and 2013, and the mean proportion of unburned shrubland decreased from 0.73 in 1979 to 0.22 in 2014. Diets in post-burn years were more diverse and had a lower proportion of some shrub-associated species, such as black-tailed jackrabbits ( Lepus californicus ) and mountain cottontails ( Sylvilagus nuttallii ), and a higher proportion of American Coots ( Fulica americana ), Mallards ( Anas platyrhynchos ), Piute ground squirrels ( Urocitellus mollis ), and Rock Pigeons ( Columba livia ) compared with pre-burn years. A high proportion of waterfowl represented a novel change in Golden Eagle diets, which are typically dominated by mammalian prey. Nestling survivorship was positively associated with the proportion of black-tailed jackrabbits and negatively associated with the proportion of Rock Pigeons in eagle diets. Rock Pigeons are a vector for Trichomonas gallinae , a disease-causing protozoan lethal to young eagles. Nesting attempts were more likely to fail (all young die) in the post-burn period compared with the pre-burn period. Dietary shifts are a common mechanism for predators to cope with landscape change, but shifts away from preferred prey to disease vectors affect nestling survivorship and could lead to population-level effects on productivity.

Idaho↗
USGS2021

Golden Eagle

The Golden Eagle inhabits a wide range of latitudes and habitats throughout the Palearctic and into northern Africa, where it is largely resident. In North America, its breeding distribution includes most of Canada and Alaska, as well as the western half of the United States and northern and western Mexico. Most eagles that nest in northern Canada and interior and northern Alaska migrate thousands of kilometers to wintering grounds. Southern eagles tend to be resident year-round, but some make northward, latitudinal, or altitudinal migrations when not on territory. During the non-breeding season, Golden Eagle occurs in Mexico, every U.S. state, and in the southern parts of Canada. It is most common in western North America, especially near open spaces that provide hunting habitat with ample prey, near cliffs or trees that supply nesting sites, and topography that creates updrafts essential for flight. Recent research has shown that the Golden Eagle is more common than once thought in eastern North America as well as in forested areas continent-wide, and that young individuals may summer in large numbers in the vast and productive wetlands of northernmost North America.

Book chapter↗
USGS2020

Ecological insights from three decades of animal movement tracking across a changing Arctic

The Arctic is entering a new ecological state, with alarming consequences for humanity. Animal-borne sensors offer a window into these changes. Although substantial animal tracking data from the Arctic and subarctic exist, most are difficult to discover and access. Here, we present the new Arctic Animal Movement Archive (AAMA), a growing collection of more than 200 standardized terrestrial and marine animal tracking studies from 1991 to the present. The AAMA supports public data discovery, preserves fundamental baseline data for the future, and facilitates efficient, collaborative data analysis. With AAMA-based case studies, we document climatic influences on the migration phenology of eagles, geographic differences in the adaptive response of caribou reproductive phenology to climate change, and species-specific changes in terrestrial mammal movement rates in response to increasing temperature.

Science↗
USGS2019

Effects of nest exposure and spring temperatures on golden eagle brood survival: An opportunity for mitigation

We examined Golden Eagle ( Aquila chrysaetos ) brood survival in relation to spring temperatures and exposure of nests to afternoon sun in southwestern Idaho from 1970 through 2012. Most (77%) nests classified as shaded in a subset of 96 nests had northwest to east aspects, and most (71%) nests classified as exposed had south to west aspects. We analyzed survival of 1154 Golden Eagle broods in 64 territories. Golden Eagle brood survival at shaded and exposed nests did not differ when the daily maximum temperature was <32.2°C. Survival in exposed nests declined as the number of days with maximum temperature ≥32.2°C increased, but survival in shaded nests did not change. All broods survived from hatching to fledging age in eight exposed nests with artificial shade structures installed over a 6-yr period. During the same period, 7 of 42 broods in nests without shade structures failed to reach fledging age, with two failures (29%) attributed to thermal stress. Use of artificial shade structures in exposed nests may reduce or prevent mortality caused by heat stress, and thus might be a potential tool for mitigation of “take” from anthropogenic structures and activities. Additional experimentation under an adaptive management framework could provide more information about the effectiveness of using shade structures to offset nestling mortality associated with increasing temperatures predicted by climate change models.

Idaho↗
USGS2019

Using motion-activated cameras to study diet and productivity of cliff-nesting Golden Eagles

Studies of cliff-nesting raptors can be challenging because direct observations of nest contents are difficult. Our goals were to develop a protocol for installing motionactivated trail cameras at Golden Eagle (Aquila chrysaetos) nests to record diet information and productivity, and to estimate prey detection probability using different diet study methods. In 2014 and 2015, we installed cameras at 12 Golden Eagle nests with 18—42 d old nestlings. Following installation, we monitored adult behavior from direct observation and post-installation image review. At two nests, adult eagles did not return to nests or exhibited behaviors suggesting avoidance of the cameras, but returned to the nests after cameras were removed. We visited the ten remaining nests every 4 d to collect prey remains and pellets to generate prey-specific detection estimates for both images, and prey remains and pellets. Compared to inspection of prey remains and pellets, cameras recorded twice the number of prey (622 vs. 316), were more likely to detect the smallest and largest prey, and cost half as much. Cameras recorded productivity, fledging dates, and in one case, a nestling death. Trail cameras may be a reliable and cost-effective option to address clearly defined research goals and obtain required information about eagle behavior and nest contents. However, cameras should be used judiciously because installation creates a persistent manipulation at the nest. Camera appearance should be minimized, and post-installation monitoring that allows for timely responses to nest avoidance behavior by adult eagles is important to prevent adverse effects on nesting success.

Idaho↗
USGS2018

Prevalence and risk factors of Trichomonas gallinae and trichomonosis in golden eagle (Aquila chrysaetos) nestlings in western North America

Avian trichomonosis, caused by the protozoan Trichomonas gallinae , affects bird-eating raptors worldwide. Raptors can develop trichomonosis by feeding on infected prey, particularly Rock Pigeons (C olumba livia ), which are a reservoir for T. gallinae . Raptors may be particularly vulnerable to T. gallinae infection in degraded habitats, where changes in resources may cause raptors to switch from foraging on native prey to synanthropic avian species such as Rock Pigeons. Golden Eagles ( Aquila chrysaetos ) typically forage on mammals; however, habitat across much of their range is experiencing degradation through changes in land use, climate, and human encroachment. In 2015, we examined the prevalence of T. gallinae infection in Golden Eagle nestlings across western North America and conducted an intensive study on factors associated with T. gallinae infection and trichomonosis in southwestern Idaho. We found T. gallinae infection in 13% (12/96) of eagle nestlings across 10 western states and in 41% (13/32) of nestlings in southwestern Idaho. At the Idaho site, the probability of T. gallinae infection increased as the proportion of Rock Pigeons in nestling diet increased. Nestlings with diets that consisted of ≥10% Rock Pigeons had a very high probability of T. gallinae infection. We compared historical (1971–81) and recent (2014–15) diet data and incidence of trichomonosis lesions of nestling eagles in Idaho and found that the proportion of Rock Pigeons in eagle diets was higher in recent versus historical periods, as was the proportion of eagle nestlings with trichomonosis lesions. Our results suggested that localized shifts in eagle diet that result from habitat degradation and loss of historical prey resources have the potential to affect Golden Eagle nestling survival and supported the hypothesis that land use change can alter biologic communities in a way that might have consequences for disease infection and host susceptibility.

Journal of Wildlife Diseases↗
USGS2017

Spatial and temporal patterns in golden eagle diets in the western United States, with implications for conservation planning

Detailed information on diets and predatory ecology of Golden Eagles ( Aquila chrysaetos ) is essential to prioritize prey species management and to develop landscape-specific conservation strategies, including mitigation of the effects of energy development across the western United States. We compiled published and unpublished data on Golden Eagle diets to (1) summarize available information on Golden Eagle diets in the western U.S., (2) compare diets among biogeographic provinces, and (3) discuss implications for conservation planning and future research. We analyzed 35 studies conducted during the breeding season at 45 locations from 1940–2015. Golden Eagle diet differed among western ecosystems. Lower dietary breadth was associated with desert and shrub-steppe ecosystems and higher breadth with mountain ranges and the Columbia Plateau. Correlations suggest that percentage of leporids in the diet is the factor driving overall diversity of prey and percentage of other prey groups in the diet of Golden Eagles. Leporids were the primary prey of breeding Golden Eagles in 78% of study areas, with sciurids reported as primary prey in 18% of study areas. During the nonbreeding season, Golden Eagles were most frequently recorded feeding on leporids and carrion. Golden Eagles can be described as both generalist and opportunistic predators; they can feed on a wide range of prey species but most frequently feed on abundant medium-sized prey species in a given habitat. Spatial variations in Golden Eagle diet likely reflect regional differences in prey community, whereas temporal trends likely reflect responses to long-term change in prey populations. Evidence suggests dietary shifts from traditional (leporid) prey can have adverse effects on Golden Eagle reproductive rates. Land management practices that support or restore shrub-steppe ecosystem diversity should benefit Golden Eagles. More information is needed on nonbreeding-season diet to determine what food resources, such as carrion, are important for overwinter survival.

Journal of Raptor Research↗
USGS2017

Coming to terms about describing Golden Eagle reproduction

Clearly defined terms are essential for reporting and understanding research findings, and inconsistent terminology can complicate efforts to compare findings from different studies. In this article, we reiterate and clarify recommended terms for describing Golden Eagle ( Aquila chrysaetos ) territory occupancy and reproduction. Several authors have provided recommendations for reporting data on raptor reproduction, but our literature review showed that authors continue to use different, often ambiguous and undefined, terms. The inconsistent use of terminology by researchers has been continued and expanded by lawmakers, regulators, and managers, perpetuating confusion. We recommend that authors clearly define and reference all terminology that they use, and we caution against use of the term “active” to describe a nest or nesting territory, because it is tainted with a history of inconsistent use. We provide a glossary of recommended terms for Golden Eagles and other large, long-lived raptors.

Journal of Raptor Research↗
USGS2014

Temporal and spatial changes in golden eagle reproduction in relation to increased off highway vehicle activity

We used >40 years of data on golden eagles ( Aquila chrysaetos ) nesting in southwestern Idaho, USA, to assess whether the proportion of territories and pairs producing young has changed over time, and whether territories in areas where off highway vehicle (OHV) use has increased significantly were less likely to be productive than those in areas that continued to have little or no motorized recreation. The proportion of territories that produced young was similar across southwestern Idaho from the late 1960s to 1999. After a dramatic increase in OHV use from 1999 to 2009, occupancy and success of territories in close proximity to recreational trails and parking areas declined, and the proportion of these territories producing young differed significantly from territories not impacted by OHVs. We could not pinpoint which types of motorized activity are most disturbing, nor could we identify disturbance thresholds at which eagles abandon their eggs, their young, and finally their territory. Timing, proximity, duration, and frequency of disturbance could all play a role. &copy; 2014 The Wildlife Society.

Idaho↗
USGS2013

Estimating raptor nesting success: old and new approaches

Studies of nesting success can be valuable in assessing the status of raptor populations, but differing monitoring protocols can present unique challenges when comparing populations of different species across time or geographic areas. We used large datasets from long-term studies of 3 raptor species to compare estimates of apparent nest success (ANS, the ratio of successful to total number of nesting attempts), Mayfield nesting success, and the logistic-exposure model of nest survival. Golden eagles (Aquila chrysaetos), prairie falcons (Falco mexicanus), and American kestrels (F. sparverius) differ in their breeding biology and the methods often used to monitor their reproduction. Mayfield and logistic-exposure models generated similar estimates of nesting success with similar levels of precision. Apparent nest success overestimated nesting success and was particularly sensitive to inclusion of nesting attempts discovered late in the nesting season. Thus, the ANS estimator is inappropriate when exact point estimates are required, especially when most raptor pairs cannot be located before or soon after laying eggs. However, ANS may be sufficient to assess long-term trends of species in which nesting attempts are highly detectable.

Journal of Wildlife Management↗
USGS2013

Interactions between a group of Golden Eagles and a herd of North American elk

Raptors are generally considered solitary predators (Schoener 1969), but occasionally they interact socially (Brown and Amadon 1968). Certain raptor species (e.g., Swallow-tailed Kites [ Elanoides forficatus ] and Swainson's Hawks [ Buteo swainsoni ]) concentrate in aggregations in response to localized, abundant food sources (Ellis et al. 1993). Many raptor species engage in group hunting (Ellis et al. 1993), and social foraging is a routine strategy for some species (e.g., Harris's Hawks [ Parabuteo unicinctus ]; Bednarz 1988, Ellis et al. 1993]. Raptors generally engage in group hunting to pursue elusive or large prey (Ellis et al. 1993). Occasionally individuals of conspecific raptors engage in play as a group sometimes involving chases of prey species (Palmer 1988). In this letter, we report interactions between a large group of Golden Eagles and a herd of adult and juvenile Rocky Mountain elk ( Cervus canadensis nelsoni ) in late autumn.

Idaho↗
USGS2012

Frequency of nest use by golden eagles in southwestern Idaho

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 year's 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.

Idaho↗
USGS2011

Migration patterns, use of stopover areas, and austral summer movements of Swainson's hawks

From 1995 to 1998, we tracked movements of adult Swainson's 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. Swainson's 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 Swainson's 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-km 2 austral summer range, where they frequently moved long distances (up to 1600 km). Conservation of Swainson's Hawks must be an international effort that considers habitats used during nesting and non-nesting seasons, including migration stopovers.

The Condor↗
USGS2008

Use of body mass, footpad length, and wing chord to determine sex in Swainson's Hawks

Many studies of avian ecology require an expedient means to determine sex, and the use of molecular techniques has provided an effective and accurate means to determine sex of raptors in the field ( Sarasola and Negro 2004 , Donohue and Dufty 2006 ). Sometimes investigators need to rely on morphometric measurements to determine sex of monochromatic species such as Swainson's Hawks ( Buteo swainsoni ) because they lack funds or facilities to use molecular techniques or they are analyzing extant data. Discriminant analyses conducted on morphometric measurements have been effective for sexing many raptor species (e.g., Edwards and Kochert 1986 , Bavoux et al. 2006 , Donohue and Dufty 2006 ). Sarasola and Negro (2004) recently reported on the effectiveness of seven morphometric measurements as means to identify sex of Swainson's Hawks on the hawk's austral summer areas in Argentina. They proposed a combination of the length of forearm, wing chord, and tail as an effective means to determine sex, with an overall accuracy of 93%. However, Sarasola and Negro (2004) did not assess the effectiveness of using footpad length (sometimes called toe-pad) to classify sex of these hawks. Footpad length and mass were quite effective in sexing Golden Eagles ( Aquila chrysaetos ), a species with a degree of dimorphism similar to that of Swainson's Hawks ( Snyder and Wiley 1976 ), with an overall accuracy of 98% ( Edwards and Kochert 1986 ). We here report the utility of using footpad length and mass, as well as wing chord length, as a means of sexing Swainson's Hawks on the nesting grounds.

Idaho↗