Conservation and Ecology of Birds – Raptors

Contributed Paper
ROOM: Room 235 – Mesilla
SESSION NUMBER: 33
 

10:30AM Recent Colonization of North American Urban Landscapes by Accipiter Hawks
Jennifer D. McCabe; Benjamin Zuckerberg
Urbanization causes the simplification of animal communities dominated by exotic and invasive species with few top predators. In recent years, however, many animal predators (e.g., coyotes, cougars, and hawks) have become increasingly common in urban environments. As predator recovery is central to the mission of conservation biology, this colonization of urban environments represents a unique experiment in predator colonization and its associated ecological consequences. One such predator that is recovering from decades of widespread population declines are accipiter hawks. These woodland hawks are widely distributed throughout North America that are increasingly common in urban and suburban landscapes. Using data from Project FeederWatch, a national citizen science program, we quantified 25 years (1990-2015) of changes in the spatiotemporal dynamics of accipiter hawks in Washington D.C. and Chicago. We estimated change in hawk occupancy over time and identified the environmental characteristics associated with occupancy for two accipiter hawk species, Cooper’s Hawk (Accipiter cooperii) and Sharp-shinned Hawk (Accipiter striatus), using Bayesian hierarchical models and remotely sensed temperature and land cover data. We found the proportion of sites recording the presence of accipiter hawks increased from 10% in the early 1990’s to over 80% in 2015. This increase in occupancy followed a discrete pattern of establishment, growth, and saturation. We found that hawks were more strongly associated with remnant forest patches. Furthermore, hawk occupancy appeared to stabilize more rapidly in urban landscapes supporting a greater proportion of large-bodied feeder birds. As hawks colonized, we found that their tolerance for urban landscapes to increase, and in later years, they become increasingly associated with impervious surface. The implications of returning predators and altered ecological dynamics in urban environments is of critical importance to conservation biology, and integrating remote sensing observations and citizen science allowed for an unprecedented investigation of the urban characteristics facilitating predator colonization.
10:50AM The Return of Bald Eagles: Spatiotemporal Dynamics of a Recovering Apex Predator and Shifting Management Impacts
Jennyffer Cruz; Steven Windels; Wayne Thogmartin; Shawn Crimmins; Ben Zuckerberg
Bald eagles (Haliaeetus leucocephalus), just like wolves (Canis lupus) and black bears (Ursus americanus), have been rewilding North America. In the USA, the recovery of these apex predators has been facilitated by federal law mandating their protection. Buffer areas around “at-risk” nests have been closed to human access in National Parks to minimize disturbance on nesting bald eagles, but the ongoing benefits of this strategy remain unknown. We aimed firstly to quantify the long-term dynamics of bald eagle recovery in Voyageurs National Park (VNP), Minnesota. We used data from repeated aerial surveys of nest occupancy and productivity during 1973-2016, which we combined into an Integrated Population Model (IPM) to provide robust demographic estimates including: nest-level measures of occupancy, success, and high productivity, as well as population-level measures of abundance, growth rate, nest success rate, nest productivity and brood size. Secondly, we aimed to evaluate potential changes in the effectiveness of management at different stages of eagle recovery during 1991-2016. The breeding population of bald eagles remained small (<10 pairs) during the 70s and early 80s, increasing steadily in the late 80s, 90s and 2000s up to ~50 breeding pairs, with some population-level parameters indicating potential density-dependence in the later decade. At a nest-level, management significantly improved the mean probabilities that a nest was occupied and successful, but not that it was highly productive. As avian predators recover throughout their former ranges, rigorous strategies are needed to monitor the dynamics of their recovery. Our study is a clear demonstration of the benefits of using IPMs in producing robust estimates of recovery dynamics based on multiple data sources and assessing the potential impacts of management strategies on recovering avian populations.
11:10AM Survival and Dispersal of Juvenile Golden Eagles in the Southern Great Plains and Trans Pecos Regions
Natasia Mitchell; Dale Stahlecker; Ben Skipper; Robert Murphy; Clint Boal
Golden eagles (Aquila chrysaetos) are apex predatory birds with delayed maturity, low reproductive rates, long life spans, and no natural predators. Little information is available for golden eagles in the southern Great Plains and Trans Pecos regions of North America. In 2015 and 2016 we attached GPS transmitters to 21 nestling eagles to assess their survival rates, dispersal patterns, and habitat associations. Survival across the first six months ranged from 72 – 80%, with first year survival of 60%. Sex had no influence on survival, but there was a temporal affect with 50% of mortalities occurring during the first two months. Home range sizes were variable, with an average 15,137km2 during the first 6 months for the 2015 cohort but only 3,070km2 for the 2016 cohort. Further, eagles in the southern Great Plains had a substantially greater risk of encountering wind energy facilities than those in the Trans Pecos. We found 39% and 72% of the marked eagles in the southern Great Plains had home ranges that overlapped, respectively, 5km and 50km buffers around turbine fields; the closest approach detected by GPS locations was 10m. In contrast, the closest any marked eagle from the Trans Pecos approached a wind energy center was 86km. We suspect topography and dominate land cover in the different regions of origin were highly influential on home range and habitat associations. Eagles in the Trans Pecos appear to be more sedentary due to the favorable habitat conditions of remote and contiguous arid grasslands situated between rugged mountain ranges. Eagles in the southern Great Plains are highly mobile due to the dispersed availability of foraging areas among a landscape dominated by crop and livestock production; however, this mobility may lead to higher encounters with risk factors such as wind energy centers.
11:30AM Dynamic Multistate Occupancy Models Indicate a Cost of Reproduction in Bald Eagles
Tammy L. Wilson; Joshua H. Schmidt
Monitoring programs often focus on status and trend of state variables such as occupancy or abundance, which can lead to important conservation actions. However, such approaches may provide incomplete information about important system dynamics. More detailed assessments of dynamics can lend insight into how populations may respond to changes in environmental stressors, and long term monitoring studies are uniquely positioned to provide information about state transitions through time. Here we use dynamic multistate site-occupancy models to analyze 23 years of bald eagle nest monitoring data collected in Lake Clark National Park and Preserve (LACL). We evaluated transitions between unoccupied (no reproduction attempted), nesting (reproduction attempted), and successful (≥1 chicks reared to fledging age) states to determine if weather and food availability affected these transitions. We found that successful nests were more likely to be unoccupied in the subsequent year, suggesting a potential cost of reproduction for bald eagles in Alaska. We found no evidence of an effect of weather or food resources, consistent with a stable population.
11:50AM First-Year Dispersal of Golden Eagles from Natal Areas in the Southwestern United States and Implications for Conservation
Robert K. Murphy
Knowledge of dispersal from natal areas by pre-breeding-age Golden Eagles (Aquila chrysaetos) in North America is sparse, though crucial for conservation planning. During 2010–2016, we used satellite telemetry to document movement behavior of pre-breeding-age Golden Eagles from the Colorado Plateau and Southern Rocky Mountains of the southwestern United States. Here we report on (1) first-year dispersal timing, distances, strategies, and survival; (2) influences of age, sex, nest-mates, and area of origin; and (3) progressive distancing from natal nests and coinciding space use, including overlap between individuals’ home ranges at the end of their first and second year. Our dataset included 293,960 GPS fixes from 66 Golden Eagles that dispersed at age ˂1 year. Most (65.2%) initiated dispersal during 16 September–21 November (median = 22 October, 191 days after median hatch date). We could assign each of 60 eagles to 1 of 4 first-year dispersal categories based on maximum distance traveled from natal nests: short-distance (SD), generally <120 km (66.7% of eagles); moderate-distance (MD), 120-500 km (16.7%); long-distance (LD) >500 km (13.3%); and Other (3.3%). LDs dispersed at younger ages than SDs and were more likely to be from the arid half of our study area. First-year survival was significantly lower for LDs. Overlap of 95% kernel density home ranges at ages 12 and 24 months was 42.2% (± 6.4 SE) for 26 SDs and 26.5% (± 9.5) for 8 MDs. Our data indicate that, during at least their first and second years of life, most Golden Eagles from the Colorado Plateau and Southern Rocky Mountains remain within 120 km of their nests, where they experience high survival and are relatively settled by the end of their first year. As such, these landscapes are key habitat for at least first- and second-year eagles as well as breeding pairs.

 

Contributed Paper
Location: Albuquerque Convention Center Date: September 25, 2017 Time: 10:30 am - 12:10 pm