Wendy A. Estes-Zumpf

Natal Dispersal by Pygmy Rabbits (Brachylagus idahoensis)

Abstract Multiple factors likely influence natal dispersal behavior of juvenile mammals, which is typically male-biased. Because of their small body size and specific habitat requirements, pygmy rabbits (Brachylagus idahoensis) are expected to exhibit limited dispersal. We predicted that dispersal would be male-biased, that juveniles born later in the year would disperse farther, and that juveniles would be more likely to disperse away from areas of higher habitat saturation. We used radiotelemetry to study dispersal of 61 juvenile pygmy rabbits (31 males and 30 females) from shortly after emergence from natal burrows (April–July) to the beginning of the next breeding season (mid-March) during 2004–2006. Juveniles dispersed before 12 weeks of age, and typically completed dispersal movements within 1 week. Both sexes exhibited a high rate of dispersal (males = 90%; females = 80%); however, juvenile females settled more than 3 times farther from their natal areas than males. Median natal dispersal distances for males and females were 1.0 km (range = 0.03–6.5 km) and 2.9 km (range = 0.02–11.9 km), respectively. Dispersing juveniles crossed gravel roads and perennial streams; however, rabbits tended to initiate dispersal movements away from nearby streams. Mortality rates for male and female juvenile rabbits were 69.2% and 88.5%, respectively, and were highest during the first 2 months after emergence from the natal burrow. We found no evidence that date of emergence, body condition, or habitat saturation influenced dispersal frequency or distance in juvenile pygmy rabbits. Results indicate that pygmy rabbits are capable of dispersing long distances and suggest that their conservation will require land management at broader spatial extents.

Dispersal, gene flow, and population genetic structure in the pygmy rabbit (Brachylagus idahoensis)

Abstract Dispersal and gene flow are significant components of metapopulation structure and dynamics. We examined gene flow in the pygmy rabbit (Brachylagus idahoensis), a sagebrush specialist that occurs in small, isolated populations in the Great Basin region and is believed to have limited dispersal abilities. We examined genetic diversity, gene flow, and population genetic structure, and investigated the effects of putative barriers to gene flow in 8 sample locations within 2 study areas in Idaho during 2002–2006. Potential barriers included secondary roads, highways, creeks, and agricultural pastures. Distance between sample locations ranged from 0.5 to 32 km. We expected that gene flow would be limited and that moderate levels of genetic structure would be apparent among sample locations separated by barriers and distances over several kilometers. However, analyses based on 15 microsatellite loci from 239 rabbits revealed low to moderate levels of genetic differentiation among sample locations. Bayesian cluster analyses suggested that sample locations separated by <14 km comprised 1 genetic cluster with high levels of gene flow among sample locations within clusters. We documented no significant evidence of a sex bias in dispersal based on sex-specific FST among sample locations, and relatedness (r), mean assignment index (mAI), and variance of assignment index (vAI) within sample locations; however, spatial autocorrelation suggested that juvenile females might disperse farther than males. These results indicate that dispersal capabilities of pygmy rabbits greatly exceed previous estimates, and that creeks and roads were not effective barriers to gene flow in our study areas.

Survival of Juvenile Pygmy Rabbits

Abstract Until recently, natal behavior of pygmy rabbits (Brachylagus idahoensis) was largely unknown, and no information on survival of free-ranging juveniles was available. We evaluated survival of radiotagged juvenile pygmy rabbits at 2 sites in east-central Idaho, USA, during 2004 and 2005. We captured juveniles (n  =  58) shortly after they emerged from natal burrows. Mortality rates were high and variable, ranging from 27% for females during 2004 to 63% for males during 2005. Approximately 69% of mortalities were attributed to predation. We evaluated variables influencing juvenile survival through 18 weeks old using known-fate models in Program MARK. We expected survival to decline around the age of natal dispersal and to be lower for young born later in the season. We evaluated 14 candidate models that included sex, year, study area, and relative date of birth within each year. Model selection results did not indicate strong support for any single combination of variables, and 8 competing models all included effects of relative date of birth, year, and study area. These results revealed substantial variability in survival of juveniles across multiple factors, and we documented similar patterns for adult pygmy rabbits. Such high variability in survival over relatively small spatial and temporal scales might contribute to marked fluctuations in populations of pygmy rabbits and, hence, managers interested in monitoring this species might consider monitoring multiple populations across broader geographic areas to assess regional trends in numbers.

PERMANENT GENETIC RESOURCES: Ten polymorphic microsatellite markers for the pygmy rabbit (Brachylagus idahoensis)

We developed 10 polymorphic microsatellite loci for the pygmy rabbit (Brachylagus idahoensis). Nine of the 10 loci amplified reliably and had a low frequency of null alleles. Number of alleles per locus ranged from four to 12, and observed and expected heterozygosities ranged from 0.26 to 0.89 and from 0.63 to 0.88, respectively. These loci will be useful in determining population genetic structure and assessing patterns of gene flow in the pygmy rabbit.

EVALUATION OF RADIO-TRANSMITTERS ON JUVENILE RABBITS: APPLICATION TO THE SEMIFOSSORIAL PYGMY RABBIT (BRACHYLAGUS IDAHOENSIS)

Researchers doing telemetry studies involving external transmitter attachments on young small mammals often employ expandable or breakaway collars. This method has been used for arctic ground squirrels (Spermophilus parryii plesius; Byrom and Krebs 1999), snowshoe hares (Lepus americanus; O’Donoghue and Bergman 1992, Gillis and Krebs 2000), chuditch (Dasyurus geoffroii; Soderquist and Serena 2000), and others to reduce the risk of mortality if a transmitter fails or if a leg or lower jaw becomes entangled in the collar (Soderquist 1993). Expandable collars also reduce the need to repeatedly capture and refit radio-collars on growing individuals, but they may increase the likelihood that jaws or appendages of juvenile lagomorphs will become caught. One alternative for attachment of radio

Modeling the Distribution of Migratory Bird Stopovers to Inform Landscape-Scale Siting of Wind Development

Conservation of migratory birds requires understanding the distribution of and potential threats to their migratory habitats. However, although migratory birds are protected under international treaties, few maps have been available to represent migration at a landscape scale useful to target conservation efforts or inform the siting of wind energy developments that may affect migratory birds. To fill this gap, we developed models that predict where four groups of birds concentrate or stopover during their migration through the state of Wyoming, USA: raptors, wetland, riparian and sparse grassland birds. The models were based on existing literature and expert knowledge concerning bird migration behavior and ecology and validated using expert ratings and known occurrences. There was significant agreement between migratory occurrence data and migration models for all groups except raptors, and all models ranked well with experts. We measured the overlap between the migration concentration models and a predictive model of wind energy development to assess the potential exposure of migratory birds to wind development and illustrate the utility of migratory concentration models for landscape-scale planning. Wind development potential is high across 15% of Wyoming, and 73% of this high potential area intersects important migration concentration areas. From 5.2% to 18.8% of each group’s important migration areas was represented within this high wind potential area, with the highest exposures for sparse grassland birds and the lowest for riparian birds. Our approach could be replicated elsewhere to fill critical data gaps and better inform conservation priorities and landscape-scale planning for migratory birds.

Individual Identification of the Endangered Wyoming Toad Anaxyrus baxteri and Implications for Monitoring Species Recovery

Abstract Monitoring the fates of individuals after release in the wild is essential for building effective species recovery programs. Current conservation efforts for the endangered Wyoming Toad (Anaxyrus baxteri) are limited by the size and number of toads that can be individually marked using invasive tagging techniques. We evaluated the use of natural patterns of wart-like glands on the dorsum of Wyoming Toads as a potential identification technique. We photographed 194 known-identity individuals (822 total images, representing 1,554 true matching-image pairs of the same individuals) from two captive-breeding facilities in 2011 and 2012. Spot patterns provided stable markings from metamorphosis through adult life stages, and naïve observers correctly matched 100% of a subset of photo pairs “by eye.” In contrast, computer-assisted identification performed relatively poorly: the two software platforms tested (Wild-ID and Hotspotter) failed to match 47% and 64% of true matching-image pairs, respectively. The use of higher-quality cameras with faster automatic focusing speeds yielded the largest improvement in matching success of any variable tested when using identification software. Simulated capture–recapture data demonstrated that using software to identify individuals would bias abundance estimates high by up to 920%.

First record of multiple paternity in the pygmy rabbit ( Brachylagus idahoensis ): evidence from analysis of 16 microsatellite loci

ABSTRACT. Although promiscuity is believed to be common among leporids, little is known about the mating system of free-ranging pygmy rabbits (Rrachylagus idahoensis). We used 16 polymorphic microsatellite markers and DNA extracted from tissue samples of 10 rabbits from 2 litters collected in east central Idaho to evaluate paternity. We incorporated maternal genotypes for better resolution and employed an exclusion approach to detect multiple paternity. Our results demonstrated multiple paternity at 6 of the 16 loci tested for each litter. These findings support the expectation that pygmy rabbits have a promiscuous mating system. It has been proposed that multiple paternity could lead to higher effective population sizes and help small populations maintain diversity. Given that pygmy rabbits persist in small and fragmented populations, a promiscuous mating system might be important for maintaining genetic diversity in free-ranging populations and could be advantageous for the captive breeding program.

Genetic Evidence Confirms the Presence of Pygmy Rabbits in Colorado

Abstract The pygmy rabbit Brachylagus idahoensis is a sagebrush-obligate species of conservation concern that occurs in the Great Basin and adjacent intermountain areas in the western United States...