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Congeneric species often share ecological niche space resulting in competitive interactions that either limit co-occurrence or lead to niche partitioning. Differences in fundamental nutritional niches mediated through character displacement or isolation during evolution are potential mechanisms that could explain overlapping distribution patterns of congenerics. We directly compared nutritional requirements and tolerances that influence the fundamental niche of mule (Odocoileus hemionus) and white-tailed deer (O. virginianus), which occur in allopatry and sympatry in similar realized ecological niches across their ranges in North America. Digestible energy and protein requirements and tolerances for plant fiber and plant secondary metabolites (PSMs) of both deer species were quantified using in vivo digestion and intake tolerance trials with six diets ranging in content of fiber, protein, and PSMs using tractable deer raised under identical conditions in captivity. We found that compared with white-tailed deer, mule deer required 54% less digestible protein and 21% less digestible energy intake per day to maintain body mass and nitrogen balance. In addition, they had higher fiber, energy, and dry matter digestibility and produced glucuronic acid (a byproduct of PSM detoxification) at a slower rate when consuming the monoterpene α-pinene. The mule deers’ enhanced physiological abilities to cope with low-quality, chemically defended forages relative to white-tailed deer might minimize potential competitive interactions in shared landscapes and provide a modest advantage to mule deer in habitats dominated by low-quality forages.

For herbivores, nutrient intake is limited by the relatively low nutritional quality of plants and high concentrations of potentially toxic defensive compounds (plant secondary metabolites [PSMs]) produced by many plants. In response to phytochemical challenges, some herbivores selectively forage on plants with higher nutrient and lower PSM concentrations relative to other plants. Pygmy rabbits (Brachylagus idahoensis) are dietary specialists that feed on sagebrush (Artemisia spp.) and forage on specific plants more than others within a foraging patch. We predicted that the plants with evidence of heavy foraging (browsed plants) would be of higher dietary quality than plants that were not browsed (unbrowsed). We used model selection to determine which phytochemical variables best explained the difference between browsed and unbrowsed plants. Higher crude protein increased the odds that plants would be browsed by pygmy rabbits and the opposite was the case for certain PSMs. Additionally, because pygmy rabbits can occupy foraging patches (burrows) for consecutive years, their browsing may influence the nutritional and PSM constituents of plants at the burrows. In a post hoc analysis, we did not find a significant relationship between phytochemical concentrations, browse status, and burrow occupancy length. We concluded that pygmy rabbits use nutritional and chemical cues while making foraging decisions.

A quarter of all lagomorph species worldwide are threatened with extinction. Captive breeding programs, such as that developed for the Columbia Basin (CB) pygmy rabbit (Brachylagus idahoensis), sometimes are implemented as emergency conservation measures to restore small, genetically distinct populations. However, small source populations also may have low genetic diversity, which may influence attributes related to fitness, including growth, survival, and reproduction. We used mixed-effects regression models to explore the influence of genetic pedigree (% CB) on pairing success, growth, and survival during the 10-year captive breeding program at Washington State University, which included controlled pairings and outbreeding with pygmy rabbits from Idaho. Pairing success, juvenile growth, and juvenile survival declined with increasing CB pedigree of 1 or both parents, suggesting inbreeding depression among the small number of related founders. Demographic variables such as age, sex, and previous pregnancies, and environmental variables such as month and temperature at birth also were associated with production of pygmy rabbits. Our study illustrates the difficulty of retaining a unique genome of a small source population while simultaneously producing enough rabbits for restoration into natural habitat as part of endangered species recovery programs.

The Columbia Basin pygmy rabbit (Brachylagus idahoensis) is critically endangered and the focus of a captive-breeding program. However, reproductive success in captivity to date has not been sufficient to sustain reintroduction efforts. The goal of this study was to investigate patterns of fecal progestagen and glucocorticoid excretion in females during mating, gestation, and lactation and identify hormonal relationships to reproductive success. Fresh fecal samples were collected from 48 adult, female rabbits over 3 breeding seasons at a frequency of 4–7 samples per week. Results showed that a large (17-fold) increase in progestagen concentrations 1 day after mating provides a reliable means of determining if a successful mating occurred. In general, higher glucocorticoid concentrations during the breeding season, specifically during mating and gestation, were associated with lower reproductive success. Females that failed to conceive during the breeding season had higher glucocorticoid and lower...

Parents often face a trade-off between allocating resources to many young with lower survival, or fewer young with higher survival. To examine trade-offs in litter size and juvenile survival in mule deer, and how survival was influenced by the nutritional condition of the female, we compared the survival of 30 twin and singleton mule deer (Odocoileus hemionus) fawns during their 1st summer in eastern Washington. Overall fawn mortality was high (51.6%), especially during the 1st half of the summer (61.3%). Coyote predation caused 58.3% of all identified fawn mortalities. Twin fawns had a risk of dying 2.6 times higher than single fawns, and the difference between twin and singleton survival was most drastic during the first 1.5 months of life. Body fat of females during their last trimester of pregnancy predicted the number of fetuses they were carrying and whether they had at least 1 fawn surviving until the fall, but not the number of fawns surviving. Under these conditions, a litter size of 2 would be considered optimal because mothers giving birth to twins produced an average of 0.92 fawns by fall, whereas mothers producing singles ended up with only 0.75 fawns. However, our model suggested that a population producing only twins would be expected to increase only 4% faster than one producing only singletons.

As part of a captive-breeding program to restore extirpated Columbia Basin pygmy rabbits (Brachylagus idahoensis) to their native habitat in Washington, we documented mating and parental care behavior of these lagomorphs, which was previously unknown. Pygmy rabbits bred from late February through early June, and mating behavior consisted of chasing and brief copulations. Although presented with 1–4 mating partners and 1–6 mating opportunities annually, only 74% of females became pregnant each year. Unlike other lagomorphs, females dug a 16- to 35-cm natal burrow, usually separate from the residential burrow system, an average of 13 days after a successful copulation. Twenty-four days after copulation, females gave birth to 2–7 young at the entrance of the natal burrow and then covered the entrance. Females returned to nurse 1 or 2 times per day, until young emerged from burrows about 15 days after birth. Females averaged 1.3 litters per year, rarely (2%) producing 4 litters. Except for digging a natal burrow, mating and parental care in pygmy rabbits is similar to that of other lagomorphs. Understanding reproductive behavior is critical for captive breeding and reintroduction of pygmy rabbits, and efforts to reduce the consequences of genetic bottlenecks and inbreeding in captivity.

Olfactory communication among mammals remains poorly studied yet may be key to understanding their ecology. This is particularly true for mammalian carnivores, which rely extensively on scent marking for communication. Previous research suggests that carnivore latrines play a large role in both intra- and interspecific communication. Despite the apparent complexity of mammal use of latrines, little work has examined behavior patterns of species that visit latrines. We used motion-triggered video cameras to study use and behavior of mammals at ocelot ( Leopardus pardalis ) latrines in Costa Rica. We documented temporal patterns of use by the focal species (ocelots), diversity of mammalian species using latrines, and behaviors that occurred at these sites. Ocelots showed peaks in visitation every 60–67 days and a shorter gap between intersexual versus intrasexual visits, supporting the idea that ocelot latrines are used to communicate information about reproductive status. Fourteen terrestrial mammal species visited the latrines, and these species engaged in a variety of behaviors, including mark investigation, scent marking, and acceptance of scent marks. The complexity and frequency of behaviors by nonfocal species suggest that latrines may play as important a role in communication for these other species as they do for ocelots. La comunicacion olfativa entre mamiferos ha sido poco estudiada, sin embargo puede ser la clave para el entendimiento de su ecologia. Esto es particularmente cierto para mamiferos carnivoros quienes dependen extensivamente de el marcaje de rastros olfativos para su comunicacion. Estudios previos siguieren que las letrinas juegan un rol importante en la comunicacion intra- e inter-especifica. A pesar de la aparente complejidad del uso de letrinas por parte de mamiferos, pocos trabajos han examinado los patrones de comportamiento de las especies que las visitan. Utilizamos camaras de videos sensibles al movimiento para estudiar el uso y comportamiento de mamiferos en letrinas de ocelotes ( Leopardus pardalis ) en Costa Rica. Documentamos los patrones de uso temporal por parte de especies focales (ocelotes), la diversidad de especies de mamiferos y los comportamientos que ocurrieron en estos lugares. Los resultados indican que el uso por parte de los ocelotes muestran picos de visitas cada 60 a 67 dias y un intervalo mas corto para visitas inter-sexuales que para visitas intra-sexuales. Esto apoya la idea de que las letrinas de los ocelotes son utilizadas para comunicar estatus reproductivos. Un total de catorce mamiferos terrestres visitaron las letrinas y estas especies mostraron una variedad de comportamientos, incluyendo investigacion, marcaje y aceptacion de rastros olfativos. La complejidad y frecuencia de comportamientos por especies no focales, sugieren que las letrinas pueden jugar un rol importante en la comunicacion de otras especies como lo es para los ocelotes.