Sylvilagus Nuttallii Research Articles

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

Abstract 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.

Systematics of the mountain-inhabiting cottontails (Sylvilagus) from southwestern United States and northern Mexico (Mammalia: Lagomorpha: Leporidae)

The skull morphology of four species of cottontails from the mountains and plateaus of southwestern United States and northern Mexico, currently recognized as Sylvilagus nuttallii, S. cognatus, S. robustus, and S. holzneri (=S. floridanus holzneri), was analyzed using multivariate statistics. Based on 26 or 30 measurements taken on each of 350 adult skulls, and formulation of 16 pooled samples, with each representing a different geographic population, the results show there are two species-level distinctions in skull type. Cottontails from southern Utah, northern and east-central Arizona, and northern New Mexico show morphological overlap among geographically adjacent samples and all have a highly arched skull. These are referable to S. nuttallii. Cottontails from central Arizona, central New Mexico, and western Texas southward along the Sierra Madre Occidental to Durango, Mexico, and Sierra Madre Oriental to central Coahuila, Mexico show morphological overlap among geographically adjacent samples and all have a relatively flat skull. These are referable to S. holzneri. Both S. nuttallii and S. holzneri are polytypic in the study area. Sylvilagus n. pinetis is restricted to the White Mountains of Arizona. Those north and west of the Colorado River in Arizona and Utah are referable to S. n. nuttallii and those from southeastern Utah, northeastern Arizona and northern New Mexico are referable to S. n. grangeri. The population of cottontails previously referred to S. cognatus from central New Mexico is indistinguishable from topotypical S. holzneri from southeastern Arizona as well as populations from southwestern New Mexico, Chihuahua, and Sonora, Mexico. Cottontails previously referred to S. robustus, from the Guadalupe Mountains of New Mexico and Texas, southward in the mountains of western Texas, and the Sierra Madre Oriental to central Coahuila, Mexico, average larger in overall size and, on average, have proportionately larger auditory bullae and are referable to S. holzneri robustus. The relationship of S. holzneri to other mountain/plateau-inhabiting taxa, outside the study area in central and southern Mexico remains to be resolved.

Pathology of Lagovirus europaeus GI.2/RHDV2/b (Rabbit Hemorrhagic Disease Virus 2) in Native North American Lagomorphs.

Rabbit hemorrhagic disease, a notifiable foreign animal disease in the US, was reported for the first time in wild native North American lagomorphs in April 2020 in the southwestern US. Affected species included the desert cottontail (Sylvilagus audubonii), mountain cottontail (Sylvilagus nuttallii), black-tailed jackrabbit (Lepus californicus), and antelope jackrabbit (Lepus alleni). Desert cottontails (n=7) and black-tailed jackrabbits (n=7) collected in April and May 2020 were necropsied at the US Geological Survey National Wildlife Health Center and tested positive for Lagovirus europaeus GI.2, also known as rabbit hemorrhagic disease virus 2 (GI.2/RHDV2/b), by real-time PCR at the US Department of Agriculture's Foreign Animal Disease Diagnostic Laboratory. Gross and microscopic lesions were similar to those reported in European rabbits (Oryctolagus cuniculus) and other hare (Lepus) species with GI.2/RHDV2/b infection; they included epistaxis (12/13; 92%); massive hepatocellular dissociation (14/14; 100%) and necrosis or apoptosis (11/11; 100%); pulmonary congestion (12/12; 100%), edema (12/13; 92%), and hemorrhage (11/12; 92%); and acute renal tubular injury (3/8; 38%). As in previous reports, massive hepatocellular dissociation and necrosis or apoptosis was the most diagnostically distinct finding. As North American Sylvilagus and Lepus species appear to be susceptible to fatal GI.2/RHDV2/b infection, additional work is needed to understand the host range, pathogenicity, and potential population effects of GI.2/RHDV2/b in North America.

Body Weight as an Indicator of Vulnerability to Domestic Cat Predation for Juveniles of Three Species of Cottontail Rabbits (Sylvilagus spp.) in Colorado, USA: Implications for Release Criteria.

Cottontail rabbits (Sylvilagus spp.) are frequently admitted to wildlife rehabilitation facilities due to predation by domestic cats (Felis catus). Our retrospective study (2015-19) of three species (Sylvilagus audubonii, Sylvilagus floridanus, and Sylvilagus nuttallii) indicated that once juveniles reached a weight over 220 g, they were unlikely to present due to domestic cat interactions. This information should be incorporated into release criteria for these species.

FOOD HABITS OF COYOTES (CANIS LATRANS) IN THE VALLES CALDERA NATIONAL PRESERVE, NEW MEXICO

Wildlife managers needed to understand coyote (Canis latrans) ecology in order to develop management plans on the nascent Valles Caldera National Preserve in northern New Mexico. Managers concerned about low elk (Cervus elaphus) recruitment had observed an increase in sightings of coyotes and observations of coyote predation on elk calves. Our objective was to identify and quantify coyote diet, and assess the temporal variation in coyote diet on the Valles Caldera National Preserve, particularly as related to elk calf consumption. We examined coyote food habits using 1,385 scats analyzed monthly from May 2005 to November 2008. The most frequent taxa were rodents (predominantly voles from the genus Microtus, and northern pocket gophers, Thomomys talpoides), elk, insects from the orders Orthoptera (grasshoppers and crickets) and Coleoptera (beetles), mountain cottontail rabbit (Sylvilagus nuttallii), and plant material (mainly grass). We detected rodent and elk in scats during all months of the study and were each present in 54% of scats overall. We identified elk remains in 43% of spring scats, 72% of winter scats, and 56% of fall scats. During summers, we could distinguish calf from adult elk hair: 8% of summer the scats contained adult elk hair and 39% contained calf elk hair. The frequency of prey items varied significantly over most seasons and years, with notable exceptions being that elk did not vary among summers and winters, and rabbits were a consistent diet item through all seasons. The high frequency of elk in the coyote diet bears further study on the density of elk calves, the vulnerability of elk to predation, the nutritional impacts from the quality of forage available to elk, and the role of hunting and other mammalian predators in providing carcasses.

Preferences of Specialist and Generalist Mammalian Herbivores for Mixtures Versus Individual Plant Secondary Metabolites.

Herbivores that forage on chemically defended plants consume complex mixtures of plant secondary metabolites (PSMs). However, the mechanisms by which herbivores tolerate mixtures of PSMs are relatively poorly understood. As such, it remains difficult to predict how PSMs, singly or as complex mixtures, influence diet selection by herbivores. Although relative rates of detoxification of PSMs have been used to explain tolerance of PSMs by dietary specialist herbivores, few studies have used the rate of detoxification of individual PSMs to understand dietary preferences of individual herbivores for individual versus mixtures of PSMs. We coupled in vivo experiments using captive feeding trials with in vitro experiments using enzymatic detoxification assays to evaluate the dietary preferences and detoxification capacities of pygmy rabbits (Brachylagus idahoensis), dietary specialists on sagebrush (Artemisia spp.), and mountain cottontails (Sylvilagus nuttallii), dietary generalists. We compared preference for five single PSMs in sagebrush compared to a mixture containing those same five PSMs. We hypothesized that relative preference for individual PSMs would coincide with faster detoxification capacity for those PSMs by specialists and generalists. Pygmy rabbits generally showed little preference among individual PSMs compared to mixed PSMs, whereas mountain cottontails exhibited stronger preferences. Pygmy rabbits had faster detoxification capacities for all PSMs and consumed higher concentrations of individual PSMs versus a mixture than cottontails. However, detoxification capacity for an individual PSM did not generally coincide with preferences or avoidance of individual PSMs by either species. Cottontails avoided, but pygmy rabbits preferred, camphor, the PSM with the slowest detoxification rate by both species. Both species avoided β-pinene despite it having one of the fastest detoxification rate. Taken together our in vivo and in vitro results add to existing evidence that detoxification capacity is higher in dietary specialist than generalist herbivores. However, results also suggest that alternative mechanisms such as absorption and the pharmacological action of individual ormixtures of PSMs may play a role in determining preference of PSMs within herbivore species.

Clostridial Enterotoxemia and Coccidiosis in Weanling Cottontail Rabbits ( Sylvilagus audubonii, Sylvilagus floridanus, Sylvilagus nuttallii) from Colorado, USA.

Wild cottontail rabbits ( Sylvilagus spp.), especially young individuals, are one of the most frequent wildlife species presented for rehabilitation at wildlife rehabilitation centers. These species are challenging to rehabilitate, with gastrointestinal (GI) disease being a major cause of morbidity and mortality during the weaning stage. Two organisms, Clostridium spiroforme and Eimeria spp., are frequently associated with GI disease in young domestic rabbits ( Oryctolagus cuniculus) and can result in high rates of morbidity and mortality in this species. Here we present evidence that these two pathogens also play an important role in GI disease in young cottontail rabbits ( Sylvilagus audubonii, Sylvilagus floridanus, Sylvilagus nuttallii) undergoing rehabilitation.

Interacting effects of ambient temperature and food quality on the foraging ecology of small mammalian herbivores

Both temperature and diet quality play an important role in the time and energy budgets of small mammalian herbivores. However, little is known about how temperature and diet quality interact to influence diet selection, nutrient extraction, and energetics, and how these effects might differ among species. Therefore, we examined the effects of diet quality and temperature on aspects of the foraging ecology of two species of lagomorphs, pygmy rabbits (Brachylagus idahoensis), which are small dietary specialists, and mountain cottontail rabbits (Sylvilagus nuttallii), which are larger dietary and habitat generalists. In a series of feeding experiments, we investigated 1) the effects of temperature on selection of plant fiber and the plant secondary metabolite 1,8 cineole in their diets, 2) effects of temperature and plant fiber on daily intake, digestion, and passage of food, 3) effects of plant fiber and 1,8 cineole on resting metabolic rate, and 4) how these interactions differ between the rabbit species. Both species chose to eat more total food and a greater proportion of high fiber food that passed more quickly through the digestive system in colder temperatures. However, temperature did not affect how much 1,8 cineole the rabbits consumed nor how thoroughly they digested food. Food quality affected how well they digested the dry matter in the food, but not their resting metabolic rate. Understanding how the interactions between ambient temperature and food quality affect selection of diets and intake by small mammalian herbivores, and the physiological mechanisms governing these choices, is useful for predicting how these species might respond to changes in both temperature and food quality and inform conservation and restoration strategies.

Habitat Use by Nuttall’s Cottontails (<i>Sylvilagus nuttallii nuttallii</i>) at their Northern Range Edge (British Columbia, Canada)

in Canada, Nuttall’s Cottontails (Sylvilagus nuttallii nuttallii) occur in southcentral British Columbia (BC), where they are federally listed as a species of special Concern due to their presumed small populations and limited distribution in fragmented habitats. Their habitat use and movement patterns are poorly known at this northern edge of their distribution. We used livetrapping, radio-collaring, and fecal pellet surveys to examine Nuttall’s Cottontails’ use of remaining patches of native habitat as well as use of human-impacted areas. Cottontails were present in low densities and only about half of presumably suitable patches of native sagebrush-steppe were occupied. Cottontails were more likely to occur in shrubby habitat, but at a fine scale cottontails used areas that had a lower density of shrubs and finer substrates. movement patterns differed significantly between areas of varying habitat quality, with longer movements in natural habitat. one radio-collared male cottontail used anthropogenic habitats adjacent to native habitat; this use corresponds with landowner reports. However, it is not clear whether Nuttall’s Cottontails are able to use anthropogenically-impacted areas to maintain populations or in areas where such habitats are not near native habitats. our results suggest that these animals are rare and occur primarily in remnant patches of shrub-steppe within BC.

The balancing act of foraging: mammalian herbivores trade-off multiple risks when selecting food patches.

Animals face multiple risks while foraging such as the risk of acquiring inadequate energy from food and the risk of predation. We evaluated how two sympatric rabbits (pygmy rabbits, Brachylagus idahoensis, and mountain cottontail rabbits, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush-steppe of western North America respond to different types and levels of perceived risks (i.e., fitness cost × probability of occurrence), including fiber and toxins in food, exposure to predation, and distance from a refuge. We measured food intake by the rabbits at paired food patches that varied in these risks and used the method of paired comparisons to create a relative ranking of habitat cues, which revealed an animal's perceived risk on a single scale representing an integrated response to a variety of risks. Pygmy rabbits perceived exposure to predation risk and distance from a burrow as riskier than did cottontails, whereas cottontails perceived dietary toxin as riskier. Pygmy rabbits consumed lower quality food, containing higher fiber or toxins, thereby avoided feeding in exposed patches or traveling far from their burrow to forage. In contrast, cottontails fed in exposed patches and traveled farther from the burrow to obtain higher quality food. We have shown how risks can be integrated into a single model that allows animals to reveal their perceptions of risks on a single scale that can be used to create a spatially explicit landscape of risk.

Pinyon-juniper removal has long-term effects on mammals

Removing tree cover is a common forest management practice, and pinyon-juniper woodlands in the western United States have been the focus of tree reduction efforts for decades. The scale and intensity of tree removal practices are expected to increase as technology advances and as land managers are tasked with meeting multiple objectives, including fire prevention and habitat enhancement for livestock and wildlife of conservation concern. However, the long-term consequences of pinyon-juniper removal on animal communities are virtually unknown. The objectives of this study were to assess whether mammal habitat use differs between reference pinyon-juniper woodlands and stands that were mechanically disturbed by chaining more than 40years ago, and to determine if these differences are associated with particular habitat characteristics. We used remotely triggered wildlife cameras to evaluate differences in mammal habitat use of historically chained sites (n=22) and reference sites (n=22) in northwestern Colorado. Our results demonstrate marked differences in habitat use between chained sites and reference woodlands for most detected mammal species. Bobcat, mountain lion, American black bear, golden-mantled ground squirrel, and rock squirrel all showed a negative response to historically chained sites, indicating long-term effects of tree removal on these species. In contrast, habitat use of chipmunk, mountain cottontail, and coyote did not differ between chained and reference sites. For most species, habitat use was influenced by specific vegetation characteristics, such as proportion of tree cover, which could be factored into management decisions. By understanding the long-term consequences of tree removal for diverse mammal species, we are better equipped to adapt forest management practices to benefit species of both economic and conservation concern.

Benefits of jasmonate-dependent defenses against vertebrate herbivores in nature.

Endogenous jasmonates are important regulators of plant defenses. If and how they enable plants to maintain their reproductive output when facing community-level herbivory under natural conditions, however, remains unknown. We demonstrate that jasmonate-deficient Nicotiana attenuata plants suffer more damage by arthropod and vertebrate herbivores than jasmonate-producing plants in nature. However, only damage by vertebrate herbivores translates into a significant reduction in flower production. Vertebrate stem peeling has the strongest negative impact on plant flower production. Stems are defended by jasmonate-dependent nicotine, and the native cottontail rabbit Sylvilagus nuttallii avoids jasmonate-producing N. attenuata shoots because of their high levels of nicotine. Thus, endogenous jasmonates enable plants to resist different types of herbivores in nature, and jasmonate-dependent defenses are important for plants to maintain their reproductive potential when facing vertebrate herbivory. Ecological and evolutionary models on plant defense signaling should aim at integrating arthropod and vertebrate herbivory at the community level.

Selection of food patches by sympatric herbivores in response to concealment and distance from a refuge.

SummarySmall herbivores face risks of predation while foraging and are often forced to trade off food quality for safety. Life history, behaviour, and habitat of predator and prey can influence these trade‐offs. We compared how two sympatric rabbits (pygmy rabbit, Brachylagus idahoensis; mountain cottontail, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush‐steppe of western North America respond to amount and orientation of concealment cover and proximity to burrow refuges when selecting food patches. We predicted that both rabbit species would prefer food patches that offered greater concealment and food patches that were closer to burrow refuges. However, because pygmy rabbits are small, obligate burrowers that are restricted to sagebrush habitats, we predicted that they would show stronger preferences for greater cover, orientation of concealment, and patches closer to burrow refuges. We offered two food patches to individuals of each species during three experiments that either varied in the amount of concealment cover, orientation of concealment cover, or distance from a burrow refuge. Both species preferred food patches that offered greater concealment, but pygmy rabbits generally preferred terrestrial and mountain cottontails preferred aerial concealment. Only pygmy rabbits preferred food patches closer to their burrow refuge. Different responses to concealment and proximity to burrow refuges by the two species likely reflect differences in perceived predation risks. Because terrestrial predators are able to dig for prey in burrows, animals like pygmy rabbits that rely on burrow refuges might select food patches based more on terrestrial concealment. In contrast, larger habitat generalists that do not rely on burrow refuges, like mountain cottontails, might trade off terrestrial concealment for visibility to detect approaching terrestrial predators. This study suggests that body size and evolutionary adaptations for using habitat, even in closely related species, might influence anti‐predator behaviors in prey species.

Modeling trade-offs between plant fiber and toxins: a framework for quantifying risks perceived by foraging herbivores.

When selecting habitats, herbivores must weigh multiple risks, such as predation, starvation, toxicity, and thermal stress, forcing them to make fitness trade-offs. Here, we applied the method of paired comparisons (PC) to investigate how herbivores make trade-offs between habitat features that influence selection of food patches. The method of PC measures utility and the inverse of utility, relative risk, and makes trade-offs and indifferences explicit by forcing animals to make choices between two patches with different types of risks. Using a series of paired-choice experiments to titrate the equivalence curve and find the marginal rate of substitution for one risk over the other, we evaluated how toxin-tolerant (pygmy rabbit Brachylagus idahoensis) and fiber-tolerant (mountain cottontail rabbit Sylviagus nuttallii) herbivores differed in their hypothesized perceived risk of fiber and toxins in food. Pygmy rabbits were willing to consume nearly five times more of the toxin 1,8-cineole in their diets to avoid consuming higher levels of fiber than were mountain cottontails. Fiber posed a greater relative risk for pygmy rabbits than cottontails and cineole a greater risk for cottontails than pygmy rabbits. Our flexible modeling approach can be used to (1) quantify how animals evaluate and trade off multiple habitat attributes when the benefits and risks are difficult to quantify, and (2) integrate diverse risks that influence fitness and habitat selection into a single index of habitat value. This index potentially could be applied to landscapes to predict habitat selection across several scales.

Detecting pygmy rabbits (Brachylagus idahoensis) using DNA extracted from fecal pellets of mixed-species groups

Noninvasive genetic sampling is an essential tool for studying elusive and endangered species. However, the DNA from noninvasive genetic sampling tends to be low in quantity and quality, which leads to poor DNA amplification. Using fecal pellets of pygmy rabbits (Brachylagus idahoensis) collected in February, March, and November 2011, we tested a possible solution of increasing the amount of sample by combining multiple pellet groups during DNA extraction. One potential drawback of this approach is accidental mixing of samples from multiple species. This study evaluates the mitochondrial DNA (mtDNA) species identification success rate for pygmy rabbit (PY) fecal DNA when mixed with eastern cottontail (Sylvilagus floridanus; EC) fecal pellet DNA at lower frequencies (1PY:3EC and 2PY:6EC) and eastern cottontail or mountain cottontail (S. nuttalli) pellet samples at an equal frequency (4:4). We found that successful detection of pygmy rabbit DNA using a species-specific mtDNA polymerase chain reaction (PCR) test varies from 0% to 95% depending on the competing species and PCR protocol. From these results, we conclude that if samples are unintentionally mixed, the species with a greater number of pellets within the sample will be more likely to be detected. Also, if pellet piles are intentionally mixed to reduce sampling cost, the protocol should be optimized to maximize DNA amplification for the focal species; however, there will be reduced detection rates depending on the quality and quantity of the focal species DNA within the sample. © 2013 The Wildlife Society.

Shifting Prehistoric Abundances of Leporids at Five Finger Ridge, a Central Utah Archaeological Site

The faunal assemblage from Five Finger Ridge, an archaeological site in central Utah that was occupied by the Fremont from approximately AD 1100 to 1350, shows marked transitions in the relative abundances of 3 leporid taxa. At the time of initial occupation of the site, Sylvilagus audubonii and Lepus sp. dominated the assemblage but through time were gradually replaced by Sylvilagus nuttallii. I contextualized the shifting frequencies of these species using independent paleovegetation data. The data collectively suggest that the altitudinal range of the leporid species shifted during occupation of the site as a response to expanding pinyon-juniper woodlands.

Host-specificity of myxoma virus: Pathogenesis of South American and North American strains of myxoma virus in two North American lagomorph species

The pathogenesis of South American and North American myxoma viruses was examined in two species of North American lagomorphs, Sylvilagus nuttallii (mountain cottontail) and Sylvilagus audubonii (desert cottontail) both of which have been shown to have the potential to transmit the South American type of myxoma virus. Following infection with the South American strain (Lausanne, Lu), S. nuttallii developed both a local lesion and secondary lesions on the skin. They did not develop the classical myxomatosis seen in European rabbits ( Oryctolagus cuniculus). The infection at the inoculation site did not resolve during the 20-day time course of the trial and contained transmissible virus titres at all times. In contrast, S. audubonii infected with Lu had very few signs of disseminated infection and partially controlled virus replication at the inoculation site. The prototype Californian strain of myxoma virus (MSW) was able to replicate at the inoculation site of both species but did not induce clinical signs of a disseminated infection. In S. audubonii, there was a rapid response to MSW characterised by a massive T lymphocyte infiltration of the inoculation site by day 5. MSW did not reach transmissible titres at the inoculation site in either species. This might explain why the Californian myxoma virus has not expanded its host-range in North America.

On the Cranial Osteology of the Lagomorpha

The Section of Mammals, Carnegie Museum of Natural History houses skulls from seven genera of extant lagomorphs (one ochotonid and six leporids). Described and illustrated are the external surfaces of the bones of the skull of the North American pika Ochotona princeps (Richardson, 1828) and also illustrated is the volcano rabbit Romerolagus diazi (Ferrari-Pérez, 1893). Comparisons of selected craniomandibular features are made between O. princeps, R. diazi, and the following additional leporids: Pronolagus crassicaudatus (I. Geoffroy, 1832), Lepus capensis Linnaeus, 1758, Oryctolagus cuniculus (Linnaeus, 1758), Sylvilagus nuttallii (Bachman, 1837), and Brachylagus idahoensis (Merriam, 1891). Also included in the comparisons based on published descriptions are the following extinct taxa: Prolagus, the Sardinian pika, a Quaternary ochotonid; Palaeolagus, a late Eocene-Oligocene stem lagomorph; Mimolagus, an early Oligocene mimotonid; Mimotona, a Paleocene mimotonid; Gomphos, an early Eocene stem lagomorph; and Rhombomylus, an early Eocene eurymylid. Characters are identified that support various hypotheses of phylogenetic relationships among the studied taxa.

Is Size of Fecal Pellets a Reliable Indicator of Species of Leporids in the Southern Rocky Mountains?

Abstract: In the southern Rocky Mountains, USA, snowshoe hares (Lepus americanus) and mountain cottontails (Sylvilagus nuttallii) are syntopic. Previous researchers used size of fecal pellets to identify leporid species in the Southern Rockies, a common criterion for identifying species of cervids. We measured 655 fecal pellets from 10 mountain cottontails and 2,374 fecal pellets from 23 snowshoe hares. We found no relationship between the body weight of mountain cottontails and the size of their fecal pellets (r = 0.04, F = 0.01, P = 0.91) but found one for snowshoe hares (r = 0.48, F = 9.3, P = 0.005). Although the 2 species differed in the size of their fecal pellets, the difference between means (1.2 mm) was sufficiently small to require measuring individual pellets and is only applicable to individuals of adult size. Although fecal pellet counts may be used to estimate presence and relative abundance of snowshoe hares in the absence of syntopic leporids, where multiple species of leporids are syntopic this method may yield misleading results.

SNOWSHOE HARE (LEPUS AMERICANUS) AND MOUNTAIN COTTONTAIL (SYLVILAGUS NUTTALLII) BIOGEOGRAPHY AT THEIR SOUTHERN RANGE LIMIT

We surveyed snowshoe hare (Lepus americanus) and mountain cottontail (Sylvilagus nuttallii) in coniferous forests in northern New Mexico. L. americanus was restricted to the Sangre de Cristo and San Juan ranges in a narrow band of elevations corresponding to subalpine coniferous forest. In contrast, S. nuttallii was widely distributed and virtually cosmopolitan, occupying a wide range of elevations and vegetation zones, including subalpine coniferous forest where it was syntopic with L. americanus. Previous reports about the distribution and ecological associations of these species at their southern limits indicated broader ecological associations for L. americanus and narrower ecological associations for S. nuttallii. Historical reports about the biogeography of these species likely were based on misinterpretation of leporid sign and specimen records. We make recommendations for reducing problems associated with the interpretation of anecdotal natural history information and specimen records.