A new southern distribution record for Pacific Marten Martes caurina

ThePacific Marten is a mesocarnivore that is native to western North America, with a distribution that ranges from the boreal forests of southern British Columbia to the southern terminus of the Rocky Mountains in north-central New Mexico. Martens are considered a state-threatened species in New Mexico, and the southern extent of their range is unclear. We documented a sighting of a Pacific Marten at 35.835, -105.750, north-east of Santa Fe that is farther south than any confirmed marten sighting since 1884. It is unknown if this sighting represents the documentation of a population or just a lone individual. It is unlikely that marten populations would extend much farther south, as this is near the southern terminus of the Rocky Mountains. However, a systematic survey to determine the distribution of this southern population would inform conservation of Pacific Martens within the state.

ISSN 0974-7907 (Online); ISSN 0974-7893 (Print) Pacific Martens were likely never common in New Mexico, which is at the southern edge of their range (Image 1), but are now rare and classified as threatened in the state (Threatened and Endangered Species of New Mexico 2020). The New Mexico Department of Fish and Game has completed multiple surveys for martens in New Mexico since 1997. Pacific martens have been consistently found in the North Central mountains near Taos and Chama (Long et al. 2015), with martens seeming to be most abundant in Taos County (Long et al. 2015). It is unclear, however, if the surveys have clearly defined the southern boundary of the population, and individuals at the southern end of their range could be going undetected.
Here we report a recent Pacific Marten detection and explore its implications for the marten population in the Rocky Mountains. On 4 September 2020, during a hike in the Rocky Mountains north-east of Santa Fe, New Mexico, we observed a Pacific Marten at 35.835, -105.750 (Image 2). This detection is farther south than any confirmed Pacific Marten sighting in the published literature since 1884 (Image 3). In 1884, two specimens were collected by L. Dyche in the Las Vegas Mountains; however, the exact locality information for these specimens is not known, and our observation could be anywhere from 0 to 15 km farther south (Durrant 1952) (Image 3).
It is unknown if this sighting represents the documentation of a population or just a lone individual. There have been unverified scat and tracks, which are notoriously difficult to identify accurately, in the same J TT general area (Long 2001;Long et al. 2015). Thus, it is possible Pacific Martens have been present in the area but have gone undetected, or that martens are expanding back into the southern extent of their historic range. It is unlikely that Pacific Martens will be found farther south as potential suitable habitat is limited to high elevation forests that are only found in the Rocky Mountains (Long 2001), which end nearby. In addition, as climate and land use change progresses, species ranges may also shift further north or higher in elevation to track climate,

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weather, or structural features (e.g., complex forest) that they are adapted to (Martin et al. 2021). A systematic survey to determine the occupancy and abundance of martens in the southern limit of the population could be a valuable follow up study. Calls for public observations, including posting observations to sites readily available to scientists such as iNaturalist (www.inaturalist.org), could also be beneficial in determining locations in the rugged Rocky Mountains where Pacific Martens are either expanding or may have persisted.

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