Combined field and clinical methods clarify mortality causes and survival patterns of Pacific martens

Abstract

Quantifying the demography of wildlife populations is imperative to evaluating population trends. Understanding patterns of influential demographic parameters often requires investigation of mechanisms influencing demography, which can be difficult to determine for cryptic species. We radiotracked Pacific martens (Martes caurina), a small-bodied and elusive mesocarnivore, to estimate survival, determine causes of mortality, and assess co-occurring pathological conditions.We tracked 18 female and 33 male martens for an average (±SD, range) of 16.35 months (±8.7, 1-41) from 2009-2013 and 2015-2017 in northern California. Annual survival rates were 0.81 (95% CI = 0.66-0.95) and 0.68 (95% CI = 0.57-0.79) for female and male martens, respectively. We documented 16 marten mortalities, 13 of which were suspected predation events. Seven mortalities were empirically linked to predation via clinical forensic evidence, with bobcats (Lynx rufus; n = 5) representing the majority of predator species identified. The proximate cause of mortality for 1 marten was attributed to toxicosis from anticoagulant rodenticide exposure, which has not been previously reported in free-ranging martens. Our findings suggest the timing of marten mortality aligned with reproductive periods that incurred increased energetic requirements, which may result in increased predation risk. We propose continued pairing of field and clinical assessments to

Conservation of rare and cryptic species: Challenges of uncertainty and opportunities for progress

“…Many species are affected by chronic threats that are difficult to mitigate, emerging threats that are poorly understood, or the interaction of multiple threats that may have dire consequences (Brook et al, 2008). In our case study, contemporary threats to small and disparate Humboldt marten populations include disease outbreaks (e.g., Smith et al, 2006), reduced genetic diversity (e.g., Lino et al, 2019), habitat loss due to increased wildfire (e.g., Abatzoglou et al, 2021), and exposure to anticoagulant rodenticides (e.g., Martin et al, 2022; Wengert et al, 2021). Addressing threats and supporting species recovery is imperative, but difficult when faced with limited funding, complicated logistics, and regulatory hurdles.…”

American marten occupancy and activity patterns at the southern extent of their range in the eastern United States

“…We also predicted that marten occupancy and detectability would be lower further away from reported release sites given the limited number of anecdotal reports of marten in southern Vermont. We predicted that occupancy and detectability would be negatively associated with the presence of coyote, red fox, gray fox ( Urocyon cinereoargenteus ), and bobcat (Martin et al., 2022 ) but not fisher (Manlick et al., 2017 ). We also predicted that marten would show substantial overlap in daily activity patterns with fisher based on the recent work of Manlick et al.…”

Structural complexity characterizes fine‐scale forest conditions used by Pacific martens

“…Similar sites are used by reproductive female martens for denning when rearing their altricial offspring (Delheimer et al 2021 a ). Denning and resting locations are typically concealed and secure, offering a necessary degree of protection, as martens are subordinate carnivores that can be killed by a suite of larger predators (Thompson 1994, Bull and Heater 2001, McCann et al 2010, Woodford et al 2013, Wilk and Raphael 2018, Martin et al 2022 a ).…”