Pine martens (Martes americana) consume a variety of food types annually but seasonal foraging is restricted to a subset of available prey. Winter foods include chickarees (Tamiasciurus douglasii), voles (Microtus spp.), snowshoe hares (Lepus americanus), and flying squirrels (Glaucomys sabrinus), whereas ground-dwelling sciurids (Spermophilus spp. and Eu- tamias spp.) comprise the bulk of the diet during the remainder of the year. Activity also is variable by season, with martens foraging at night during winter and by day during summer. Seasonal marten activity does not appear associated with optimal ambient temperature but instead appears synchronized with the activity of prey.
Although the composition of diets of pine marten (Martes americana) is well studied (see Zielinski et al., 1983) direct observations of marten predatory behavior are rare. During a 15-month investigation of marten ecology at Sagehen Creek, California (Spencer et al., 1983; Zielinski et al., 1983), we sometimes observed marten in acts of predation. Observations involved five marked marten and one or more unmarked marten. Observations typically were made through 7- or 8-power binoculars, from 4 to 20 m away, after a radio-collared marten was located with a hand-held receiver. Marten were remarkably tolerant of observers and often ignored their presence, especially when intent on prey. The following accounts illustrate the repertoire of hunting techniques observed.
Stephens’ kangaroo rat (Dipodomys stephensi) is an endangered species of open grasslands or very sparse scrub. Found primarily in the inland valleys of western Riverside County, it is known to occupy a few scattered grasslands in northern San Diego County, particularly on and near Camp Pendleton, the Fallbrook Naval Weapons Station, Lake Henshaw, Rancho Guejito, and Ramona. Stephens’ kangaroo rat resembles the Dulzura kangaroo rat closely, differing by averaging larger in certain measurements, in having a broader face and less distinctly striped tail, and other subtle features. It eats seeds primarily, along with some green vegetation and occasional insects.
The critically endangered Pacific pocket mouse (Perognathus longimembris pacificus), feared extinct for over 20 years, was “rediscovered” in 1993 and is now documented at four sites in Orange and San Diego Counties, California. Only one of these sites is considered large enough to be potentially self-sustaining without active intervention. In 1998, I gathered a team of biologists to initiate several research tasks in support of recovery planning for the species. The PPM Studies Team quickly determined that species recovery would require active trans- locations or reintroductions to establish new populations, but that we knew too little about the biology of P. l. pacificus and the availability of translocation receiver sites to design such a program. Recovery research from 1998 to 2000 therefore focused on (1) a systematic search for potential translocation receiver sites; (2) laboratory and field studies on non-listed, surro- gate subspecies (P. l. longimembris and P. l. bangsi) to gain biological insights and perfect study methods; (3) studies on the historic and extant genetic diversity of P. l. pacificus; and (4) experimental habitat manipulations to increase P. l. pacificus populations. Using existing geographic information system (GIS) data, we identified sites throughout the historic range that might have appropriate soils and vegetation to support translocated P. l. pacificus. Re- connaissance surveys of habitat value were completed in all large areas of potential habitat identified by the model. Those sites having the highest habitat potential are being studied with more detailed and quantitative field analyses. The surrogate studies helped us design individ- ual marking and monitoring methods and will be used to test translocation methods before applying them to P. l. pacificus. Genetic results suggest that P. l. pacificus populations were naturally fairly isolated from one another prior to modern development, that genetic diversity will continue to erode in the small populations that remain, and that individuals from extant populations could probably be mixed if maximizing genetic diversity in any newly established populations is an important recovery goal. Local populations should be increased in situ be- fore they can supply donor animals for translocations. Experimental habitat management (shrub thinning) at one occupied site yielded a short-term, positive, behavioral response of mice to thinned habitat plots. However, the overall population seems to be in decline, and long-term population responses to habitat manipulations are not yet evident. The approach of the PPM Study Team has been to proceed cautiously and scientifically to obtain critical in- formation and to design a translocation program, but we are prepared to recommend swift action to prevent extinction despite “insufficient data.” At this point, political and economic obstacles to species recovery seem larger than obstacles presented by scientific uncertainty.
This Conservation Assessment document summarizes the current state of knowledge about fishers and fisher habitat in the southern Sierra Nevada, building on the copious information already summarized for the West Coast Assessment (Lofroth et al. 2010, 2011; Naney et al. 2012), but with specific focus on the southern Sierra Nevada. In addition to synthesizing published literature and agency reports, the Assessment summarizes abundant new scientific information from recent fisher studies and habitat modeling efforts in California. As of this writing (January 2015), much of this new content has not yet been published in the peer-reviewed literature; consequently, this Assessment was subjected to independent scientific peer review by 5 experts on fishers and forest ecology, and revised accordingly.
The size of the hippocampus, a forebrain structure that processes spatial information, correlates with the need to relocate food caches by passerine birds and with sex-specific patterns of space use in microtine rodents. The influences on hippocampal anatomy of sexual selection within species, and natural selection between species, have not yet been studied in concert, however. Here we report that natural space-use patterns predict hippocampal size within and between two species of kangaroo rats (Dipodomys). Differences in foraging behavior suggest that Merriam’s kangaroo rats (D. merriami) require better spatial abilities than bannertail kangaroo rats (D. spectabilis). Sex-specific differences in mating strategy suggest that males of both species require more spatial ability than females. As predicted, hippocampal size (relative to brain size) is larger in Merriam’s than in bannertail kangaroo rats, and males have larger hippocampi than females in both species. Males of a third species (D. ordii) also have smaller hippocampi than Merriam’s kangaroo rat males, despite being similar to Merriam’s in brain and body size. These results suggest that both natural and sexual selection affect the relative size and perhaps function of mammalian hippocampi. They also reassert that measures of functional subunits of the brain reveal more about brain evolution than measures of total brain size.
*Note: This publication comes from a book chapter from Biology and Conservation of Martens, Sables, and Fishers: A New Synthesis (1st edition).
Conservation and management of Martes populations are increasingly informed by quantitative models that predict habitat suitability and population viability. Recent modeling efforts to support fisher (Martes pennanti) reintroduction plan- ning in the state of Washington (USA) and conservation of an isolated fisher population in the southern Sierra Nevada (California, USA) have integrated re- sults from empirical static habitat models, such as resource-selection functions, with those from dynamic population-viability and vegetation models. Additional methods have been developed to identify habitat linkages with potential impor- tance for maintaining interpopulation dispersal. While such modeling frame- works can be useful in integrating data on species distribution, demography, and vegetation response to disturbance, the associated increased data requirements may also increase uncertainty regarding model projections to different places or times. The costs associated with reintroductions generally justify the use of such models to inform the planning process before substantial resources are commit- ted. Given the challenges posed by increasing human demands on forest ecosys- tems, well-constructed quantitative models can be key tools for enhancing the success of wildlife conservation efforts, as long as model uncertainty is consid- ered explicitly, and model results are used for informing decisions rather than predicting outcomes.
We used Maxent distribution models and MC1 to investigate effects of climate and vegetation on the distribution of martens (Martes caurina) and fishers (Pekania pennanti) in the Sierra Nevada, California, under current and projected future conditions. Both species are forest carnivores of conservation concern in California, where they reach their southernmost distributions. The species occupy similar ecological niches and may compete in the elevation band where their ranges overlap—but martens mostly occupy higher elevations with deep, persistent snow, and fishers occupy lower elevations with less snow. We systematically varied types of environmental variables (climate, vegetation, terrain, presence or absence of the other species) included in Maxent models and compared area‐under‐curve (AUC) values to determine what variables best predict current distributions. Terrain variables and presence or absence of the competing species did not add significantly to model fit. For fishers, models using both climate and vegetation variables outperformed those using only vegetation; for martens, there was no significant difference between vegetationonly, climate‐only, and vegetation + climate models. We then prepared climate + vegetation Maxent models using MC1‐derived variables that best approximated the variables used in the best current (benchmark) models, compared predicted distributions with benchmark models, and projected distributions to mid‐ and late 21st century using MC1 vegetation projections and an array of downscaled general circulation models (GCMs) and emission scenarios at three resolutions (10 km, 4 km, 800 m). The finest available GCM resolution (800 m) provided the best spatial congruence between MC1‐derived models and benchmark models. Regardless of GCM emission scenario, predicted marten distribution shifted to higher elevations, became more fragmented, and decreased in area by 40−85% (depending on scenario) compared to current distributions. Predicted changes in fisher distribution were more variable across GCM scenarios, with some increases and some decreases in extent and no consistent elevation shifts—suggesting high uncertainty in climate change effects on fishers. Management to benefit these species should consider ways of sustaining appropriate vegetation conditions within their preferred climate envelopes via adaptive management.
Abstract:
Season affects many characteristics of populations and, as a result, the interpretations of surveys conducted at different seasons. We explored seasonal variation in occupancy using data from four studies on the Pacific marten Martes caurina. Detection surveys were conducted during winter and summer using either cameras or track stations. We conducted a ‘multiple location, paired season’ analysis using data from all four study areas and a ‘multiple season’ analysis using seasonally replicated occupancy data collected at one of the areas. In the former analysis, summer occupancy estimates were significantly lower than winter and per visit probabilities of detection were indistinguishable between seasons. The probabilities of detection for the complete survey protocol were high (0.83 summer, 0.95 winter). Where summer and winter surveys were replicated, probability of occupancy was > 5 times higher in winter (0.52) than summer (0.09). We considered the effect of seasonal variation in occupancy on the habitat models developed using summer and winter survey data. Using the same habitat suitability threshold (0.5), the weighted average of winter models predicted significantly more suitable habitat than summer models. The habitat predicted by the summer model was at higher elevation, and was distributed among more, and smaller, patches of habitat than the model developed using winter data. We expect a similar magnitude of differences if summer or winter data were used to monitor occupancy. The higher occupancy in winter is probably due to the abundance of young animals detected during dispersal. Summer survey results reflect the distribution of territory-holding adults, thus these surveys may reliably detect breeding individuals and represent reproductive habitat. The implications of season on the interpretation of survey results, and corresponding habitat models and monitoring programs, provide a challenge to managers that make decisions about habitat management for martens, and other species with disparate occupancy among seasons.
Season effects many characteristics of populations and, as a result, the interpretations of surveys conducted at different seasons. We explored seasonal variation in occupancy using data from four studies on the Pacific marten Martes caurina. Detection surveys were conducted during winter and summer using either cameras or track stations. We conducted a ‘multiple location, paired season’ analysis using data from all four study areas and a ‘multiple season’analysis using seasonally replicated occupancy data collected at one of the areas. In the former analysis, summer occupancy estimates were significantly lower than winter and per visit probabilities of detection were indistinguishable between seasons. The probabilities of detection for the complete survey protocol were high (0.83 summer, 0.95 winter). Where summer and winter surveys were replicated, probability of occupancy was > 5 times higher in winter (0.52) than summer (0.09). We considered the effect of seasonal variation in occupancy on the habitat models developed using summer and winter survey data. Using the same habitat suitability threshold (0.5), the weighted average of winter models predicted significantly more suitable habitat than summer models. The habitat predicted by the summer model was at higher elevation, and was distributed among more, and smaller, patches of habitat than the model developed using winter data. We expect a similar magnitude of differences if summer or winter data were used to monitor occupancy. The higher occupancy in winter is probably due to the abundance of young animals detected during dispersal. Summer survey results reflect the distribution of territory-holding adults, thus these surveys may reliably detect breeding individuals and represent reproductive habitat. The implications of season on the interpretation of survey results, and corresponding habitat models and monitoring programs, provide a challenge to managers that make decisions about habitat management for martens, and other species with disparate occupancy among seasons.