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 Southern Sierra Nevada Fisher Conservation Strategy provides science-based guidance for conserving and recovering an isolated population of Pacific fisher (Pekania pennanti) in the southern Sierra Nevada (Figure 1) by reducing threats and increasing the quality and resiliency of fisher habitat. The strategy is based on the best available scientific information on fishers and their habitats in the area, as summarized in the Southern Sierra Nevada Fisher Conservation Assessment (Spencer et al. 2015; hereafter, Conservation Assessment). Nevertheless, uncertainties remain concerning the potential effects of fires, climate change, management actions, and other factors on fishers and their habitat. The Strategy must therefore be implemented within an adaptive management framework to allow adjustments as new information accrues from monitoring and other sources. The Strategy should therefore be considered a “living document” that is regularly updated with new information. See Sections 9 and 10 for research and analytical tasks to be implemented in the near future, and the results used to update this Version 1.0 Strategy document and associated data sets and decision-support tools.
The Strategy is intended to meet the needs of multiple agencies with an interest in fisher conservation and land management in the Sierra Nevada, including the USDA Forest Service (USFS), National Park Service (NPS), US Fish and Wildlife Service (USFWS), California Department of Fish and Wildlife (CDFW), Sierra Nevada Conservancy (SNC), and other local, state, federal, tribal, and private entities whose actions may affect fishers or their habitat . As such, the Strategy is intended to be compatible with diverse agency missions, objectives, and legal requirements.
The Strategy was developed to be implemented over about 30 years, after which it should be comprehensively re-evaluated to ensure that the conservation measures remain relevant and effective. Some aspects should be reviewed and updated within the first 2-3 years of implementation to refine methods, guidelines, maps, or other aspects as needed. Thereafter, the Strategy should be updated every 4-6 years to support important agency processes, such as land management plan revisions. Essential datasets (e.g., vegetation, fire, and management data) should be updated regularly as part of the adaptive management process—ideally annually or at least every 5 years.
*Thumbnail photo by Christina Schaefer.
Variation in body size, especially mass, is a function of local environmental conditions for any given species. Recent recorded decreases in body size of endotherms have been attributed to climate change in some cases. This prediction is based on the trend of smaller body size of endotherms in warmer climates (Bergmann’s rule) and it implies genetic responses rather than phenotypic flexibility. Alternatively, selection for smaller body size or lower mass could be explained by the starvation-predation hypothesis, where lighter individuals have a higher probability of escaping pursuing predators, such as raptors. Evidence that climate warming is driving patterns of size selection in birds in recent times has been mixed. We inspected data on 40 bird species contributed by bird ringers to the South African Ringing Scheme (SAFRING) for changes in body mass and condition as a function of time (year), minimum temperature of the day of capture, maximum temperature of the previous day, and rainfall data in the south-western Cape Floristic Region (fynbos) around Cape Town, South Africa, for the period 1988–2015. The region shows a warming trend over the study period (0.035 °C yr−1). Interannual body mass and condition change were poorly explained by year or temperature. High daily minimum temperature explained loss of body condition for four species, whereas evidence from recaptured birds indicated negative effects of increasing maximum daily temperature, as well as rain. For the alternative hypothesis, because raptor abundance is stable or only weakly declining, there is little evidence to suggest these as a driver influencing mass trends. Any decrease in body mass over the study period that we observed for birds appear more likely to be plastic responses to stress associated with temperature or rainfall at this time, rather than systematic selection for smaller body size, as predicted by Bergmann’s Rule.
Biological communities are increasingly faced with novel urban habitats and their response may depend on a combination of biological and habitat traits. The response of pollinator species to urban habitats are of particular importance because all species involved in the pollination mutualism may be affected. Nectarivorous bird communities worldwide show varying tolerances to urban areas, but studies from Africa are lacking. We investigated nectarivorous bird communities in a medium‐sized South African city and asked which biological and garden traits best predict the community assembly of specialist and opportunistic nectarivorous birds. Information was collected on garden traits and the frequency of nine nectarivorous bird species for 193 gardens by means of a questionnaire. Information on biological traits of birds was obtained from published literature. Habitat generalism and tree nesting were identified as the most important biological traits influencing bird occurrence in gardens. A greater diversity of indigenous bird‐pollinated plants and the presence of sugar water feeders increased the numbers of nectar specialist birds and species richness of nectarivorous birds. While bird baths increased the species richness of nectar specialist birds, opportunistic birds’ urban adjustment was further facilitated by large vegetated areas in gardens and limited by the distance to the nearest natural habitat. In conclusion, though some biological traits and dispersal barriers seem to limit urban adjustment, a combination of natural and artificial nectar resource provisioning could facilitate this adjustment.
We all delight in seeing a colourful sunbird flit into our garden to visit some flowers, especially when one of the shyer species comes through. Have you thought about why some sunbirds are common in gardens while others are so rare? And whether they will disappear as urban development increases?
These questions are important to us if we are to enjoy the presence of sunbirds and other nectarivorous birds in our gardens. But the questions are far more important to plants, because nectar-feeding birds pollinate specific plants, enabling them to produce seeds. This mutual relationship fosters plants dependent on the birds, while the birds in turn rely on the plants for food.
As cities grow, they tend to crowd out natural areas, and residential areas are of- ten avoided by birds. If the development of towns and cities means that nectar- bearing plants and nectar-feeding birds become isolated in small fragments of natural habitat, both birds and plants will suffer. However, urban areas with gar- dens can be made less hostile and some brave or adaptable birds will enter and use these new habitats.
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.