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.
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.
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.
Escalating harvest of remnant old-growth forests in the Pacific Northwest has precipitated concern for marten (Martes amaericana) as an old-growth dependent species (Meslow et al. 1981). Although recent studies have increased our understanding of marten habitat requirements (Koehler adn Hornocker 1977, Soutiere 1979, Steventon and Major 1982), little in-depth research has been done in the Pacific states. Also, the influences of specific forest attributes on marten selection of resting and foraging sites have been insufficiently quantified. This study details marten selection of resting and foraging habitats in the northern Sierra Nevada.