Marten and fisher responses to fluctuations in prey populations and mast crops in the northern hardwood forest

Many forest tree species produce seed (mast) crops that are consumed by a variety of wildlife species and these pulsed resources may mediate interactions among predator and prey populations. In the northern hardwood forests of New York, we investigated interactions among mast production, prey abundance, and harvests of American martens (Martes americana) and fishers (Martes pennanti) during 1988–2009. Mast production for beech (Fagus grandifolia), sugar maple (Acer saccharum), and mountain ash (Sorbus americana) was synchronous and an alternate-year pattern in production was evident for most of the time series. We documented considerable temporal variation in summer small mammal relative abundance and our numerical response models received substantial support for 5 of the 8 species, indicating lagged responses to autumn mast crops. Trap response of martens to the autumn production of beech mast and mountain ash berries was immediate and numerical responses to the relative abundance of small mammal prey occurred during the preceding summer. The age structure of the marten harvest differed based on the dominant alternate-year pattern of summer prey relative abundance and autumn mast production (χ²₄ = 33.06, P < 0.001). The proportion of juvenile marten in the autumn harvest was 52% and 34% following summers when small mammal relative abundance was high and low, respectively and these differences resulted in a persistent cohort effect that was apparent until age 3.5. Trap response of fishers to the autumn production of beech mast was immediate and numerical responses to the relative abundance of Sciurid prey occurred during the preceding summer. Marten and fisher harvests fluctuated similarly among New York, Maine, and New Brunswick, which may indicate regional synchronization of mast crops and responses of martens and fishers to similar prey dynamics. A better understanding of how food availability influences demographic responses and trapping vulnerability of martens and fishers would aid our ability to manage harvests of these species on a sustained yield basis. © 2011 The Wildlife Society.     

Does size dimorphism reduce competition between sexes? The diet of male and female pine martens at local and wider geographical scales

Sex-specific niche segregation is often used to explain sexual size dimorphism (SSD). However, whether food niche partitioning between sexes occurs as a case of sexual size dimorphism or by other mechanisms, such as behavioural dimorphism or habitat segregation, remains poorly understood. To evaluate the nature and extent of food-niche differentiation between sexes in a solitary predator I examined variation in the diet of male and female pine martensMartes martes Linnaeus, 1758 in years of high and low rodent abundance. Small mammals were the most important prey for pine martens in years of both low and high rodent abundance (occurring in more than 49% of scats). Birds, invertebrates and plant material were relatively common food items in summer diet, whereas ungulate carcasses were often consumed in autumn—winter. In general, males consumed more ungulate carcasses, plant material, amphibians and reptiles than did females, whereas females preyed more on squirrels and birds than males. There was significant seasonally dependent, between-sex variation in the occurrence of shrews, small rodents, other mammals, birds and invertebrates in marten diet. Whereas the occurrence of bank vole, birds, carcasses and plant material changed between sexes, seasons and years with various rodent abundances, both sexes consumed larger prey and had increased food niche breadth in years of low compared with high rodent abundance. Neither prey size nor food niche breadth were significantly different between males and females. The food-niche overlap between sexes was consistently lower in spring and in years of low rodent abundance. A wider geographical comparison of different marten populations showed that the diet of males and females varied significantly between locations. Females consistently preyed on squirrels and birds, whereas males fed more often on ungulate carcasses and plant material. Local and geographical comparison of male and female diets suggest that food-niche partitioning between male and female pine martens changes across different habitat and food conditions, and is not related to sexual size dimorphism, but rather to behavioural differences between sexes.     

Temporal Changes in Population Dynamics of American Martens

ABSTRACT Population parameters of American martens (Martes Americana) are often monitored to guide management actions. In order to better understand changing marten population demographics, we estimated marten abundance and several population parameters on a portion of northeast Chichagof Island (NCI), Southeast Alaska, USA, using capture-mark–recapture methods in combination with radiotelemetry and compared these data with demographic estimates derived from the trapper catch from the larger NCI area. We found that capture probability remained relatively high across trapping sessions by using a standard live-trapping protocol, and we found no evidence of capture probability being consistently affected by population or environmental factors. Estimated marten numbers varied greatly over the period, ranging from a low of 14.1 martens (0.17/km²) during winter 1997–1998 to a high of 45.6 martens (0.55/km²) during winter 1995–1996. The annual trend was for decreasing numbers from winter 1990–1991 to winter 1992–1993, then increasing numbers through winter 1995–1996. By winter 1996–1997, numbers had dropped substantially and remained low through 1997–1998. All population parameters varied temporally, including annual survival (0.34–1.00), sex ratio (1.0–3.5), mean age (0.5–2.9), body condition (-0.08–1.35), and fecundity (0.44–2.70). Yearly trapper catches on NCI varied greatly from 19 to 354 martens (0.02 martens/km² to 0.31 martens/km²) because of changing trapper effort and marten abundance. We found mean ages of carcasses a good predictor of population mean age, but sex ratios were highly variable. Marten numbers and fecundity were strongly correlated with rodent abundance, especially long-tailed voles (Microtus longicaudus). By monitoring demographic parameters of the population or trapper-caught carcasses, managers can gain insight into temporal population dynamics. Also, total captures of individuals may provide a useful estimate of marten numbers without the expense of radiocollaring and tracking individuals because population estimates were highly correlated with number of individuals captured during a standard survey. Because of their high vulnerability to trapping, close monitoring of marten populations is important for the conservation and sustained-yield management of the species. A tracking strategy developed with input data on preseason abundance and age structure may be the best management approach, especially for small populations with limited immigration.     

Diet,nesting density,and breeding success of rough-legged buzzards (Buteo lagopus) on the Nenetsky Ridge,Arctic Russia

The rough-legged buzzard, a circumpolar avian predator, is usually defined as rodent specialist in the tundra but as a generalist in the boreal zone, leaving open the question of where the shift in feeding strategy occurs. Here, we investigated the diet and breeding biology of buzzards as well as abundance of their possible prey during 5 years in the low-Arctic shrub tundra on the Nenetsky Ridge, Russia. We employed three complementary methods to assess the diet of this Arctic predator—pellet dissection, identification of prey remains on nests, and stable isotope analysis—to overcome their respective limitations. We documented fluctuations in abundances of the likely prey, namely rodents, ptarmigans, and hares. Nesting density of buzzards changed substantially over the years, but did not track the abundance cycle of the rodents. The number of buzzard fledglings was relatively low (1.08 ± 0.3) and did not change according to the density of rodents. In the year when rodents were at their lowest abundance, diet analyses of nestlings documented a shift from rodents to alternative prey, with a decrease in the proportion of tundra voles and an increase in proportion of hares, ptarmigans, and ducks. Here, we argue that buzzards may adopt different feeding strategies along the gradient from generalists to specialists. While the rough-legged buzzard is usually considered a small rodent specialist, our study shows that it can shift to alternative prey where or when rodents are scarce and when alternative prey are sufficiently abundant to provide subsistence for breeding.     

Predation on rodents in Białowieza primeval forest, Poland

Autumn and winter predation on bank vole Clethrtonomys glareolus and yellow-necked mouse Apodemus flavicollis was studied in 1985/86-88/89 in an 11 2 km² area of the Bialowieza National Park Rodents regularly increased in numbers from spring to autumn and decreased throughout winter Out of 23 species of predators, the most common were tawny owl Strix aluco (43-57 adult ind 10 km⁻²) weasel Mustela ntvahs (17-27 ind), buzzard Buteo buteo (12-16) and pine marten Martes martes (5-8) Voles and mice were the staple food for two specialists the stoat Mustela erminea and the weasel, and two generahsts the tawny owl and the pine marten The generalists exploited different alternative prey when rodents were scarce tawny owl -amphibians, marten - small mammals, and the red fox Vulpes vulpes - ungulate carcasses and hares The depth of snow and abundance of voles were two major factors shaping the contribution of voles to tawny owl and marten diets No such relationships were found for mice and generalist predators The predation by 8 species (tawny owl, buzzard, marten, weasel, stoat, polecat Mustela putortus fox, and raccoon dog Nyctereutes procyonoides) from 1 October to 15 April in 1986/87, 87/88, and 88/89 was estimated to be on average 28-35 voles and 14-17 mice ha Estimates suggested that three species were responsible for 86-95% of the total predation impact tawny owl (56-71%), weasel (11-21%) and marten (10-15%) The predation impact was similar to the annual decrease in rodent numbers from autumn till spring voles 35 (SD 111) lnds ha^-1in autumn and 8 (SD 2 6) lnds ha^-1in spring, and mice 24 (SD 16 3) mds ha⁻¹ in autumn and 3 (SD 2 5) in spring Predation, therefore, was regarded as the main agent of rodent mortality throughout autumn and winter     

Avian top predator and the landscape of fear: responses of mammalian mesopredators to risk imposed by the golden eagle

Top predators may induce extensive cascading effects on lower trophic levels, for example, through intraguild predation (IGP). The impacts of both mammalian and avian top predators on species of the same class have been extensively studied, but the effects of the latter upon mammalian mesopredators are not yet as well known. We examined the impact of the predation risk imposed by a large avian predator, the golden eagle (Aquila chrysaetos, L.), on its potential mammalian mesopredator prey, the red fox (Vulpes vulpes, L.), and the pine marten (Martes martes, L.). The study combined 23 years of countrywide data from nesting records of eagles and wildlife track counts of mesopredators in Finland, northern Europe. The predation risk of the golden eagle was modeled as a function of territory density, density of fledglings produced, and distance to nearest active eagle territory, with the expectation that a high predation risk would reduce the abundances of smaller sized pine martens in particular. Red foxes appeared not to suffer from eagle predation, being in fact most numerous close to eagle nests and in areas with more eagle territories. This is likely due to similar prey preferences of the two predators and the larger size of foxes enabling them to escape eagle predation risk. Somewhat contrary to our prediction, the abundance of pine martens increased from low to intermediate territory density and at close proximity to eagle nests, possibly because of similar habitat preferences of martens and eagles. We found a slightly decreasing trend of marten abundance at high territory density, which could indicate that the response in marten populations is dependent on eagle density. However, more research is needed to better establish whether mesopredators are intimidated or predated by golden eagles, and whether such effects could in turn cascade to lower trophic levels, benefitting herbivorous species.     

Prey choice by marten during a decline in prey abundance

Summary We examined variation in diet choice by marten (Martes americana) among seasons and between sexes and ages from 1980–1985. During this period prey populations crashed simultaneously, except for ruffed grouse (Bonasa umbellus) which was common at the beginning and end of the study, and masked shrews (Sorex cinereus) which were abundant in 1983. Marten were catholic in selection of prey and made use of most available mammalian prey, ruffed grouse, passerine birds, berries, and insects. Diet niche was widest during the latter three years when prey was scare, particularly in late winter. Diet niche breadth was negatively correlated with abundance of all common prey species. Proportion of small prey species in the diet was correlated with absolute abundance of those species, but proportion of some large prey was related to their relative abundance. Diet choice varied among years and among seasons. Berries and insects were common in summer diets while large prey, particularly varying hare (Lepus americanus), were more frequent in winter diet than in summer diet. We found little evidence that any small mammal species was a preferred prey. Sexual size dimorphism between the sexes did not affect prey choice, nor did age. Reduced foraging effort in winter resulted in a wider diet niche only when prey was scarce. The only prediction of optimal foraging models fully supported by our data was a wider diet niche with reduced prey abundance. However, among the three most profitable prey species choice was dependent on the absolute abundance of the most profitable type (varying hare). We suggest that marten primarily forage for large prey but employ a strategy which results in encounters with small prey as well. These small prey are eaten as they provide energy at minimal cost, between captures of large prey.     

Nutritional ecology provides insights into competitive interactions between closely related Martes species

1. Closely related predator species often share several prey items, making it hard to differentiate the effects on their feeding habits of variation in food availability and of competition. We hypothesised that we could overcome this obstacle by quantifying and comparing nutritional niches.
2. We reviewed dietary studies that assessed the relative bulk of each food item, as either per cent biomass or per cent mean volume, in the diet of two closely related species, pine marten Martes martes and stone marten Martes foina, and calculated the nutrient profiles (intakes of protein, lipids and carbohydrates) of each diet.
3. Both martens’ diets were tightly clustered (mean values: 47% of energy from protein, 39% from lipid, and 14% from carbohydrate). In allopatry, the nutritional niches of the two species did not differ, but in sympatry, the stone marten ate more carbohydrates and less protein than the pine marten. In allopatry, the protein intake of the stone marten remained high (45–52%) in very different habitats, from cultivated lowland to Alpine forests.
4. Our data suggest that stone marten frugivory may, at least partially, be the result of interspecific competition. By analysing dietary data in the framework of nutritional ecology, we could compare the feeding requirements of pine martens and stone martens more effectively than by using classical estimates of trophic niche overlap at the food item level. This approach may help to shed light on the trophic relationships of other competing species.

     

A non-invasive approach to determining pine marten abundance and predation

A non-invasive approach was used to investigate variation in pine marten (Martes martes) abundance between the midlands and east of Ireland, and to determine the frequency of occurrence of squirrels and other small mammals in the diet. Remotely plucked hair samples were genotyped to differentiate between individual animals, and real-time polymerase chain reaction (PCR) was used to identify predator and prey DNA in scats. Macro analysis of prey remains was carried out on a sub sample of scats and the results from both methods are compared. Non-invasive techniques were successful in determining the presence and relative abundance of the pine marten at woodland level. As expected, abundance was found to be higher in the core population of the midlands than in the east. Pine martens were found to reach higher numbers per km² of forested habitat in Ireland than their British or European counterparts. Both traditional hard part analysis and molecular dietary analysis of mammalian prey yielded similar results. We provide the first evidence of the European pine marten predating upon the North American grey squirrel (Sciurus carolinensis) in its invasive range. While the grey squirrel was not available as a prey item in any of the midlands sites, it was available in the east, where it featured significantly more frequently in the diet than the native red squirrel. In both the midlands and the east the woodmouse is the most frequently occurring mammal in the diet.     

Summer food of sympatric red fox and pine marten in the German Alps

Based on fecal analyses, we compared summer diet composition and trophic niche breadth for the sympatric red fox Vulpes vulpes (n=55 scats) and pine marten Martes martes (n=64) in the foothills of the German Alps. Mammals accounted for 41 and 51% of the consumed biomass by pine martens and red foxes, respectively, and no single mammal species exceeded 8% of the diet. The larger red fox consumed a wider range of prey sizes than the smaller pine marten, and both consumed large amounts of plants and also insects. Whereas the Levins index suggested that both predators have specialist feeding niches, the Shannon-Wiener index showed that both predators were relatively generalist. Despite its preliminary nature, our study suggests that a strict distinction between generalist and specialist trophic niches is not justified for medium-sized carnivores in the Alps, particularly as results greatly depend on the indices used.     

Food habits of genetically identified pine marten (<Emphasis Type="Italic">Martes martes</Emphasis>) expanding in agricultural lowlands (NW Italy)

We assessed the diet of pine marten (Martes martes) expanding in the heavily human-altered agricultural plain of the River Po, northern Italy. Between February 2008 and November 2009, surveys were carried out twice a week during seasonal sampling sessions of three to four consecutive weeks. To distinguish the faecal samples from those of sympatric carnivores, a polymerase chain reaction-restriction fragment length polymorphism method was applied. The availability of small mammals was assessed by the analysis of 59 barn owl (Tyto alba) pellets. A total of 109 pine marten faeces were analysed. Its diet consisted of fruit, rodents, lagomorphs and birds. Seasonal variation occurred for fruit, which prevailed in summer, and rodents, which were more preyed upon in autumn. In winter, the diet of the pine marten was almost totally based on vertebrates, and lagomorphs were the main source of protein in summer. Use of small mammals differed significantly from their availability, voles, particularly bank vole Myodes glareolus, being preferred to mice (Apodemus sp.) and rats (Rattus sp.). Medium-size mammals formed about 18% of pine marten diet, a value generally reported for high-latitude habitats. In agricultural areas, the pine marten proved to be an opportunistic predator, able to face the reduced availability of small mammals by preying upon medium-size prey and fruit.     

Burying beetle Nicrophorus investigator reproduction on Pacific salmon carcasses

Abstract.  1. In many undisturbed watersheds along the Pacific Rim, anadromous salmon ( Oncorhynchus spp.) provide a predictable source of carrion to the riparian zone, largely due to horizontal transfer of salmon carcasses by bears ( Ursus spp.) and other vertebrates.
2. Burying beetles are important members of the north-temperate carrion fauna, and may utilise salmon carcasses and remnants for breeding. In this study, isotopic and observational data are reported that demonstrate previously unrecognised Nicrophorus investigator (Zetterstedt) reproduction on large salmon carcasses from five watersheds in coastal British Columbia.
3. Stable isotope signatures (δ¹⁵N and δ¹³C) of adult beetles collected in autumn indicate a diet of salmon origin in all but one individual from all watersheds, suggesting that this beetle–salmon association is widespread. Comparison of autumn isotope signatures to individuals collected randomly in summer suggests that isotope signatures represent the larval carrion source from the previous autumn rather than immediate adult diet.
4. In a survey of N. investigator use of salmon carcasses from two watersheds, 35 broods were observed on chum and pink salmon carcasses, including 16 natural brood complexes containing over 100 larvae, and five ranging from 250 to 750 larvae.
5. Overall, north-coastal populations of N. investigator breed on the rich and reliable salmon resource and may exhibit a system of communal breeding on these carcasses. This is most relevant when the dramatic reduction in salmon spawning biomass over the last century is considered.     

Comparative analyses on food habits of Japanese marten,Siberian weasel and leopard cat in the Tsushima islands,Japan

Food habits of three sympatric carnivore mammals in the Tsushima islands of Japan were studied during 1986–91. Scats of the Tsushima marten (n=1236), the Siberian weasel (n=218) and the Tsushima leopard cat (n=350) were collected monthly and the food items were determined by scat contents analysis. Marten was omnivorous showing a high level of diversity of food throughout the year. The important foods for marten were fruits and berries from spring to autumn, insects in summer and autumn and small mammals all year round. Leopard cat preferred to hunt wood/mice and birds, and remained a flesh meat specialist throughout the year. Weasel was intermediate between marten and leopard cat, but was slightly biased towards the flesh meat eater. The three carnivores do not compete against one another for food, except for small rodents. A conflict for food between leopard cat and weasel was suggested to be more intense than that of other combinations based on diet overlapping. Marten may be characterized as an opportunistic generalist. When interspecific competitors existed, or human disturbance to the habitat occurred, the preferential flexibility of the marten to alternative food resources might become more advantageous than the other two species.     

Spatial organisation and dynamics of the pine marten Martes martes population in Białowieza Forest (E Poland) compared with other European woodlands

We studied factors affecting density and spacing patterns in the pine marten Martes martes population inhabiting temperate forests of Bia?owieza National Park, eastern Poland. From 1985/1986 to 1995/1996 marten densities ranged from 3.63 to 7.57 individuals 10 km^?2 (mean 5.4) and were positively correlated with abundance of forest rodents in the previous year. The rate of marten population growth was inversely density‐dependent and positively related to rodent density. Annual mortality rate averaged 0.384 and tended to be negatively related to marten densities. Mean annual home range of males (2.58 km², SE=0.24) was larger than that of females (1.41 km², SE=0.20). Seasonal home ranges also differed significantly between males and females. Both sexes held the smallest ranges in December–January. Female ranges increased in April–May, whereas those of males increased in June–September when they were mating. Fidelity of pine martens to their home ranges was very high. The mean shift between arithmetic centres of seasonal ranges was 0.25 km, and the ranges recorded in two consecutive seasons overlapped, on average, by 87–90%. We observed very little home range overlap between neighbouring male (mean 4–6%) or female (mean 6%) marten. Year round the neighbouring individuals of the same sex neither avoided nor attracted each other. Females attracted males only during the spring‐summer mating season. A review of other studies has documented that winter severity and seasonal variation in ecosystem productivity were essential factors shaping the biogeographic variation in pine marten densities between 41^o and 68^oN. The density of marten populations increased in areas with mild winters and lower seasonality. Maximum population densities (indicative of habitat carrying capacity) were correlated with mean winter temperature. In Europe, male home ranges increased with decreasing forest cover in a study area, whereas female ranges varied positively with rodent abundance.     

Increased autumn rainfall disrupts predator–prey interactions in fragmented boreal forests

There is a pressing need to understand how changing climate interacts with land‐use change to affect predator–prey interactions in fragmented landscapes. This is particularly true in boreal ecosystems facing fast climate change and intensification in forestry practices. Here, we investigated the relative influence of autumn climate and habitat quality on the food‐storing behaviour of a generalist predator, the pygmy owl, using a unique data set of 15 850 prey items recorded in western Finland over 12 years. Our results highlighted strong effects of autumn climate (number of days with rainfall and with temperature <0 °C) on food‐store composition. Increasing frequency of days with precipitation in autumn triggered a decrease in (i) total prey biomass stored, (ii) the number of bank voles (main prey) stored, and (iii) the scaled mass index of pygmy owls. Increasing proportions of old spruce forests strengthened the functional response of owls to variations in vole abundance and were more prone to switch from main prey to alternative prey (passerine birds) depending on local climate conditions. High‐quality habitat may allow pygmy owls to buffer negative effects of inclement weather and cyclic variation in vole abundance. Additionally, our results evidenced sex‐specific trends in body condition, as the scaled mass index of smaller males increased while the scaled mass index of larger females decreased over the study period, probably due to sex‐specific foraging strategies and energy requirements. Long‐term temporal stability in local vole abundance refutes the hypothesis of climate‐driven change in vole abundance and suggests that rainier autumns could reduce the vulnerability of small mammals to predation by pygmy owls. As small rodents are key prey species for many predators in northern ecosystems, our findings raise concern about the impact of global change on boreal food webs through changes in main prey vulnerability.     

Nest loss in capercaillie and black grouse in relation to the small rodent cycle in southeast Norway

Summary The relationship between nest loss in boreal forest grouse and the fluctuations in small rodents was studied at Varaldskogen in southeast Norway during 1979–1986, covering two complete rodent cycles. Nest loss in capercaillie (N=174) and black grouse (N=81) was calculated according to Mayfield (1975) based on nests from radio-equipped hens (N=77) and nests found by other methods (N=178). Small rodent density was measured by snap trapping during spring and autumn. Losses varied as predicted by the classical alternative prey hypothesis (Hagen 1952 and Lack 1954, as elaborated by Angelstam et al. 1984): high losses during rodent crash years (85.5% capercaillie, 51% black grouse), and smaller losses during peak years (54.5% capercaillie, 32.5% black grouse). Losses were inversely related to autumn abundance of rodents in capercaillie (P<0.05), but the correlation was not significant for black grouse (0.10<P<0.20). In capercaillie, the only species with an adequate sample for analysis, no relationship was detected between spring density of rodents and nest loss. Losses during the prepeak years were nearly as high as during crash years, a result inconsistent with the model. We conclude that the numerical response of predators to their cyclic main prey (i.e. small rodents) probably play a main role during the low phase and prepeak year, whereas the dietary shift is most important during the peak and crash year of the cycle.     

Ecological links between salmon,large carnivore predation,and scavenging birds

We compared scavenging bird abundance and diversity across 17 estuaries on the Central Coast of British Columbia, Canada in relation to landscape characteristics and biomass of spawning salmon and senescent and depredated salmon carcasses. We discovered that all metrics for spawning salmon and carcass biomasses were strong predictors of scavenger abundance and diversity. Specifically, Shannon’s diversity, which emphasizes rare species richness, and total abundances of scavengers, corvids (Corvus spp.), and small and large gulls (Larus spp.) were most strongly predicted by total biomass of carcasses. In contrast, the abundance of bald eagles Haliaeetus leucocephalus was most strongly predicted by biomass of carcasses that had been killed or scavenged by other predators (mostly bears and wolves). Simpson’s diversity, which emphasizes evenness of common species, was best predicted by total spawning salmon biomass. Estuary area also featured prominently among top predictors of most scavenger metrics. Our results suggest a link between terrestrial salmon predators and bald eagles, and that available salmon biomass is important for maintaining the abundance and diversity of scavenging birds that congregate at estuaries throughout the spawning season.     

Feeding ecology of the critically endangered Valencia letourneuxi (Valenciidae)

Valencia letourneuxi is a critically endangered freshwater fish in urgent need of targeted conservation. Little information is however available on its life history and feeding ecology; therefore, food resource utilization by V. letourneuxi was studied in its most abundant known Greek population of Chiliadou stream. The diet of this population appears to be dominated by microcrustaceans, Dipteran larvae, Acari, and Mollusca. Its feeding is highly dependent on seasonal prey availability and diversity, with niche overlap being low only between winter and the rest of the seasons, indicating that only during winter its diet differs significantly in relation to the other seasons. There are no significant sex- and size-related dietary shifts. This V. letourneuxi population is characterized by a generalist feeding strategy and appears to consist mostly of individuals with broad niches. Its generalist feeding pattern and dietary flexibility permits it to fully exploit this very diverse and rich habitat and may account for the high local abundance of this population.     

Decline in American marten occupancy rates at Sagehen Experimental Forest,California

We compared the distribution and frequency of American marten (Martes americana) detections during historic surveys and a recent survey on the Sagehen Experimental Forest (SEF) in the Sierra Nevada Mountains, California. This area has been the location of 9 previous marten surveys during 1980–1993, each involving a systematic detection/non-detection survey on the same grid. These data are a time series of information on the occupancy of martens that can be related to habitat change in the study area. Our objectives were to 1) resurvey martens in SEF using methodology similar to previous studies to assess current marten occupancy; 2) evaluate changes in marten occupancy during the period 1980–2008; and 3) examine associations between marten occurence and changes in habitat and landscape metrics. Current marten occupancy was estimated using surveys conducted in summer 2007, winter 2007–2008, and summer 2008. From 1978 to 2007 there was a decrease in predicted habitat patch size, core area, and total amount of marten habitat in the study area, as well as an increase in distance between patches. Marten detections in 2007–2008 were approximately 60% lower than in surveys in the 1980s. We detected no martens in the summers of 2007 and 2008, and 10 detections in winter 2007–2008 were limited to higher elevations in the southwestern portion of SEF. No martens were detected in the lower elevations where most of the recent forest management activity occurred. We suggest that the marten population at SEF has been negatively affected by the loss and fragmentation of habitat. We recommend that future management of forests in the Sagehen basin focus on restoring and connecting residual marten habitat to improve habitat quality for martens. © 2011 The Wildlife Society.     

Effects of Pacific salmon spawning and carcass availability on the caddisfly Ecclisomyia conspersa (Trichoptera: Limnephilidae)

1. The effects of spawning coho (Oncorhynchus kisutch) and chum salmon (Oncorhynchus keta) on the limnephilid caddisfly Ecclisomyia conspersa were evaluated by experimentally excluding salmon from the upper 14‐m stretch of a spawning channel by a wire‐meshed fence. Density, and development and growth rates, of larvae upstream of the fence (without salmon) were compared with those downstream (with salmon). 2. Larval density in the stretch with salmon declined during spawning, but increased again after spawning subsided and the carcasses of dead fish became available. In the stretch with salmon, larval density on salmon carcasses was seven to 37 times greater than on the adjacent channel substratum. The rate of larval development in the stretch with salmon was greater than that in the stretch without salmon. Two months after carcasses became available, 98% of larvae sampled from the stretch with salmon were in the fifth instar, compared to only 23% from the stretch without salmon. Body weight of E. conspersa in the stretches with and without salmon increased by an average of 3.04 and 2.38 mg, respectively, over a 6‐month period. 3. ¹⁵N values of larvae from the stretch with salmon increased following the arrival of the fish, suggesting that the larvae were feeding on salmon‐derived material, such as eggs and carcasses, which contain a high proportion of the heavier stable isotope. In contrast, ¹⁵N values of larvae from the stretch without salmon remained relatively constant throughout the experiment. The availability of salmon carcasses as a high‐quality food source late in larval development may increase survival and fecundity of E. conspersa. 4. These substantial differences were consistent with the view that they were due to the experimental exclusion of salmon and salmon carcasses from the upstream stretch, though the study was un‐replicated and thus precludes ascribing causation more definitely.