Food habits of stoatsMustela erminea and weaselsMustela nivalis in Denmark

StoatsMustela erminea Linnaeus, 1758 and weaselsMustela nivalis Linnaeus, 1766 exploit the same array of prey species at different frequencies according to body size. The rabbitOryctolagus cuniculus, which typically is the dominant prey for stoats in temperate parts of Europe, is absent in Denmark. The present study based on gastrointestinal tract contents examines the food habits of sympatric stoats (n=112) and weasels (n=132) from Denmark. Rodents were the most important prey group for both stoats and weasels, constituting 77% and 84% of their diet respectively, expressed as frequency of occurrence. No differences were detected in the proportions of major prey groups between sexes within species, but between species the diets differed. Stoats ate birds and birds’ eggs more often than weasels did, while weasels ate more insectivores. Stoats ate more oftenMicrotus voles and water voleArvicola terrestris than weasels did, while weasels ate more bank voleClethrionomys glareolus and moleTalpa europaea. There was a larger dietary overlap between sympatric stoats and weasels in Denmark than in other dietary studies in areas where rabbits were available.     

Limitation of reproduction by feeding condition in a carabid beetle,Carabus yaconinus

1. Effects of the amount of food consumed on reproduction of the carabid beetle, Carabus yaconinus B., were studied in the laboratory by rearing beetles at different food levels, and the feeding and oviposition rates in the field were estimated on the basis of the relationships between the amount of food consumed, body weight and egg production obtained in the experiment.
2. The maximum amount of food consumed was 150 mg of minced beef per day. The number of eggs laid per day and the mean body weight increased with an increase in the amount of food consumed. High mortality occurred only when the beetles consumed less than 25 mg of minced beef per day.
3. The ratio of current body weight to the minimum one just before death by starvation, W/W_min, was used for the estimation of the rates of food consumption and egg production. The relationships between mean W/W_min ratio, the amount of food consumed and the number of eggs laid per day were clarified.
4. The relationships between ovary states (ovary weight and the number of mature eggs in the ovary) and W/W_min ratio were examined for the females caught in the field. Females with higher values of W/W_min ratio had more mature eggs.
5. The amount of food consumed by females in the field during the reproductive period was estimated to be 50–70% of the maximum value attained in the experiment and the estimated rate of oviposition was 45–59% of the maximum rate attained in the experiment.

     

Studies of the metabolism,food consumption and assimilation efficiency of a small carnivore,the weasel (Mustela nivalis L.)

Summary The average respiratory quotient of weasels was 0.73. There were significant differences in average daily metabolic rate (ADMR) between the sexes and six experimental temperatures. As temperature decreased the mean ADMR increased, with a relatively greater rise for females. Regression equations of ADMR on temperature were Y=483.2–9.6X kcal/kg/day for males, and Y=625.3–15.0X kcal/kg/day for females. The minimum metabolic rate measured for males was 6.6 kcal/kg/h, and the maximum 25.7 kcal/kg/h. The relationship between ADMR and body weight varied with different temperatures, but was consistent with the hypothesis that ADMR was proportional to metabolic weight. The energetic costs of activity for my captive weasels were more than 20% of their daily total energy expenditure. Data on metabolism supported the conclusion that long, thin mustelids lose heat faster than normally-shaped mammals of the same weight.The calorific contents of foods, faeces and urine from feeding trials were determined. There were significant differences in the calorific content of faeces between the sexes, and of faeces and urine between diets.Four natural foods (Microtus, Apodemus, rabbit, starling) were offered during feeding trials. Daily food consumption varied between the diets, but small weasels always ate relatively more than large ones. Mean consumption was 0.33 g/g/day for males, and 0.36 g/g/day for females. Weasels on low-bulk diets (rabbit, starling) lost at least as much energy in urine as in faeces. There were significant differences in assimilation efficiency between the sexes and diets. The average efficiency for males was 78.2%, and 79.8% for females. Bulky foods lowered assimilation efficiencies by up to 9%.Daily energy requirements for maintenance calculated from ADMR data were compared with those from feeding trials. On the Microtus diet weasels expended 18.6–30.1% more energy on maintenance than predicted by the ADMR results, whereas on the other diets they expended 2.7–31.4% less energy. Estimates from ADMR data were probably more accurate.     

Observations of a wild polar bear (<Emphasis Type="Italic">Ursus maritimus</Emphasis>) successfully fishing Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and Fourhorn sculpin (<Emphasis Type="Italic">Myoxocephalus quadricornis</Emphasis>)

Polar bears, Ursus maritimus, throughout their range, are nutritionally dependent on ringed (Phoca hispida) and bearded seals (Erignathus barbatus), which are predominantly caught on the sea ice. Other marine prey species are caught and consumed, but less frequently. As the annual sea ice retreats, polar bears throughout their range are forced ashore, where they mostly live off their stored adipose tissue. However, while land-bound they have been observed catching birds and terrestrial mammals. Although polar bears evolved from brown bears (U. arctos), direct observations of polar bears diving for and catching fish have not been reported. Here, we document observations of a young male polar bear catching Arctic charr (Salvelinus alpinus) and Fourhorn sculpin (Myoxocephalus quadricornis) by diving in Creswell Bay, Nunavut. We recorded six search bouts, where six fish were caught during dives, which were preceded by a snorkel. The average dive and snorkel length was (mean ± SD) 13 ± 5 and 6 ± 2 s, respectively.     

Endozoochorous seed dispersal by sympatric mustelids, Martes melampus and Mustela itatsi, in western Tokyo, central Japan

We investigated seed dispersal by two sympatric mustelid species, the Japanese marten (Martes melampus) and Japanese weasel (Mustela itatsi), along an intercity forest path in western Tokyo, central Japan, from Jul 2007 to Jul 2008. We aimed to investigate the effect of food/habitat preference of these mustelids (martens are semi-arboreal frugivores while weasels are terrestrial carnivores) on their seed dispersal characteristics, which determine their efficacy as seed dispersers. In total, we analyzed 478 fecal samples collected from the two mustelids (N_marten = 381, N_weasel = 97). The proportions of feces containing seeds for martens and weasels were 81.4% and 55.7%, respectively. The number of plant species whose seeds were found within the feces were 28 and 17, respectively. Almost all seeds within feces of both mustelids were intact. The number of plant species whose seeds were found within a single fecal sample ranged from one to four, but no significant difference was detected between the two mustelids. However, marten feces contained a significantly greater number of seeds of most plant species as well as total number of seeds than did weasel feces. The numbers of plant species and seeds represented in marten feces varied seasonally, but those represented in weasel feces did not. Our findings suggest the possibility that both mustelids act in some ways as seed dispersers, although martens seem to disperse a greater diversity and total amount of seeds.     

Seventeen years of predation by one suburban cat in New Zealand

Abstract

The 558 prey items brought home by one domestic cat, recorded over its 17‐year lifetime, included 221 mice, 63 rats, 35 rabbits, 4 hares and 2 weasels. The cat hunted up to 600 m from the house, and prey was caught both inside and outside the 0.5 ha garden. Of the 223 birds brought in, 54 were native, including 43 silvereyes (Zosterops lateralis), but those killed were quickly replaced, so there was always a resident population of 1–2 pairs. The other known native birds comprised five fantails (Rhipidura fuliginosa), four warblers (Gerygone igata), a kingfisher (Halcyon sancta), and a shining cuckoo (Chrysococcyx lucidus). Only nine skinks (Cyclodina aenea) and one frog (Litoria raniformis) were brought in. The abundance of birds and reptiles in the garden showed no apparent change over the 17 years compared with the previous 15‐year‐period without a cat. By contrast, the cat exterminated the rabbit population in the garden, and “farmed” surrounding burrows during its whole life; all other prey killed declined in frequency after the cat was 8–9 years old.     

Dietary variations of predaceous caddisfly larvae (Trichoptera: Rhyacophilidae,Polycentropodidae and Arctopsychidae) from British Columbian streams

The diets of larval Rhyacophilidae (Rhyacophila inculta), Polycentropodidae (Polycentropus variegatus) and Arctopsychidae (Parapsyche almota and P. elsis) from five streams in the University of British Columbia Research Forest, British Columbia (Canada), are recorded and related to feeding mode/constructional activities and prey representation in the habitat. Particular attention was paid to the extent of dietary overlap and the degree of intraspecific dietary variations between streams. An overall similarity of the diets of the study species was notable and all commonly consumed chironomid (Diptera) larvae, Simulium (Diptera) and Zapada (Plecoptera), although there was interspecific variation in the relative importance of these items. Polycentropus variegatus and Parapsyche spp. ate Baetis and Paraleptophlebia, the latter predators also consuming Hydrachnellae (Acarina). Other prey were generally of minor importance and consequently interspecific dietary overlaps were high. Differences in the range of prey consumed by predaceous Trichoptera were apparent. Free-foraging R. inculta which selectively consumed sedentary simuliid larvae had the narrowest niche breadth. Parapsyche spp. and Polycentropus variegatus foreguts generally contained an over-representation of chironomid larvae compared to their proportionate occurrence in the benthos, and these caddisflies exhibited high niche overlap. The relative importance of chironomids as food for Parapsyche spp. and Polycentropus variegatus is attributed to prey behaviour, i.e. drift, and poorly developed escape responses when they are caught on the predator's net.     

The stoat Mustela erminea population decline in northern Belarus and its consequences for weasels Mustela nivalis

Abstract

In northern Belarus, we have documented a decline in the local stoat Mustela erminea population following the naturalisation of the American mink Mustela vison. The most likely cause is the reduction in the density and distribution of the main prey of stoats, the riparian voles (the water vole Arvicola terrestris and the root vole Microtus oeconomus), due to excessive predation by mink. Since the stoat population has declined, the number of weasels Mustela nivalis in marshlands has increased and their mean body mass has increased, correlated with the higher number and mean weights of rodents available for weasels in marshland compared with forest habitats.     

Role of fruits in the diet of small mustelids (<Emphasis Type="Italic">Mustela</Emphasis> sp.) from the western Italian Alps

The food habits of both weasels and stoats (Mustela nivalis and M. erminea) and the occurrence of fruit in their diet were studied by scat analysis in the Gran Paradiso National Park (western Italian Alps). Being impossible to distinguish between stoats and weasels scats, they were grouped together as the genus Mustela. Despite the high consumption of small rodents, which represented the main food item in the diet of small mustelids (41.5% in mean volume), wild fruits (mainly Rosaceae and Ericaceae) were also relatively common (23.3% in mean volume). Fruits were exploited throughout the year, with an intensive use in seasons of high availability. Their consumption did not significantly differ between habitat types, despite a significant decrease of fruit availability from deciduous mixed forest to alpine prairie. This evidence suggests that this trophic behaviour could represent a consolidated feeding strategy of both weasels and stoats, which seem to adopt an opportunistic behaviour as shown by larger size mustelids. We argue that fruits, owing to their good availability and high profitability, could play an important role in the diet of small mustelids in alpine habitats, slackening their well-documented dependence on rodents.     

Spatiotemporal distribution and resource use of scoliid wasps (Hymenoptera) in coastal sand dunes

The spatial and temporal distributions of scoliid wasps in the coastal sand dunes at Hakoishi, Kyoto Prefecture, Japan, were investigated using three different sampling methods in 2002 and 2003. Of eight scoliid species collected in the present study, five species, Scolia historionica, Campsomeriella annulata, Scolia decorata, Scolia oculata, and Megacampsomeris schulthessi, were dominant. The flying insects caught by Malaise traps and flower‐visiting insects caught by insect nets were mostly males, and this biased pattern was due to the active mate‐searching behavior of male wasps and their frequent visits to flowers to supplement energy consumed by such behavior. Given that the ground traps caught females exclusively, female wasps seemed to actively engage in host‐searching behavior on and below the ground. Of the wasps caught by Malaise traps and flower‐visit sampling, five dominant species showed spatially different habitat use: S. historionica and C. annulata mainly occupied the grassland zone on the plain (Gp), S. decorata occupied the grassland zone on the terrace (Gt) and the forest zone (Fp), S. oculata occupied the small scrub zone on the plain (Sp), and M. schulthessi occupied the small scrub zone on the terrace (St). Ground trap samples also indicated that S. historionica and C. annulata shared habitats. On the basis of the observed seasonal changes in wasp abundance and the degree of wing wear as an index of wasp age, S. historionica and C. annulata are thought to be bivoltine species, whereas S. decorata, S. oculata, and M. schulthessi are thought to be univoltine species. These scoliid wasp species may play an important role in pollinating coastal plants in the grassland zone.     

Distribution and abundance of small mammals in relation to habitat in Pureora Forest Park

Populations of ship rats (Rattus rattus), Norway rats (R. norvegicus), feral house mice (Mus musculus), stoats (Mustela erminea), weasels (M. nivalis), and ferrets (M. furo) were sampled with killtraps every three months from November 1982 to November 1987 in logged and unlogged native forest and in exotic plantations of various ages at Pureora Forest Park, central North Island. Mice (n=522 collected) were fewest in unlogged native forest, more abundant in road edge cutover forest, and most abundant in a young (5-10 year old) plantation. Traps catching most mice were set in dense ground cover under a low, sparse canopy. Ship rats (n=1793) were absent from the young plantation, present but not abundant in older exotic forest, and abundant in all native forest regardless of logging history. Traps set on warmer, steeper sites caught most ship rats, and those set in early successional habitats caught fewest. There was a marked reciprocal relationship between the distributions of ship rats and of mice: the proportion of mice in the total catch of rodents decreased significantly at the least, disturbed forest sites (P <0.001). Most (81%) Norway rats (n=43) were caught in a single trap in unlogged native forest on the bank of a stream. Stoats (n=57) were most abundant in the older exotic plantations; weasels (n=16) in the young plantation and along road edges in native forest; and ferrets (n=11) in unlogged native forest. Hedgehogs (n=290) were common in unlogged native forest far from any roads and also in older exotic forest. Our data suggest that selective logging and conversion to exotics have different effects on each of the six species we monitored. We hypothesise that (1) selective logging is likely to stimulate temporary increases in the numbers of mice and weasels, but not rats or stoats, and (2) after conversion to exotic forest, mice and occasionally weasels will be abundant at first but will gradually be replaced by ship rats and stoats as the forest matures.     

Mustela or Vison? Evidence for the taxonomic status of the American mink and a distinct biogeographic radiation of American weasels

The American mink’s relationship to the weasels in Mustela has been uncertain. Karyological, morphological, and phylogenetic comparisons to Eurasian Mustela support placing the mink outside the genus as Neovison vison. However, genetic comparisons that incorporate other endemic American Mustela suggest the interpretation of N. vison’s position to Mustela has been handicapped by biased geographic sampling. Here, we analyzed mitochondrial cytochrome-b from all weasels endemic to the Americas, including two poorly known South American species (M. felipei, M. africana), weasels native to North America (M. vison, M. frenata, M. nigripes), Mustela migrant to North America (M. erminea, M. nivalis), palearctic Mustela, and other American members of Mustelidae. Bayesian and likelihood inference methods were used to construct a phylogeny of Mustela, and relaxed Bayesian phylogenetic techniques estimated ages of divergence within the genus using priors calibrated by fossil ages. Our analyses show that the American mink and the smaller Mustela endemic to the Americas represent a distinct phylogenetic heritage apart from their Eurasian cousins, and biogeographic barriers like the Bering and Panamanian land bridges have influenced the evolutionary history of Mustela in the Americas.     

Recent history,current status,conservation and management of native mammalian carnivore species in Great Britain

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The Biology of Eurypharynx pelecanoides (Pisces,Eurypharyngidae)

This paper is based on 760 Atlantic specimens of pelican eels caught from off Iceland to 48°S in depths between 2750 and c. 500 m. Stomach contents from 120 specimens show a varied diet dominated by crustaceans, fish and squid. The frequent occurrence of Sargasso weed consumed by Eurypharynx indicates a lack of prey-item discrimination. The forward directed eyes appear to enable stereoscopic prey localization, possibly aided by the well developed lateral line. The huge gape is unsuitable for suction feeding. It is proposed that prey engulfing is accomplished by a forward thrust of the head by which the produced water pressure will expand the buccal cavity to a volume several times that of the fish itself. When ripening, males especially show morphological changes in some characters, indicating that the pelican eel breeds only once, a condition which seems to be the rule among eels.     

Long-distance dispersal by a parasitoid (Anagrus delicatus,Mymaridae) and its host

Summary We demonstrate that an egg parasitoid, Anagrus delicatus (Mymaridae, Hymenoptera) and its host, Prokelesia marginata (Delphacidae, Homoptera) regularly disperse 1 km or more in a north Florida saltmarsh. Anagrus delicatus were caught on yellow sticky traps on offshore islets and oyster bars throughout the spring, summer, and fall, whereas P. marginata were caught during one pulse in the spring. Parasitism rates were higher on offshore islets than at mainland sites, even though egg densities were higher at the mainland sites. The majority of parasitoids caught offshore were females. Long-distance dispersal by A. delicatus may be a cause of inverse density-dependent or density-independent spatial patterns of parasitism and may represent a risk-spreading strategy.     

Movement patterns of a specialist predator,the weasel<Emphasis Type="Italic">Mustela nivalis</Emphasis> exploiting asynchronous cyclic field vole<Emphasis Type="Italic">Microtus agrestis</Emphasis> populations

We investigated habitat selection and movement characteristics of male weaselsMustela nivalis Linnaeus, 1766 during the breeding season through radio-telemetry in Kielder Forest (KF) in order to assess how weasel movement is influenced by prey dynamics, mate searching and predation risk, and whether the scale of weasel movement corresponds to the spatial scale of the asynchronous, multi-annual vole population cycles observed in KF. Weasels used habitats with a high proportion of grass cover to a much larger extend than habitats with less grass cover and moved through the latter habitats faster and / or straighter. Habitats with high amounts of grass cover also had the highest field vole abundance, although total rodent abundance did not differ between habitats. The selection of this habitat by weasels might reflect weasels preferring field voles as prey or avoiding habitats with little grass cover and high intraguild predation risk. Five out of 8 male weasels radio-tracked had low day-to-day site fidelity and moved between different clear cuts. Three other males were resident in a single clear cut. This variation may reflect mate searching by male weasels. The observation that most weasels (5 out of 8) roamed over large areas and the scale of their dispersal potential suggests, that if they regulated vole populations, they should have a greater synchronising effect on the spatial scale of vole population dynamics than what is observed in vole populations in KF.     

August diet of age-0 Pacific halibut in nearshore waters of Kodiak Island,Alaska

Synopsis The objective of this study was to describe the diet of age-0 Pacific halibut,Hippoglossus stenolepis, for the inshore waters of Kodiak Island, Alaska during August 1991. Stomach contents were identified from 170 age-0 halibut captured inshore of the eastern and southern coasts of Kodiak Island, and were analyzed in relation to halibut size, location, depth and substrate of capture. One hundred sixty-eight of 170 fish had eaten crustaceans, of which the predominant prey taxa were Mysidacea (34.3%), Cumacea (33.1%), Gammaridea (26.6%) and Caridea (3.9%). In five of six capture locations, mysids and amphipods were predominant prey. In the remaining area, Sitkinak Strait, cumaceans were the primary food source. At depths less than 10 m, mysids were the predominant prey taxa. Gammarid amphipods were of primary importance at depths of 10–30 m. Halibut captured from 30–70 m fed mainly on cumaceans. Cumaceans and gammarid amphipods were consumed by halibut caught on gravel substrate. Fish caught on substrates of sand and mud fed mainly on mysids and amphipods. Cumaceans were also consumed on sandy substrates. Fish 45 mm fed on cumaceans. An ontogenetically related shift in diet occurred at 46–55 mm TL, at which size the halibut's primary prey began to shift from cumaceans to mysids. Fish of 46–75 mm consumed increasingly greater proportions of mysids, amphipods and shrimps. The diet of age-0 Pacific halibut along the Kodiak coast during August was related to predator size, and location, depth, and substrate type of capture.     

The response of tsetse flies to artificial baits in relation to age, nutritional and reproductive state

In various vegetation types in Zimbabwe, the catches of Glossina pallidipes Austen and G. morsitans morsitans Westw. (Diptera: Glossinidae) at a target baited with odour (acetone, 1-octen-3-ol and two phenols) were positively correlated with catches of the same species at an unbaited net. No correlation existed between target catches and hand net catches of tsetse flies sitting on the vegetation. G. pallidipes females caught at a target and at an unbaited net were older than those caught from vegetation. Of the female G. pallidipes caught at the target, 46% were in the first 3 days of pregnancy. Of those caught at the unbaited net, significantly fewer, 21%, were in this stage. G. pallidipes males caught from vegetation contained more fat (3.07±0.333 mg) than those caught at the unbaited net (2.06±0.339 mg) or at the target (2.19±0.218 mg). It is inferred that target catches consisted predominantly of tsetse which were already in flight when they sensed the stimuli from the target, and that target catches were biased towards female G. pallidipes in the first 3 days of pregnancy.     

Ontogenetic changes in the diet of the sandbar shark, <Emphasis Type="Italic">Carcharhinus plumbeus</Emphasis>, in lower Chesapeake Bay and Virginia (USA) coastal waters

This study describes the diet of the sandbar shark, Carcharhinus plumbeus, highlighting differences in diet within various regions of the Virginia (USA) nursery area, as well as ontogenetic changes in diet. Stomach samples were obtained in 2001 and 2002 from 232 sharks caught by gillnets or longlines. Historical data from the Virginia Institute of Marine Science (VIMS) Shark Ecology Program were also analyzed. Ontogenetic changes in diet were evident, with crustacean prey decreasing in frequency with increasing shark size, and elasmobranch prey importance increasing with increasing shark size. Whereas previous research in Chincoteague Bay, VA showed the blue crab, Callinectes sapidus, was the dominant crustacean in sandbar shark diet, the mantis shrimp, Squilla empusa, dominated the crustacean portion of the diet in this study. Differences in diet of sharks were observed among locations within the study area. Small juveniles (≤80 cm precaudal length) in the lower Chesapeake Bay ate more fishes, whereas Eastern Shore juveniles ate more crustaceans. Crustacean prey items varied among locations along the Eastern Shore, with more portunid crabs consumed in waters near Wachapreague and more mantis shrimp consumed near Sand Shoal Inlet. Our study showed that Carcharhinus plumbeus is a generalist predator and is thus unlikely to strongly impact the population of any particular prey species, and in turn is not likely to be strongly affected by fluctuations in abundance of a single prey species.     

Effect of water depth on predation frequency by diving beetles on mosquito larvae prey

Diving behavior and its frequency may differ among species of mosquito larvae because of differences in predation pressure. The present study aimed to investigate the relationship between water depth and predation frequency on two mosquito species, Culex tritaeniorhynchus (wetland breeder) and Aedes albopictus (container breeder), by the diving beetle Eretes griseus. Culex tritaeniorhynchus spends more time at the surface than A. albopictus, which spends more time thrashing underwater. When intact mosquito larvae of both species were present, the diving beetles consumed almost all A. albopictus larvae (98.3%). After all the A. albopictus larvae had been consumed, the diving beetles began to prey on C. tritaeniorhynchus. In order to compare the effect of position on the predation preference of the diving beetles, equal numbers of both species were heat‐killed and allowed to settle on the bottom of the container. When all the dead mosquito larvae had sunk to the bottom of a plastic container, the diving beetles caught both mosquito species at random. These results indicate that mosquito larvae near the surface were eaten less frequently by diving beetles than those at the bottom. The low diving frequency of C. tritaeniorhynchus is regarded as a form of anti‐predatory behavior.