Why are shrews so small? The costs and benefits of small size in northern temperateSorex species in the context of foraging habits and prey supply

This paper reviews the ecological advantages and disadvantages of very small body size inSorex Linnaeus, 1758 shrews living at high latitudes with cold winters. It examines the feeding and foraging habits of small and large shrews in the context of prey supply, location of winter prey sources, territory requirements, habitat exploitation and inter-specific competition. Data on feeding habits and prey availability show that the major costs of small size are a reduction in food niche breadth and prey biomass resulting from restrictions on the type and size of prey eaten, and large territory requirements. Major benefits of small size are the ability to subsist on small, numerous and accessible arthropods with high encounter rates, enabling coexistence with larger congeners and exploitation of low-productivity habitats less suitable for larger earthworm-eating species. Small size, coupled with low per capita food intake, is shown to be of special adaptive value in cold winters when food supply is restricted mostly to small arthropods, and earthworms are few.     

Feeding ecology of the armored shrew, from the north-eastern Democratic Republic of Congo

The diet of Scutisorex somereni (Soricomorpha: Soricidae) from forests in the Democratic Republic of Congo was investigated to elucidate its feeding ecology in the context of its unique spinal modifications. It ate a wide range of small and large invertebrates, including representatives of Coleoptera, Formicidae, Lepidoptera and Diptera larvae, Chilopoda, Diplopoda and Araneae, but the principal prey was Oligochaeta. All diet samples contained Oligochaeta and these contributed 38–45% of prey volume. While 64% of prey occurrences were <10 mm in length, 56% of prey volume comprised invertebrates >26 mm, mostly large Oligochaeta (some of >50 mm). Soil-dwelling prey comprised 46% by composition (59% by volume) of the diet. Besides its peculiar skeletal modifications, it has an exceptionally long intestine relative to its body size. It was concluded that S. somereni is primarily an earthworm-eating shrew and partially subterranean rather than truly fossorial in foraging mode. Its diet and foraging mode cannot explain the unique vertebral modifications of this zoological curiosity.     

Dietary separation in three species of shrew inhabiting water-cress beds

The diets of three species of shrew (Neomys fodiens, Sorex araneus and S. minutus) living sympatrically in an area of water-cress beds were investigated over a two-year period by faecal analysis of live-trapped animals. Thirty-eight different prey types were identified in the diet of N. fodiens , 25 in the diet of S. araneus and 18 in S. minutus. The most important prey items of N. fodiens in all months were freshwater crustaceans and cased trichopteran larvae. Other important items were terrestrial gastropods, coleopterans and dipterans. Neomys fodiens foraged underwater throughout the year and 33–67% of its prey were of aquatic origin. Major prey items of S. araneus throughout the year were lumbricids, terrestrial gastropods and coleopterans. Araneids, isopods and coleopterans were the dominant dietary items of S. minutus. All terrestrial prey items were taken in greater proportions by S. araneus and S. minutus than by N. fodiens , excepting lumbricids which were never eaten by S. minutus. Dietary overlap was greatest between S. araneus and S. minutus at 57%, followed by N. fodiens and S. araneus (44%) and least similar were N. fodiens and S. minutus (36%).     

Food niche overlap and ecological separation in a multi-species community of shrews in the Siberian taiga

An investigation of the feeding habits and prey availability in a community of seven species of shrew (Insectivora: Soricidae) inhabiting the taiga of Central Siberia was carried out with the aim of quantifying levels of niche overlap and elucidating modes of ecological separation amongst these coexisting species. All species took a wide range of invertebrate prey, and overlap in the numbers of shared prey taxa was high, but differences in dietary composition of certain taxa reduced overlap between most species. Small species fed almost exclusively on small arthropods, mostly Araneae, Chilopoda and Coleoptera, while medium and large-sized species took high proportions of oligochaetes. Prey were mostly taken in proportions approximately equal to their availability, although certain prey appeared to be selected. All shrews took prey in a range of sizes, and the high dietary occurrence of small invertebrates reflected their availability and high encounter rate in field samples. Dietary occurrence of small prey was negatively correlated, and large prey positively correlated, with body size of shrew. Smaller shrews were predominantly ground-surface foragers while larger species were more subterranean, with body size and dietary occurrence of soil prey being positively correlated. Differences in prey size and foraging mode reduced niche overlap between shrew species of widely differing sizes. Each shrew species did not occupy a separate, well-defined food niche. Instead, the community was sub-divided into three functional groups: large and small species which tended towards specialization with relatively low levels of overlap, and intermediate, generalist species with higher levels of overlap.     

Habitat occurrence and feeding ecology of Crocidura montis and Lophuromys flavopunctatus on Mt. Elgon, Uganda

The distribution, habitat occurrence and feeding ecology of Crocidura montis and Lophuromys flavopunctatus coexisting in the afro‐alpine zone on Mt. Elgon, Uganda, are described. Crocidura montis was the only shrew species occupying the afro‐alpine zone, but was not found in forested habitats below 3200 m. While there was considerable overlap in habitat occurrence between the two species, C. montis was most abundant in the montane grassland and in drier sites while L. flavopunctatus occupied a wider range of habitats and wetter sites. C. montis ate a diversity of invertebrates, the most important being Coleoptera, Araneae and Lumbricidae. Invertebrates, mostly Diptera larvae, Lumbricidae and Coleoptera, formed a major component of the L. flavopunctatus diets, plus plant material (particularly Hepaticae and monocots). The arthropod components of the diets reflected their abundance in pitfall samples.     

Food resources and foraging habits of the common shrew,Sorex araneus: does winter food shortage explain Dehnel's phenomenon?

It is widely assumed that winter is a critical time for homeotherms because of decreased ambient temperatures coupled with reduced food supply. Shrews are excellent models for investigating overwintering strategies, not only because of their particularly small size, high energy requirements relative to their size and short fasting endurance, but also the dramatic reduction in body size (Dehnel's phenomenon) exhibited by soricine shrews in northern temperate winters. The cause of Dehnel's phenomenon is poorly understood but food supply is implicated. To test the hypothesis that winter at higher latitudes is a period of food shortage for small homeotherms, we compared feeding habits of common shrews, Sorex araneus, and abundance and biomass of their prey in winters and summers in northeastern Poland using scat analysis combined with pitfall and ground core sampling for invertebrates. Ground‐surface activity and numbers of invertebrates in pitfall traps were greatly reduced in winter but, contrary to prediction, no significant differences between winter and summer were found in total numbers and biomass of prey invertebrates in ground core samples. However, certain prey types changed seasonally with respect to numbers, biomass and distribution in the soil profile, which was reflected in shrews’ food composition and foraging behaviour. Dehnel's phenomenon appears not to be caused by reduction in total prey numbers and biomass, at least in our study area. Smaller body mass coupled with lowering of absolute food requirements may have important survival value in winter with its reduced numbers of certain major prey coupled with increased difficulty of locating and extracting invertebrates within the soil profile resulting in higher energetic costs of foraging.     

First results on the feeding ecology of sympatric shrews (Insectivora: Soricidae) in the Tai National Park,Ivory Coast

The feeding ecology of a multi-species community of shrews inhabiting secondary forest and cacao-coffee plantations in the Tai National Park (Ivory Coast) was investigated. A total of 553 shrews were captured and 194 alimentary tracts were examined. Ten species were found, includingSylvisorex megalura and nine species ofCrocidura, forming a series with respect to body size. New ecological data on these little known African species are presented. All species of shrews ate a wide diversity of arthropods, with Coleoptera, Araneae, Formicidae and Diplopoda making the largest dietary contributions. Lumbricidae were eaten by two species.C. obscurior had an exceptionally long intestine for its size but there was no evidence of dietary specialisation in this or other shrew species. All species investigated ate predominantly small prey and there was no correlation between size of prey items consumed and body mass of shrew species. There was little evidence of resource partitioning amongst the shrews, despite differences in body size.     

Geographical distribution and habitat occurrence of the Water Shrew (Neomys fodiens) in the Weald of South-East England

A survey of 96 sites in a range of riparian habitats in the catchments of five rivers during June–August 1998 used the bait tube method to investigate the geographical distribution and habitat occurrence of Water Shrews (Neomys fodiens) in the Weald of South‐East England. Water Shrews were found at 42% of sites, and were widely distributed in all river catchments except the Mole. They occurred in many riparian habitats, including rivers, streams, canals and ditches, with a range of physical and biotic characteristics. There were no signs of habitat avoidance in response to human disturbance but Water Shrews were absent from the river catchment with lowest water quality. Logistic regression analysis was used to model the effect of habitat variables on the presence of Water Shrews, with current speed, water depth, bank incline and bank‐side vegetation identified as important variables. Fast‐flowing shallow waters had a significant positive effect on their presence, whereas scarce herbaceous vegetation and a bank of low incline had a significant negative effect. These habitat variables appear to be reliable indicators of the probability of finding Water Shrews at a particular site, and have implications for habitat management and conservation.