DESPERATELY SEEKING . . . WATER SHREW (NEOMYS FODIENS) AND HARVEST MOUSE (MICROMYS MINUTUS) IN BROADLAND A D R I A N J. D. JOWITT & MARTIN R. P E R R O W Water shrew (Neomys fodiens) and Harvest mouse ( M i c r o m y s minutus), although relatively well distributed are probably Britain's two least known small mammals. The status of both species is uncertain, compounded by a paucity of records and the lack of scientific study (Trout, 1978; Churchfield, 1984ab, 1985, 1991). However, recent work on the small mammal fauna in reed-beds in Broadland, East Anglia (Perrow & Jowitt in press) has revealed that this habitat supports a highly diverse Community in which Water shrew and Harvest mouse are important components. Work in reed-beds in Czechoslovakia (Holisova, 1975; Obrtel, 1975; Pelikan, 1975) has also shown that reed-beds are an outstanding habitat for these species. Previous mammal studies in Broadland are limited to larger rodent species (Leuze, 1976; Gosling & Baker, 1991) and the available information (apart f r o m the recent studies above) on small mammals is rather anecdotal in nature (George, 1992). Indeed, information on small mammals in wetlands in Britain is very limited (Flowerdew, et al., 1977). The Water shrew is thought to be at risk from habitat destruction or change through abstraction and pollution and the like (Churchfield, 1991) in what have been regarded as traditional sites, such as streams and water-cress beds. However, Perrow & Jowitt (in press) report densities in reed-beds far in excess of that previously recorded in Britain i.e. 3.2/ha (Churchfield, 1984b). T h e managed (cut) bed, with its specific flooding regime, supported the highest numbers (9/ha). This is very similar to the seasonal average described by Pelikan (1975) in his studies of reed-beds in central E u r o p e . T h e reasons behind the suitability of reed-beds as habitat for Water shrew may be partly a function of size, in that reed-beds typically provide a block of u n b r o k e n habitat which contrasts with stream-sides and water-cress beds which are at best of limited size and best described as linear or corridor habitat. Furthermore, other fen types (e.g. sedge beds) and carr woodland appear to be highly suitable for Water shrew, but this remains untested. Most fen types, including drier litter fen, are also likely to be important for Harvest mouse, which has declined as a result of changing agricultural practice in cereal crops (Perrow & Jordan, 1992), with which'it is often associated. T h e species now appears to be largely restricted to what is probably its ancestral habitat, tall natural grassland. T h e transitory nature of 'dry' natural grassland as a result of management changes and not least, through vegetational succession means that wet natural grassland such as reed-beds are likely to be more stable, easily-protected habitat. This is partly due to the great number of larger reed-beds being either owned, leased or managed as nature reserves (Bibby & Lunn, 1982).
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Management regimes Reed has been harvested, during the winter, for centuries for the thatching industry using traditional hand-held sythes and maigues (sickles). Nowadays, it is more often harvested by mechanical means (often modified ricecutters) on an annual (single-wale) or biennial (double-wale) basis. Around a third of the total British reed crop comes from Broadland alone (George, 1992) and the region may be considered to be the centre of thatching reed production. In recent times, the shift to mechanisation has resulted in the abandonment of harvesting on small beds to concentrate on larger ones (Bibby & Lunn, 1982), leaving many areas unmanaged. This has led to the cutting (or more rarely burning) of reed, which arrests the successional processes, on some sites for conservation purposes. This is often undertaken for birds such as Marsh harrier (Circus aeruginosus), Bittern (Botaurus stellaris) and Bearded tit (Panurus biarmicus) (Bibby & Lunn, 1982; Andrews & Ward, 1991). Reed-dominated communities although floristically species-poor also contain several nationally rare plant species including Marsh sow-thistle (Sonchuspalustris) and Marsh pea (Lathyruspalustris), as well as many rare insects (Shirt, 1987), which also attract attention. If management is conducted solely during the summer months, then the development of beds of Saw-sedge (Cladium mariscus) is favoured. This is also a traditional crop, as capping for thatched roofs. Beds are usually harvested on a three to four year rotation and are usually cut by hand-held scythes. The sedge then produces new shoots which undergo some development before winter. Managed sedge-beds often contain plant species of national rarity, including Milk parsley (Peucedanum palustre) the food plant of the protected Swallowtail butterfly (Papilio machaon). If summer management of the wetter sites is more frequent (perhaps annual or biennial) then litter fen may develop. This variable fen type may be dominated by herbs, rushes and/or grasses and may be floristically rieh. It was traditionally managed and harvested for both livestock food and bedding (especially for the horses pulling cabs in London). Currently, with no economic incentives, management by regulĂ¤r mowing (and perhaps light grazing) is largely undertaken only on nature reserves by the relevant organisations in order to promote habitat diversity (habitat mosaic). Carr woodland is a typical late successional State o f f e n in Broadland. With the abandonment of management such as harvesting and water level control, increased litter accumulation and drying-out allows trees (alder and sallow particularly) and other woody plants to invade. Fen which has been invaded by trees is increasing throughout Broadland at the expense of true fen and is often seen as a degradation of habitat quality. Well established carr woodland, on the other hand, is a unique habitat type which is worthy of SSSI (Site of Special Scientific Interest) status (e.g. at Alderfen Broad), of which swamp carr, containing Tussock sedge (Carex paniculata), is the rarest and most spectacular variant. Overall, the various gross habitat types can be seen as a continuum influenced by water level and management regime. This ultimately means that there is a great deal of scope in creating specific habitat types suitable for Water shrew and/or Harvest mouse and/or small mammals in general. Trans. Suffolk Nat. Soc. 29 (1993)
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Aims Broadland, with its national concentration of extensive stands of reed as well as large areas of other wetland habitat (total fen 2,200 ha, carr 3,000 haBroads Authority, 1987) is the prospective national stronghold of both Water shrew and Harvest mouse. The first aim of the proposed study is therefore to discover if W a t e r shrew and Harvest mouse are widely distributed within Broadland and with which habitat(s) they are associated. Many of these habitats do, however, require management to retain their quality (Rowell & Fojt, 1988), but this is conducted with little or no idea of the potential effects upon small mammals, which is in direct contrast to the specific management prescriptions for nationally rare birds. The second aim, therefore, is to discover which management regimes are the most suitable for Water shrew and Harvest mouse. Methods Live-trapping is being used to survey the small mammal populations in each of the four main Vegetation types under study, reed, sedge, litter fen and carr, in all five of the river Valleys that drain Broadland, the Bure and its tributaries the Ant and the Thurne, the Yare and the Waveney. This will yield information on small mammal community composition and gross distribution of Water shrew and Harvest mouse, perhaps according to overall land use and water quality, both of which vary considerably between catchments. In addition, as each Vegetation type is replicated by river (i.e. 5 replicates) statitistical comparison of the number (density) of animals sampled is possible, which will indicate habitat preferences. F u r t h e r m o r e , to assess the effect of management regime on small mammals (numbers, species richness, diversity etc.) each distinct regime for reed (single-wale, double-wale and unmanaged) and sedge (managed and unmanaged) is also to be replicated in each river Valley. This gives a grand total of 7 habitat types with 35 replicate samples. In order to compare between habitat types, all samples must be taken virtually simultaneously and/or Over a period when the populations of animals are relatively constant. Therefore, sampling is being conducted f r o m September to D e c e m b e r , after recruitment of young individuals into the population is complete and before wholescale winter mortality (Corbet & Harris, 1991). For Water shrews mortality is highest during and immediately after the breeding season (Churchfield, 1991). Each sample consists of a 49 point (7 x 7) trapping grid, each point being 10m apart. T h e area sampled is thus some 3600m 2 ( 6 0 x 6 0 m ) in total. At each trap point two traps are being used, one to sample aerial habitat (Perrow, et al., 1992) and the other, a Longworth, to sample ground habitat, giving a total of 98 traps per grid. Trapping is being conducted over a four-day period, twice-daily, with a pre-bait period of three days beforehand. Baits include a mix of seeds (wheat, sunflowers and small seeds such as millets etc. for Harvest micePerrow & Jowitt, in press) and large numbers of blowfly pupae for shrews
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(which are also used on pre-bait). Captured animals are sexed, weighed and individually marked by fur-clipping. To help explain some of the variability between samples, irrespective of Vegetation type, Information is also being gathered on water depth, litter depth and vegetational composition. This approach has been successful in teasing apart the habitat requirements of mammals within each treatment type in reed-beds (Perrow & Jowitt, in press). Finally, information on the diet and dietary choice of shrews, Water, Common (Sorex araneus) and Pygmy (Sorex minutus), is also being gathered. For each shrew captured, faecal samples are taken according to the methods of Churchfield (1984a). Combined with a knowledge of the invertebrate fauna, sampled by pitfall trapping and cores (Ditlhogo, et al., 1992), this will also help in explaining the reasons behind any habitat preferences exhibited by Water shrew and elucidate whether competitive interactions between the shrew species (Churchfield, 1992) is likely in these wetland habitats.
Summary The current survey (in progress at the time of writing) will determine the gross distribution, status, habitat preferences and effects of management on Water shrew and Harvest mouse as well as the diverse small mammal fauna that have been captured in reed-beds previously (Common shrew, Pygmy shrew, Bank vole (Clethrionomys glareolus), Field vole (Microtus agrestis), Water vole (Arvicola terrestris), Wood mouse ( A p o d e m u s sylvaticus) and Weasel (Mustela nivalis) - Perrow & Jowitt, in press). Management of these sites is at present conducted with little knowledge of its effects upon these mammal species. Furthermore, the reasons behind the habitat preferences will be investigated by monitoring environmental variables. This will be taken one step further for Water shrews by determining dietary preferences and potential competitive interactions with sympatric species. This study, when added to previous work on the reed itself (van der Toorn & Mook, 1982), other plants (Cowie et al., 1992), birds (Laursen, 1977; Bibby & Lunn, 1982; Andrews & Ward, 1991) and invertebrates (Ditlhogo et al., 1992) will provide the scientific basis for the management decisions undertaken in these habitats.
Acknowledgements We are indebted to the Vincent Wildlife Trust for funding the project and to representatives of the Broads Authority, Norfolk Naturalists Trust, How Hill Trust and RSPB for providing sites and information.
References Andrews, J. & Ward, D. (1991). The management and creation of reedbeds, especially for rare birds. British Wildlife, 3(2), 81-91.
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Suffolk Natural History, Vol. 29 Bibby, C. J. & Lunn, J. (1982). Conservation ofreed beds and their avifauna in England and Wales. Biological Conservation, 23, 167. Broads Authority (1987). Broads Strategy and Management Plan. Authority, Norwich, England. Churchfield, J. S. (1984a). Dietary Separation in three species of shrew inhabiting water-cress beds. J. Zool. (London), 204, 211. Churchfield, J. S. (1984b). An investigation of the population ecology of syntopic shrews inhabiting water-cress beds. J. Zool. (London), 204, 229. Churchfield, J.S. (1985). The feeding ecology of the European Water shrew. Mammal Review, 15(1), 13. Churchfield, J. S. (1991). Water shrew Neomys fodiens. In: The Hand of British Mammals, 3rd edition. Blackwell Scientific Publications, Oxford, England. Churchfield, J. S. (1992). The Natural History of Shrews. Christopher H Mammal Series, A & C Black, London. Cowie, N. R., Sutherland, W. J. Ditlhogo, M. K. M. & James, R. (1992). The effects of conservation management on reedbeds. II. Thefloraand litter disappearance, J. Appl. Ecol., 29, 277. Corbet, G. B. & Harris, S. (1991). The Handbook of British Mamma edition. Blackwell Scientific Publications, Oxford, England. Ditlhogo, M. K. M., James, R., Laurence, B. R. & Sutherland, W. J. (1992). The effects of conservation management on reedbeds. I. Invertebrates. J. Appl. Ecol., 29, 265. Flowerdew, J. R., Hall, S. J. G. & Clevedon Brown, J. (1977). Small rodents their habitats and the effects of flooding at Wicken Fen, Cambridgeshire. J. Zool. (London), 182, 323. George, M. (1992). The land use, ecology and conservation of B Packard Publishing Ltd., Chichester, England. Gosling, L. M. & Baker, S. J. (1991). Coypu Myocastor coypus. In: T Handbook of British Mammals, 3rd edition. Blackwell Scientific Pub tions, Oxford, England. Holisova, V. (1975) The foods eaten by rodents in reed swamps of Nesyt fishpond. Zoologicke Listy, 24(3), 223. Laursen, K. (1977) Rorskaerets effekt pa en bastend af smafugle (in Danish with an English summary. Dansk orn. Foren. Tiddsskr. 71, 95-101. Leuze, C. C. K. (1976) Social behaviour and dispersion in the water vole, Arvicola terrestris (L.). Unpubl. PhD thesis, University of Aberdeen, Scotland. Obrtel, R. (1975) Animal food eaten by rodents in the reed swamps of Nesyt pond. Zoologicke Listy, 24(4), 325-334. Pelikan, J. (1975) Mammals of Nesytfishpond,their ecology and production. Acta Scientifica Naturalium (BRNO), 9(12), 1-45. Perrow, M. R. & Jordan, M. J. R. (1992). The influence of agricultura use uponpopulations of harvestmouse (Micromys minutus P to TERF, Hoescht UK, King's Lynn, England. Perrow, M. R., Peet, N. B. & Jowitt, A. J. D. (1992). The small mammals of drainage ditches-the influence ofstructure. Trans. Suffolk Nat. Soc. ,2 3.
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Perrow, M. R. & Jowitt, A. J. D. (1993). The small mammal Community in beds of Common reed (Phragmites australis), with special reference to the Harvest mouse (Micromys minutus) and Water shrew (Neomys fodiens). Mammal Review, (in press). Rowell, T. A. & Fojt, W. J. (1988). Management of reed. In: The peatland management handbook. ed. by T. A. Rowell, pp. 1-10. Nature Conservancy Council, Peterborough, England. Shirt, D. B. (1987). British Red Data Book, 2 Insects. Nature Conservancy Council, Peterborough, England. Toorn, J., van der & Mook, J. H. (1982). The influence of environmental factors and management on stands of Phragmites australis. 1. Effects of burning, frost and insect damage on shoot density and shoot size. J. Appl. Ecol., 19, 477. Trout, R. C. (1978). A review of studies of wild Harvest mice (Micromys minutus (Pallas)). Mammal Review, 8(4), 143. Adrian J. D. Jowitt & Martin R. Perrow, E C O N , Ecological Consultancy, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ.
Immigrant butterflies Large White butterflies (Pieris brassicae L.) appeared in vast numbers in 1992. Owen Douglas and I happened to visit Happisburgh cliffs, Norfolk, on July 23 at the height of the influx of these not too populĂ¤r immigrants. It was an extraordinary sight: thousands and thousands of these insects along the cliffs, stopping momentarily at flowers but almost immediately moving on under some mysterious compulsion. The Overall movement at that point was along the cliffs rather than from the sea and inland. Nine days later on the riverbank at Santon Downham Warren, on the Norfolk side, a Clouded Yellow butterfly (Colias croceus Geoffr.) passed quickly by me. I lost it almost immediately and careful searching of lucerne fields over the following weeks produced no more, but a reliable observer reported one in his garden in St. Dominic Drive, Brandon, Suffolk. DĂźring my wartime boyhood in Surrey Clouded Yellows seemed to be a normal sight but the Santon Downham specimen was the first I have seen north of the Thames. Locally, 1992 was also an excellent year for Holly Blue butterflies (Celastrina argiolus L.) which I suspect are becoming much more common than they were 10 years ago. Another interesting feature of 1992 was the vast numbers of dragonflies in many parts of Breckland, including Santon Downham churchyard and in the King's Forest. They comprised two species: the Common Darter ( S y m p e t r u m striolatum (Charpentier)) and the Migrant Hawker (Aeshna mixta Latreille). J. L. Raincock.
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Jowitt, A. J. D. & Perrow, M. R.