Water shrew survey booklet

Transcription

1 NORTHUMBRIA MAMMAL GROUP Compiled by Kevin O Hara for the Northumbria Mammal Group, with the support of the Local Heritage Initiative and Northumberland Wildlife Trust. Water shrew survey booklet Photography by Dr Steve Furness Northumberland Northumberland Wildlife Trust Ltd Garden House St Nicholas Park Gosforth Newcastle upon Tyne NE3 3XT Tel: (0191) Fax: (0191) mail@northwt.org.uk Web: Reg Charity No Design by: E.Beamsley - ebeamsley@hotmail.com Compiled by Northumberland Wildlife Trust

2 RECOGNITION Water shrew Water shrews are semi-aquatic insectivores, found most often in habitats close to fresh water, although they do inhabit beaches at certain times of the year, where they feed on sandhoppers. Their breeding season is between April and September and during this time 2-3 litters of young are produced. Water shrews spend most of their time searching for food as they need to eat roughly half of their body weight daily. Freshwater invertebrates make up the largest proportion of their diet, although terrestrial invertebrates such as worms and beetles, are also consumed. Water shrews favour the vegetated banks of shallow, unpolluted rivers, streams and still waters. Latin name: Neomys fodiens Status native. Protected under schedule 6 of the Wildlife and Countryside Act 1981 conservation status unknown, although thought to be a declining distribution, throughout mainland Britain. Absent from Ireland. Appearance: BACKGROUND TO THE SURVEY The water shrew is one of Britain s least known mammals, and there is concern that it may be undergoing a decline in numbers and occurrence as a result of habitat loss, pollution, pesticide use (sheep dips) and predation from nonnative species such as North American mink. Despite a widespread geographical distribution in Britain, there is little information on its occurrence, habitat preference and population status. Additionally, there are still large gaps in its distribution records. One of the reasons for the lack of knowledge about this mammal, is the difficulty associated with surveying such a small, unobtrusive animal whose field signs (faecal pellets and tracks) are easily overlooked amongst dense vegetation. Aims of the survey To provide a baseline against which to monitor future changes, to water shrew populations. To establish the habitat requirements and preferences of water shrews, and to examine the potential impact of both habitat, and water quality changes on water shrew populations. To gather sufficient records to provide a database for the assessment of the conservation needs of water shrews, and to produce habitat management guidelines for these mammals. This survey will employ an easy-to-use bait tube method to investigate the current distribution of the water shrew. Black fur on back and a silver grey/white underside. Often has a white patch above the eyes. Size up to 10cm in length, with a 4 7cm long tail.12 18g in weight. Typical size of a water shrew 1 Water shrew survey booklet 2

3 THE BAIT TUBE METHOD The bait tube method, designed by Dr Sara Churchfield, encourages water shrews to visit short lengths of plastic tube by baiting one end with food. Faecal pellets (scats), deposited in the tube by the shrews and other small rodents, can then be identified and separated. Scats of water shrews are distinguishable from other shrew species, as they are the only ones that will contain the remains of aquatic invertebrate prey. GRID REFERENCING YOUR SITE To enable us to analyse your data we need you to record the grid reference of your sites. To do this you will need an ordnance survey map of your area. Pinpoint your chosen location by eye, and then take a grid reference from your map, please follow the example below: Water shrew Bait tube in a ideal location Choosing suitable sites for the survey Each survey pack contains enough equipment for you to survey two sites simultaneously. Sites should be situated at least 1km apart and the surveying methods for different types of site vary. Rivers, streams, ditches. Choose a 40m stretch of the watercourse, and at 10m intervals place one bait tube firmly on the ground amongst the bank vegetation. Ponds, lakes, fens, bogs. Where space permits, place bait tubes at 10m intervals. If the site is small then place the tubes at approximately equal distances around the site. Record the 2-letter reference code found on the map. The National Grid divides Britain into 100km squares, each with its own two letter reference. For this region it will be either NZ, NT, NU or NY. Next you need to take the Eastings reading. This is the horizontal reading off the map. This will give you the first two numbers of the square your site is in, for example 71 grid line. As we need a 6 figure grid reference we must estimate how many tenths are within that square, and estimate the location against this figure, thus we have for example NZ 716. The Eastings reading is, therefore, 716. The same method needs to be applied to the Northings reading, If the location lies four tenths north of gridline 44, then the Northings reading is 444. The whole grid reference you need to quote is, therefore, NZ There are diagrammatic example on all ordnance survey maps to assist further. 3 Water shrew survey booklet 4

4 RECORDING SITE DETAILS AND HABITAT CHARACTERISTICS To determine the types of habitat used most commonly by water shrews it is important that habitat characteristics are recorded. A number of field forms have been included in your pack, and more can be photocopied or supplied as required. You need to fill in a form for each site you visit when you first lay out the bait tubes. At the top of each form you need to record your name, the site name and grid reference, the dates you visited the site and the number of bait tubes laid down at each site. In the boxes lower down the sheet, e.g. habitat type, water depth, choose just one option within each box by placing a cross in the appropriate circle. We can only record one option on the database, and we will have to exclude data from our records if more than one circle per box is crossed. If you are unsure of the answer, then please record this in the comments box at the bottom of the form. Placing bait tubes next to the river bank. PUTTING TOGETHER THE BAIT TUBES The bait tubes are 20cm long (4cm wide), pieces of white plastic waste pipe. To prevent the bait spilling out of the tube, cover one end with a piece of muslin and secure it in place with a rubber band. The recommended bait is blowfly pupae. These are available from fishing tackle shops, where they are known as casters, and are sold by the pint for around 3 (one pint should suffice many tubes). You will need to locate a supply of this bait, as this cannot easily be provided by The Northumbria Mammal Group as the casters need to be frozen to prevent them emerging into adult flies. A small tablespoon full of casters (approx ) should be placed in each tube, close to the covered end. Bait tube within an ideal location Bait tubes can be washed out and re-used as often as required. For your local fishing tackle shop try and click on Tackle shops of the UK, or try your local Yellow pages under fishing tackle shops. Alternatives for bait include frozen prawns, flaky fish food, tinned cat food or trout pellets, although all are inferior to casters. PLACING THE BAIT TUBES AT YOUR CHOSEN SITES The following factors need to be considered when positioning the bait tubes: At least 4 tubes should be placed at each site. Always place tubes in habitats with ready access to water. Place tubes within 2-3m of the water s edge; the closer the better. Tubes placed in bank side vegetation are most likely to be visited by the shrews. Sites with no vegetation are not recommended. In bog or fen sites, place bait tubes in dry places, for example: grass tussocks above water level, to avoid them being flooded during the survey period. All bait tubes should be placed high enough above the water level to prevent flooding. Bait tubes can be secured with wire hoops if necessary. Place them either horizontally to the watercourse, or with the entrance facing away from the water depending on the bank structure and vegetation type on site. Tubes should be left for 2 weeks. During this time you do not need to visit or rebait the tubes. To help in finding the tubes at the end of the 2 week period, tie brightly coloured string or wool to nearby vegetation or marker sticks. Please remove these markers after the survey is completed. After leaving the bait tubes for two weeks the scats can be dried and collected The tubes can then be rinsed and placed at two more sites for a 2- week period. This will give us information from a total of four sites. You can survey more sites if you wish, just repeat the above process. 5 Water shrew survey booklet 6

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6 COLLECTING THE SCATS AND WHAT TO DO WITH THEM NEXT HOW TO DISTINGUISH SHREW FROM RODENT SCATS This can be achieved with the aid of a hand lens. The following guidelines may assist. Collect and dry the bait tubes (put them in a shed or similar for a couple of days). Remove the dried tube contents including scats etc into a storage receptacle, such as an empty film canister (avaliable from photographic shops) or into a small plastic bag. Lids of film canisters should be taped securely to prevent them opening during posting. Scats from all tubes at a single site can be collected and stored in the same receptacle. However, please keep scats from different sites separate. Scats are most easily identified if they are intact rather than crushed, although it is still possible to make positive identifications from very small fragments. Label your samples with your name and site identification details. If you are confident about distinguishing rodent from shrew scats, you can sort through your samples and only send us the shrew scats. If you are not confident about distinguishing between rodent, and shrew scats don t worry, just send the whole sample to us, where we will examine them. Please remember to include your field forms with the grid reference, site, habitat data and your name and address. We cannot include your site in the database, nor identify your scats, if you do not send us the field form. Rodent scats: Brown/black in colour. Cylindrical and pointed at one end. 3-5mm in length. Tough and difficult to crush, vole scats are more rounded, and soft like putty when fresh. Fibrous texture when broken apart. Smooth surface. Shrew scats: Black/gray in colour, pale gray when dry. Oval with a sharp point at one end. 3-5mm in length. Easy to crumble. White or silvery fragments of their prey visible. Uneven and irregular surface. If you are confident at identifying the remains of freshwater invertebrates and therefore, identifying water shrew scats, then please do so. This will require the use of a binocular microscope. Some workshops will be run to assist volunteers, who wish to learn to carry out their own water shrew scat identification. Please see Northumberland Wildlife Trust website at or call NWT for details on: (0191) Water shrew survey booklet 10

7 SURVEY CHECKLIST The following summarises the full survey methodology used: HEALTH, SAFETY AND CARE OF THE COUNTRYSIDE Please take care with personal safety during the course of your survey Read through this information leaflet. 2. Make your 4 bait tubes. 3. Choose suitable sites to place your tubes. 4. Place your tubes at your chosen sites and leave for two weeks. 5. Record site details and habitat characteristics on the field forms provided. 6. Collect tubes and store scats (faecal pellets) in envelope provided. 7. Wash the bait tubes and repeat steps four to six at two further occasions for two weeks. 8. Label scat samples with your name, the site name and the grid reference. 9. Send scat samples and field forms to Northumberland Wildlife Trust at the address overleaf. Field studies in the vicinity of water can be hazardous, especially if there are steep banks. Where possible it is best to work in pairs. The Mammal Group takes no responsibility for personal injury, incurred by volunteers during the course of their surveys. Handling of faecal material from small wild mammals presents no danger of disease, provided that reasonable precautions are taken to minimise any possible risks. Remember to wash your hands after collecting the bait tubes and extracting and sorting the scats from the field sites - especially before eating or drinking. Cuts or abrasions on the hands should be covered by sticking plaster or rubber gloves. Take particular care with these simple precautions in sites where brown rats are common, as there may be a risk of Weil s disease (leptospirosis). For more information and free publications call the health and safety executive on Caution: Do not trespass. If you choose to carry out your survey on private land that does not belong to you e.g on a nature reserve or other officiallyprotected area, then make sure you have permission to enter the area and set your bait tubes. The Mammal Group takes no responsibility for anyone caught trespassing without permission. 11 Water shrew survey booklet 12

8 NOTES 13 Water shrew survey booklet 14