Species detection and distribution of small mammals on the Great Fen using the bait tube methodology

Transcription

1 Species detection and distribution of small mammals on the Great Fen using the bait tube methodology Helen Bailey* & Paul Tinsley- Marshall *Great Fen Volunteer Reserves Officer, Great Fen Monitoring Officer, Wildlife Trust BCN, Countryside Centre, Chapel Road, Ramsey Heights, Cambridgeshire, PE26 2RS. paul.tinsley- Summary Small mammals are an essentail component of terrestiral and wetland ecosystems, particulalry as key prey items for predatory birds and animals. There is a paucity of data on UK small mammal populations, and as one of the first surveys of this kind on the Great Fen, this study contibutes to both local and national understanding. The Mini Mammal Monitoring bait tube method, co- oordinated by The Mammal Society, was carried out on the Great Fen during October 2012 over 2 km x 2km survey tetrads. DNA analysis was carried out on faeces collected, in order to determine the species identity. The survey was particulalry concerend with determining the presence of Water Shrew, a wetland specialist know from previous surveys and records on the Great Fen. Six species were detected within the survey sites: Harvest Mouse, Wood Mouse, Bank Vole, Field Vole, Pygmy Shrew and Common Shrew. No Water Shrew DNA was detected. Knowing which species are present is essential in efforts to conserve them, and consequently in efforts to conserve their predators. Water Shrew has been recorded casually since this survey, so it is suprising that none were detected. Resources for monitoring are often limited and projects require prioritisation. Following this documentaion of species present, a by- proxy method of small mammal monitoring using bird survey data is suggested. Introduction Small mammals are an essential component of many terrestrial and semi- wetland ecosystems, however at a national level it is not well known whether populations are increasing, stable or declining, as data on UK populations are still extremely limited. The Great Fen is no exception with very little data on small mammal distributions collected to date. Small mammals are key prey items for many predatory birds and mammals. Variability in their populations will affect many species; on the Great Fen these include Barn Owl, Short- eared Owl, Long- eared Owl, Little Owl, Kestrel, Common Buzzard, Red Kite, Marsh Harrier, Hen Harrier, and other predatory birds such as the winter migrant, the Great Grey Shrike. Mamalian carnivores such as stoats and weasels are also particularly vulnerable to variation in populations of small mammals. The relationship between predator and prey is closely linked with fluctuations in one having an effect on the other. Small mammals are an essential component to the functioning of many terrestrial habitats including semi- wetland ecosystems, and are vunerable to changes in habitat quality. Many of our native small mammal species are under pressure from a number of factors including habitat destruction, due to the removal of hedgerows, intensive Page 1 of 9

2 farming practices and persecution, as small mammals are often considered pests because of potential damage to property as well as feeding on crops and other food stuffs. Modern large- scale farming practices can reduce hedgerow connectivity and the suitability of field margin habitats. The Great Fen aims to redress declines in wetland habitat quality and availablity, and monitoring can provide indications of changes small mammal pouplations, and inform future management policies to protect ecosystem integrity. Monitoring small mammal populations is also important for the effective management of conflict with humans. Often viewed as pests, they can damage property, cause significant economic loss to farmers by feeding on, and nesting in, stored products, and damage areas of woodland regeneration and agriforestry. Some are also seen to pose a health risk through disease transmission. The Mini Mammal Monitoring scheme (MMM) presents a simple, standardsied methodology suitable for use by amature volunteers, and has the considareble advantage that live trapping is not nessasary, vastly decreasing the time and experience required. Non- invasive bait tubes allow the recorder to gather evidence of small mammals from the collection of faeces, which undergoes DNA analysis to identify each species present. The survey has previously been carried out on the Great Fen during 2010 at Summer Standing. The results of this survey identified the presence of the presence of Water Shrew and Field Mouse on Summer Standing (Hughes and Stroh, 2011). One of the primary aims of this study was to attempt to determine the extent of Water Shew distribution, an under- recorded wetland specialist species. Method The survey followed the Mammal Society bait tube methodology detailed in the references. Plastic piping bait tubes measuring 4cm diameter and 20cm long were baited with moist fruit (e.g. cabbage stalk, carrot or apple) and meal worms or castors (blowfly pupae). Nylon material was secured over one end with an elastic band to prevent spillage of the food once in situ. Every tetrad (2km x 2km BNG map square) in which land is managed by the Great Fen partnership was selected for survey. Within each tetrad one or two 100 m long line transects were selected. These transects were mapped using hand held hand held GPS units. The habitat type of each location was recorded in accordance with the Mammal Society Classification Codes detailed in Table 1. Each transect was devided into 10 metre sections and in the centre of each section a bait tube was placed, hidden within the vegetation. The location of each was marked with garden canes to enable effective relocation. Figure 1: Diagramatic representation of a 100 metre transect Page 2 of 9

3 Table 1 Habitat Classification Codes General habitat Specific habitat type General Habitat Specific habitat type Woodland 1 Deciduous Riparian 12 Rivers 2 Mixed 13 Streams 3 Coniferous 14 Canals Open Farmland 4 Permanent grassland 15 Standing Water 5 Grass leys Moorland & Lowland Heath 16 Heather moorland 6 Arable land 17 Acid grassland 7 Orchards 18 Lowland heath Field Boundaries 8 Hedgerows Coastal 19 Saltmarsh 9 Fence lines 20 Sand dunes 10 Walls 21 Cliffs/downs 11 Ditches Urban 22 Road verges Care was taken to ensure the bait tubes were positioned away from areas where water levels could fluctuate and therefore flood the tubes and their contents and also away from areas that livestock could potentially interfere with them. DNA kits were ordered from The Mammal Society at a cost of 10 for one transect or 15 for two transects. Bait tubes and samples were dried overnight. All faeces, including hard and soft pellets and smears, were collected the next day using wooden sticks in the DNA kit to place in the bags provided. It was essential to double bag samples for hygiene security when posted. The site name and sampler name was recorded on the bags and on the site card, and sent with an import licence, to the laboratory address specified by The Mammal Society. Only faecal matter was submitted for DNA analysis; the presence of other material in the sample may nullify results, including plant material, mud, sawdust etc, so this was removed.after 48 hours the bait tubes were collected and dried for 24 hours. Once dried the faecal matter including hard pellets, soft pellets and smears, within the tubes, was scraped out into double skin plastic bags, for hygiene reasons, before being sent for DNA analysis. Results DNA anaysis of the faecal matter collected from the bait tubes (Table 2) indicates that out of 23 sites, 17 sites had evidence of at least one species of small mammal, while six of the sites had no evidence of any small mammal species. Harvest Mice were detected at two sites,wood Mice at thirteen, Bank Voles at eight, Field Voles at four, Pygmy Shrew at four and Common Shrew at Page 3 of 9

4 five. Water Shrew was not detected at any of the sites. Holme Fen East had the greatest number of detected species, with four of seven possible species recorded. Table 2 Small mammal species detected at the Great Fen from faecal DNA analysis Site Name Tetrad Harvest mouse Wood mouse Bank vole Field vole Pygmy shrew Common shrew Water shrew Species count Corney's Farm TL 2286 nd nd nd nd nd nd nd 0 Darlow's Farm North TL 2286 nd nd nd nd nd nd nd 0 Darlow's Farm South TL 2284 nd nd nd nd nd 2 Five Arches Pit TL 2082 nd nd nd nd 3 Gamsey Wood TL 2280 nd nd nd nd nd 2 Holme Fen East TL 2088 nd nd nd 4 Holme Fen West TL 1888 nd nd nd nd 3 Holme Lode (Engine Farm) TL 2290 nd nd nd nd nd 2 Holme Lode Central (East) TL 2090 nd nd nd nd 3 Holme Lode Central (West) TL 2090 nd nd nd nd 3 Holme Lode West TL 2290 nd nd nd nd nd nd 1 Holme Lode West TL 1890 nd nd nd nd 3 Middle Farm Central TL 2084 nd nd nd nd nd nd 1 Middle Farm North TL 2086 nd nd nd nd nd nd nd 0 Middle Farm South TL 2084 nd nd nd nd nd 2 New Decoy Farm TL 2288 nd nd nd nd nd nd 1 Old Decoy Farm TL 2288 nd nd nd nd nd 2 Old Decoy Farm East TL 2488 nd nd nd nd nd nd nd 0 Ramsey Heights TL 2484 nd nd nd nd nd nd 1 Summer Stranding TL 2088 nd nd nd nd nd nd nd 0 Woodwalton Fen North TL 2284 nd nd nd nd nd nd nd 0 Woodwalton Fen South TL 2282 nd nd nd nd nd 2 Woodwalton Marsh TL 2080 nd nd nd nd nd nd 1 Notes: nd = none detected, = detected Page 4 of 9

5 Bank vole Wood mouse Harvest mouse Field vole Pygmy shrew Common shrew Figure 2 Tetrads sampled on the Great Fen and species recoreded. Note not all tetrads displayed were used within the Small Mammal Survey and therefore do not show any results. Page 5 of 9

6 The small mammal species of the Great Fen Harvest mouse (Micromys minutus) The harvest mouse is Britain s smallest rodent weighing between 4-6g with a tail slightly longer than its body, up to about 6 cm in length. Its distribution is mainly in southern and central England, but is also present in northern and eastern England. Its ideal habitat includes, grasslands, hedges and woodland edges, where it favours long tussocks of grass to build its woven nest. It has a mainly vegetarian diet but will eat a small number of invertebrates. The harvest mouse is a priority species in the UK Biodiversity Action Plan (UK BAP). Its main threats are loss of habitat through habitat destruction and possibly changes in farming practises Image Chris Barber; Wikimedia Commons Wood Mouse (Apodemus sylvaticus) The wood mouse is found throughout the UK in many habitats. It often avoids predation due to being excellent at leaping long distances. Threats to the wood mouse are loss of woodland and hedgerow habitat and persecution. Autumn berries and seeds are gathered and stored ready for the winter. This species is nocturnal and therefore has good night vision. Image Anne Burgess; Wikimedia commons Page 6 of 9

7 Bank Vole (Myodes glareolus) Image Sylvia Duckworth Wikimedia Commons Bank Voles are one of Britain s commonest mammals, found in a variety of habitats including, urban areas, rivers and wetlands, heathland, arable farmland and grassland. It particularly favours woodland that has brambles and dense ground cover. They measure 7-11 cm and weigh 20-35g. They feed on soft fruits, berries, seeds, the leaves of shrubs and herbs, snails and insects. Bank Voles nest in underground burrows of which little research has been carried out. Although common they are important in the food chain for many predators, especially Tawny Owls, Foxes and Stoats. Field Vole (Microtus agrestis) Measuring up to 13 cm with a tail of about 4cm and weighing 18-60g, the field vole is one of Britain s most common mammals. It is found in most areas of Britain but is absent from many islands. Its ideal habitat includes, grassland, heathland and moorland. They spend most of their time in runs and burrows. They eat seeds, roots, and leaves with a preference for grasses. Nests are built from shredded grass. Although common their main threat is habitat loss and fragmentation of field margins, hedgerows and woodlands. Image Phil Williams; Wikimedia Commons Page 7 of 9

8 Pygmy shrew (Sorex minutus) Image Stella Nutella; Wikimedia Commons) With its long snout, the pygmy shrew is 4-6 cm long with a tail 3-5 cm long and weighs 2-6g. Its high metabolic rate means it needs to eat up to 125% of its bodyweight in food daily. Its diet consists of insects,woodlice and arachnids. The Pygmy shrew is widespread over Britain and Ireland where groundcover exists, in urban locations, gardens, deciduous and mixed woodlands, grassland and arable, using vegetation as burrows and tunnels. It is protected under the Wildlife and Countryside Act The Pygmy shrew is vulnerable to extreme weather conditions and habitat loss. Its main predators are owls and other avian predators. Common shrew (Sorex araneus) (Image Soricida; Wikimedia Commons The Common shrew is the second most common British mammal. It is very widespread found in many habitats. Its body is 4-8 cm with a tail 2-4 cm long. It has a high metabolism so must eat frequently, foraging at the surface day and night feeding on, worms, slugs and snails. Its main predator includes, tawny and barn owls, foxes, stoats and kestrels. Although very common, this species is protected under Schedule 6 of Wildlife and Countryside Act (1981) as are all shrews. Water shrew (Neomys fodiens) (Image Accipiter; Wikimedia commons) Water shrews are the largest of the British shrews measuring 6-9 cm long with a tail of 4-7cm long. This semi- aquatic small mammal is found mainly in wetland and aquatic habitats, but may be seen in drier habitats, mainly when the young are leaving the nest to find new territories. This shrew does not hibernate so can be seen all year round. Its diet is carnivorous, feeding on freshwater shrimps, water skaters, mayfly larvae and caddis larvae they also will eat frogs, newts, small fish, earthworms, snails and beetles. They stun their prey with venomous saliva. The population of water shrew is of a very low density making it hard to assess the population size. The main threats come from habitat loss and water pollution. Page 8 of 9

9 Conclusions, management and monitoring recommendations The mini mammal survey carried out within the Great Fen indicated that of the seven possible species six were present. The Great Fen lie outside of the range of the Yellow- necked Mouse. Although the Mini Mammal Monitoring Survey is undertaken within a single forty eight hour period annually, it provides a very good indication of the species that are present within an area, as the timing is designed to capture the peak in density and activity following breeding. This survey has been a useful exersize in determining the small mammal species present on the Great Fen and their geographical distribution. While the advatage of the bait tube method is that it is non- invasive and has low resource requirements, it does not allow estimates of population size to be made, as with mark- recapture live trapping studies. This however is not deemed a high priority in this instance. It is likely that current management practices such as reversion from arable to grassland comunities, hay cutting and grazing, will benefit small mammals. Fluctuations in population will be refelcetd in predatory bird numbers, and birds are a primary monitoring priority. Bird survey data can act as a proxy for trophic interactions such as prey availability, and in situations where resources are limited and monitoring efforts need to be prioritised, this will provide adequate information. Acknowledgements The Mini Mammal Monitoring was undertaken by Great Fen Volunteers including, Martin Lovell, Alex Rowell, Paula Monaghan and Helen Bailey. References The Mammal Society, Mini Mammal Monitoring, The Bait Tube Method. [online] Hughes,F. and Stroh, P. (2011) Esme Fairburn Annual Report Monitoring and evaluating landscape scale wetland restoration projects, The Wicken Fen Vision Project and The Great Fen Restoration Project. Anglian Rushin University. The Wildlife Trusts, Species A- Z [online] All Images used with open access permission from Wikimedia Commons [online] Page 9 of 9