Effect Of Habitat Characteristics On Bat Distribution Biology Essay

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Alterations in habitat are believed to be the main cause of population declines in many species of bat and therefore understanding species-habitat relationships is vital for conservation practices, such as land management practices, to be successful (Altringham, 1996). Despite this, few studies of this nature have been conducted. Many management practices are currently based on qualitative studies, largely as quantitative results are not available. Although this data is valuable, it can sometimes be inaccurate (Walsh & Harris, 1996a). Studies based on the distribution of bats are very important, in determining the status of a species and to identify sites of biological importance (Cowley et al. 2000).

Bats which utilise one or more established roosts usually remain faithful to these sites over many generations and as a result find it difficult to re-establish themselves in new roosts (Altringham, 1996). This decreases the ability of bat populations to recover when declines occur (Vaughan et al., 1997). This inability to recover is expected due to the longevity, low reproductive output and high survivorships of bats (Findley, 1993). This is further complicated by the numerous species-habitat interactions which are involved in roost selection, such as temperature, humidity and habitat corridors (Entwistle et al., 1997; Walsh & Harris, 1996b).

Bat Habitat

Bat distribution must be examined using several habitat features (Vaughan et al., 1997). It is of particular importance to analyse the coarse grained features of habitat, for example altitude and vegetation type, to understand bat distribution (Warren et al., 2000). In order for bat conservation management to be successful, habitat alterations on both a large and small scale must be taken into consideration, to accurately predict the effect of land management practices (Warren et al., 2000). For the purposes of this study, data has been obtained for the following species:

Brown long-eared bats (Plecotus auritus) have been found to favour buildings as their summer roosts (Entwistle et al., 1997). These building have commonly been found to be older and have partitioned roofs (Entwistle et al., 1997). Roosts were usually within 0.5km of both woodland and riparian habitats (Entwistle et al., 1997).

The Common Pipistrelle (Pipistrellus pipistrellus) is a generalist species and forages in a wide variety of habitats, including farmland, woodland, gardens, lakes and hedgerows (Vaughan et al., 1997). This species roosts in both new and old buildings, trees and bat boxes (Barlow & Jones, 1999). Roosts were commonly found near water and hedgerows (Vaughan et al., 1997). Woodland has been found to be particularly important as roosts are usually found within close proximity to a tree over 10m tall and within a 50m radius of cover (Jenkins et al., 1998). The reasons for this are thought to be an abundance of prey species and the use of hedgerows as habitat corridors (Oakeley & Jones 1998). This species usually avoids open habitat such as grassland and moorland (Limpens et al., 1989).

The Soprano Pipistrelle (Pipistrellus pygmaeus) commonly forages in riparian habitats and has also been associated with tree lines (Vaughan et al., 1997). Tree lines are most likely used for navigation purposes, as Soprano bats consistently use the same flight lines (Downs & Racey, 2006). Roosts may be found in buildings, trees and bat boxes (Lourenço & Palmeirim, 2004). Similarly to the common pipistrelle, this species typically avoids open habitats (Downs & Racey, 2006).

Myotis spp. (Brandt's, Daubenton's and Natterer's) have been found to inhabit many types of habitat but are almost always found within range of rivers/lakes (Vaughan et al., 1997). Brandt's bats tend to prefer woodland and hedgerow habitat. They occasionally roost in trees and bat boxes but more commonly roost in old buildings (Parsons & Jones, 2003). Daubenton's bats favour parkland and woodland which is near calm, open water (Parsons & Jones, 2003). Roosts are usually found in hollow trees, in buildings or under bridges (Mayle, 1990). Parkland and woodland is also favoured by Natterer's bats; however they prefer densely vegetated, riparian habitat (Swift, 1997). Natterer's generally roost in buildings but are sometimes found to use bat boxes (Mayle, 1990). These three species have been combined for the purposes of this study as they are found in very similar habitat, commonly share roosts and due to similarities in morphology, distinguishing between them can be very difficult (Jones, 1991).

Only 3% of Britain is covered by freshwater (Bunce & Heal, 1984), nevertheless the majority of bats are found in and around riparian habitat (Vaughan et al., 1997). Therefore, it is believed that waterbodies may be a critical habitat feature for bats in Britain. Despite this, little is currently known about which type of waterbody (rivers/lakes/ponds etc) is favoured by bat populations (Vaughan et al., 1997). Woodland is also a critical habitat for many species of British bat (Walsh & Harris, 1996b). This is, in part, due to the numerous possible roosting sites available in this type of habitat (Walsh & Harris, 1996b). There is still much to be discovered about bat preference for these two habitat features and there are likely to be several other habitat characteristics which also have an impact.

Research Methods

Data from Cumbria's County Records Office, collected between 1987 and 2009 will be analysed. The data will need to be filtered to include only those records with 6 figure grid references so the exact location can be plotted. The study will include the following species: Brown Long eared (Plecotus auritus), Common pipistrelle (Pipistrellus pipistrellus), Soprano pipistrelle (Pipistrellus pygmaeus) and Myotis spp. (Brandt's, Natterer's and Daubenton's). I will use a geographical information system (GIS) to generate maps by overlaying the data on several descriptors of landscape structure. These descriptors will include habitat features such as rivers and woodland habitat. I will analyse these results using regression models in the statistical programme, R.

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