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Estimating Badger Group Sizes in Different Landscapes in England and Wales - SE3132

This project aims to generate estimates of typical badger social group size in different landscapes, to be used in conjunction with sett abundance estimates from a national badger sett survey, to produce estimates of badger abundance in England and Wales.
A Defra (Project SE3129) funded badger survey of England and Wales (BSEW) is currently underway, aimed at up providing an updated assessment of the badger population status in the two countries. This survey is using a well established methodology focussing on surveying plots of land for main setts. Within a badger group territory there is often a larger ‘main’ sett, which tends to be occupied most or all of the time, with other, smaller setts being used more sporadically. Main setts are considered a good proxy for the presence of a badger social group, and have been used as such in several large-scale surveys (Cresswell et al, 1990; Feore et al, 1994; Smal et al, 1995; Wilson et al, 1997).
A drawback of previous national surveys has been the limited available data on typical group sizes, causing difficulties in translating the estimated abundance of social groups into meaningful estimates of badger abundance. This is particularly problematic as it is known from long-term intensive studies that badger population size can vary due to changes in numbers of social groups, or changes in group sizes, or both (e.g. Rogers et al 1997). Additionally, badger social group size may vary over time and space. Relatively small bias in estimates of group size could lead to significant error if applied to estimates of social group abundance at national or regional scales. Therefore, ideally this variability in group size would be incorporated into analyses of the BSEW survey results, in order to produce estimates of badger population size for England and Wales that are as accurate as possible, in addition to estimates of social group abundance.
In this study, we propose to estimate mean (or median, as appropriate) badger social group size by landscape type, in a way that will complement the BSEW results. We propose to collect data on group size from a sample of social groups in each of the different landscape types from which the BSEW 1-km survey squares are drawn. We aim to use hair traps to snag or ‘capture’ badger hairs from locations at and near setts. The traps will be visited on a number of days during a sampling period of pre-determined length at each sett, and hairs collected on each visit. The hairs will be genotyped to give an individual genetic fingerprint for each badger from which hairs were trapped. A number of mathematical population estimation techniques based on rarefaction and capture-recapture approaches have been developed in recent years for use on indirectly sampled genetic data such as this. We will apply these as appropriate, given the nature of the data collected, to estimate group size at all setts sampled. These data will analysed to produce typical group size estimates for the different landscape types.
The estimates of typical group size can then be used to multiply with the estimate number of social groups in each landscape type generated from the BSEW. Hence, variability in badger group size will be properly incorporated into the national population assessment, providing estimates with minimum bias at a national and regional level.

i) Produce contemporary estimates of typical badger social group size in 6 Land Class Groups which form the basis of the sample stratification for the BSEW.
ii) Quantify the variability in badger social group sizes between and within Land Class Groups.
iii) Use these group size estimates as multipliers for the BSEW. That is, for each Land Class Group, multiply the estimated number of social groups by the typical group size (mean or median, as appropriate) to give an estimate of badger abundance, with confidence intervals.
iv) Provide a baseline of typical group sizes across different landscapes, which can act as a baseline for future surveys.
Time-Scale and Cost
From: 2012

To: 2013

Cost: £363,494
Contractor / Funded Organisations
Fields of Study
Animal Health