Bovine TB: Research project summary
Project SE3107: Develop methods to estimate badger population density
Project duration: 6 years
Effective strategies for monitoring and managing badger populations requires
application of reliable methods for estimation of abundance and population
density. Prior to this project the only reliable method was live capture-mark-recapture
which was prohibitively labour intensive. This project evaluated four
methods to estimate and monitor badger abundance.
1.) Sett activity surveys: A scoring system for recording activity at badger setts was developed; this scored sett appearance to assess badger activity. Badger numbers correlated only weakly with sett activity levels, which were heavily influenced by factors such as weather and season. This method could be used within large areas over time where significant population changes are likely. This method should be used when evidence of population change is the only requirement, or as an adjunct to other methods. Of the methods tested this is the easiest and cheapest to carry out. It requires no specialist equipment, and only one visit to each sett.
2.) Faecal accumulation rate: This method is based on quantifying the rate of accumulation of badger droppings at latrines near setts. At the first visit to a latrine faeces are counted and marked with chalk dust, at subsequent daily visits new faeces are counted. This method is most applicable for monitoring sites over time where information is held on the number and configuration of social groups, or could be determined by baitmarking. It is more labour intensive than sett surveys, with a minimum of 5 visits to each sett required.
3.) Faecal DNA recovery: A method for recovering DNA from faecal samples taken from latrines near setts was developed. The unique genotypes derived from the samples were treated with statistical methods used in mark-recapture of animals, and an estimator was used which generated estimates of abundance which were close to the true population. In one RBCT trial (of 30km2) area systematic sampling and genotyping of droppings deposited at latrines was set up. The aim was to investigate patterns of individual latrine use, and an estimate the number of resident badgers. Unfortunately the lab failure to provide genotypes of the majority of samples meant that no analyses could be done. This highlights the considerable difficulty of the laboratory process associated with this approach. Further work is required to make this method reliable.
4.) Distance sampling: This was the only true direct observation method tested where animals were actually seen and counted. Spotlighting was carried out in open habitat along line transects within a population of known size, and produced a realistic estimate of abundance. This method can be carried out over small areas on foot, or over large areas from vehicles on roads to provide relative density estimates. The estimation of true density requires a correction factor for the amount of time spent by badgers in open, surveyable land. The technique was shown to be successful and time efficient.
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July 7, 2008