Population changes of brown long-eared bats (Plecotus auritus) in bat boxes at Thetford Forest

Following establishment of a population in the boxes, immigration was probably a small proportion of the total recruitment, the remainder coming from reproduction within the population. A redistribution of the boxes over a wider area after 8 yr had no effect on male recruitment and only a slight transient effect on female recruitment. The total population increased during the study from 73 to 140 bats giving a doubling time of c10 yr. The female population showed exponential growth with an intrinsic rate of increase of 0.072, while the growth rate of the male population declined. The juvenile sex ratio was biased towards males during the first 5 yr but did not vary from unity thereafter. The overall sex ratio was biased significantly towards females in the first 4 yr and the last 3 yr of the study. Estimates of survival excluded bats that may have emigrated. The annual survival rate showed female survival to be 0.86 after correction for the rate of increase; the uncorrected male survival rate was 0.60. Annual survival rates for each year of the study were also obtained from a maximum likelihood estimate; these showed that the mean female survival rate for the period of study was 0.780±0.035 (SEM) while the mean male survival rate was 0.623±0.076. The estimate of the mean number of young born per female each year was 0.548±0.094. -from Authors