Abstract
A nursery roost of the soprano pipstrelle bat Pipistrellus pygmaeus has been moni- tored continuously between 1 April and 27 September (Weeks 1�26) for 20 yr to promote conser- vation of the species, which declined over the last century. The long-term study, essential to esti- mate a reliable population trend, is linked to environmental changes as possible causes of decline. The main emergence was from May to July (Weeks 6�18) when 550 ± 190 (SD) P. pygmaeus were counted. Analysis showed that the year-to-year change in population size of female P. pygmaeus (ΔN)and the time of the peak exit count of the females from the roost in May to June could be pre- dicted from the integrated air temperature (degree days, D) between 1 January and 31 March. The regression of ΔN on D showed a statistically significant linear regression line defined by ΔN = 1.31�0.0015 D (R 2 = 38.4%; p = 0.005). ΔN = 1.04 to 1.33 reflected a stable to increasing population (Years 1�7 and 15�20). ΔN = 0.78 to 1.00 reflected a stable to decreasing population (Years 8�14). The regression of the time of the first peak exit count, calculated as the number of weeks from 1 April, on D showed a statistically significant linear regression line defined by Weeks = 12.75�0.020 D (R 2 = 32.8%; p = 0.008). Rising temperatures between January and March would be detrimental to P. pygmaeus populations.
Highlights
Monitoring the conservation status of breeding colonies of Pipistrellus species is necessary since populations have declined since 1972 (Mitchell-Jones et al 1999), but there are few quantitative studies of microchiropteran bats at species level to ensure good conservation practice (Hutson et al 2001)
The main aims of this study were to determine if the year-to-year change in population size of the females, and the time of the peak exit count of the females from the roost in May to June, could be predicted from the integrated air temperature between 1 January and 31 March
Visual emergence counts made at the east end of the roost for verification with the automated exit counts in 2000 (Week 17) and 2002 (Week 9) confirmed the same number of bats were recorded with the 2 methods, 65 and 69, respectively
Summary
Monitoring the conservation status of breeding colonies of Pipistrellus species is necessary since populations have declined since 1972 (Mitchell-Jones et al 1999), but there are few quantitative studies of microchiropteran bats at species level to ensure good conservation practice (Hutson et al 2001). Commitment to long-term monitoring schemes is critical (Robinson et al 2005), yet only a handful of studies have examined climate change and bats (Jones et al 2009, Sherwin et al 2013). Population declines can be rapid when reproductive rates are slow (Jones et al 2009), but bat populations are amenable to direct monitoring through nursery roost counts to assess long-term changes (Walsh et al 2001). Half of all insectivorous bats are endangered (Racey & Entwistle 2003), and in the UK the number of pipistrelles has declined (Stebbings 1988, Walsh et al 2001, Barlow et al 2014). Stebbings (1988) reported that the roost counts of Pipistrelle spp. decreased by 62% from 1978 to 1987. Jones et al (2009) proposed that bat populations are declining due to environmental stresses and habitat change as a result of urbanisation, industrialisation and pollution, especially by agricultural organic matter and ammonia in water bodies
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