Spring weather conditions influence breeding phenology and reproductive success in sympatric bat populations

Abstract

Climate is known to influence breeding phenology and reproductive success in temperate-zone bats, but long-term population level studies and interspecific comparisons are rare. Investigating the extent to which intrinsic (i.e. age), and extrinsic (i.e. spring weather conditions), factors influence such key demographic parameters as the proportion of females becoming pregnant, or completing lactation, each breeding season, is vital to understanding of bat population ecology and life-history traits. Using data from 12 breeding seasons (2006-2017), encompassing the reproductive histories of 623 Myotis daubentonii and 436 Myotis nattereri adult females, we compare rates of recruitment to the breeding population and show that these species differ in their relative sensitivity to environmental conditions and climatic variation, affecting annual reproductive success at the population level. We demonstrate that (1) spring weather conditions influence breeding phenology, with warm, dry and calm conditions leading to earlier parturition dates and advanced juvenile development, whilst cold, wet and windy weather delays birth timing and juvenile growth; (2) reproductive rates in first-year females are influenced by spring weather conditions in that breeding season and in the preceding breeding season when each cohort was born. Pregnancy and lactation rates were both higher when favourable spring foraging conditions were more prevalent; (3) reproductive success increases with age in both species, but at different rates; (4) reproductive rates were consistently higher, and showed less interannual variation, in second-year and older M. daubentonii (mean 91.55% ± 0.05 SD) than M. nattereri (mean 72.74% ± 0.15 SD); (5) estimates of reproductive success at the population level were highly correlated with the size of the juvenile cohort recorded each breeding season. Improving understanding of the influence of environmental conditions, especially extreme climatic fluctuations, and the identification of critical periods (i.e. spring for reproductive female bats in temperate zones), which have disproportionate and lasting impacts on breeding phenology and reproductive success at a population level, is critical for improving predictions of the likely impact of climate change on bat populations.

Live fast, don't die young: Survival–reproduction trade‐offs in long‐lived income breeders

“…The dependence of breeding parameters on environmental conditions has previously been shown both in capital breeders (e.g. Hamel et al., , ) and income breeders, including our two study species (Linton & Macdonald, ). Bat populations are likely to be sensitive to weather conditions experienced during the breeding season (Jones et al.…”

“…The timing of ovulation and fertilization and the duration of the gestation period are influenced by spring weather conditions (Racey & Swift, ). In our study system, parturition typically occurs during late May to mid‐June in M. daubentonii and 1–2 weeks later in M. nattereri (Linton & Macdonald, ). Juveniles become volant and are weaned at 5–6 weeks of age.…”

“…Transition to pregnancy happens in the early spring period. Transition between pregnancy and lactation happens when females give birth in late May/June (Linton & Macdonald, ).…”

Differences in seasonal survival suggest species‐specific reactions to climate change in two sympatric bat species

“…In comparison with other mammals of a similar body size, hibernating bats are exceptionally long‐lived (Munshi‐South & Wilkinson, ; Wilkinson & Munshi‐South, ). With their low annual reproductive output (Linton & Macdonald, ), bats’ population dynamics are driven mainly by adult mortality (Fleischer et al, ). Consequently, information on survival of hibernating bats which are, as bats in general, of high conservation concern (Habitats Directive 92/43/EEC, 1992) is of particular importance in times of global climate change with an expected increase in temperatures, changed precipitation patterns, and a higher frequency of extreme weather events, which all may affect seasons differently (IPCC, ).…”

“…In comparison with other mammals of a similar body size, hibernating bats are exceptionally long-lived (Munshi-South & Wilkinson, 2010;Wilkinson & Munshi-South, 2002). With their low annual reproductive output (Linton & Macdonald, 2018), bats' population dynamics are driven mainly by adult mortality (Fleischer et al, 2017).…”