Data from: Spring weather conditions influence breeding phenology and reproductive success in sympatric bat populations.

1. 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. 2. 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. 3. Using data from twelve breeding seasons (2006 - 2017),
encompassing the reproductive histories of 623 Myotis daubentonii and 436
M. 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. 4. We demonstrate
that i) 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, ii) 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, iii) Reproductive success increases with
age in both species, but at different rates, iv) Reproductive rates were
consistently higher, and showed less inter-annual variation, in
second-year and older M. daubentonii (mean 91.55% ± 0.05 SD) than M.
nattereri (mean 72.74% ± 0.15 SD), v) Estimates of reproductive success at
the population level were highly correlated with the size of the juvenile
cohort recorded each breeding season. 5. 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.