Data from: Onset of autumn shapes the timing of birth in Pyrenean chamois more than onset of spring

1. In seasonal environments, birth dates are a central component for a
species’ life history, with potential long-term fitness consequences. Yet
our understanding of selective pressures of environmental changes on birth
dates is limited in wild mammals due to the difficulty of data collection.
In a context of rapid climate change, the question of a possible mismatch
between plant phenology and birth phenology also remains unanswered for
most species. 2. We assessed whether and how the timing of birth in a
mountain mammal (isard, Rupicapra pyrenaica) tracked changes in plant
growing season, accounting for maternal traits, individual heterogeneity,
and population density. We not only focused on spring conditions but also
assessed to what extent onset of autumn can be a driver of phenological
biological events and compared the magnitude of the response to the
magnitude of the environmental changes. We relied on a 22-year study based
on intensively monitored marked individuals of known age. 3. Births were
highly synchronized (80% of kids born within 25 days) and highly
repeatable (84%; among-females variation of 9.6 days, withinfemale
variation of 4.2 days). Individual phenotypic plasticity allows females to
respond rapidly to inter-annual changes in plant phenology but did not
prevent the existence of a mismatch: a 10-day advance in the autumn or
spring plant phenology led to 3.9 and 1.3 days advance in birth dates,
respectively. 4. Our findings suggest that plant phenology may act as a
cue to induce important stages of the reproductive cycle (e.g., conception
and gestation length), subsequently affecting parturition dates, and
stressed the importance of focusing on long-term changes during spring for
which females may show much lower adaptive potential than during autumn.
These results also question the extent to which individual plasticity
along with high heterogeneity among individuals will allow species to cope
with demographic consequences of climate changes.