DOI: 10.5061/dryad.j3tx95xbh
title: Exploring causal components of plasticity in grey seal birthdates: effects of intrinsic traits, demography, and climate

description: Change in breeding phenology is often a response to environmental forcing,
 but less is known of the mechanism underlying such changes and their
 fitness consequences. Here we report on changes in the breeding phenology
 from a 27-year longitudinal study (1991-2017) of individually marked,
 known-aged grey seals (Halichoerus grypus) on Sable Island, Nova Scotia,
 Canada. We used Generalized Linear Mixed Models to test hypotheses about
 the influence of fixed factors (maternal age, parity, previous
 reproductive success, pup sex, colony density, AMO, NAO, and SST) and a
 random factor (female identity) on parturition dates. We also examined the
 consequences of the shift in birthdates on maternal energy investment in
 offspring as measured by pup weaning mass. Birthdates were known for 2768
 pups of 660 known-age females. For 494 females with ≥ 2 parturition dates,
 repeatability as measured by the intraclass correlation was high
 (mean=0.66). 87% of the variation in birthdates was explained by a mixed
 effects model that included intrinsic and extrinsic fixed effects. Most of
 the explained variation was associated with the random effect of female
 identity. Parity was the most important intrinsic fixed effect, with
 inexperienced mothers giving birth later in the season than multiparous
 females. Over almost 3 decades, mean birthdates advanced by 15 days. The
 mixed model with intrinsic effects and population size, the detrended AMO
 from the previous year and mean NAO in the previous 3 years explained 80 %
 of the variation with 21 % of variation from the fixed effects. Both
 primiparous and multiparous individuals responded to the climate forcing,
 and there was strong evidence for heterogeneity in the response. The shift
 in birthdates did not impact pup weaning mass. Females exhibited
 considerable phenotypic plasticity indicating that climate driven changes
 in breeding phenology may not always have measurable consequences.
description: <strong>BDmodeldat.csv: </strong>Data for the
 intrinsic model of birthdate (Year can be used to link to environmental
 covariates reported in MeanBDdat.csv). MomID: unique identifier for
 female grey seal Year: breeding season (December
 of year-1 to January of year) pup was born (also PupCohort)
 BirthDay: day of birth in
 breeding season (days since Dec 1) MomAge: female age in year pup
 was born MomParity: number of pups or
 pregnancies observed PupSex: 1 is male, 2 is female, 0
 is unknown MomPrevSuccess: 1 is previously
 successful, 0 is previously unsuccessful <strong>MeanBDdat.csv: </strong>Environmental covariates and mean birthdate estimated from random effects of the intrinisc model.  Year: breeding Season (December of year-1 to January of year) MeanBD: estimated mean birthdate in the breeding season (days since Dec 1) from random effects in the intrinsic birthdate model NumSeals: estimated total population supported by breeding colony on Sable Island in previous year AMOdt: AMO in previous year AMOdt3yr: Mean AMO in previous 3 years NAO: NAO in previous year NAO3yr: Mean NAO in previous 3 years SprSST: sea surface temperature from the Fisheries and Oceans Research Vessel Trawl survey in the previous year <strong>WMmodeldat.csv: </strong>Data required to model pup weaning mass as a function of maternal and pup covariates including birthdate. Year: breeding season (December of year-1 to January of year) pup was born (also PupCohort) MomID: unique identifier for female grey seal PupWM: pup weaning mass in kg MomAge: female age in year pup was born MomParity: number of pups or pregnancies observed PupSex: 1 is male, 2 is female, 0 is unknown MomPrevSuccess: 1 is previously successful, 0 is previously unsuccessful BirthDay: day of birth in breeding season (days since Dec 1) MeanBD: estimated mean birthdate from random effects in the intrinsic birthdate model BDAnomaly: day of birth in breeding season (days since Dec 1) less the MeanBD for that year