Data from: Rethinking 'normal': the role of stochasticity in the phenology of a synchronously breeding seabird

1. Phenological changes have been observed in a variety of systems over the past century. There is concern that, as a consequence, ecological interactions are becoming increasingly mismatched in time, with negative consequences for ecological function. 2. Significant spatial heterogeneity (inter-site) and temporal variability (inter-annual) can make it difficult to separate intrinsic, extrinsic, and stochastic drivers of phenological variability. The goal of this study was to understand the timing and variability of breeding phenology of Adélie penguins under fixed environmental conditions, and to use those data to identify a 'null model' appropriate for disentangling the sources of variation in wild populations. 3. Data on clutch initiation were collected from both wild and captive populations of Adélie penguins. Clutch initiation in the captive population was modeled as a function of year, individual, and age to better understand phenological patterns observed in the wild population. 4. Captive populations displayed as much inter-annual variability in breeding phenology as wild populations, suggesting that variability in breeding phenology is the norm and thus may be an unreliable indicator of environmental forcing. The distribution of clutch initiation dates was found to be moderately asymmetric (right skewed) both in the wild and in captivity, consistent with the pattern expected under social facilitation. 5. The role of stochasticity in phenological processes has heretofore been largely ignored. However, these results suggest that inter-annual variability in breeding phenology can arise independent of any environmental or demographic drivers and that synchronous breeding can enhance inherent stochasticity. This complicates efforts to relate phenological variation to environmental variability in the wild. Accordingly, we must be careful to consider random forcing in phenological processes, lest we fit models to data dominated by random noise. This is particularly true for colonial species where breeding synchrony may outweigh each individual's effort to time breeding with optimal environmental conditions. Our study highlights the importance of identifying appropriate null models for studying phenology.AGE_matAges of captive breeding female Adelie penguins (in years) at SeaWorld San Diego from 1992 to 2015. Each column represents a year, each row represents a different individual. Negative values for a given individual/year indicate that this female had not yet been born (to avoid NAs in the matrix). These data are used in the hierarchical model in Youngflesh et al. Journal of Animal Ecology.CID_matClutch initiation dates (arbitrary julian day) for captive female Adelie penguins at Sea World San Diego from 1992 to 2015. Columns represent years, rows represent individuals. These data are used in the hierarchical model in Youngflesh et al. Journal of Animal Ecology.Captive_CIDClutch initiation dates (CID) for female Adelie penguins at Sea World San Diego from 1992 to 2015. Columns are YEAR (year of interest), FEMALE_ID (id number for each female), and J_CID (arbitrary julian day for CID). These data are used to calculate variance and plot CID over time in Youngflesh et al. Journal of Animal Ecology.Wild_CIDClutch initiation dates (CID) for female Adelie penguins at Admiralty Bay, Antarctica (62.2 S, 58.4 W) from 1986 to 2012. Data was collected as part of the U.S. Antarctic Marine Living Resources (AMLR) program at the National Oceanic and Atmospheric Administration (NOAA). Columns are YEAR (year of interest) and J_CID (arbitrary julian day for CID). These data are used to calculate variance and plot CID over time in Youngflesh et al. Journal of Animal Ecology. The AMLR program can be contacted directly concerning these data: jefferson.hinke@noaa.gov.Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: OPP/GSS 1255058; 1341474; 101693