DOI: 10.5061/dryad.s1c5m5k
title: Data from: Non-linear effect of sea ice: Spectacled Eider survival declines at both extremes of the ice spectrum

description: Understanding the relationship between environmental factors and vital
 rates is an important step in predicting a species’ response to
 environmental change. Species associated with sea ice are of particular
 concern because sea ice is projected to decrease rapidly in polar
 environments with continued levels of greenhouse gas emissions. The
 relationship between sea ice and the vital rates of the Spectacled Eider,
 a threatened species that breeds in Alaska and Russia and winters in the
 Bering Sea, appears to be complex. While severe ice can impede foraging
 for benthic prey, ice also suppresses wave action and provides a platform
 on which eiders roost, thereby reducing thermoregulation costs. We
 analyzed a 23-year mark-recapture dataset for Spectacled Eiders nesting on
 Kigigak Island in western Alaska, and tested survival models containing
 different ice and weather-related covariates. We found that much of the
 variation in eider survival could be explained by the number of days per
 year with &gt;95% sea ice concentration at the Bering Sea core
 wintering area. Furthermore, the data supported a quadratic relationship
 with sea ice rather than a linear one, indicating that intermediate sea
 ice concentrations were optimal for survival. We then used matrix
 population models to project population trajectories using General
 Circulation Model (GCM) outputs of daily sea ice cover. GCMs projected
 reduced sea ice at the wintering area by year 2100 under a moderated
 emissions scenario (RCP 4.5) and nearly ice-free conditions under an
 unabated emissions scenario (RCP 8.5). Under RCP 4.5, stochastic models
 projected an increase in population size until 2069 coincident with
 moderate ice conditions, followed by a decline in population size as ice
 conditions shifted from intermediate to mostly ice-free. Under RCP 8.5,
 eider abundance increased until 2040 and then decreased to near
 extirpation toward the end of the century as the Bering Sea became
 ice-free.
description: Annual_ice_combProjected sea ice data (number of days with &gt;95% sea ice cover and &lt;15% sea ice cover) for the Spectacled Eider core wintering area. Data from Global Circulation Models were downloaded from archives of CMIP5 GCM outputs (see Table S3 for a list of models).Historical sea ice dataThis file contains observed sea ice concentrations extracted for the core SPEI wintering area from daily gridded (25 km resolution) estimates that were derived from passive microwave satellite imagery using the Bootstrap Algorithm and disseminated by the National Snow and Ice Data Center, Boulder, CO. Data Citations: (1) Comiso, J. C. 2017. Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS, Version 3. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/7Q8HCCWS4I0R. (2) Cavalieri, D. J., C. L. Parkinson, P. Gloersen, and H. J. Zwally. 1996, updated yearly. Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data, Version 1. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/8GQ8LZQVL0VL.spei_winter_ice.xlsxSPEI encounter historiesThe data file contains encounter histories for Spectacled Eiders captured on Kigigak Island, Alaska from 1992-2015.Encounter_hist_SPEI.csv