DOI: 10.5061/dryad.m73n280
title: Data from: Low fitness at low latitudes: wintering in the tropics increases migratory delays and mortality rates in an Arctic breeding shorebird

description: 1. Evolutionary theories of seasonal migration generally assume that the
 costs of longer migrations are balanced by benefits at the non-breeding
 destinations. 2. We tested, and rejected, the null hypothesis of equal
 survival and timing of spring migration for High Arctic breeding
 sanderling Calidris alba using six and eight winter destinations between
 55° N and 25° S, respectively. 3. Annual apparent survival was
 considerably lower for adult birds wintering in tropical West-Africa
 (Mauritania: 0.74 and Ghana: 0.75) than in three European sites (0.84,
 0.84 and 0.87) and in subtropical Namibia (0.85). Moreover, compared with
 adults, second calendar-year sanderlings in the tropics, but not in
 Europe, often refrained from migrating north during the first possible
 breeding season. During northward migration, tropical-wintering
 sanderlings occurred at their final staging site in Iceland 5-15 days
 later than birds wintering further north or south. Namibia-wintering
 sanderlings tracked with solar geolocators only staged in West-Africa
 during southward migration. 4. The low annual survival, the later age of
 first northward migration and the later passage through Iceland during
 northward migration of tropical-wintering sanderlings, in addition to the
 skipping of this area during northward but not southward migration by
 Namibia-wintering sanderlings, all suggest they face issues during the
 late non-breeding season in West-Africa. 5. Migrating sanderlings defy
 long distances but may end up in winter areas with poor fitness prospects.
 We suggest that ecological conditions in tropical West-Africa make the
 fuelling prior to northward departure problematic. 
description: Data on timing of
 northward migration of Sanderlings (Calidris alba) through
 Icelanddata_Sanderling.csvR-script used to analyse timing of northward migration of Sanderlings (Calidris alba) through IcelandR script used to analyse timing of northward migration of Sanderlings through Iceland. Explanations can be found in the script and in the accompanying dataset, as well as in the Methods section in the paper.TimingNorthwardMigration_JAE_V4_20190904.RSanderling Calidris alba bill and wing lengths and body mass at non-breeding areas at various latitudesThe data file contains data of bill and wing lengths and body mass of 2,872 individual Sanderlings (Calidris alba) captured at winter locations between northern Scotland and Namibia. “lat” indicates the average latitude per winter area of capture in decimal degrees, “year” indicates the year of capture. “bill” is the measured bill length in mm, “wing”the wing length in mm and “mass”the body mass in grams. Each row concerns an individual; no individual occurs twice in the dataset. Not always each variable was measured for each individual. Further details can be found in the methods section in the manuscript.Reneerkens_Sanderling_Biometrics.csvSolar geolocation of Sanderlings (Calidris alba), LUX files from Intigeo-W65A9, Migrate Technology Ltd. solar geolocatorsLux files as downloaded from 7 solar geolocation devices (Intigeo-W65A9, Migrate Technology Ltd.) from Sanderlings Calidris alba. See manuscript for details. The data are not to be used for publication without prior permission by the owners.Geolocator tracks LUX.zipIndividual encounter histories of Sanderlings Calidris alba at four winter areas along the East-Atlantic flyway captured as first-year birds or olderThe data file contains individual encounter histories of 2,342 Sanderlings (Calidris alba) that were captured and individually colour-marked in either, England, Portugal, Mauritania or Ghana and were observed between 2007-2013 in their winter area (between 1 October– 31 March; season 1, e.g. 2007.1) and/or during summer (between 1 April - 30 September; season 2, e.g. 2007.2) at least 2 latitudinal degrees north of each individual’s average winter latitude. Encounter histories are binary (0: not observed, 1: observed). The encounter history of an individual starts with the first capture in its winter area, and age (juv= first-year of life, ad= &gt;1old) refers to the age upon first capture. Further details can be found in the methods section in the manuscript.Reneerkens_multievent_Sanderling.csvIndividual encounter histories of Sanderlings Calidris alba at winter areas along the East-Atlantic flywayThe data file contains individual encounter histories of 1,358 adult Sanderlings (Calidris alba) that winter in six different areas, England, France, Portugal, Mauritania, Ghana or Namibia and were observed between 2007-2013 in their winter area (between 1 October– 31 March) during summer (between 1 April -30 September) at least 2 latitudinal degrees north of each individual’s average winter latitude. Encounter histories are binary (0: not observed, 1: observed). The encounter history of an individual starts with the first observation in its wintering region in the year after marking. Further details can be found in the methods section in the manuscript.Reneerkens_Sanderling_seasonal_survival.csvSanderling Calidris alba ages at non-breeding areas at various latitudesThe data file contains data of age (juvenile, i.e. less than 1 year old, or adult, i.e. 1 year old or older) of 2,728 individual Sanderlings (Calidris alba) captured between 1 October and 31 March northern Scotland and Namibia. Each row represents a single individual which id is indicated with a unique “birdID”. Whether the bird was a juvenile (1) or not (0) is indicated by clumn “juv”. The date (“date) and day of year (“doy”) of capture are given too as well as the country in which each individual was captured. Further details can be found in the methods section in the manuscript.age_lat.csvSanderling Calidris alba sex at non-breeding areas at various latitudesThe data file contains data of sex (female or male) of 1,380 individual Sanderlings (Calidris alba). Each row represents a single individual which id is indicated with a unique “birdID”. Whether the bird was a female (1) or male (0) is indicated by column “female”. The day of year (“doy”) and year (“year”) of capture are given too as well as the country (“counry”) in which each individual was captured. Further details can be found in the methods section in the manuscript.sex_lat.csv