DOI: 10.5061/dryad.000000010
title: Individual variation in migratory behavior in a sub-arctic partial migrant shorebird

description: Migratory behavior can differ markedly amongst individuals within
 populations or species. Understanding the factors influencing this
 variation is key to understanding how current environmental changes might
 influence migratory propensity and the distribution and abundance of
 migratory species across their range. Here, we investigate variation in
 migratory behavior of the partially migratory Eurasian oystercatcher
 (Haematopus ostralegus) population breeding in Iceland. We use resightings
 of color-ringed adults and stable isotopes to determine whether
 individuals migrate or remain in Iceland during winter and test whether
 individual migratory strategies vary in relation to sex, body size and
 breeding location. We also explore individual consistency in migratory
 strategy and test whether assortative mating with respect to strategy
 occurs in this population. The proportion of migrants and residents varied
 greatly across breeding locations, but not with respect to sex or body
 size. Individuals were consistent in migratory strategy between years and
 there was no evidence of assortative mating by migratory
 strategy. We use these findings to explore factors underlying the
 evolution and maintenance of partial migration at high latitudes.
description: The study took place from the south to the north-west of Iceland
 during the summers 2013-2017 and was expanded to the north-east and east
 in 2017. Incubating oystercatchers were captured on the nest using a
 spring trap, and individually marked with unique color-ring combinations.
 For each individual we measured tarsus + middle toe length to the nearest
 millimeter and collected a sample of 4-5 chest feathers (grown on
 wintering sites during the pre-nuptial moult) for isotopic analysis. For a
 subset of birds, we also collected a sample of blood for molecular sex
 determination. <b>Molecular sex determination </b> DNA was extracted from blood samples using a standard ammonium acetate technique (dx.doi.org/10.17504/protocols.io.knycvfw) and diluted to a working concentration of 10–50 ng/μL. The sex of individuals was then determined using the molecular methods set out in Fridolfsson & Ellegren (1999). <b>Stable isotope analysis</b> Prior to isotopic analysis, feathers were washed in a 2:1 chloroform/methanol solution, left to dry overnight in a fume cupboard and cut into small fragments. Each sample was then weighed (from 0.45 to 0.55 mg) with a microbalance, packed in tin capsules, and loaded into a combustion Costech elemental analyser coupled to a Thermo Scientific Delta XP continuous flow isotopic ratio mass spectrometer and a Conflo III interface. Carbon and nitrogen stable isotope ratios are reported as <i>δ</i>values in parts per thousand(‰) deviations from the international standards Vienna Pee Dee Belemnite (V-PDB) for <i>δ</i><sup>13</sup>C and AIR N<sub>2</sub>for <i>δ</i><sup>15</sup>N. Replicate measurements of the internal laboratory standard (collagen) indicated measurement errors of 0.2‰ and 0.1‰ for <i>δ</i><sup>13</sup>C and <i>δ</i><sup>15</sup>N, respectively.