DOI: 10.5061/dryad.8sf7m0cjn
title: Effects of pair migratory behaviour on breeding phenology and success in a partially migratory shorebird population

description: In migratory systems, variation in individual phenology can arise through
 differences in individual migratory behaviours, and this may be
 particularly apparent in partial migrant systems, where migrant and
 resident individuals are present within the same population. Links between
 breeding phenology and migratory behaviour or success are generally
 investigated at the individual level. However, for breeding phenology in
 particular, the migratory behaviours of each member of the pair may need
 to be considered simultaneously, as breeding phenology will likely be
 constrained by timing of the pair member that arrives last, and carry-over
 effects on breeding success may vary depending on whether pair members
 share the same migratory behaviour or not. We used tracking of marked
 individuals and monitoring of breeding success from a partially migrant
 population of Eurasian oystercatchers (Haematopus ostralegus) breeding in
 Iceland to test whether (a) breeding phenology varied with pair migratory
 behaviour; (b) within-pair consistency in timing of laying differed among
 pair migratory behaviours; and (c) reproductive performance varied with
 pair migratory behaviour, timing of laying and year. We found that annual
 variation in timing of laying differed among pair migratory behaviours,
 with resident pairs being more consistent than migrant and mixed pairs,
 and migrant/mixed pairs breeding earlier than residents in most years but
 later in one (unusually cold) year. Pairs that laid early were more likely
 to replace their clutch after nest loss, had higher productivity and
 higher fledging success, independent of pair migratory behaviour. Our
 study suggests that the links between individual migratory behaviour and
 reproductive success can vary over time and, to a much lesser extent, with
 mate migratory behaviour and can be mediated by differences in laying
 dates. Understanding these cascading effects of pair phenology on breeding
 success is likely to be key to predicting the impact of changing
 environmental conditions on migratory species.
description: <em><strong>Individual tracking of Icelandic
 oystercatchers</strong></em><br><br>Since 2013,
 incubating oystercatchers in the south, west and north-west Iceland have
 been captured, measured and individually marked with coloured leg-rings.
 Adults were caught on the nest using a spring-trap and feather samples
 were collected for stable isotope analysis (see Méndez et al. 2020 for
 details). Through a network of volunteer observers reporting sightings of
 marked individuals throughout the wintering range, the migratory behaviour
 (resident or migrant) of 186 of the 537 marked individuals has been
 identified. For the remaining 351 individuals, migratory behaviour has
 been determined using a discriminant function analysis of stable isotope
 ratios (δ13C and δ15N), after calibration using the isotopic signatures of
 those individuals that were observed during winter within or outside
 Iceland (Méndez et al.,
 2020).<br><br><em><strong>Nest monitoring and
 breeding data collection</strong></em><br><br>From
 mid-April each year (2015-2018), we surveyed study areas every 2-3 days to
 search for returning colour-marked individuals, and to find and monitor
 pairs and nests until hatching or clutch loss. Laying date (the date when
 the first egg was laid) was estimated by back-calculating from hatching
 dates (assuming one egg is laid per day and 28 days of incubation,
 starting when last egg is laid) or incubation stage, using the egg
 flotation method (Liebezeit et al., 2007). For each breeding attempt
 (including replacement clutches following clutch loss), we recorded clutch
 size and the outcome (successful if at least one chick hatched or failed
 if predated, trampled or abandoned). Oystercatchers
 remain in the vicinity of the nest after hatching their chicks and feed
 them throughout the growing period. Chicks were metal-ringed just after
 hatching and individually-marked with colour rings at around two weeks old
 (when tarsus length was sufficient to fit the rings). Families were
 monitored every 3-4 days until all chicks were fledged or lost, allowing
 productivity (number of chicks fledged per pair) and fledging success
 (number of chicks fledged in nests where at least one egg hatched) to be
 recorded.<br><br><em><strong>References</strong></em><br><br>Liebezeit, J. R., Smith, P. A., Lanctot, R. B., Schekkerman, H., Tulp, I., Kendall, S. J., … Zack, S. W. (2007). Assessing the development of shorebird eggs using the flotation method: species-specific and generalized regression models. Condor, 109, 32–47. <br>Méndez, V., Alves, J. A., Þórisson, B., Marca, A., Gunnarsson, T. G., & Gill, J. A. (2020). Individual variation in migratory behaviour in a sub-arctic partial migrant shorebird. Behavioral Ecology. doi: 10.1093/beheco/araa010