Migration route, stopping sites, and non-breeding destinations of adult Black-tailed Godwits breeding in southwest Frysl\xe2n, The Netherlands

Mo A Verhoeven,A H Jelle Loonstra,Christiaan Both,Theunis Piersma,Alice D Mcbride,Nathan R Senner

doi:10.1007/s10336-020-01807-3

Abstract

In this paper, we extend our understanding of the migration of Black-tailed Godwits (Limosa limosa limosa) by describing: (1) the orientation and geographic locations of individual migratory routes and (2) the spatial distribution of godwits across seasons and years. We accomplish this using satellite-tracking data from 36 adult godwits breeding in the 200-ha Haanmeer polder in The Netherlands, from 2015 to 2018. During both southward and northward migration, godwits used a narrow migratory corridor along which most individuals made stops within a network of sites, especially the Bay of Biscay, France and Doñana, Spain. Most sites were used consistently by the same individuals across years. However, sites in Morocco were used during northward migration by 75% of individuals, but not revisited by the same individual across years. After southward migration, a small proportion (15%) of godwits spent the entire non-breeding period north of the Sahara, but most (85%) crossed the Sahara and spent at least part of the non-breeding season among seven coastal sites in West Africa and one site in the Inner Niger Delta. Although site-use patterns varied among individuals, individuals showed high site fidelity and were consistent in the number of sites they used from year to year. The considerable differences in the spatial distribution of individuals that breed within a kilometre of one another raise questions about the causes and consequences of individual migratory differences. We discuss that full annual cycle tracking of juveniles from birth to adulthood is needed to understand the source of these individual differences. Our results on the spatial distribution of godwits throughout their annual cycle lay an important foundation of information that can be used to help conserve this declining species.

Highlights

Seasonal migration, the round-trip movement between a breeding location and one or more non-breeding locations, is a strategy that allows organisms to exploit the fitness benefits of being at a breeding location at certain times of the year, while avoiding the costs of staying there continually (Alerstam et al 2003; Winger et al 2019)
It means that to conserve a population, researchers must first learn about the migratory routes, stopover sites, and non-breeding locations on which the population relies (Piersma and Baker 2000; Webster and Marra 2005)
Our goal in this study is to describe the spatial distribution of Continental Black-tailed Godwits (Limosa limosa limosa, hereafter “godwits”) throughout their annual cycle and to assess whether individuals have consistently different migratory routes

Summary

Introduction

The round-trip movement between a breeding location and one or more non-breeding locations, is a strategy that allows organisms to exploit the fitness benefits of being at a breeding location at certain times of the year, while avoiding the costs of staying there continually (Alerstam et al 2003; Winger et al 2019). For example, the apparent dichotomy between obligate and facultative migrants; in some species, all individuals migrate each year (obligate), while in other species, only some individuals migrate in some years (facultative; Newton 2008) Such differences are thought to be largely context specific, reflecting differences in the ecological circumstances experienced by species, populations, or individuals (Alerstam et al 2003). It means that to conserve a population, researchers must first learn about the migratory routes, stopover sites, and non-breeding locations on which the population relies (Piersma and Baker 2000; Webster and Marra 2005) This knowledge about a population’s distribution is necessary to develop, in turn, an ecological understanding of why the population relies on certain geographic areas but not others, and what effect the conditions at such sites might have on the population’s demography (Alves et al 2013; Rakhimberdiev et al 2018). This ecological understanding can be used to further conservation efforts directly—for example, by assessing which sites are of the highest priority to conserve, what can be done to improve conditions at those sites in the event of degradation, and whether there are similar alternative sites available elsewhere (Reynolds et al 2017; Chan et al 2019a; Rushing et al 2020)

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