Interacting Roles of Breeding Geography and Early-Life Settlement in Godwit Migration Timing

Phil F Battley,David S Melville,Rob Schuckard,Adrian C Riegen,Jesse R Conklin,Ian Southey,Murray A Potter,Ángela M Parody-Merino,Thomas Burns,Peter A Langlands

doi:10.3389/fevo.2020.00052

Abstract

While avian migration timing is clearly influenced by both breeding and non-breeding geography, it is challenging to identify the relative and interdependent roles of endogenous programs, early-life experience, and carry-over effects in the development of adult annual schedules. Bar-tailed godwits Limosa lapponica baueri migrate northward from New Zealand towards Asian stopover sites during the boreal spring, with differences in timing between individuals known to relate to their eventual breeding-ground geography in Alaska. Here, we studied the timing of northward migration of individual godwits at three sites spanning 1,100 km of New Zealand’s 1,400-km length. A lack of morphological or genetic structure among sites indicates that the Alaskan breeding population mixes freely across all sites, and larger birds (southern breeders) tended to migrate earlier than smaller birds (northern breeders) at all sites. However, we unexpectedly found that migration timing varied between the sites, with birds from southern New Zealand departing on average 9.4–11 days earlier than birds from more northerly sites, a difference consistent across four years of monitoring. There is no obvious adaptive reason for migration timing differences of this magnitude, and it is likely that geographic variation in timing within New Zealand represents a direct response to latitudinal variation in photoperiod. Using resightings of marked birds, we show that immature godwits explore widely around New Zealand before embarking on their first northward migration at age 2–4 years. Thus, the process by which individual migration dates are established appears to involve: (1) settlement by sub-adult godwits at non-breeding sites, to which they are highly faithful as adults; (2) a consequent response to environmental cues (i.e. photoperiod) that sets the local population’s migration window; and (3) endogenous mechanisms, driven by breeding geography, that establish and maintain the well-documented consistent differences between individuals. This implies that behavioral decisions by young godwits have long-lasting impacts on adult annual-cycle schedules, but the factors guiding non-breeding settlement are currently unknown.

Highlights

In birds, breeding ground geography, or geographic variation in breeding phenology, can be a major determinant of migration timing (e.g., Both, 2010; Conklin et al, 2010; Emmenegger et al, 2014; Briedis et al, 2016; Ouwehand et al, 2016), and associated processes of molt (Conklin and Battley, 2011a) and migratory fueling (Fry et al, 1972; Scheiffarth et al, 2002)
Migration timing can be very consistent within individuals, it is subject to annual variation based on environmental conditions (Duriez et al, 2009; Conklin and Battley, 2011b), and can be modified over time through social information and individual improvement (Mueller et al, 2013; Sergio et al, 2014)
Migration timing in birds is thought to be controlled by an internal circannual clock that is entrained by photoperiod (Gwinner, 1996a)

Summary

Introduction

In birds, breeding ground geography, or geographic variation in breeding phenology, can be a major determinant of migration timing (e.g., Both, 2010; Conklin et al, 2010; Emmenegger et al, 2014; Briedis et al, 2016; Ouwehand et al, 2016), and associated processes of molt (Conklin and Battley, 2011a) and migratory fueling (Fry et al, 1972; Scheiffarth et al, 2002) This likely occurs through a combination of inheritance (genetic and/or parental effects) and response to early-life conditions (Ciarleglio et al, 2010), resulting in individuals showing natal site-fidelity (at least at a regional scale) and having a circannual program that enables timely arrival for breeding. This means that annual-cycle schedules are not a product of the natal site, but can be modified by experience and both biotic and abiotic conditions after the first southbound migration

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Results

Conclusion