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

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 toward Asian stopover sites during the boreal spring, with differences in timing between individuals known to relate to their eventual breedingground 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 4 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.

Advancement in long-distance bird migration through individual plasticity in departure

“…While there are clearly fundamental endogenous components to migration, there is increasing evidence for substantial capacity for change within certain timing windows that are presumably set by heritable processes and photoperiod 58 . In New Zealand, there is latitudinal variation in the timing of godwit migration, with birds in the southern part of the non-breeding range (with longer photoperiods) departing significantly earlier than those further north 59 . Across all studied sites, larger (southern-breeding) birds migrated earlier on average than smaller (northern-breeding) birds, implying both external (photoperiodic) control of the population migration timing, and internal (i.e., endogenous program) control of individual schedules.…”

Differential population trends align with migratory connectivity in an endangered shorebird

“…The northward migration of individuals from southeast Australia was on average 2.5–3 weeks ahead of that of individuals from northwest Australia. Intraspecific spatial variation in migration timing has been found in other migratory shorebird species (Alves et al, 2013; Battley et al, 2005; Buehler & Piersma, 2008; Conklin, Battley, Potter, & Fox, 2010; van Bemmelen et al, 2019), including in bar‐tailed godwit Limosa lapponica from New Zealand, where individuals occupying more southerly nonbreeding sites depart earlier than those occupying more northerly nonbreeding sites (Battley et al, 2020). While the specific causes of latitudinal variation in migration timing of far eastern curlew are not known, earlier migration is suggestive of southerly breeding areas because by breeding at more southern latitudes (closer to the equator), early arriving individuals can reduce their exposure to harsher climatic conditions that occur farther north in spring (Smith, Gilchrist, Forbes, Martin, & Allard, 2010).…”

Local adaptation from afar: migratory bird populations diverge in the initiation of reproductive timing while wintering in sympatry

“…Resident juncos (J. h. carolinensis) had elevated T earlier than migrant SCJUs; among migratory SCJUs, the T response was negatively correlated with breeding latitude [18]. Studies on collared flycatchers (Ficedula albicollis) and bar-tailed godwits (Limosa lapponica) provide convincing evidence that breeding latitude influences the timing and duration of life-history stages in the subsequent year [27][28][29].…”