Flexible Seasonal Timing and Migratory Behavior: Results from Stonechat Breeding Programs

Abstract

Rigid schedules of long-distance migrants could be among candidate traits for adaptive migratory syndromes. This prediction was tested on stonechats, passerines that differ widely in migratory behavior and seasonal schedules. Stonechats in Europe are short-distance migrants and multiclutched, whereas African residents and Siberian long-distance migrants usually raise single broods. In captivity, all subspecies displayed endogenous cycles of reproductive development and molt. The subspecies differed in time afforded to life cycle stages. Under conducive aviary conditions, African stonechats were multibrooded, whereas Siberian stonechats did not add clutches. This difference in flexibility was exclusively related to the length of breeding windows. Stonechats also differed in premigratory preparations. Postjuvenile molt started early in Siberian stonechats, but in European and African stonechats, depended strongly on hatching date. In contrast, all subspecies shortened molt duration at the same rate when hatched from late broods. Plasticity of Zugunruhe timing was identical in Siberian and European subspecies and nearly compensated for hatching late. The stonechat data suggest a refined understanding of temporal plasticity in long-distance migrants. Overall, plasticity was not reduced, but was differently organized. Apparently rigid migrant schedules were related to short breeding cycles and inflexible molt onset. Short windows for breeding and juvenile development could provide safety measures for timely departure. Once molt was initiated, temporal plasticity of long-distance migrants matched that of less migratory conspecifics. In addition to adjusting endogenous programs, stonechats differed in implementing them in the field. Modifying the conditions under which programs are expressed may be an efficient way to enhance seasonal plasticity.

Adaptations to migration in birds: behavioural strategies, morphology and scaling effects

“…Populations of differing migratory habits appear to respond differently to external cues (e.g. shortened day length), with long-distance migrants breeding at high latitudes showing less flexibility than non-migrants at equatorial latitudes (Helm et al 2005). This could be an insurance adaptation in migrants to get away from deteriorating ecological conditions in time, but it also shows that residents are 'pre-adapted' to develop migration or, alternatively, that they have evolved from migrants and retain certain characteristics from their migratory past.…”

Avian circannual clocks: adaptive significance and possible involvement of energy turnover in their proximate control

“…Zugunruhe in captive birds shows distinct responsiveness to photoperiod, typically in accordance with calendar responses noted in the wild (Gwinner 1968(Gwinner , 1971(Gwinner , 1972a(Gwinner ,b, 1988. Thus, in various species, including sylviid warblers and stonechats, captive birds initiate fall migratory restlessness at similar day length conditions as free-living conspecifics (Gwinner, Helm et al 2005;Helm 2006). Circannual rhythms and programmed responses to photoperiod have been found for many other migration-related traits, including migratory direction Berthold 2001;Mouritsen 2003).…”

“…These differences persist under constant conditions (Gwinner 1971(Gwinner , 1972b. In-depth documentation of moult rhythms also comes from different subspecies of stonechats (Gwinner et al 1983Gwinner 1995;Helm et al 2005). European stonechats depart from their birthplaces at a leisurely pace in late summer and thus have a relatively long time available for concluding their pre-migratory moult.…”

“…In addition to these differences under constant conditions, birds from different latitudes differ in the way they respond to day length cues. Their responses can be characterized by population-specific reaction norms to photoperiod that differ in overall timing as well as plasticity to day length information (Silverin et al 1993;Helm & Gwinner 1999, 2001Gwinner & Helm 2003;Helm et al 2005;Hahn & McDougall-Shackleton 2008).…”

Circadian control of nocturnal songbird migration

“…Species-and population-specific differences in annual rhythmicity, however, depend strongly on differences in photoperiodic reaction norms and on latitudinal photoperiodic variation (Gwinner et al 1989, Helm et al 2005, Noorwijk et al 2006, Coppack 2007, Maggini and Bairlein 2010.…”