Birds use individually consistent temperature cues to time their migration departure

Abstract

A fundamental issue in migration biology is how birds decide when to start their journey, given that arriving too early or too late in a variable environment reduces individual fitness. Internal circannual regulation and predictable cues such as photoperiod prepare birds for migration, while variable external cues such as temperature and wind are thought to fine-tune departure times; however, this has not been demonstrated at the key point at which an individual animal decides to start migrating. In theory, environmental cues correlated between departure and arrival sites allow informed departure decisions. For 48 satellite-tracked Asian houbara Chlamydotis macqueenii, a medium-distance migrant with climatic connectivity between wintering and breeding areas, each tracked across multiple years, spring departure was under individually consistent temperature conditions, with greater individual repeatability than for photoperiod or wind. Individuals occupied a range of wintering sites latitudinally spanning 1,200 km but departed at lower temperatures from more northerly latitudes. These individual departure decisions produced earlier mean population-level departure and arrival dates in warmer springs. Phenological adjustments were fully compensatory, because individuals arrived on the breeding grounds under similar temperature conditions each year. Individuals’ autumn departure decisions were also repeatable for temperature but less distinct than for spring, likely because of relaxed time constraints on leaving breeding grounds and the use of wind as a supplementary departure cue. We show that individual-level departure decisions informed by local temperatures can preadapt a population to adjust its population-level phenology in response to annual variability in spring temperatures without requiring genetic change in reaction thresholds.

Ontogenetic shifts from social to experiential learning drive avian migration timing

“…Methods to disentangle within-individual variation, such as phenotypically plastic behavioral responses, versus inter-individual variation, such as fixed behavioral traits, offer promising approaches for exploring the ontogeny of behavioral plasticity in heterogeneous populations 32 . For migratory species, flexibility in migration timing contributes to a population’s capacity to adapt to global change 23 , 33 , 34 . Consequently, understanding why individuals within the same population differ in their migratory plasticity and ability to track resources is needed not only to advance basic biological knowledge but also to manage populations in the face of anthropogenic environmental change.…”

Eurasian Stone-curlews Burhinus oedicnemus breeding in Italy show a remarkable inter and intra-population variability of migratory behaviour

“…2021). In a medium-distance steppic migrant, the Asian houbara Chlamydotis macqueenii , the effect of temperature was stronger in spring rather than in autumn, as departure decisions were less repeatable for temperature in autumn rather than in spring (Burnside et al . 2021).…”

“…As the sample size of tracked birds was relatively small, we considered a small set of variables which are known to affect the likelihood of departure (see e.g. Liechti 2006, Conklin & Battley 2011, Dänhardt & Lindström 2001, Grönroos et al 2012, Duijns et al 2017, Burnside et al 2021 to avoid data dredging. We considered the period starting about 25 days before the departure of the first bird, i.e.…”

“…Investigating the migratory strategies of different populations, the geographical range of their movements and the degree of migratory connectivity is an important contribution for understanding the factors affecting populations trends (Webster et al 2002, Taylor & Norris 2010, Finch et al 2017. Furthermore, understanding how migration phenology is influenced by proximate meteorological factors can help to understand how a species would react to the ongoing climate change (Gill et al 2014, Haest et al 2018, Burnside et al 2021, Linek et al 2021.…”

“…The timing of migration was expected to be quite variable,as short-distance migrants usually show a quite flexible migratory schedule (Pulido & Widmer 2005, Newton 2008, Pulido & Berthold 2010, Monti et al 2018b; this variability should be particularly high in autumn, when there is no compelling need to reach the wintering sites (Shamoun Baranes et al 2006, Nilsson et al 2013. Autumn migration was expected to be significantly affected by meteorological variables, such as wind conditions (Liechti 2006, Conklin & Battley 2011, Grönroos et al 2012, Duijns et al 2017, temperature (Burnside at al. 2021), and atmospheric pressure (Dänhardt & Lindström 2001).…”