Individuality in bird migration: routes and timing

Abstract

The exploration of animal migration has entered a new era with individual-based tracking during multiple years. Here, we investigated repeated migratory journeys of a long-distance migrating bird, the marsh harrier Circus aeruginosus, in order to analyse the variation within and between individuals with respect to routes and timing. We found that there was a stronger individual repeatability in time than in space. Thus, the annual timing of migration varied much less between repeated journeys of the same individual than between different individuals, while there was considerable variation in the routes of the same individual on repeated journeys. The overall contrast in repeatability between time and space was unexpected and may be owing to strong endogenous control of timing, while short-term variation in environmental conditions (weather and habitat) might promote route flexibility. The individual variation in migration routes indicates that the birds navigate mainly by other means than detailed route recapitulation based on landmark recognition.

Individual variability in the migratory path and stopovers of a long-distance pelagic migrant

“…Repeated measures of single individuals can also provide fundamental cues to understanding the causes of variability in migratory behaviour (for example, the relative role of genetic background versus environmental conditions; van Noordwijk et al 2006), and also to unveil the mechanisms underlying long-distance navigation (Alerstam 2006;Guilford et al 2011). By repeatedly tracking individual birds it was possible, for example, to show that (at least some) terrestrial long-distance migrants do not rely on learned visual maps of landscape features for most of the journeys to and from the wintering areas (Vardanis et al 2011).…”

“…Some species are clearly more faithful than others to their wintering sites, routes, stopovers and timings (Sutherland 1998;Catry et al 2004). Most studies carried out so far on fidelity to migratory paths and stopovers have focused on species that migrate mostly over land, such as passerines, storks, geese and raptors (Fox et al 2002;Berthold et al 2004;Catry et al 2004;Alerstam et al 2006;Vardanis et al 2011;Stanley et al 2012). While some studies have analysed spatial consistency during migration in pelagic travellers (Hunter et al 2003;Phillips et al 2005;Broderick et al 2007;Guilford et al 2011), none have attempted to disentangle the fidelity to routes or paths from individual consistency in winter destinations.…”

“…This individual-based approach has been made possible by technological advances in tracking systems, which have allowed researchers to discover the previously unknown migratory routes of several species (e.g. Green et al 2002;Alonso et al 2008;Bairlein et al 2012), and to analyse in detail intraindividual variation in migratory patterns, such as year to year consistency in time and space Guilford et al 2011;Vardanis et al 2011;Stanley et al 2012). Repeated measures of single individuals can also provide fundamental cues to understanding the causes of variability in migratory behaviour (for example, the relative role of genetic background versus environmental conditions; van Noordwijk et al 2006), and also to unveil the mechanisms underlying long-distance navigation (Alerstam 2006;Guilford et al 2011).…”

“…Individuality in behavioural traits is increasingly becoming the focus of studies of animal ecology (Dall et al 2004), including those related to migratory movements (Alerstam 2006;Vardanis et al 2011;Brodersen et al 2012). This individual-based approach has been made possible by technological advances in tracking systems, which have allowed researchers to discover the previously unknown migratory routes of several species (e.g.…”

Climate change alters the optimal wind-dependent flight routes of an avian migrant

“…Such behavioural adjustments, by learning from individual experience or by observing others, can happen relatively quickly [29,30]. It has been previously shown that birds, including soaring raptors, have high phenotypic plasticity of migratory routes [31,32]. However, it remains unclear whether Oriental honey-buzzards have the necessary adaptive potential relative to the speed of climate change.…”