Flexible reaction norms to environmental variables along the migration route and the significance of stopover duration for total speed of migration in a songbird migrant

Abstract

BackgroundPredicting the consequences of continuing anthropogenic changes in the environment for migratory behaviours such as phenology remains a major challenge. Predictions remain particularly difficult, because our knowledge is based on studies from single-snapshot observations at specific stopover sites along birds’ migration routes. However, a general understanding on how birds react to prevailing environmental conditions, e.g. their ‘phenotypic reaction norm’, throughout the annual cycle and along their entire migration routes is required to fully understand how migratory birds respond to rapid environmental change.ResultsHere, we provide direct evidence that northern wheatears (Oenanthe oenanthe) from a breeding population in Alaska adjusted their probability to resume migration as well as the distance covered per night, i.e. travel speed, to large-scale environmental conditions experienced along their 15,000 km migratory route on both northwards and southwards migrations. These adjustments were found to be flexible in space and time. At the beginning of autumn migration, northern wheatears showed high departure probabilities and high travel speeds at low surface air temperatures, while far away from Alaska both traits decreased with increasing air temperatures. In spring, northern wheatears increasingly exploited flow assistance with season, which is likely a behavioural adjustment to speed up migration by increasing the distance travelled per night. Furthermore, the variation in total stopover duration but not in travel speed had a significant effect on the total speed of migration, indicating the prime importance of total stopover duration in the overall phenology of bird migration.ConclusionNorthern wheatears from Alaska provide evidence that the phenotypic reaction norm to a set of environmental conditions cannot be generalized to universal and persistent behavioural reaction pattern across entire migratory pathways. This highlights the importance of full annual-cycle studies on migratory birds to better understand their response to the environment. Understanding the mechanisms behind phenotypic plasticity during migration is particularly important in the assessment of whether birds can keep pace with the potentially increasing phenological mismatches observed on the breeding grounds.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-017-0203-3) contains supplementary material, which is available to authorized users.

Fuel loads acquired at a stopover site influence the pace of intercontinental migration in a boreal songbird

“…The modal peak in stopover duration at 13 days during both years suggests that there is an optimal duration that most individuals adhered to at this site. Migratory strategies in long-distance migrants are thought to be under tighter endogenous control when compared to short distance-migrants, giving rise to a centralization of phenotypes 58, 62 and this may well be the case for the stopover duration of Grey-cheeked Thrush in northern Colombia. Whether birds are behaving according to a ‘constant stopover duration’ rule of thumb to approach time-minimization 61 or whether there is a mixture of strategies within the population will have to be assessed by future studies considering more stopover sites throughout the species migratory route.…”

“…There are examples in the literature where, like in our study, birds that depart later, do so with higher fuel loads and migrate faster 57, 63 , as well as evidence to the contrary where late departures arrive later to their destination 53, 64 . A recent study found that individuals can modify the pace of migration in response to environmental conditions, and that they can respond differently to the same conditions depending on the stage of their migration 62 . Although we lack the data to tease apart these possibilities, all the other sources of evidence from this study point towards a time-minimization strategy for the Grey-cheeked Thrush.…”

Effects of migration distance and sex on stopover timing and refueling by Wilson's Warblers

“…Finally, migrating Northern Wheatears ( O. o. oenanthe ) closer to their breeding site in Alaska had shorter stopovers and faster flight speeds than migrants closer to their wintering sites in Africa (Schmaljohann et al. ).…”

Geolocators reveal migratory connectivity between wintering and breeding areas of Golden-winged Warblers

“…) because most migratory birds spend most of their time at stationary locations between relatively short periods of migratory movements (Schmaljohann et al. ). Latitudinal estimates are not accurate around each equinox when length of day is relatively equal everywhere (Ekstrom , Lisovski et al.…”