Endogenous Programs and Flexibility in Bird Migration

Abstract

Endogenous programs that regulate annual cycles have been shown for many taxa, including protists, arthropods, fish, mammals and birds. In migration biology, these programs are best known in songbirds. The majority of songbirds rely on a genetic program inherited from their parents that will guide them during their first solo-migration. The phenotypic components of the program are crucial for their individual fitness and survival, and include time components, direction, and distance. This program is constructed to both guide behavior and to regulate flexible responses to the environment at different stages of the annual cycle. The migration program is driven by a circannual rhythm, allowing for, and resetting, carry-over effects. With experience, the migration decisions of individual migrants may be based on information learnt on breeding sites, wintering sites, and en route. At the population level, substantial variation in route choice and timing of migration may be explained by inherited variation of program components, by interactions with environmental and social factors, and by individual learning. In this review we will explore the components of endogenous migration programs and discuss in what ways they can lead to flexibility and variation in migration behavior.

Evolution of chain migration in an aerial insectivorous bird, the common swift Apus apus

“…Åkesson et al 2012). The migration patterns observed are the result of both inherited differences and those that arise between individuals through their distinctive ontogenetic experiences (Åkesson et al 2012Wellbrock et al 2017;Åkesson and Helm 2020).…”

“…Swifts are highly responsive to dynamic foraging conditions due to their highly mobile lifestyle (Hedenström et al 2016), and are therefore the most likely birds not to show the kinds of historical legacies that are likely to shape the evolution of leapfrog patterns so common in other birds (Newton 2008). Swifts are thereby different from the vast majority of obligate and mostly nocturnal migrants that need to rely on evolved less temporally flexible decision-making systems (Åkesson and Helm 2020). Although competition for breeding sites may be a key driver in the evolution of chain migration and body size evolution in swifts as suggested here, we believe that the pattern likely is enforced by the differential circannual timing and habitat choice-related decisions to a dynamic resource gradient during nonbreeding that differ between northern and southern populations of swifts.…”

Migrating Curlews on Schedule: Departure and Arrival Patterns of a Long-Distance Migrant Depend on Time Rather than on Wind Conditions

“…In conclusion, the absence of clear relationships between departure decision and wind/weather parameters suggests that curlews behave conservatively and follow an individual time schedule driven by an internal genetic trigger [14,[51][52] (see discussion on repeatability below). If their individual departure day happens to coincide with headwind conditions, the birds seem to account for this by ying at higher altitudes.…”

“…In a recent review, [52] presented evidence for genetic control of the timing of bird migration. However, the authors also found much individual variation in this genetic programme as a result of interactions with environmental and social factors, as well as due to individual learning.…”

Chasing the sun: When to migrate, when to breed

“…We know much of what we know because of experiments that have exposed birds to fixed day lengths. If birds are held on a constant light to dark ratio of 12L:12D, they will cycle though the phases of the annual cycle, migratory restlessness, gonadal growth and molt, being first stimulated, then suppressed, then stimulated again in a circannual pattern (Åkesson & Helm, 2020). But if they are held at 16L:8D, they will grow their gonads that later collapse and remain collapsed indefinitely because the bird remains in a constant photorefractory state (Dawson, 2015).…”