Timing avian long-distance migration: from internal clock mechanisms to global flights

Abstract

Please refer to our instructions for authors for full details on manuscript preparation. Please note that this template should act as a guide on content, but doesn't necessarily need to be followed for style and formatting. Our typesetters will set your manuscript into house style after acceptance.*Author for correspondence (Susanne.akesson@biol.lu.se). †Present address: Department of Biology, Lund University, Ecology Building, SE-223 62 Lund, Sweden 2 Summary Migratory birds regularly perform impressive long-distance flights, which are timed relative to the anticipated environmental resources at destination areas that can be several thousand kilometres away. Timely migration requires diverse strategies and adaptations that involve an intricate interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarise the clock mechanisms that enable them to succeed. We examine the following challenges: departing in time for spring and autumn migration, in anticipation of future environmental conditions; using clocks on the move, for example for orientation, navigation, and stopover; strategies of adhering to, or adjusting the time program while fitting their activities into an annual cycle; and keeping pace with a world of rapidly changing environments. We then elaborate these themes by case studies representing long-distance migrating birds with different annual movement patterns and associated adaptations of their circannual programs. We discuss the current knowledge on how endogenous migration programs interact with external information across the annual cycle, how components of annual cycle programs encode topography and range expansions, and how fitness may be affected when mismatches between timing and environmental conditions occur. Lastly, we outline open questions and propose future research directions. Non-technical summaryMigratory birds perform impressive long-distance flights, timed relative to the availability of resources in different geographical areas. To manage this birds use different strategies including an interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarise the clock mechanisms that enable them to meet these challenges. We discuss how range expansions affect components of annual cycle programs, and how mismatches between timing and environment may affect reproductive success.3

Two sides of a coin: ecological and chronobiological perspectives of timing in the wild

“…Ecological studies of migratory birds also echo the findings on chronotypes described above for chronobiology (figure 3). Studies of repeated journeys of individuals in some species have revealed between-individual variation in combination with high individual consistency [16,[93][94][95][96]. Similar findings have been reported for daily behaviours of animals, where chronotype has become an increasingly popular measure [55,[97][98][99][100][101].…”

“…Extensions include tracking of individuals across the lifespan or in the context of conspecific interactions. One group whose timing has been studied in particular detail are migratory birds, which exploit annual resource peaks across the globe [16]. Very much in parallel to findings in chronobiology, ecological studies on these and other groups have demonstrated various degrees of plasticity in timing, for example, in response to weather or between seasons.…”

“…Organisms can substantially alter the ways they experience abiotic cycles, for example, by modifying their micro-environment (e.g. by retreating to shelters or hibernacula, or building nests) or by undertaking migrations [16,19]. High specificity of biotic effects is well established.…”

“…Shifts also occur seasonally, for example, to nocturnality of diurnal birds during the migration season, which can be triggered endogenously by circannual rhythms. They are characterized by distinct changes in the circadian system, for example, in free-running period length [16,72,115].…”

“…In their interactions with the environment, organisms benefit from internal clocks for anticipating conditions that are remote in time and space (e.g. [16]); for tracking time in environments where temporal information is unavailable or misleading (e.g. in caves or hibernacula); and for reference time-consulting to correctly use environmental information (e.g.…”