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Background: Small songbirds respond and adapt to various geographical barriers during their annual migration. Global flyways reveal the diverse migration strategies in response to different geographical barriers, among which are high-elevation plateaus. However, few studies have been focused on the largest and highest plateau in the world, the Qinghai–Tibet Plateau (QTP) which poses a significant barrier to migratory passerines. The present study explored the annual migration routes and strategies of a population of Siberian Rubythroats (Calliope calliope) that breed on the north-eastern edge of the QTP. Methods: Over the period from 2021 to 2023, we applied light-level geolocators (13 deployed, seven recollected), archival GPS tags (45 deployed, 17 recollected), and CAnMove multi-sensor loggers (with barometer, accelerometer, thermometer, and light sensor, 20 deployed, six recollected) to adult males from the breeding population of Siberian Rubythroat on the QTP. Here we describe the migratory routes and phenology extracted or inferred from the GPS and multi-sensor logger data, and used a combination of accelerometric and barometric data to describe the elevational migration pattern, flight altitude, and flight duration. All light-level geolocators failed to collect suitable data. Results: Both GPS locations and positions derived from pressure-based inference revealed that during autumn, the migration route detoured from the bee-line between breeding and wintering grounds, leading to a gradual elevational decrease. The spring route was more direct, with more flights over mountainous areas in western China. This different migration route during spring probably reflects a strategy for faster migration, which corresponds with more frequent long nocturnal migration flights and shorter stopovers during spring migration than in autumn. The average flight altitude (1856 ± 781 m above sea level) was correlated with ground elevation but did not differ between the seasons. Conclusions: Our finding indicates strong, season-dependent impact of the Qinghai–Tibet Plateau on shaping passerine migration strategies. We hereby call for more attention to the unexplored central-China flyway to extend our knowledge on the environment-migration interaction among small passerines. [ABSTRACT FROM AUTHOR]

Avian long-distance migration requires refined programming to orchestrate the birds' movements on annual temporal and continental spatial scales. Programming is particularly important as long-distance movements typically anticipate future environmental conditions. Hence, migration has long been of particular interest in chronobiology. Captivity studies using a proxy, the shift to nocturnality during migration seasons (i.e., migratory restlessness), have revealed circannual and circadian regulation, as well as an innate sense of direction. Thanks to rapid development of tracking technology, detailed information from free-flying birds, including annual-cycle data and actograms, now allows relating this mechanistic background to behaviour in the wild. Likewise, genomic approaches begin to unravel the many physiological pathways that contribute to migration. Despite these advances, it is still unclear how migration programmes are integrated with specific environmental conditions experienced during the journey. Such knowledge is imminently important as temporal environments undergo rapid anthropogenic modification. Migratory birds as a group are not dealing well with the changes, yet some species show remarkable adjustments at behavioural and genetic levels. Integrated research programmes and interdisciplinary collaborations are needed to understand the range of responses of migratory birds to environmental change, and more broadly, the functioning of timing programmes under natural conditions. [ABSTRACT FROM AUTHOR]

Seasonal migration is a dynamic natural phenomenon that allows organisms to exploit favourable habitats across the annual cycle. While the morphological, physiological and behavioural changes associated with migratory behaviour are well characterized, the genetic basis of migration and its link to endogenous biological time-keeping pathways are poorly understood. Historically, genome-wide research has focused on genes of large effect, whereas many genes of small effect may work together to regulate complex traits like migratory behaviour. Here, we explicitly relax stringent outlier detection thresholds and, as a result, discover how multiple biological time-keeping genes are important to migratory timing in an iconic raptor species, the American kestrel (Falco sparverius). To validate the role of candidate loci in migratory timing, we genotyped kestrels captured across autumn migration and found significant associations between migratory timing and genetic variation in metabolic and light-input pathway genes that modulate biological clocks (top1, phlpp1, cpne4 and peak1). Further, we demonstrate that migrating individuals originated from a single panmictic source population, suggesting the existence of distinct early and late migratory genotypes (i.e. chronotypes). Overall, our results provide empirical support for the existence of a within-population-level polymorphism in genes underlying migratory timing in a diurnally migrating raptor. [ABSTRACT FROM AUTHOR]

After cross-equatorial wintering, migratory birds reliably return to their natal grounds, but a population of cliff swallows recently switched breeding hemisphere. They inverted their annual cycle and migration directions almost instantaneously. [ABSTRACT FROM AUTHOR]

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 summarize 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 programme 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 programmes. We discuss the current knowledge on how endogenous migration programmes interact with external information across the annual cycle, how components of annual cycle programmes 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. [ABSTRACT FROM AUTHOR]

Migrant species express wide varieties of movement strategies that closely mirror patterns of resource distribution. Resources can vary predictably in space and time (e.g., seasonal peaks of productivity in temperate regions) or can be unpredictable in one or both dimensions. Evolution of migration strategies and the underlying physiological and behavioral mechanisms are therefore diverse, but similarities have been noted. To understand how migrants respond to environmental cues, we focus on species that represent extremes along a continuum between obligate versus facultative migratory behavior and address the physiological mechanisms regulating these movements. Obligate migrants, which travel on highly predictable schedules, generally rely on the annual change in daylength and circannual rhythms to initiate the vernal and, where known, the fall phases of migration. Facultative species may show similar seasonal preparations in cases where resources are temporally predictable, but appear to rely more heavily upon local supplementary cues in the environment to initiate migrations. In general, the physiological response mechanisms to environmental cues that coordinate migratory movements include perception of the environmental cue and transduction to neuroendocrine and endocrine systems. Clearly, there are huge gaps in our knowledge in this area, but published studies of each of the migratory types suggest striking parallels. Based on a comparison of the physiological aspects of the divergent migratory patterns, we emphasize that the migratory types are not completely distinct. Instead, the differences of migration patterns and responsiveness to cues reflect differences in the relative contributions of common physiological mechanisms that underly the control of movements. A more complete understanding of migratory physiology requires continued descriptive studies, particularly in a greater diversity of model systems, in addition to experimental methods that utilize innovative tracking technology as well as behavioral and physiological innovations to draw attention to different levels of organization. Comprehending the physiological mechanisms underlying migratory patterns will be vital for knowing how migrants respond to current environmental cues and anticipating their reactions to future conditions. [ABSTRACT FROM AUTHOR]

Songbirds are generally considered diurnal, although many species show periodic nocturnal activity during migration seasons. From a breedingrange perspective, such migratory species appear to be diurnal because they are observed to nest and feed their young during the day. But are they really exclusively diurnal? The authors tested how a passerine long-distance migrant, the Eurasian reed warbler, schedules movements during the breeding period by tracking birds in 2 experimental situations: 1) Birds experienced simulated nest loss and were monitored during their search for alternative locations, and 2) birds were translocated to reed beds at distances from 2 to 21 km and tracked during homing. The simulated unpredictable events disrupted normal breeding, forced birds to move over relatively long distances, and triggered rapid change in diel activity. In all but 1 case, birds resorted to nocturnality to find their way home and to search for new places to breed. Nocturnality during the breeding season indicates that songbird schedules are far more flexible than previously assumed. The reasons for nocturnal movements are poorly understood. Among the presumed advantages, the reduced predation pressure at night stands out because it is advantageous for movements on local as well as global scales. Predation may be particularly relevant for inhabitants of fragmented habitats, which encounter unfavorable conditions when crossing gaps in their preferred habitat. Therefore, similar selection pressures around the year may have favored the evolution of a general circadian mechanism for switches to nocturnality. Furthermore, the novel finding of homing and dispersal at night may give leads toward understanding the still enigmatic navigational abilities of songbirds. [ABSTRACT FROM AUTHOR]

Timing is crucial in seasonal environments. Passerine birds typically use a combination of physiological mechanisms and environmental cues to ensure that breeding, moult and migration occur without major temporal overlap and under the most favourable conditions. However, late in the breeding season some individuals initiate additional clutches , whereas others initiate moult. Such alternative strategies are thought to reflect trade-offs between reproductive benefits and timely investment in maintenance and survival. The degree of seasonal plasticity differs between species, depending on the mechanisms that govern their annual routine. Migrants are generally under pressure to complete breeding and moult before the autumn departure and often show little plasticity. We studied seasonal plasticity of breeding and moult schedules in the European Stonechat Saxicola rubicola. This species, an obligate short-distance migrant in Central Europe, sometimes initiates late clutches after typically at least two earlier breeding attempts. Based on life-history theory and on observations in captivity, which revealed photoperiodic regulation of breeding and moult, we predicted relatively little seasonal plasticity in Stonechats. We further predicted that reproductive gains of late breeders should be offset by reduced survival. These predictions were tested on long-term field data, using Underhill–Zucchini models to estimate moult. Late breeding occurred in c. 40% of pairs and increased their reproductive success by a third. Both sexes modified moult timing but in different ways. Late breeding females postponed moult approximately until chick independence without compensating for delay by faster moult. Males started moult on time and overlapped it with breeding, associated with markedly slowed plumage change. Sex differences in moult score increased with lay date, but due to their respective modifications, both sexes delayed moult completion. Nonetheless, we could not detect any evidence for survival costs of late breeding. Breeding and moult of European Stonechats appear relatively flexible, despite migratory schedules and photoperiodic programs for seasonal timing. Individuals can modify seasonal behaviour in late summer, presumably depending on their condition, and may profit considerably from extended breeding. [ABSTRACT FROM AUTHOR]

Rigid schedules of long-distance migrants could be among candidate traits for adaptive migratory syndromes. This prediction was tested on stonechats, passerines that differ widely in migratory behavior and seasonal schedules. Stonechats in Europe are short-distance migrants and multiclutched, whereas African residents and Siberian long-distance migrants usually raise single broods. In captivity, all subspecies displayed endogenous cycles of reproductive development and molt. The subspecies differed in time afforded to life cycle stages. Under conducive aviary conditions, African stonechats were multibrooded, whereas Siberian stonechats did not add clutches. This difference in flexibility was exclusively related to the length of breeding windows. Stonechats also differed in premigratory preparations. Postjuvenile molt started early in Siberian stonechats, but in European and African stonechats, depended strongly on hatching date. In contrast, all subspecies shortened molt duration at the same rate when hatched from late broods. Plasticity of Zugunruhe timing was identical in Siberian and European subspecies and nearly compensated for hatching late. The stonechat data suggest a refined understanding of temporal plasticity in long-distance migrants. Overall, plasticity was not reduced, but was differently organized. Apparently rigid migrant schedules were related to short breeding cycles and inflexible molt onset. Short windows for breeding and juvenile development could provide safety measures for timely departure. Once molt was initiated, temporal plasticity of long-distance migrants matched that of less migratory conspecifics. In addition to adjusting endogenous programs, stonechats differed in implementing them in the field. Modifying the conditions under which programs are expressed may be an efficient way to enhance seasonal plasticity. [ABSTRACT FROM AUTHOR]

Suggests the application of an integrative framework for studying bird migration. Importance of understanding the evolution of migratory behavior in given lineages of birds; Recommendation of three component traits of the migratory syndrome for closer phylogenetic analysis.