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Studies on the migratory behavior of songbirds are important to inform full annual cycle conservation. We remotely tracked the early fall migratory movements of both juvenile and adult Savannah Sparrows (Passerculus sandwichensis) that were tagged on their natal/breeding territories in southwestern Ontario, Canada, where the Motus Wildlife Tracking System has the highest density of automated receivers in North America. Our primary aims were to describe and compare adult and juvenile migratory movements during the early part of migration, compare frequency of detection of juveniles versus adults as a proxy for minimum apparent survival, and describe potential migration routes and overwintering areas. Juveniles initiated migration approximately a month earlier than adults. Both juveniles and adults typically made their first migratory flight in a southwest direction, but some juveniles displayed subsequent exploratory movements that were not in a southwest direction, potentially to collect information for next year's breeding site selection. Detection rates early in migration were similar, but low, for adults and juveniles (34% and 39% respectively), suggesting that juveniles that had survived the fledgling period likely did not experience high mortality during the subsequent 2 months prior to their fall migration. Long-distance detections of 2 adults preliminarily suggest that individuals from this southern Ontario breeding region may travel west of the Appalachian Mountains along the Mississippi flyway during fall migration. Our study aligns with previously reported patterns of age-specific migratory behavior from other Savannah Sparrow populations and contributes to our overall understanding of the migratory ecology of this species.

Individual migration has been regarded as an important factor for the evolution of cooperation in mobile populations. Motivations of migration, however, can be largely divergent: one is highly frustrated by the vicinity of an exploiter or defector, while other enthusiastically searches cooperator mates. Albeit both extreme attitudes are observed in human behavior, but their specific impacts on wellbeing remained unexplored. In this work, we propose an orientation-driven migration approach for mobile individuals in combination with the mentioned migration preferences and study their roles in the cooperation level in a two-dimensional public goods game. We find that cooperation can be greatly promoted when individuals are more inclined to escape away from their defective neighbors. On the contrary, cooperation cannot be effectively maintained when individuals are more motivated to approach their cooperative neighbors. In addition, compared with random migration, movement by leaving defectors can promote cooperation more effectively. By means of theoretical analysis and numerical calculations, we further find that when individuals only choose to escape away from their defective neighbors, the average distance between cooperators and defectors can be enlarged, hence the natural invasion of defection can be efficiently blocked. Our work, thus, provides further insight on how different migration preferences influence the evolution of cooperation in the unified framework of spatially social games.

Full-annual-cycle (FAC) models integrate seasonal demographic and environmental processes to elucidate the factors that limit and regulate animal populations. Unlike traditional, breeding-season-focused models of migratory populations, FAC population models include the effects on population dynamics of events in both the breeding and the nonbreeding season (i.e. winter and migration). Given that migratory birds can spend most of the year away from the breeding grounds and face seasonally specific threats and limitation, FAC models can provide critical and unique insights about their population dynamics. We review existing FAC population model types, including demographic network models, seasonal matrix models, and individual-based models, with examples of each type. We also suggest some approaches new to FAC population modeling—integrated population models and integral projection models—and make recommendations for the development and implementation of these models. Incorporating model components such as density dependence, migratory connectivity (the demographic linkages between breeding and nonbreeding areas), and seasonal interactions can be critical for model realism but can also increase model complexity and development time. Much of the development of FAC population models has been more theoretical than applied. The main limitation to the application of the developed models is availability of empirical data for all annual stages, particularly knowledge of migratory connectivity and density-dependent seasonal survival. As these data become more available, the models outlined here should find additional uses.

Migrating birds make strategic decisions at multiple temporal and spatial scales. They must select flight altitudes, speeds, and orientations in order to maintain preferred directions of movement and to minimize energy expenditure and risk. Spring flights follow a rapid phenology, but how this rapid transit translates to in-flight decisions is not clear. We described flight strategies of nocturnally migrating landbirds using 6 weather surveillance radars during spring (2013–2015) and fall (2013–2014) migratory periods in the eastern United States to investigate seasonal decision-making patterns and how climate change may influence these trends. During spring, we found groundspeed and airspeed of migrants to be significantly higher than those of fall migrants; compensation for wind drift was also significantly greater during spring. Our results indicate that birds make more rapid and precise flights in spring that are only partially explained by meteorological phenomena. Future applications at greater spatial scales will allow direct comparisons of in-flight behaviors with predictions from migration theory.

The gut microbiota is a large and diverse community of microorganisms that provides many beneficial functions to the animal host; however, any change in the host's external or internal environment can affect microbiota composition. Migratory passerines arriving at stopover sites show highly variable microbiotas, which is likely reflective of the widely different habitats and foods utilized by migrants prior to arrival. If the previous environmental conditions led to the observed initial variability, then the microbiotas of birds should become more similar through stopover when migrants are in the same habitat and able to utilize similar resources. During spring 2014, migratory Swainson's Thrush (Catharus ustulatus), Wood Thrush (Hylocichla mustelina), and Gray Catbird (Dumetella carolinensis) were captured at a site in southwest Louisiana, USA, (1) upon arrival after crossing the Gulf of Mexico and (2) ≥1 day later during stopover. Fecal samples were collected and the microbial communities in them were analyzed using next-generation sequencing. The microbiotas of the majority of birds showed distinct shifts in community composition and became more similar during stopover, with birds stopping at the site for longer periods showing more pronounced changes in their microbiotas. These results are consistent with the hypothesis that local food-resource availability heavily influences the microbiotas of passerines; however, it is likely that gut remodulation during stopover after having crossed an ecological barrier also played a role.

The availability of detailed information that encompasses the geographic range of a species, spans a long-term temporal range, and yields individual information (e.g., age and sex), is a principle challenge in ecology. To this end, the North American Bird Banding Laboratory maintains a unique and underutilized dataset that can be used to address core questions of phenological change in migratory birds. We used records from 1966 to 2015 to quantify how the timing of migration has shifted in a long-distance migrant, the Black-throated Blue Warbler (Setophaga caerulescens). Additionally, we examined age and sex differences in the timing of migratory movements. We observed that early spring migrants passed through sites ∼1.1 days earlier per decade and the peak of spring migration also occurred earlier over the 50 yr of this study. Additionally, phenological change was more rapid with increasing latitude during peak spring migratory periods. During fall, the peak of migration stayed consistent across the 50 yr studied, but the migratory season showed protraction overall. During spring, males consistently migrated earlier than females and adults migrated earlier than young individuals. During fall, there was no difference in timing between males and females, but young birds migrated earlier than adults. Additionally, migration proceeded faster in spring compared with the fall. This study reveals differential strategies in migrant timing, across seasons, age groups, and by sex, and shows that en route adjustments across latitude may account for changes in migrant timing. This basic information about such a fundamental ecological process is crucial to our understanding of migration and we must utilize these unique data to appreciate critical shifts at relevant scales of migration.

Predictable seasonal changes in resources are thought to drive the timing of annual animal migrations; however, we currently understand little about which environmental cues or resources are tracked by different migratory bird species across the planet. Understanding which environmental cues or resources birds track in multiple migratory systems is a prerequisite to developing generalizable conservation plans for migratory birds in a changing global environment. Within the New World, climatic differences experienced by Nearctic–Neotropical migratory (NNM; i.e. breed in North America and spend the nonbreeding period in the Neotropics) and Neotropical austral migratory (NAM; i.e. breed and spend the nonbreeding period wholly within South America) bird species suggest that their migratory strategies may be shaped by unique selective pressures. We used data gathered from individuals fitted with light-level geolocators to build species distribution models (SDMs) to test which environmental factors drive the migratory strategies of species in each system. To do so, we evaluated whether temperature, precipitation, and primary productivity (NDVI) were related to the seasonal distributions of an NNM (Eastern Kingbird [Tyrannus tyrannus]) and NAM species (Fork-tailed Flycatcher [T. savana]). Both Eastern Kingbird and Fork-tailed Flycatcher locations were positively correlated with high precipitation during their nonbreeding seasons. Eastern Kingbird locations were positively correlated with both NDVI and temperature during their breeding season and both pre- and post-breeding migrations. Fork-tailed Flycatcher locations were positively correlated with both temperature and precipitation during both migrations, but only temperature during the breeding season. The value of extending the application of geolocator data, such as in SDMs, is underscored by the finding that precipitation was such an important predictor of the nonbreeding distributions of both types of migrants, as it remains unclear how global climate change will affect wet–dry cycles in the tropics.

The phenology of migrating birds is shifting with climate change. For instance, short-distance migrants wintering in temperate regions tend to delay their migration in fall during spells of warmer temperature. However, some species do not show strong shifts, and the factors determining which species will react to temperature changes by delaying their migration are poorly known. In addition, it is not known whether a slower migration or a postponed departure creates the observed delays in fall migration because most studies occur far south of the boreal breeding areas making it difficult to separate those 2 mechanisms. We used 22 yr of data at a northern observatory in eastern North America, at the southern edge of the boreal forest, to examine how 21 short-distance migrants responded to changing temperatures. We investigated if those species responding to temperature share life-history features (i.e. diet, size, total migration distance, breeding habitat, timing of migration). The period of migration in each species was, by far, the most important factor predicting the response of a species to temperature. Eight of the 13 species migrating in October changed their migration onset with temperature (usually by delaying migration by 1–2 days/°C), while the migration timing of none of the 8 species migrating in September was dependent on temperature. Furthermore, the absence of a greater migration delay by birds breeding farther from the study site (i.e. Arctic-breeding birds) suggests the mechanism is a postponed departure rather than a slower migration. We conclude that temperature variations in late fall influence the conditions on the breeding grounds, so that birds still present at that time benefit more from postponing their departure in warm weather.

Migratory birds spend most of their journeys at stopover sites where they rest and refuel. Many migrants are in steep decline, and understanding their behavior within and among migrations is crucial for developing effective conservation strategies across the full annual cycle. One of the most rapidly declining songbirds in North America is the Rusty Blackbird (Euphagus carolinus; 85–95% decline over the past 50 yr), and stopover ecology is a major gap in our knowledge of its annual cycle. We utilized an automated telemetry array in western Lake Erie and the Motus Wildlife Tracking System to track landscape-scale movements, stopover duration, departure behavior, and between-season site fidelity in this species. We found that stopover duration during both fall and spring was nearly 1 mo (mean = 25.5 days)—exceptionally long for a passerine. During spring, birds in both poor condition and high degree of molt had longer stopovers, post-departure flights were relatively long for a songbird, and tailwinds predicted departure in both seasons. Many individuals made landscape-scale (10–35 km) relocations during stopover. Site fidelity was high for a passerine, in terms of both route and stopover site. Taken together, these behaviors describe a migration strategy that largely matches the staging behavior of shorebirds. Lastly, we found that Rusty Blackbirds migrate directly across Lake Erie and migrate primarily at night, which might expose them to mortality from offshore wind development. Collectively, our results indicate that high-quality stopover habitat may be critically important to Rusty Blackbird populations. More broadly, our results highlight the need to expand the scale of stopover studies, and to further explore all aspects of species' annual cycles to understand potential limiting factors on populations.

We investigated movements of a western population of Veeries (Catharus fuscescens) breeding in the Okanagan region of British Columbia, Canada, in 2013–2014 using light-level geolocators. We tracked 9 individuals and incorporated a state-space Kalman filter model approach to estimate movement parameters. During migration, Veeries traversed the Rocky Mountains, Great Plains, Gulf of Mexico, and Caribbean Sea with stopovers generally closer to the shorter orthodromic (great circle) route than a loxodromic (straight line) route between breeding and first wintering grounds, particularly on fall migration. Birds initially settled in the south-central portion of the Amazon basin in Brazil at sites that were 666 ± 299 km apart, suggesting low migratory connectivity. Intra-tropical movements were observed for 8 of 9 (88.9%) birds, with second wintering sites an average of 1,447 ± 472 km to the northwest (initial bearing x̄ = 316 ± 16°). Veeries typically followed a pattern of loop migration at the Gulf of Mexico, with more birds using the Yucatan Peninsula to stop and reorient toward destinations on spring migration (n = 7) vs. fall migration (n = 2). Western Veeries follow a presumed ancestral (eastern) migration route, but this route is also the shortest (great circle) route between breeding and wintering grounds, even though this route was only ~100 km shorter than the straight line route. Eight Veeries (88.9%) underwent a post-breeding, pre-migratory movement up to 628 km (x̄ = 263 ± 152 km) away from breeding territories, possibly to molt. We encourage researchers utilizing light-level geolocators to apply similar state-space modeling approaches to reduce the influence of observers and erroneous location estimates on analysis and interpretation of geolocator data.