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38 results for “migration strategies”
Data from: Satellite tracking of American Woodcock reveals a gradient of migration strategies
<p>Diversity in behavior is important for migratory birds in adapting to dynamic environmental and habitat conditions and responding to global change. Migratory behavior can be described by a variety of factors that comprise migration strategies. We characterized variation in migration strategies in American Woodcock (<em>Scolopax minor</em>), a migratory gamebird experiencing long-term population decline, using GPS data from approximately 300 individuals tracked throughout eastern North America. We classified woodcock migratory movements using a step-length threshold, and calculated characteristics of migration related to distance, path, and stopping events. We then used principal components analysis (PCA) to ordinate variation in migration characteristics along axes that explained different fundamental aspects of migration, and tested effects of body condition, age-sex class, and starting and ending location on PCA results. The PCA did not show evidence for clustering, suggesting a lack of discrete strategies among groups of individuals; rather, woodcock migration strategies existed along continuous gradients driven most heavily by metrics associated with migration distance and duration, departure timing, and stopping behavior. Body condition did not explain variation in migration strategy during the fall or spring, but during spring adult males and young females differed in some characteristics related to migration distance and duration. Starting and ending latitude and longitude, particularly the northernmost point of migration, explained up to 61% of the variation in any one axis of migration strategy. Our results reveal gradients in migration behavior of woodcock, and this variability should increase the resilience of woodcock to future anthropogenic landscape and climate change.</p>
Sex, body size, and winter weather explain migration strategies in a partial migrant population of American Kestrels (Falco sparverius)
<p>Given increasing evidence that climate change affects the annual cycles of birds, it is important to understand the mechanisms underlying individual migration strategies and population-level patterns in partial migrants. In this study, we found that thermoregulation (body size and winter temperatures) was a key driver of American Kestrel (<em>Falco</em> <em>sparverius</em>) migration decisions. The annual proportion of migrants in the population, however, was not explained by winter weather and may be the result of differential survival. We measured stable hydrogen isotope values (δD) of talon tissues collected from 501 breeding and overwintering birds to distinguish migrant from resident kestrels in a partially migratory population of American Kestrels in southwestern Idaho in 2013–2021. We then evaluated drivers of migration decisions by assessing potential correlates of migration strategies, whether individuals switched migration strategies between years, and whether the proportion of migrants in the population changed over time or was correlated with winter weather. Male kestrels were 1.6 times more likely to migrate than females, and in colder than average winters, smaller birds of both sexes were more likely to migrate than larger birds. Only 27% of 26 recaptured individuals showed evidence of switching their migration strategies on an annual basis. There was no temporal trend in the proportion of migrants in the population, but proportions varied between years. Interestingly, there was no association between winter minimum temperature anomalies and annual migrant proportions in the population, suggesting that differential over-winter survival, or other stochastic processes, may play an important role in population composition. As winters continue to warm, fewer kestrels may migrate and more may remain resident on breeding grounds. However, it is unclear how changes in migration strategies might affect population-level patterns and resilience to climate change.</p>
Data from: Satellite tracking of American Woodcock reveals a gradient of migration strategies
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Sex, body size, and winter weather explain migration strategies in a partial migrant population of American Kestrels (Falco sparverius)
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Data for: Does migration distance influence intra-individual variation in migratory behaviour in a seabird species with diverse migration strategies?
<p>GPS tracking data from adult lesser black-backed gulls (<em>L. fuscus) </em>with 2 – 7 years of tracking data per individual from several colonies in the Netherlands, Belgium and the UK. This data has gone through initial cleaning to remove faulty GPS locations was combined with meta data from colonies to create a single .RDS file. </p> <p>Result for the manuscript "High repeatability in migratory behaviours in a generalist seabird regardless of migration strategy" can be obtained from this data using the R scripts at https://github.com/jbrow247/LBBG_MigrationPlasticity_Pub. </p>
Cross-seasonal effects in the American Woodcock: conditions prior to fall migration relate to migration strategy and its implications for conservation
<p>How post-breeding habitat quality and body composition of migratory birds carry over to influence fall migration strategies and residency merits consideration when creating cross-seasonal conservation plans, especially in breeding populations that are partial migrants. We assessed the influence of post-breeding habitat quality on departure body composition and fall migration patterns in a southern New England breeding population of American Woodcock (<em>Scolopax minor</em>). Woodcock that overwintered near breeding areas (<em>n</em>=5) had less fat upon capture in fall and used lower quality habitat during the fall than birds that eventually departed on migration (<em>n</em>=17). Woodcock that departed earlier were long-distance migrants that had inhabited higher-quality landscapes prior to migration, departed with less fat or similar fat stores, stopped over for shorter periods on migration, and arrived earlier on their more southerly wintering areas. In contrast, woodcock that departed later were short-distance migrants that had inhabited lower quality landscapes prior to migration yet stored similar or more fat upon departure, stopped over for longer periods on migration, and arrived relatively late to their more northerly wintering areas. These differences in migration strategies were evident under the same fall environmental conditions and did not appear related to individuals responding to their own condition as would be expected if they were class condition-based carry-over effects. As such, the southern New England breeding population of woodcock are best categorized as non-facultative partial migrants (i.e., includes residents, short-distance migrants, and long-distance migrants) that demonstrate weak connectivity between life stages; such populations are excellent for the study of the costs and benefits of migration. The stopover and wintering areas used by woodcock in the coastal mid-Atlantic deserve conservation and management attention in order to preserve critical habitat throughout their wintering range.</p>
Migration strategies, performance and annual activity budget in a short-distance migrant, the common starling Sturnus vulgaris
<p><span>Migratory birds typically separate energetically demanding parts of the annual cycle like breeding, moult, and migration with some species engaging in so-called moult-migration. Moult-migration is known to occur in starlings from the northern breeding populations, however, little is known about the dynamics of this phenomenon and the costs and benefits for the involved individuals. Here, using state-of-the-art multi-sensor geolocators, we gathered information about the annual cycles of 10 starlings from two breeding sites in Latvia. We used a novel analytical approach based on atmospheric pressure measurements to reveal that all but one of the tracked individuals migrated to wintering sites in the British Isles. Tracking data exposed two separate migration strategies – (1) departure from the breeding grounds in mid-June soon after chick fledging with long stationary periods at moulting sites approx. 900 km westward (n = 5 of 10); (2) residing in close vicinity of the breeding sites up until the end of October (n = 5 of 10). Accelerometer data revealed significantly higher activity budgets during moult for the individuals exhibiting moult-migration. Furthermore, birds that underwent moult-migration arrived at the breeding sites in the following year on average 10 days later and showed significantly higher activity levels during the pre-breeding period compared to birds without moult-migration. Activity tracking also showed that 67% of all migratory flights were performed during the night, contradicting previous assumptions of starlings being predominantly diurnal migrants. Maximum recorded flight altitudes reached 2500 m.a.s.l. and the longest uninterrupted flight lasted 22.5 hours. Our results highlight energetic trade-offs of moult-migration in starling, but their downstream consequences remain to be tested.</span></p>
Data from: Contrasting long-term trends in juvenile abundance of a widespread cold-water salmonid along a latitudinal gradient: Effects of climate, stream size and migration strategy
<p><span>A changing climate reshapes the range distribution of many organisms, and species with relatively low thermal optima, like many salmonids, are increasingly expected to face local population extinctions at lower latitudes. Understanding where and how fast these changes are happening is of pivotal importance for successful mitigation and conservation efforts.</span></p> <p><span>We used an extensive electrofishing database to explore temporal trends of brown trout juveniles (<em>Salmo</em> <em>trutta</em> L.) in 218 locations from 174 Swedish streams, over the last 30 years (1991–2020). We hypothesized that 1) declines in abundance have occurred predominately in the warmer, southern regions, while increases have occurred in the colder, northern regions, 2) larger stream sizes may partly offset negative effects of climate, and 3) migrating and resident populations are affected differently by a warming climate.</span></p> <p><span>We found that abundance of brown trout juveniles generally declined in warmer regions, especially in smaller streams (≤ 6 m wide), while the abundance increased in colder regions. In larger streams, negative effects of higher temperatures were seemingly buffered, as we found lower rates of decline or even positive trends. The rate of change (i.e. the slopes of the trends in abundance) was more pronounced towards the climate extremes and was on average zero in regions with a normal annual air temperature (average temperature over 30-year period) around 5–6 ºC. Warmer climate had stronger effects on migrating compared to resident populations, suggesting that climate-induced loss of stream connectivity could be an additional factor that hinders recruitment in anadromous populations in a changing climate.</span></p> <p><span>Considering predictions of increasing temperatures and frequency of summer droughts, management of cold-water salmonid populations should focus on conserving and restoring riparian vegetation, wetlands, climate and thermal refugia, and habitat integrity overall. Such measures may, however, not suffice for small streams at lower latitudes, unless hydrological connectivity is maintained.</span></p>
A gradual migratory divide determines not only the direction of migration but also migration strategy of a social migrant bird
<p>Migratory divides separate populations of migratory animals, facilitating the evolution of intraspecific differences in migration strategies. Migration strategies are expected to be different for birds using different flyways and environments, but the knowledge regarding the impact of the flyway on individual migration strategies is scarce. By using satellite tracking and neckband resightings, we reveal the existence and structure of a gradual migratory divide between two European flyway populations of greylag geese <em>Anser anser</em>. Birds breeding at the far end of the Gulf of Bothnia in the Baltic Sea coast use the Western Flyway; those breeding in the Gulf of Finland the Central Flyway and those breeding between these extremes scatter to the two flyways. By using Gaussian process modelling, we show that migration strategies differed between the flyways. The birds using Western Flyway migrated earlier in autumn, performed longer annual migration and made a clear stopover during migration, whereas the birds using Central Flyway flew directly to their wintering sites. The gradual migratory divide that also divides migration strategies provides insights to migratory divides in birds with learned migration. Distinct migration strategies in different flyways provide exciting possibilities to further study the factors driving migration strategies.</p>
Merging computational fluid dynamics and machine learning to reveal animal migration strategies
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Data from: Contrasting long-term trends in juvenile abundance of a widespread cold-water salmonid along a latitudinal gradient: Effects of climate, stream size and migration strategy
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Migration strategies, performance and annual activity budget in a short-distance migrant, the common starling Sturnus vulgaris
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Nocturnal but not diurnal threats shape stopover strategy in a migrating songbird
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A gradual migratory divide determines not only the direction of migration but also migration strategy of a social migrant bird
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Cross-seasonal effects in the American Woodcock: conditions prior to fall migration relate to migration strategy and its implications for conservation
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Evolution of population-specific migration routes in the great reed warbler <em>Acrocephalus arundinaceus</em>: Evidence of a novel spring migration strategy
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Data from: A hidden Markov model to identify and adjust for selection bias: an example involving mixed migration strategies
An important assumption in observational studies is that sampled individuals are representative of some larger study population. Yet, this assumption is often unrealistic. Notable examples include online public-opinion polls, publication biases associated with statistically significant results, and in ecology, telemetry studies with significant habitat-induced probabilities of missed locations. This problem can be overcome by modeling selection probabilities simultaneously with other predictor–response relationships or by weighting observations by inverse selection probabilities. We illustrate the problem and a solution when modeling mixed migration strategies of northern white-tailed deer (Odocoileus virginianus). Captures occur on winter yards where deer migrate in response to changing environmental conditions. Yet, not all deer migrate in all years, and captures during mild years are more likely to target deer that migrate every year (i.e., obligate migrators). Characterizing deer as conditional or obligate migrators is also challenging unless deer are observed for many years and under a variety of winter conditions. We developed a hidden Markov model where the probability of capture depends on each individual's migration strategy (conditional versus obligate migrator), a partially latent variable that depends on winter severity in the year of capture. In a 15-year study, involving 168 white-tailed deer, the estimated probability of migrating for conditional migrators increased nonlinearly with an index of winter severity. We estimated a higher proportion of obligates in the study cohort than in the population, except during a span of 3 years surrounding back-to-back severe winters. These results support the hypothesis that selection biases occur as a result of capturing deer on winter yards, with the magnitude of bias depending on the severity of winter weather. Hidden Markov models offer an attractive framework for addressing selection biases due to their ability to incorporate latent variables and model direct and indirect links between state variables and capture probabilities.
Data from: Migration strategies and annual space-use in an Afro-Palaearctic aerial insectivore – the European nightjar Caprimulgus europaeus
Obligate insectivorous birds breeding in high latitudes travel thousands of kilometres during annual movements to track the local seasonal peaks of food abundance in a continuously fluctuating resource landscape. Avian migrants use an array of strategies when conducting these movements depending on e.g. morphology, life history traits and environmental factors encountered en route. Here we used geolocators to derive data on the annual space-use, temporal pattern and migratory strategies in an Afro-Palaearctic aerial insectivorous bird species – the European nightjar Caprimulgus europaeus. More specifically, we aimed to test a set of hypothesises pertaining to the migration of a population of nightjars breeding in south-eastern Sweden. We found that the birds wintered across the central and western parts of the southern tropical Africa almost entirely outside the currently described wintering range of the species. The nightjars performed a narrow loop migration across Sahara, with spring Sahel stopovers significantly to the west of autumn stops indicative to an adaptive response to winds during migration. To our surprise, the migration speed was faster in the autumn (119 km d− 1) than in the spring (99 km d− 1), possibly due to the prevailing wind regimes over the Sahara. The estimated flight fraction in both autumn (14%) and spring (12%) was almost exactly as the theoretically predicted 1:7 time relationship between flights and stopovers for small birds. The temporal patterns within the annual cycle indicate that individuals follow alternative spatiotemporal schedules that converge towards the breeding season. The positive relationship between the spatially and temporally distant winter departure and breeding arrival suggests that individuals´ temporal fine-tuning to breeding may be constrained, leading to potential negative fitness consequences.
Data from: Habitat-mediated effects of diurnal and seasonal migration strategies on juvenile salmon survival
Behavioral decisions during periods of vulnerability to predation risk, such as migrations during the juvenile life-history stage, may strongly affect the probability of survival. Habitats through which animals migrate are heterogeneous, and risk-reducing behaviors may be more important in some habitats than others. Using biotelemetry data, diurnal and seasonal riverine migration patterns of >3800 juvenile salmon across four species, 12 watersheds, and five years were quantified to evaluate possible effects of migration timing on survival from lower river reaches to coastal waters. In small, clear rivers most salmon avoided migrating during daylight hours, and average survival of fish migrating at night (55%; 95% confidence limits 50–61%) was twice that of fish migrating in daylight (24%; CL 17-31%). Conversely, in the large, heavily silted Fraser River neither preference for nocturnal travel nor effects of diurnal timing on survival were observed. Early ocean survival was also influenced by the timing of ocean entry, but in opposite directions for fish from the Fraser River and smaller rivers. In the Fraser River, average survival for later migrants (69%; CL 60–77%) was nearly twice that of earlier migrants (38%; CL 33–44%), likely related to seasonal increases in river flow. In contrast, in smaller rivers, average survival for earlier migrants (70%; CL 65–74%) was 3-fold greater than survival for later migrants (19%; 95% CL 14–25%). Together these results demonstrate that timing decisions affecting survival of juvenile salmon during their migration are likely mediated by landscape characteristics that plausibly influence the risk of predation.
Complex post-breeding moult strategies in a songbird migrating along the East Asian flyway, the Pallas's Grasshopper Warbler Locustella certhiola
<p>Moult strategies have received relatively little attention in current ornithology, and knowledge concerning the evolution, variability, and extent of moult is sparse in many bird species. This is especially true for East Asian <em>Locustella</em> species where assumptions on moult patterns are based on incomplete information. We provide evidence indicating a complex post-breeding moult strategy and variable moult extent among Pallas's Grasshopper Warbler <em>Locustella certhiola</em>, based on data from six ringing sites situated along its flyway from the breeding grounds to the wintering areas. A detailed study revealed for the first time that in most individuals wing feather moult proceeds from the centre both towards the body and the wing-tip, a moult pattern known as partial divergent moult (which is rare among Palaearctic passerines). In the Russian Far East, where both breeding birds and passage migrants occur, a third of the adult birds were moulting in late summer. In Central Siberia, at the northwestern limit of its distribution, adult individuals commenced their primary moult partly divergently and partly with unknown sequence. During migration in Mongolia, only descendantly (i.e. from the body towards the wing-tip) moulting birds were observed, while further south in Korea, Hong Kong and Thailand the proportion of potential eccentric and divergent feather renewal was not identifiable since the renewed feathers were already fully grown as expected. We found an increase in the mean number of moulted primaries during the progress of the autumn migration. Moderate body mass levels and low fat and muscle scores were observed in moulting adult birds, without any remarkable increase in the later season. According to optimality models, we suggest that an extremely short season of high food abundance in tall grass habitats and a largely overland route allow autumn migration with low fuel loads combined with moult-migration in at least a part of the population. This study highlights the importance of further studying moult strategy as well as stopover behaviour decisions and the trade-offs among migratory birds that are now facing a panoply of anthropogenic threats along their flyways.</p>
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