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Animal Migration
... Beyond these four main approaches to investigate migratory connectivity, other methodologies have occasionally been used to extract information on animal movements between migration stages (see [50] for a more comprehensive overview). These methodologies notably include assignments based on phenotypic variation between source populations (e.g. ...
... Intrinsic advantages and drawbacks of the four main approaches to study migratory connectivity a Major developments that have succeeded in mitigating certain limitations of each approach. For details about some less common approaches to track migrants, see Hobson et al.[50] ...
Migration movements connect breeding and non-breeding bird populations over the year. Such links, referred to as migratory connectivity, have important implications for migratory population dynamics as they dictate the consequences of localised events for the whole population network. This calls for concerted efforts to understand migration processes for large-scale conservation. Over the last 20 years, the toolbox to investigate connectivity patterns has expanded and studies now consider migratory connectivity over a broader range of species and contexts. Here, we summarise recent developments in analysing migratory connectivity, focusing on strategies and challenges to pooling various types of data to both optimise and broaden the scope of connectivity studies. We find that the different approaches used to investigate migratory connectivity still have complementary strengths and weaknesses, whether in terms of cost, spatial and temporal resolution, or challenges in obtaining large sample sizes or connectivity estimates. Certain recent developments offer particularly promising prospects: robust quantitative models for banding data, improved precision of geolocators and accessibility of telemetry tracking systems, and increasingly precise probabilistic assignments based on genomic markers or large-scale isoscapes. In parallel, studies have proposed various ways to combine the information of different datasets, from simply comparing the connectivity patterns they draw to formally integrating their analyses. Such data combinations have proven to be more accurate in estimating connectivity patterns, particularly for integrated approaches that offer promising flexibility. Given the diversity of available tools, future studies would benefit from a rigorous comparative evaluation of the different methodologies to guide data collection to complete migration atlases: where and when should data be collected during the migratory cycle to best describe connectivity patterns? Which data are most favourable to combine, and under what conditions? Are there methods for combining data that are better than others? Can combination methods be improved by adjusting the contribution of the various data in the models? How can we fully integrate connectivity with demographic and environmental data? Data integration shows strong potential to deepen our understanding of migratory connectivity as a dynamic ecological process, especially if the gaps can be bridged between connectivity, population and environmental models.
Supplementary Information
The online version contains supplementary material available at 10.1186/s40462-023-00388-z.
... We explicitly investigate spatial behaviours at the individual level [32]. Even in the era of rapid development of tracking technologies, for small birds tag-size limits high spatial-and temporal-resolution tracking to radio telemetry [36,37] which is particularly valuable in cryptic species. Tracking provides a systematic unbiased tool to document space utilisation of individuals [36,38] to identify habitat attributes. ...
... Technology is fundamental to the understanding of spatial characteristics of key utilisation areas, generally unbiased by type II error, and therefore the limitations of investigating songbirds in urban environments must be implicit. For animals with a body mass of less than 50g, fully independent spatial data is still confined to radio telemetry, although there is much interest in advancing functionality with this technology [37,61]. Apparent sources of interference identified from this study alone include: aviation; reflections from buildings (as described in [36]) and transmitting radio-frequency interference which can lead to abrupt signal masking or indeterminate positions. ...
Individual responses of wild birds to fragmented habitat have rarely been studied, despite large-scale habitat fragmentation and biodiversity loss resulting from widespread urbanisation. We investigated the spatial ecology of the Short-toed Treecreeper Certhia brachydactyla, a tiny, resident, woodland passerine that has recently colonised city parks at the northern extent of its range. High resolution spatiotemporal movements of this obligate tree-living species were determined using radio telemetry within the urbanized matrix of city parks in Copenhagen, Denmark. We identified regular edge crossing behaviour, novel in woodland birds. While low numbers of individuals precluded a comprehensive characterisation of home range for this population, we were able to describe a consistent behaviour which has consequences for our understanding of animal movement in urban ecosystems. We report that treecreepers move freely, and apparently do so regularly, between isolated habitat patches. This behaviour is a possible driver of the range expansion in this species and may contribute to rapid dispersal capabilities in certain avian species, including Short-toed Treecreepers, into northern Europe. Alternatively, these behaviours might be common and/or provide an adaptive advantage for birds utilising matrix habitats, for example within urban ecosystems.
... Whether animals decide to migrate affects ecosystem functioning and has consequences on the individual (e.g., physiological), population (e.g., demography), and species level (e.g., covarying life-history traits) (Cresswell et al. 2011;Hobson et al. 2019). It is, therefore, crucial to better understand variation in migratory behavior. ...
Migration is a life-history trait that shapes individual-by-environment interactions, affecting fitness. Currently, many species are changing their migration strategies, stressing the need to identify and better understand the behavioral correlates of migration. As a partial migrant, the noctule bat, Nyctalus noctula, allows for rare intra-specific investigations of the potential behavioral causes (or consequences) of variation in migration. Here, we combined in-situ behavioral assays with stable isotope analyses to investigate whether spatial and acoustic responses to a roost-like novel environment correlate with migration strategy (local or distant). Given a migrant’s more frequent exposure to novel environments, we predicted migrants would enter a novel environment more quickly and show stronger spatial and acoustic exploration activity. However, individuals of local and distant origin did not differ in acoustic exploration (call activity per unit space), nor, contrasting to several bird studies, in spatial activity (number of chambers visited). Surprisingly, local individuals were more likely than migrants to enter the novel environment. Our findings suggest that small-scale exploration does not vary with migration, potentially because of similar selection pressures across migration strategies on small-scale exploration (e.g., exploration of roosts) as opposed to large-scale. Yet, our findings on the likelihood of entering a novel environment suggest that locals may be more risk-taking. Repeated measures would be necessary to determine if personality differences are underlying these responses. Our unique approach, combining behavioral assays with isotopic geolocation, gave us novel insight into an elusive taxon, highlighting the importance of studying behavioral correlates of migration across various taxa.
... Recent advances in technology have given us a broad understanding of large and global scales of animal movement (Cooke et al., 2004;Nathan et al., 2022). Simultaneous tracking of animals and environmental data allowed the prediction of how animals respond to environmental changes (Courbin et al., 2014;Bestley et al., 2015;Nathan et al., 2022), how animals perceive the landscape (Janmaat et al., 2021), where do animals go while migrating (Hobson et al., 2019), and the requirements, avoidances, and motivations of animal movement (Nathan et al., 2022). However, primates, despite being well-known for many aspects of their behaviour, many species still lack fine-scale assessment of their daily movements, particularly because many species are elusive or rare or because of the inherent challenges of data collection (Kamilar & Beaudrot, 2013;Pinto et al., 2013;Sanz et al., 2022). ...
The presence of other animals, both conspecifics and heterospecifics, is a major driving force for how animals organize themselves in space and time. Although theoretical models are available to explain the role of each in animal movement, fine-scale assessments of daily movement are scarce, particularly for primates. Hence, our goal was to assess whether and how the presence of conspecifics and heterospecifics influence spatiotemporal landscape use in two, wild, howler monkey (Alouatta guariba) groups. We followed the groups for 14 months in a large, continuous forest, during which we recorded their daily path length (DPL), home range, activity budget, feeding, and the presence of other groups (conspecifics) and other species (heterospecifics). The two groups differed in DPL, home range, proportion of fruits ingested, and time devoted to moving and resting. Partial least squares path modelling showed that variation in DPL was explained by the percentage of leaves or fruits ingested and by the presence of conspecifics, but not of heterospecifics. Group differences in several ecological variables emphasise the need to conduct further studies of space use with more groups in the same area to understand the underlying mechanisms of these differences. Moreover, our analysis shows that within-species interactions may be a stronger force in spatiotemporal organisation than interspecies interactions, at least in this folivorous primate. This is relevant from both a theoretical standpoint, and also when considering the consequences of habitat fragmentation and reduction. Deforestation leads to decreased resource availability and increased likelihood of encounters with conspecifics, which ultimately alters the proportion of food items ingested and increases the DPL, disrupting energy balance.
... (Franchini et al. 2017, Hobson et al. 2019. A stable isotope is a nondecaying, naturally occurring intrinsic marker (Hobson 1999, Quinby et al. 2020. ...
The Asian corn borer, Ostrinia furnacalis (Guenée), is a notorious pest of maize that migrates seasonally in Asia. Two migration peaks were found on Beihuang island in the Bohai Strait of China by observing the number of migrants. However, the origins and host plants of the migrants in the two migration periods remain unclear. Here, stable hydrogen (δ2H) and carbon (δ13C) isotope levels were measured to infer the origin and host plants of the O. furnacalis captured on Beihuang island in 2017–2019. δ2H in wings of spring-summer O. furnacalis captured from May to June ranged from −99 to −56‰, while that of autumn migrants from August to September ranged from −127 to −81‰. Based on the linear relationship between δ2H in the wing of migrants (δ2Hw) and δ2H in precipitation (δ2Hp), the spring-summer O. furnacalis likely originated from the summer maize area in the Huang-Huai-Hai Plain in China. In contrast, the autumn migrants came from the northern spring maize area in Liaoning, Jilin and Inner Mongolia. Based on δ13C, the spring-summer migrants fed on both C3 plants such as wheat (47.76%) and C4 weeds or belonged to the over winter individuals in maize field (52.24%), while the autumn migrants mainly fed on maize (C4, 91.21%). The results point to a northward migration in spring-summer and southward migration in autumn of O. furnacalis. Our study gives an important knowledge for improving the forecasting and management level of this pest.
... Migratory animals have evolved numerous morphometric, physiological, and behavioral adaptations to successfully achieve seasonal habitat movements, often involving impressive transcontinental passages (Dingle, 2014;Hobson et al., 2019). Independent of biome, vertebrate, and invertebrate adult migrants using terrestrial and aquatic habitats fuel their migratory journeys using energy-dense lipids, mainly triacyclglycerols (storage lipids), which are acquired directly from diet or are synthesized de novo, for example, from carbohydrates (McWilliams et al., 2004). ...
Introduction
Among long-distance migratory insects, the monarch butterfly (Danaus plexippus) is one of the most iconic, whose journey is fueled by nectar from flowering plants along the migratory route which may involve up to 3,500 km. Understanding how and where monarchs obtain their dietary resources to fuel migratory flight and ensure overwintering stores would provide new insights into the migratory strategy of this species and subsequently help focus conservation efforts.
Methods
This pilot study was designed as a first attempt to assess the composition, dynamics, and isotopic (δ²H, δ¹³C) composition of essential and non-essential fatty acids (FA) acquired or manufactured de novo from larval host milkweed (Asclepias spp.) by monarch butterflies and from adult emergence to overwintering.
Results
Data from controlled laboratory isotopic tracer tests suggested that adult monarchs convert their dietary energy mainly into 16:0 and 18:1 fatty acids and store them as neutral lipids in their abdomen. FA isotopic composition reflects not only dietary sources but also subsequent isotopic fractionation from metabolism. On the other hand, δ²H values of essential omega-3 fatty acid alpha-linolenic acid (ALA) correlated with δ²HWing, as markers of an individual’s geographic origin and indicated the importance of larval diet. Additionally, in wild-type females, high isotopic fractionation in δ¹³CALA between neutral and polar lipids might indicate increased bioconversion activity during gravidity. Finally, δ²HLIN showed positive H isotope fractionation from larval dietary sources, indicating that catabolic processes were involved in their manufacture. Furthermore, δ²HLIN showed a negative correlation with δ²HWing values, which could potentially be useful when investigating individual life-history traits, such as migratory catabolic efforts or periods of fasting.
Discussion
This interpretation was supported by significant larger variations in δ²HLIN and δ²HLIN overwintering monarchs compared to other FA. Altogether, our results provide the first evidence that the H isotopic analysis of individual fatty acids in migrating and overwintering monarchs can be used to infer the nutritional history of individuals including the provenance of nectaring sites used to fuel key life history events.
... From a spatial point of view, isoscapes are just maps, or series of maps at different times; from a formal point of view, isoscapes are ordinary real scalar fields, the relevant random variable being the actual isotope ratio, depicted as a function of space and, possibly, time. Isoscapes are an important tool in ecological modeling, since they can highlight spatial patterns in complex bio-and geochemical interactions, from the field of hydrology [55] to plant physiology [56,57] to animal migration [58] and to forensic science [59], naming only a few. In particular, we focus on the spatial distribution and temporal evolution of three stable isotopes from the fields of hydrology and plant physiology. ...
We developed a novel approach in the field of spatiotemporal modeling, based on the spatialisation of time, the Timescape algorithm. It is especially aimed at sparsely distributed datasets in ecological research, whose spatial and temporal variability is strongly entangled. The algorithm is based on the definition of a spatiotemporal distance that incorporates a causality constraint and that is capable of accommodating the seasonal behavior of the modeled variable as well. The actual modeling is conducted exploiting any established spatial interpolation technique, substituting the ordinary spatial distance with our Timescape distance, thus sorting, from the same input set of observations, those causally related to each estimated value at a given site and time. The notion of causality is expressed topologically and it has to be tuned for each particular case. The Timescape algorithm originates from the field of stable isotopes spatial modeling (isoscapes), but in principle it can be used to model any real scalar random field distribution.
... Stable isotope analyses of inert tissues have been widely used to assess present-day migratory connectivity patterns in various animals [24]. Feathers, hairs or claws retain the isotopic values of the geographical region where they grew and can, therefore, be traced back to those regions by relating them to known spatial variation in isotopic values or isoscapes [25]. ...
Temporal variation in the connectivity of populations of migratory animals has not been widely documented, despite having important repercussions for population ecology and conservation. Because the long-distance movements of migratory animals link ecologically distinct and geographically distant areas of the world, changes in the abundance and migratory patterns of species may reflect differential drivers of demographic trends acting over various spatial scales. Using stable hydrogen isotope analyses ( δ ² H) of feathers from historical museum specimens and contemporary samples obtained in the field, we provide evidence for an approximately 600 km northward shift over 45 years in the breeding origin of a species of songbird of major conservation concern (blackpoll warbler, Setophaga striata ) wintering in the foothills of the eastern Andes of Colombia. Our finding mirrors predictions of range shifts for boreal-breeding species under warming climate scenarios and habitat loss in the temperate zone, and underscores likely drivers of widespread declines in populations of migratory birds. Our work also highlights the value of natural history collections to document the effects of global change on biodiversity.
... Tel.: 416-884-1090Email: lanparas@ uwo.ca (e.g. Hobson & Wassenaar, 1997;Bearhop et al., 2003;Hobson et al., 2019). ...
Stable isotope measurements of insect tissues can be used to determine origin and migratory patterns. The isotopic links between diet and stored lipids in laboratory reared true armyworm moths (Mythimna unipuncta, Haw.) were investigated using δ¹³C and δ²H measurements. Newly emerged moths were fed synthetic nectars, consisting of different carbohydrate and water sources that were isotopically distinct from those in the larval diet. After 4 days of feeding, insects were sacrificed, and fat‐body lipids were extracted for isotopic analysis. When held on a constant nectar source, adult diet contributed ∼87% of the C and 44% H of lipids. For H, 27% and ∼ 17% of lipid was derived from carbohydrates and water, respectively, with the remainder presumably from the larval stage. When the isotopic composition of the nectar source was switched there was rapid and exponential temporal change in lipid isotopic profiles. The relevance of our findings to tracing origins of stored lipids in migrant Lepidoptera is discussed.
... Numerous methods from multiple disciplines have been employed to investigate migration 25 . By far the most widely used approach is to track migrant animals with passive extrinsic markers, but this is mainly suitable for large animals rather than for small insects 77 . Radar is one of the promising tools for monitoring the migration behaviors of small insects and large animals 14,78,79 . ...
BACKGROUND
The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), is a notorious pest of cruciferous plants. In temperate areas, annual populations of DBM originate from adult migrants. However, the source populations and migration trajectories of immigrants remain unclear. Here, we investigated migration trajectories of DBM in China using genome‐wide single nucleotide polymorphisms (SNPs) genotyped using double‐digest RAD (ddRAD) sequencing. We first analyzed patterns of spatial and temporal genetic structure among southern source and northern recipient populations, then inferred migration trajectories into northern regions using discriminant analysis of principal components (DAPC), assignment tests, and spatial kinship patterns.
RESULTS
Temporal genetic differentiation among populations was low, indicating that sources of recipient populations and migration trajectories are stable. Spatial genetic structure indicated three genetic clusters in the southern source populations. Assignment tests linked northern populations to the Sichuan cluster, and central–eastern populations to the southern and Yunnan clusters, indicating that Sichuan populations are sources of northern immigrants and southern and Yunnan populations are sources of central–eastern populations. First‐order (full‐sib) and second‐order (half‐sib) kin pairs were always found within populations, but ~ 35–40% of third‐order (cousin) pairs were found in different populations. Closely related individuals in different populations were found at distances of 900–1500 km in ~ 35–40% of cases, while some were separated by > 2000 km.
CONCLUSION
This study unravels seasonal migration patterns in the DBM. We demonstrate how careful sampling and population genomic analyses can be combined to help understand cryptic migration patterns in insects. © 2020 Society of Chemical Industry
The degree to which individuals within populations vary in whether, how far and what direction they disperse is central in order to understand many foundational questions in ecological entomology, including factors determining population and invasion dynamics, species' ability to respond to climate change or when designing conservation strategies for threatened species.
This study combined stable hydrogen isotope analysis of nymphal and adult wing chitin with population genetic analysis of the cytochrome c oxidase subunit I (COI) gene to understand long‐distance movements of African edible bush cricket ( Ruspolia differens ) in East Africa.
Results revealed that at most 77% of non‐swarming adults and 85% swarming adults originated locally, that is, within a range of a few hundred kilometres. In contrast, non‐local adults captured in Uganda likely originated from Ethiopia, Kenya or South Sudan based on the H isotopic evidence. Genetic analysis revealed 150 COI haplotypes with no significant differentiation among geographic source regions and no evidence of genetic isolation by movement distance.
The observed frequent long‐distance movements, together with the historical records, which indicate that the swarm movements can be irregular in their direction, suggest that the movements represent nomadism rather than regular long‐distance migration. Our results thus provide a valuable case study of what characterizes nomadic movements in insects, which have been one of the outstanding open questions in movement ecology of animals.
Mapping stable isotope gradients (isoscapes) has become a powerful tool to understand and forecast the status
and variability of marine ecosystems at different levels of ecological organization. To differentiate five marine
areas from the Southwest Atlantic Ocean towards oceanic and polar waters, a key foraging area for many marine
consumers, we built isoscapes at different spatial scales using carbon (δ13C) and nitrogen (δ15N) isotope values of
phytoplankton, zooplankton and particulate organic matter in sediment. We analyzed the isotopic variability
between marine areas in relation with oceanographic parameters (e.g. temperature, salinity) and geographical
sampling site data (e.g. latitude, longitude). We collected samples during 6 oceanographic surveys conducted in
spring and autumn between 2014 and 2019 at the Beagle Channel, the Atlantic coast of Tierra del Fuego and
Burdwood Bank. We included also published isotopic data of zooplankton from two other oceanic areas (the
Polar Frontal Zone and Polar Antarctic Peninsula waters) to construct large-scale isoscapes. We found that the
marine areas analyzed have substantially different δ13C and δ15N baselines; some differences exist between
spring and autumn but the general pattern of isotopic variability remains similar. Combining different biological
components and spatial scale analysis, isotopic variability was found to be related to variables such as seawater
temperature, depth, chlorophyll and nutrients. The generated data will enhance the efficacy of isoscapes in longterm
monitoring initiatives that documents alterations in attributes and features across marine expanses. This is
particularly pertinent to areas under legal protection, such as the oceanic Marine Protected Areas (MPAs)
established in Argentine waters
Monitoring of arthropods focuses typically on changes in population and range size over time. Yet, there are a myriad of other aspects that could and should be monitored under the ongoing global and local environmental change. Stable isotope analysis, widely employed in short-term ecological studies, has potential in long-term monitoring of arthropods. Here we discuss the use of stable isotopes in monitoring terrestrial arthropods, provide some empirical examples of the use of bulk tissue samples in stable isotope analysis, and outline future directions in using compound-specific stable isotope analysis in monitoring. We performed a literature search for 2012–2021 to see if stable isotopes have been specifically used in monitoring of terrestrial arthropods. The literature shows that stable isotopes have been successfully used to reveal ecological phenomena (dispersal, trophic interactions, resource use) that would have been difficult or impossible to detect by other means. Yet, stable isotopes have been underused in arthropod monitoring programs, but the growing number of basic studies on stable isotope ecology and methodology provides crucial basis needed for developing monitoring programs. Stable isotopes provide technically, economically and ecologically feasible addition to the traditional monitoring methods of terrestrial arthropods.
In the eastern Pacific Ocean, hawksbill sea turtles (Eretmochelys imbricata) are adapted to use coastal habitats and ecosystems uncharacteristic of most other sea turtles. Once considered extirpated from this region, hawksbills had sought refuge in estuaries, nesting on muddy banks among the tangles of mangrove roots. This population is at high risk of bycatch during fishing efforts in the estuaries (blast fishing) and adjacent coastal rocky reefs (gillnets), and is further impacted by habitat degradation from coastal development and climate change. The conservation and population recovery of hawksbills in this region is highly dependent on management actions (e.g., nest relocation, habitat protection, bycatch mitigation), and a better understanding of how hawksbills use and move between distinct habitats will help prioritize conservation efforts. To identify multi-year habitat use and movement patterns, we used stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope analysis of skin and bone growth layers to recreate movements between two isotopically distinct habitats, a nearshore rocky reef and a mangrove estuary, the latter distinguishable by low δ¹³C and δ¹⁵N values characteristic of a mangrove-based foodweb. We applied skeletochronology with sequential δ¹³C and δ¹⁵N analysis of annual growth layers, “skeleto+iso,” to a dataset of 70 hawksbill humeri collected from coastal El Salvador. The results revealed at least two unique habitat-use patterns. All turtles, regardless of stranding location, spent time outside of the mangrove estuaries during their early juvenile years (< 35 cm curved carapace length, CCL, age 0–5), showing that an oceanic juvenile stage is likely for this population. Juveniles ca. > 35 cm then began to recruit to nearshore areas, but showed divergent habitat-use as some of turtles occupied the coastal rocky reefs, while others settled into the mangrove estuaries. For turtles recruiting to the estuaries, settlement age and size ranged from 3 to 13 years and 35–65 cm CCL. For the adult turtles, age-at-sexual-maturity ranged from 16 to 26 years, and the maximum reproductive longevity observed was 33 years. The skeleto+iso also showed that adult hawksbills have long-term habitat fidelity, and the results demonstrate the importance of both mangrove estuary and nearshore rocky reefs to the conservation of hawksbills in the eastern Pacific.
Changes in phenology and distribution are being widely reported for many migratory species in response to shifting environmental conditions. Understanding these changes and the situations in which they occur can be aided by understanding consistent individual differences in phenology and distribution and the situations in which consistency varies in strength or detectability.
Studies tracking the same individuals over consecutive years are increasingly reporting migratory timings to be a repeatable trait, suggesting that flexible individual responses to environmental conditions may contribute little to population‐level changes in phenology and distribution. However, how this varies across species and sexes, across the annual cycle and in relation to study (tracking method, study design) and/or ecosystem characteristics is not yet clear.
Here, we take advantage of the growing number of publications in movement ecology to perform a phylogenetic multilevel meta‐analysis of repeatability estimates for avian migratory timings to investigate these questions. Of 2,433 reviewed studies, 54 contained suitable information for meta‐analysis, resulting in 177 effect sizes from 47 species.
Individual repeatability of avian migratory timings averaged 0.414 (95% confidence interval: 0.3–0.5) across landbirds, waterbirds and seabirds, suggesting consistent individual differences in migratory timings is a common feature of migratory systems. Timing of departure from the non‐breeding grounds was more repeatable than timings of arrival at or departure from breeding grounds, suggesting that conditions encountered on migratory journeys and outcome of breeding attempts can influence individual variation.
Population‐level shifts in phenology could arise through individual timings changing with environmental conditions and/or through shifts in the numbers of individuals with different timings. Our findings suggest that, in addition to identifying the conditions associated with individual variation in phenology, exploring the causes of between‐individual variation will be key in predicting future rates and directions of changes in migratory timings. We therefore encourage researchers to report the within‐ and between‐ individual variance components underpinning the reported repeatability estimates to aid interpretation of migration behaviour. In addition, the lack of studies in the tropics means that levels of repeatability in less strongly seasonal environments are not yet clear.
Migration encompasses a persistent, directed, often seasonal, redistribution of individuals beyond or between their home ranges, but is often incorrectly used to describe a wide range of other movement behaviours in several animal groups, including birds. Flamingos (Phoenicopteridae) are birds that are frequently, but not universally, classified as migratory. Nevertheless, movements performed by flamingos do not seem to match the scientific and ecological concept of migration sensu stricto. We discuss different bird movements and their correct typology. Based on available information concerning flamingo movements, we recommend that they be considered irruptive or nomadic species, and that correct classification is important to avoid wrongly interpreting these birds' ecology in the media and scientific works. Despite that they are not truly migratory, conservation action plans for flamingos still need to take into account their movement behaviour.
Understanding seasonal mobility, population connectivity, and site fidelity is critical for managing and preserving migratory species. We investigated the potential of coupling strontium (87Sr/86Sr) and hydrogen (δ2H) isotopes in feathers for quantitatively constraining natal origin for juvenile migratory predatory birds (raptors) using a probabilistic framework. We first calibrated single‐isotope models that predict spatial isotope variability in raptor feathers (called isoscapes) by analyzing and compiling isotope data for juvenile birds with known origins in North America and comparing their values to existing isotopic baselines in precipitation (for δ2H) and bioavailable strontium (for 87Sr/86Sr). We then compared the potential of hydrogen and strontium isotopes for refining geographic assignments either independently or combined. While yielding very different probability maps, hydrogen and strontium isotopes performed equally well at constraining regions of natal origin. However, thanks to the complementarity of these isotopes, dual δ2H and 87Sr/86Sr assignments increased predictive precision by an order of magnitude compared to either isotope alone. Lastly, we used the models to predict natal origin for juveniles with unknown origins that were sampled in southwestern Idaho, USA, during their autumn migration. The precision of geographic assignments for birds with unknown origins varied. Nevertheless, dual‐isotope assignments clearly distinguished individuals born outside of southwestern Idaho, and overall, predicted geographic assignments matched breeding ranges for the study species. Quantitative dual‐isotope geographic assignments enhance our ability to predict natal range of migratory raptors and complement other methods for monitoring movement and population connectivity. Combining isotopic data from feathers with other intrinsic geochemical and genetic data, as well as extrinsic markers, such as transmitters or bands, and niche‐modeling approaches will further refine key nesting areas for migratory birds.
Available energy stores determine stopover length, migration speed and likely survival in migrating birds. We measured energy stores by estimating fuel load in 11 species of Neotropical migrant songbirds in the Darién of Colombia over five years. We evaluated 1) whether individuals flying further from breeding origin arrived with smaller fuel loads, 2) if the ENSO (El Niño-Southern Oscillation) cycle affected fuel load and 3) if species known to migrate mostly overwater arrived with less fuel relative to those migrating overland. Breeding origin, inferred from feather δ2H values, only had a significant positive effect on fuel load in Swainson’s Thrush (Catharus ustulatus). Veery (Catharus fuscescens) and Swainson’s thrush had higher and lower fuel loads, respectively, in El Niño years. Multi-species mixed-effects models revealed support for larger fuel loads in larger-bodied species and in species taking overwater routes, contrary to our prediction. Across species, we found no support for common effects of breeding origin or ENSO on fuel loads, in contrast to community-wide effects of migration route and body-size. In general, the variables considered here explained little of the variance in fuel loads, suggesting that inter-individual differences likely have a greater impact than broad-scale factors in our study system.
Variations in stable hydrogen and oxygen isotope ratios in terrestrial animal tissues are used to reconstruct origin and movement. An underlying assumption of these applications is that tissues grown at the same site share a similar isotopic signal, representative of the location of their origin. However, large variations in tissue isotopic compositions often exist even among conspecific individuals within local populations, which complicates origin and migration inferences. Field-data and correlation analyses have provided hints about the underlying mechanisms of within-site among-individual isotopic variance, but a theory explaining the causes and magnitude of such variance has not been established. Here we develop a mechanistic modeling framework that provides explicit predictions of the magnitude, patterns, and drivers of isotopic variation among individuals living in a common but environmentally heterogeneous habitat. The model toolbox includes isoscape models of environmental isotopic variability, an agent-based model of behavior and movement, and a physiology-biochemistry model of isotopic incorporation into tissues. We compare model predictions against observed variation in hatch-year individuals of the songbird Spotted Towhee (Pipilo maculatus) in Red Butte Canyon, Utah, and evaluate the ability of the model to reproduce this variation under different sets of assumptions. Only models that account for environmental isotopic variability predict a similar magnitude of isotopic variation as observed. Within the modeling framework, behavioral rules and properties govern how animals nesting in different locations acquire resources from different habitats, and birds nesting in or near riparian habitat preferentially access isotopically lighter resources than those associated with the meadow and slope habitats, which results in more negative body water and tissue isotope values. Riparian nesters also have faster body water turnover and acquire more water from drinking (vs. from food), which exerts a secondary influence on their isotope ratios. Thus, the model predicts that local among-individual isotopic variance is linked first to isotopic heterogeneity in the local habitat, and second to how animals sample this habitat during foraging. Model predictions provide insight into the fundamental mechanisms of small-scale isotopic variance and can be used to predict the utility of isotope-based methods for specific groups or environments in ecological and forensic research.
The illegal pet trade facilitates the global dispersal of invasive alien species (IAS), providing opportunities for new pests to establish in novel recipient environments. Despite the increasing threat of IAS to the environment and economy, biosecurity efforts often lack suitable, scientifically-based methods to make effective management decisions, such as identifying an established IAS population from a single incursion event. We present a proof-of-concept for a new application of a stable isotope technique to identify wild and captive histories of an invasive pet species. Twelve red-eared slider turtles ( Trachemys scripta elegans ) from historic Australian incursions with putative wild, captive and unknown origins were analysed to: (1) present best-practice methods for stable isotope sampling of T. s. elegans incursions; (2) effectively discriminate between wild and captive groups using stable isotope ratios; and (3) present a framework to expand the methodology for use on other IAS species. A sampling method was developed to obtain carbon (δ ¹³ C) and nitrogen (δ ¹⁵ N) stable isotope ratios from the keratin layer of the carapace (shells), which are predominantly influenced by dietary material and trophic level respectively. Both δ ¹³ C and δ ¹⁵ N exhibited the potential to distinguish between the wild and captive origins of the samples. Power simulations demonstrated that isotope ratios were consistent across the carapace and a minimum of eight individuals were required to effectively discriminate wild and captive groups, reducing overall sampling costs. Statistical classification effectively separated captive and wild groups by δ ¹⁵ N (captive: δ ¹⁵ N‰ ≥ 9.7‰, minimum of 96% accuracy). This study outlines a practical and accessible method for detecting IAS incursions, to potentially provide biosecurity staff and decision-makers with the tools to quickly identify and manage future IAS incursions.
Aim
Understanding connectivity between avian breeding and non‐breeding areas is essential to understand processes affecting threatened migrants throughout their annual cycle. We attempted to establish migratory connectivity and flyway structure of the IUCN vulnerable Swan Geese (Anser cygnoides ) by combining citizen science species' distribution models (SDMs) and feather stable isotope analysis.
Locations
Russia, Mongolia and China.
Methods
We established migratory origins and movements of 46 Swan Geese from five wintering locations by integrating citizen science SDMs and feather stable hydrogen isotope (δ²H) measurements by linking feathers to precipitation isoscapes in a Bayesian probability framework.
Results
We determined multiple summering origins among Swan Geese from the most important wintering location, Poyang Lake, Jiangxi Province, China. As predicted, we found no evidence for sex‐biased differences in δ²H measurements. Four geese tracked with GPS/GSM loggers all migrated to moulting areas, which confirmed the accuracy of our predictions from δ²H assignments. Differences between summering ranges inferred from historical and modern samples coincided with major wetland loss in northeastern China since the 1950s. Despite limited historical data, we contend that this supports the hypothesis that the summering range prior to 1950 was much wider than that of the current population.
Main conclusions
This was the first Asian study to establish migratory origins of wintering Anatidae based on stable isotopes and citizen science SDMs. We advocate the wider combined application of SDMs, telemetry studies and stable isotopes to investigate effectively avian migratory connectivity, as the results from this study provided important contributions to the development of conservation measures for this threatened and declining species in East Asia.
Stopovers used by birds during migration concentrate individuals from broad geographic areas potentially providing important information on catchment areas of birds moving through these sites. We combined stable isotope (δ ² H), genetic fingerprinting and band recovery data to delineate the molt origins of Wilson’s Warblers (Cardellina pusilla) migrating through a stopover site in southwestern Canada in the fall. We assessed changes in δ ² Hf indicating latitudinal origins with ordinal date to show this species likely underwent leapfrog migration through this site. Using the combined approach to determine origins, Wilson’s Warblers migrating through southwestern Alberta in 2015 were mostly from the western boreal population (n = 155, 96%) with some individuals from the Pacific Northwest (n = 1, 0.6%), Rocky Mountain (n = 2, 1.2%) and eastern boreal (n = 3, 1.8%) populations. Our results suggest that individuals migrating through our study site come from a broad catchment area potentially from a large part of northwestern North America. Future studies should link population changes at banding stations with other information to determine associations with large-scale landscape-level drivers (e.g. climate, land use).
The sex ratio of Dark-eyed Juncos wintering in the eastern and central United States and Canada varies clinally along a latitudinal gradient. The percentage of @V @V among both museum skins and live-caught birds is @?70% in the south, 20% in the north. When abundance according to latitude is also considered, an average @V appears to winter farther south than an average @M and hence probably tends to migrate farther. Latitude alone is an excellent predictor of sex ratio (r^2 = 85%), and latitude plus 13 other measures of climate explain virtually all the variation (r^2 = 96.6%). Extreme measures of climate, as compared to mean measures, are equally predictive. Principal component analysis indicates that snowfall, temperature, and latitude are the most important climatic variables associated with sex ratio. Because @M @M average larger than @V @V and are concentrated northward, mean wing length increases with latitude and is significantly correlated with climatic measures that vary with latitude. Further, larger birds within each sex may select higher altitudes as wintering sites. Sex ratio does not vary measurably with date in wintering populations. Among possible explanations for clinal variation in sex ratio are sex-associated differences in (1) advantages of early arrival on the breeding or wintering grounds, (2) impacts of inter- and intrasexual competition, and (3) effects of low temperature and intermittent food availability. Comparison of @M @M and @V @V with respect to potential fasting endurance, a size-related metabolic parameter, indicates that at 0 degrees C an average @M should be able to fast 4% longer (1.6 h) than an average @V at standard metabolic rates. An extremely heavy @M might endured fasting up to 29% (10.7 h) longer than a very light @V. These differences may confer greater survival ability upon the @M at latitudes where snow cover can often preclude feeding.
A quantitative method for linking reproductive and nonreproductive phases of migratory life cycles is fundamental to understanding the biology of migratory organisms. Here we combine genetic (mtDNA) and biochemical (stable isotope) information to examine seasonal movements in the Swainson's Thrush (Catharus ustulatus), a Neotropical migrant. We show that when these intrinsic markers are used in concert, they can predict the site-specific origin of thrushes with 76-80% accuracy. Genetic and isotope data needed for these classifications can be obtained from migratory organisms at any phase of the life cycle. We demonstrate how this classification analysis can be used to infer breeding origins of samples gathered during the nonreproductive phases of the life cycle. Based on these results, we argue that further integration of methodologies will refine the scale at which linkages between reproductive and nonreproductive phases of the life cycle can be quantified.