Migratory Systems Research Articles

A CLASSIFICATION OF PASTORALISM IN SPAIN: UNDERSTANDING THE PAST TO ADDRESS PRESENT CHALLENGES

After centuries as a flagship economic activity, pastoralism in Spain is today in danger of collapse due to the simultaneous processes of abandonment and industrialisation. With a consensus on the need to revert this decline, a characterisation of pastoralism is needed in the design of an efficient framework for action. Through a participatory process with experts, we carried out this characterisation of Spanish pastoralism, identifying the most representative systems and communities. We studied the causes and consequences of pastoral evolution over the last 250 years, explained by biophysical, technological, governance and social parameters. We achieved a harmonised classification of eleven pastoral systems, classified into four groups with mobility parameters (large migratory systems, short-distance transterminance, daily mobile grazing and semi-wilderness). Large mobility systems were subdivided into ten pastoral communities, characterised by strong sociocultural ties beneath farm management. The consideration of pastoral systems and communities in policy can orient effective rural development, while optimising the allocation of resources for environmental conservation and climate neutrality. This article was published open access under a CC BY-NC 4.0 licence: https://creativecommons.org/licenses/by-nc/4.0/ .

Limited herbivore migration during the Last Glacial Period of Kenya.

Eastern Africa is home to the largest terrestrial migrations on Earth. Though these migratory systems have been well studied for decades, little is known of their antiquity and evolutionary history. Serially sampled strontium stable isotopes (87Sr/86Sr) from tooth enamel can be used to track migration in mammals. Here we analyse 87Sr/86Sr for 79 bovid and equid individuals representing 18 species from four localities in Kenya to characterize prehistoric migratory systems during the Last Glacial Period (115-11.7 ka). Of the species analysed, 16 lack definitive evidence for migration, including blue wildebeest (Connochaetes taurinus), Thomson's gazelle (Eudorcas thomsonii) and plains zebra (Equus quagga), which are long-distance migrants today in the Greater Serengeti Ecosystem and historically in the Athi-Kapiti Plains. Only two species, the extinct wildebeests Rusingoryx atopocranion and Megalotragus sp., were migratory. These findings suggest a possible alternative narrative about ecosystem dynamics during the Last Glacial Period and shed light on the behaviour of both extant and extinct species at this time. In particular, these results indicate that migratory behaviour in extant species either emerged during the Holocene or was more spatiotemporally constrained in the past. Our results contribute to a growing body of evidence suggesting that the structure and function of geologically recent large mammal communities in eastern Africa differed considerably from those observed in the present day.

Carry-over effects of seasonal migration on reproductive success through breeding site retention in a partially migratory bird.

Understanding the maintenance and dynamics of phenotypic polymorphisms requires unpicking key ecological mechanisms shaping the fitness costs and benefits of expressing alternative phenotypes, generating selection. Seasonal migration versus year-round residence expressed in partially migratory populations represents one common polymorphism that can experience strong selection through differential reproductive success. Yet, key hypothesised pathways that could generate such selection remain to be empirically tested. One hypothesis is that migratory tactics affect subsequent reproductive success through carry-over effects on breeding site retention and resulting breeding dispersal. By remaining in breeding areas all year round, residents could retain their preferred breeding site between years, and consequently have higher reproductive success. Conversely, migrants that escape harsh non-breeding season conditions could return in better condition, with high resource holding potential, and outcompete residents to retain their site. Such effects could further depend on migration timing and vary between years. Yet, such pathways have not been quantified, precluding empirical parameterisation of partial migration theory. We used 4 years of breeding and non-breeding season data from partially migratory European shags (Gulosus aristotelis) to test whether the three most frequent migratory tactics in this population (full resident, early migrant departing soon after breeding, and late migrant departing in late autumn) differed in their breeding site retention; whether site retention predicted reproductive success; and hence whether effects of migratory tactic on reproductive success were explicable through site retention. Overall, residents were much more likely to retain their breeding site between years than both early and late migrants, and site retention was associated with increased reproductive success. Yet, these effects varied somewhat among years: late migrants were always least likely to retain their site but had variable relative reproductive success. Path analyses revealed that effects of migratory tactic on reproductive success were only partly attributable to breeding site retention. These results indicate that multiple mechanisms underlie reproductive selection on migratory tactics, potentially contributing to maintaining behavioural polymorphisms. Yet, the clear associations between migratory tactics and local breeding dispersal reveal that these movements can be strongly interlinked across seasons, shaping overall spatioseasonal dynamics in partially migratory systems.

Estimating migration timing and abundance in partial migratory systems by integrating continuous antenna detections with physical captures.

Many populations migrate between two different habitats (e.g. wintering/foraging to breeding area, mainstem-tributary, river-lake, river-ocean, river-side channel) as part of their life history. Detection technologies, such as passive integrated transponder (PIT) antennas or sonic receivers, can be placed at boundaries between habitats (e.g. near the confluence of rivers) to detect migratory movements of marked animals. Often, these detection systems have high detection probabilities and detect many individuals but are limited in their ability to make inferences about abundance because only marked individuals can be detected. Here, we introduce a mark-recapture modelling approach that uses detections from a double-array PIT antenna system to imply movement directionality from arrays and estimate migration timing. Additionally, when combined with physical captures, the model can be used to estimate abundances for both migratory and non-migratory groups and help quantify partial migration. We first test our approach using simulation, and results indicate our approach displayed negligible bias for total abundance (less than ±1%) and slight biases for state-specific abundance estimates (±1%-6%). We fit our model to array detections and physical captures of three native fishes (humpback chub [Gila cypha], flannelmouth sucker [Catostomus latipinnis] and bluehead sucker [Catostomus discobolus]) in the Little Colorado River (LCR) in Grand Canyon, AZ, a system that exhibits partial migration (i.e. includes residents and migrants). Abundance estimates from our model confirm that, for all three species, migratory individuals are much more numerous than residents. There was little difference in movement timing between 2021 (a year without preceding winter/spring floods) and 2022 (a year with a small flood occurring in early April). In both years, flannelmouth sucker arrived in mid-March whereas humpback chub and bluehead sucker arrivals occurred early- to mid-April. With humpback chub and flannelmouth sucker, movement timing was influenced by body size so that large individuals were more likely to arrive early compared to smaller individuals. With more years of data, this model framework could be used to evaluate ecological questions pertaining to flow cues and movement timing or intensity, relative trends in migrants versus residents and ecological drivers of skipped spawning.

Projected population- and season-dependent impacts of climate change on a migratory songbird in South America

Migratory birds depend on resources located in distantly separated ecosystems, potentially making them vulnerable to rapid environmental changes across their range. Yet, we understand little about how such changes may impact birds in different migratory systems, in large part because of a lack of individual-level research throughout their annual cycle and on different continents. The Fork-tailed Flycatcher (Tyrannus savana) is a widely distributed Neotropical bird, whose nominate subspecies is composed of populations that breed at tropical and south-temperate latitudes of South America and then spend the non-breeding season in northern South America. Using movement data collected with light-level geolocators on individual migratory Fork-tailed Flycatchers from breeding populations at tropical and south-temperate latitudes, we evaluated whether different flycatcher populations vary in their vulnerability to future climate change. Results suggest that populations breeding at south-temperate and tropical latitudes will lose at least 22% of their breeding area, with most losses of south-temperate breeding areas occurring in the northern portions of those areas. Both south-temperate breeders and tropical breeders will also lose non-breeding area, with south-temperate breeders experiencing a loss of over a third of their non-breeding area, whereas tropical breeders will lose up to ~16% of that area. These results are the first to demonstrate population- and season-dependent risks to climate change for a migratory bird breeding in the Neotropics, and suggest that mitigating the impacts of climate change for birds in South America will require conservation planning that accounts for both seasonal and regional processes.

Redes, interligações e sistemas migratórios num Portugal europeu e atlântico

In this article we will justify how the characteristics of Portugal, a country of emigration and a country of immigration, result from its structural insertion at the intersection between different migratory systems: the European migratory system (in which the freedom of movement of products, services and people is the foundation of the potential of migratory circulation) and the lusophone migratory system (a post-colonial political system made up of cultural, economic and political complicities that are still being consolidated). In addition to belonging to these early migratory systems, the growing importance of a global migratory system helps to contextualize migrations from (and to) Portugal, the type and profile of migrants and furthermore to explain the social structure of Portuguese emigration and immigration in Portugal.

Effects of pair migratory behavior on breeding phenology and success in a partially migratory shorebird population.

In migratory systems, variation in individual phenology can arise through differences in individual migratory behaviors, and this may be particularly apparent in partial migrant systems, where migrant and resident individuals are present within the same population. Links between breeding phenology and migratory behavior or success are generally investigated at the individual level. However, for breeding phenology in particular, the migratory behaviors of each member of the pair may need to be considered simultaneously, as breeding phenology will likely be constrained by timing of the pair member that arrives last, and carryover effects on breeding success may vary depending on whether pair members share the same migratory behavior or not. We used tracking of marked individuals and monitoring of breeding success from a partially migrant population of Eurasian oystercatchers (Haematopus ostralegus) breeding in Iceland to test whether (a) breeding phenology varied with pair migratory behavior; (b) within‐pair consistency in timing of laying differed among pair migratory behaviors; and (c) reproductive performance varied with pair migratory behavior, timing of laying, and year. We found that annual variation in timing of laying differed among pair migratory behaviors, with resident pairs being more consistent than migrant and mixed pairs, and migrant/mixed pairs breeding earlier than residents in most years but later in one (unusually cold) year. Pairs that laid early were more likely to replace their clutch after nest loss, had higher productivity and higher fledging success, independent of pair migratory behavior. Our study suggests that the links between individual migratory behavior and reproductive success can vary over time and, to a much lesser extent, with mate migratory behavior and can be mediated by differences in laying dates. Understanding these cascading effects of pair phenology on breeding success is likely to be key to predicting the impact of changing environmental conditions on migratory species.

Modelling the responses of partially migratory metapopulations to changing seasonal migration rates: From theory to data.

Among‐individual and within‐individual variation in expression of seasonal migration versus residence is widespread in nature and could substantially affect the dynamics of partially migratory metapopulations inhabiting seasonally and spatially structured environments. However, such variation has rarely been explicitly incorporated into metapopulation dynamic models for partially migratory systems. We, therefore, lack general frameworks that can identify how variable seasonal movements, and associated season‐ and location‐specific vital rates, can control system persistence.We constructed a novel conceptual framework that captures full‐annual‐cycle dynamics and key dimensions of metapopulation structure for partially migratory species inhabiting seasonal environments. We conceptualize among‐individual variation in seasonal migration as two variable vital rates: seasonal movement probability and associated movement survival probability. We conceptualize three levels of within‐individual variation (i.e. plasticity), representing seasonal or annual variation in seasonal migration or lifelong fixed strategies. We formulate these concepts as a general matrix model, which is customizable for diverse life‐histories and seasonal landscapes.To illustrate how variable seasonal migration can affect metapopulation growth rate, demographic structure and vital rate elasticities, we parameterize our general models for hypothetical short‐ and longer‐lived species. Analyses illustrate that elasticities of seasonal movement probability and associated survival probability can sometimes equal or exceed those of vital rates typically understood to substantially influence metapopulation dynamics (i.e. seasonal survival probability or fecundity), that elasticities can vary non‐linearly, and that metapopulation outcomes depend on the level of within‐individual plasticity.We illustrate how our general framework can be applied to evaluate the consequences of variable and changing seasonal movement probability by parameterizing our models for a real partially migratory metapopulation of European shags Gulosus aristotelis assuming lifelong fixed strategies. Given observed conditions, metapopulation growth rate was most elastic to breeding season adult survival of the resident fraction in the dominant population. However, given doubled seasonal movement probability, variation in survival during movement would become the primary driver of metapopulation dynamics.Our general conceptual and matrix model frameworks, and illustrative analyses, thereby highlight complex ways in which structured variation in seasonal migration can influence dynamics of partially migratory metapopulations, and pave the way for diverse future theoretical and empirical advances.

Individual repeatability of avian migration phenology: Asystematic review and meta-analysis.

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.

Return migration from Venezuela to Europe: Back to the Roots?

The exodus from Venezuela increased in intensity until the Covid-19 pandemic. Arrivals in Europe were significantly lower than in Latin America, but also grew and displayed a shift in composition, including a decreasing percentage of people with European origins. This study investigates migration from Venezuela to Spain, Italy and Hungary, in the 21st century. It begins with a detailed theoretical framework and then examines the particular migratory flows. The analysis covers the major features of these migration moves, including antecedents, reasons and motivations, size, geographical distribution and indicators related to integration. Mixed methods are used, both qualitative and quantitative. Findings show that current emigration from Venezuela to Spain, Italy and Hungary can be considered as return migration because original flows existed in the 19th and 20th centuries, and actual counterflows not only incorporate descendants of immigrants but are also based on the existing migratory systems and networks between these countries.

Spring and autumn movements of an Arctic bird in relation to temperature and primary production

It is increasingly important to understand animal migratory movements because climate disruption is shifting plant and animal phenology at different rates across the world. We applied a Markov state‐switching model to telemetry data of a long‐distance migrant, the barnacle goose, to detect migratory movement and relate it to three proximate environmental factors: photoperiod, daily mean temperature and forage plant phenology. Spring migratory movements towards the breeding grounds were most closely related to forage plant phenology (measured by accumulated growing degree days, GDDs); high GDDs values were associated with a greater probability of transiting to a more northerly site, suggesting that spring migration is closely aligned with primary productivity. Autumn migration from the breeding grounds was most closely related to temperature; higher temperature values were associated with a greater probability of remaining settled at the current site, suggesting that autumn migration is closely aligned with atmospheric conditions. Understanding the relative influence of different environmental factors on migratory patterns may in turn provide us with insight into how continued climate disruption could influence northern migratory systems.

Grazing Into the Anthropocene or Back to the Future?

This essay examines three central components of extensive livestock production—herd composition, grazing/pasture management, and rangeland tenure. In all of these areas, fenced, and open-range forms of migratory pastoralism face a number of shared problems. Set aside the presumption that either one of these systems is technically or institutionally more advanced than the other, and it turns out that each has lessons for the other. 1. For a variety of reasons, including climate change, we can look forward to a future world with less grass, which presents a challenge for livestock producers reliant on grass feeding livestock. With little delay and minimal scientific support, East African pastoralists are already adjusting to a new woody world by diversifying the species composition of their herds to include more browsers—camels and goats. There is a potential lesson here for commercial ranchers who have traded the stability of mixed herds for the profitability of keeping sheep or cattle alone. 2. Migratory rangeland systems distribute livestock very differently than fenced, rotational systems of livestock, and pasture management. Whereas, migratory herds exploit environmental heterogeneity, fenced ranching attempts to suppress it. Emerging archaeological evidence is demonstrating that pastoralists have amplified rangeland heterogeneity for millennia; ecological research shows that this heterogeneity sustains both plant and wildlife biodiversity at the landscape scale; and new approaches to ranch management are appropriating aspects of migratory herding for use on fenced ranches. A rapprochement between the environmental sciences, ranching, and open-range migratory pastoralism has occurred and merits wider policy recognition. 3. In contemporary Africa, indigenous tenure regimes that sustain open rangelands are eroding under pressure from market penetration and state encapsulation. At the same time in the American West, there are emerging novel land tenure instruments that replicate some of the most important functional characteristics of tenure arrangements in pastoral Africa. After many false starts, it appears that some aspects of American ranching do provide an appropriate model for the preservation of the open-range migratory systems that they were once supposed to supplant. “Development” policy needs to reflect upon this inversion of roles and its implications for accommodating diversity.

Paternal effects in the initiation of migratory behaviour in birds

What determines why some birds migrate and others do not? This question is fundamental to understanding how migratory systems are responding to environmental changes, but the causes of individual migratory behaviours have proven difficult to isolate. We show that, in a partially migratory population of Eurasian oystercatchers (Haematopus ostralegus), the migratory behaviour of progeny follows paternal but not maternal behaviour, and is unrelated to timing of hatching or fledging. These findings highlight the key role of social interactions in shaping the migratory behaviour of new generations, and thus the spatio-temporal distribution of migratory populations.

Europe's essential workers: Migration and pandemic politics in Central and Eastern Europe during COVID-19.

How do countries navigate the tradeoffs between public health and economic reopening? What explains variation in state responses to COVID‐19? Historically, governments have tackled pandemics as external, nonconventional security threats, restricting immigration to protect citizens from contagious outsiders. Central and Eastern European (CEE) countries could not frame COVID‐19 this way because European integration and free‐movement migration blur the line between insiders and outsiders. This article examines the conditions and coalitions that shaped policy outcomes, and argues that migration systems played a double role in policy change: as structures for policy diffusion and as venues for migrants’ agency. Governments learned from one another's experiences, but diffusion occurred unevenly according to countries’ position within migratory systems.

Earlier and slower or later and faster: Spring migration pace linked to departure time in a Neotropical migrant songbird.

Migratory birds travel vast distances and the timing of migratory flights can affect survival and the ability to reproduce. For Neotropical migrant songbirds, early spring departure from wintering sites, early arrival to the breeding grounds and higher reproductive success have been related to the use of suitable habitats and environmental conditions during the non-breeding season. However, how migratory strategies are shaped by winter habitat choice is largely unknown due to the general inability to track birds from specific wintering habitats to stopovers or breeding destinations. We assessed how winter habitat (native forest vs. shade-grown coffee plantations) relates to spring departure date and migration pace in Swainson's Thrush Catharus ustulatus. We also determined the effect of departure date and total migration duration on the arrival date of birds detected near or within their breeding range. We used a novel application of Motus radiotelemetry arrays to track individuals from their wintering grounds in the Andes of South America along their migratory journey to North America. We found variation in migratory strategies between habitats, with birds wintering in native forest departing later than birds in coffee. We present isotopic evidence for native forest being of higher quality than shade-coffee for Swainson's Thrush and hypothesize that moister conditions in forest, as shown by stable isotope (δ13 C) analysis of thrush whole blood, provides favourable pre-migratory conditions allowing birds to delay departure from wintering grounds. Habitat, between-site and -year variation in departure date, suggests that birds made facultative adjustments to winter habitat quality and environmental conditions. Independent of habitat, birds that departed later migrated faster and this pattern was maintained along the migration route (n=44). Migrating earlier and slower or later and faster was unlikely to result in significant differences in arrival time to breeding destinations. Our findings reveal underappreciated complexity in migratory decisions by long-distance migrants that contrast with the current paradigm of earlier departures and arrival from optimal habitats. The next step is to understand the relative fitness benefits of early versus late schedules or whether each strategy is an equally good response to experienced conditions.

The seasonal imperative: Environmental drivers of livestock mobility in East Darfur, Sudan

At their furthest extent, the livestock migrations examined in this paper traverse a distance of 400 km or more along a north-south transect, crossing up to half a dozen distinct ecological zones and, upon occasion, the international border between Sudan and South Sudan. Official Sudanese recognition of the value of migratory livestock production has led in recent years to policy and legal changes that support pastoral mobility, but there remains a gap in the scientific evidence that can be called upon to inform this emerging awareness. This paper uses remotely sensed livestock tracking data to document pastoral behaviour in relation to some of the biophysical factors that are important for livestock survival and production. This research supports several policy-relevant conclusions:1. In East Darfur, long-distance migratory livestock production is remarkably resilient to rainfall fluctuations, including drought and flooding, because movement cycles are already designed to accommodate this kind of variability.2. Mobile livestock producers are exposed to human-generated disruption and increasing pressures on their mobility from expanding farms, localized conflict and insecurity, and a new international border.3. Pastoralists need sympathetic governance to mediate their interactions with other forms of land use, which is unlikely to happen unless authorities appreciate the technical sophistication and economic advantages of migratory systems.4. Migratory production in East Darfur uses locally available resources which leaves livestock owners and government free to expend cash reserves on other kinds of inputs, investments or activities.

Relationships Between the Spread of Pathogens and the Migratory Connectivity of European Wild Birds

Abstract Among emerging infectious diseases, 75 % are zoonotic. Migratory birds are important to public health because they carry emerging zoonotic pathogens or infected arthropod vectors. Disease is an important factor in the evolution of avian migrations and patterns of migratory connectivity. Research suggests that pathogen densities and diseases may influence the evolution of migratory behaviour. During the annual life cycle, European migratory birds spend: 2—4 months at the breeding locality, approximately 6 months on the wintering grounds, and several months (3 and more) on migration routes. There are many factors which determine when and where an outbreak of a disease may occur. Therefore, a complete understanding of the avian migratory systems has a high priority in the prevention of future outbreaks.

Causes and consequences of facultative sea crossing in a soaring migrant

Abstract Studying the causes and consequences of route selection in animal migration is important for understanding the evolution of migratory systems and how they may be affected by environmental factors at various spatial and temporal scales. One key decision during migration is whether to cross ‘high transport cost’ areas or to circumvent them. Soaring birds may face this choice when encountering waterbodies where convective updrafts are weak or scarce. Crossing these waterbodies requires flying using energetically costly flapping flight, while circumventing them over land permits energetically cheap soaring. We tested how several atmospheric factors (e.g. wind, thermal uplift) and geographic, seasonal and state‐related factors (sex and age) affected route selection in migrating white storks Ciconia ciconia. We used 196 GPS tracks of 70 individuals either crossing or circumventing the north‐easternmost section of the Mediterranean Sea, over Iskenderun Bay in southern Turkey. We found that westward and southward winds promoted a cross‐bay journey in spring and autumn, respectively, acting as tailwinds. Also, overall weaker winds promoted a sea crossing in spring. Sea crossing was associated with flapping flight and higher values of overall dynamic body acceleration and resulted in higher ground speed than travel over land. The combined environmental conditions and the effects of route selection on movement‐related energy costs and speed were likely responsible for an increase in the time spent flying and distance travelled of migrating storks that decided to cross the bay during spring. Notably, daily travel distances of spring migrants crossing the bay were 60 km longer than those of land‐detouring birds, allowing them to reach their destination faster but likely incurring a higher energetic flight cost. No such benefit was found during autumn. Our findings confirm that atmospheric conditions can strongly affect bird route selection. Consequently, migration timing, speed and movement‐related energy expenditure differed considerably between the two migratory seasons and the two route choices, highlighting a time‐energy trade‐off in the migration of white storks. A free plain language summary can be found within the Supporting Information of this article.

El enfoque de sistemas migratorios revisitado. Una propuesta teórica para el estudio del sistema migratorio de América Latina y el Caribe

Resumen El objetivo de este artículo es revisitar los orígenes, desarrollo, límites y potencialidades del enfoque de sistemas migratorios, para formular una propuesta teórica que, a la hora de analizar la conformación, retroalimentación y reconfiguración de los sistemas migratorios, considere el papel de la estructura, de los factores de carácter meso (como las instituciones o los colectivos) y de la agencia migrante (individual y colectiva). Partimos para ello, de una perspectiva crítica dialéctica que establece un vínculo entre los elementos del sistema con los condicionantes estructurales, al tiempo que recupera la agencia migrante, principalmente en su dimensión colectiva. Nuestra propuesta será aplicada exploratoriamente al estudio del sistema migratorio de América Latina y el Caribe en el periodo 1970-2018. Más allá de una mera descripción de los principales rasgos del sistema y sus subsistemas, tratamos de mostrar los elementos que condicionan su estabilidad y evolución, resaltando, además de los elementos clásicos de los sistemas, el peso de los condicionantes estructurales, así como de las resistencias y estrategias desarrolladas por los colectivos migrantes.

Mechanisms driving phenological and range change in migratory species.

Many migratory systems are changing rapidly in space and time, and these changes present challenges for conservation. Changes in local abundance and site occupancy across species' ranges have raised concerns over the efficacy of the existing protected area networks, while changes in phenology can potentially create mismatches in the timing of annual events with the availability of key resources. These changes could arise either through individuals shifting in space and time or through generational shifts in the frequency of individuals using different locations or on differing migratory schedules. Using a long-term study of a migratory shorebird in which individuals have been tracked through a period of range expansion and phenological change, we show that these changes occur through generational shifts in spatial and phenological distributions, and that individuals are highly consistent in space and time. Predictions of future rates of changes in range size and phenology, and their implications for species conservation, will require an understanding of the processes that can drive generational shifts. We therefore explore the developmental, demographic and environmental processes that could influence generational shifts in phenology and distribution, and the studies that will be needed to distinguish among these mechanisms of change.This article is part of the theme issue ‘Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation’.