Migration Schedules Research Articles

Synchronous timing of return to breeding sites in a long-distance migratory seabird with ocean-scale variation in migration schedules

BackgroundMigratory birds generally have tightly scheduled annual cycles, in which delays can have carry-over effects on the timing of later events, ultimately impacting reproductive output. Whether temporal carry-over effects are more pronounced among migrations over larger distances, with tighter schedules, is a largely unexplored question.MethodsWe tracked individual Arctic Skuas Stercorarius parasiticus, a long-distance migratory seabird, from eight breeding populations between Greenland and Siberia using light-level geolocators. We tested whether migration schedules among breeding populations differ as a function of their use of seven widely divergent wintering areas across the Atlantic Ocean, Mediterranean Sea and Indian Ocean.ResultsBreeding at higher latitudes led not only to later reproduction and migration, but also faster spring migration and shorter time between return to the breeding area and clutch initiation. Wintering area was consistent within individuals among years; and more distant areas were associated with more time spent on migration and less time in the wintering areas. Skuas adjusted the period spent in the wintering area, regardless of migration distance, which buffered the variation in timing of autumn migration. Choice of wintering area had only minor effects on timing of return at the breeding area and timing of breeding and these effects were not consistent between breeding populations.ConclusionThe lack of a consistent effect of wintering area on timing of return between breeding areas indicates that individuals synchronize their arrival with others in their population despite extensive individual differences in migration strategies.

Evaluating the potential of bioacoustics in avian migration research by citizen science and weather radar observations.

The study of nocturnal bird migration brings observational challenges because of reduced visibility and observability of birds at night. Remote sensing tools, especially radars, have long been the preferred choice of scientists to study nocturnal migrations. A major downside of these remote sensing tools is the lack of species-level information. With technological advances in recent decades and with improved accessibility and affordability of acoustic tools, sound recordings have steeply increased in popularity. In Europe, there is no exhaustive qualitative and quantitative evaluation of the content of such acoustic databases and therefore the value for migration science and migration-related applications, such as bird collision hazard assessments, is mostly unknown. In the present work we compared migration schedules estimated from citizen science data with quantitative temporal occurrence of species in four years of acoustic recordings. Furthermore, we contrasted acoustic recordings with citizen science observations and weather radar data from one spring and one autumn season to assess the qualitative and quantitative yield of acoustic recordings for migration-related research and applications. Migration intensity estimated from weather radar data correlated best at low levels with acoustic records including all species in spring while in autumn passerine species showed stronger correlation than the entire species composition. Our findings identify a minor number of species whose call records may be eligible for applications derived from acoustics. Especially the highly vocal species Song thrush and Redwing showed relatively good correlations with radar and citizen science migration schedules. Most long-distance passerine migrants and many other migrants were not captured by acoustics and an estimated seasonal average of about 50% of nocturnally migrating passerine populations remained undetected. Overall, the ability of acoustic records to act as a proxy of overall migration dynamics is highly dependent on the migration period and species involved.

Can arctic migrants adjust their phenology based on temperature encountered during the spring migration? The case of the greater snow goose

The reproductive phenology of many long-distance migrants breeding at high latitudes remains unresponsive or responds only slightly to climate warming. In order to adjust migration speed and arrival time on the breeding grounds, environmental cues encountered during the migration must be related to conditions prevailing at the breeding site. However, heterogeneity in rate of climate warming across latitudes may hamper the ability of birds to adjust their migration speed adequately. We examined to what extent temperatures encountered at stopovers were a good predictor of temperatures at subsequent stopovers and at the breeding site in greater snow geese (Anser caerulescens atlanticus), an Arctic species that showed little change in its breeding phenology over the past 3 decades. We also examined temperature trends at various stopovers used by geese and at the breeding site over a 40-year period. We found that warming was stronger at the Arctic stopovers and the breeding site than at southern staging areas. The mean temperature and rate of temperature change encountered at the southern stopover, where this species accumulates most of its body reserves, was weakly correlated to temperatures prevailing at more northern stopovers and the breeding site located 3,000 km further north. Correlations in temperatures between stopovers and the breeding site increased with decreasing distance between sites and as geese moved further north. Lastly, laying date was strongly related to temperature during the arrival and pre-laying period on the breeding grounds but not to temperatures encountered at stopovers during migration. Temperatures encountered along the migratory route are thus a poor predictor of temperatures prevailing at the breeding site in any given year except when geese are getting close to their breeding grounds. This may be a major constraint preventing geese from adjusting their migratory schedule to conditions on their breeding grounds and may explain why their reproductive phenology did not change despite a warming trend at the breeding site.

Lunar synchrony, geography, and individual clocks shape autumn migration timing in an avian migrant.

Timing programs in animal migrants have been selected to synchronize movements that coincide with predictable resources on the breeding and nonbreeding grounds. Migrants face potential temporal conflicts if their migration schedules benefit from synchrony to conflicting rhythms associated with annual biogeographical (circannual) cues, lunar (circalunar) cues, or individually repeatable internal clocks. We repeat-tracked individuals of an avian lunaphilic species, Eastern Whip-poor-will (Antrostomus vociferus), for two to three successive autumn migrations to determine the influence of the lunar cycle, breeding location, and individual repeatability on migration timing. Almost all birds avoided departing for migration during a full moon, likely to take advantage of the bright moonlight to facilitate visual foraging and enhance pre-migration fattening. However, groups from two latitudinally distant sampling areas adjusted their autumn departure timing differently relative to the timing of the September full moon, presumably due to differences in seasonal prey availability. Individual repeatability increased throughout autumn migration, suggesting that the factors responsible for shaping migration timing may differ for different migration stages. Our results, that lunar synchrony, local climate, and individual internal clocks appeared to account for much of the variation in migration timing in whip-poor-wills, underscore the value of measuring potentially interacting factors that shape migratory behavior at species, group, and individual levels. It remains unclear if, or how, maintaining individually repeatable annual migration schedules provides an adaptive benefit for whip-poor-wills or other lunaphilic migrants. Further clarifying the reasons for phenotypic variation in whip-poor-will migration timing will improve predictions of their abilities to adjust migratory movements under changing environmental conditions.

Individual consistency in spatiotemporal characteristics of migratory Whimbrels in the East Asian–Australasian Flyway

Many migratory birds exhibit interannual consistency in migration schedules, routes and stopover sites. Detecting the interannual consistency in spatiotemporal characteristics helps understand the maintenance of migration and enables the implementation of targeted conservation measures. We tracked the migration of Whimbrel (Numenius phaeopus) in the East Asian–Australasian Flyway and collected spatiotemporal data from individuals that were tracked for at least two years. Wilcoxon non-parametric tests were used to compare the interannual variations in the dates of departure from and arrival at breeding/nonbreeding sites, and the interannual variation in the longitudes when the same individual across the same latitudes. Whimbrels exhibited a high degree of consistency in the use of breeding, nonbreeding, and stopover sites between years. The variation of arrival dates at nonbreeding sites was significantly larger than that of the departure dates from nonbreeding and breeding sites. Repeatedly used stopover sites by the same individuals in multiple years were concentrated in the Yellow Sea coast during northward migration, but were more widespread during southward migration. The stopover duration at repeatedly used sites was significantly longer than that at sites used only once. When flying across the Yellow Sea, Whimbrels breeding in Sakha (Yakutia) exhibited the highest consistency in migration routes in both autumn and spring. Moreover, the consistency in migration routes of Yakutia breeding birds was generally higher than that of birds breeding in Chukotka. Our results suggest that the northward migration schedule of the Whimbrels is mainly controlled by endogenous factors, while the southward migration schedule is less affected by endogenous factors. The repeated use of stopover sites in the Yellow Sea coast suggests this region is important for the migration of Whimbrel, and thus has high conservation value.

Migration dynamics simulation of migratory fish in rivers

The decline of migratory fish stocks is a major problem facing the global aquatic ecosystem. Understanding the dynamics of fish migration and their entire life history is crucial for quantitatively assessing the impact of natural and anthropogenic barriers on migratory fish and to understand the mechanisms of their decline. However, this understanding is largely ambiguous due to limited field survey data in the absence of models. Although Huang and Wang (Curr. Biol. 28, 2018, 3640–3647) and Huang (iScience 19(9), 2019, 772–785) proposed a Migration Dynamics Model (MDM) to describe the upriver and downriver migration processes of the Chinese sturgeon, but a crucial intermediate link—the breeding aggregation process—is still missing, while the standard Crank-Nicolson scheme, a common computational method, of finite difference methods cannot adapt to the model parameters changing with time and space. Here we propose a six-point implicit scheme to address the complexity of model parameters. The parameters of migration speed and diffusion coefficient are decomposed into fish-related and current-related components for analyzing their effects on model parameters and estimating them. Additionally, we propose a parameterization method for the aggregation process of spawners during the breeding season by introducing a set of clustering functions. Next, we examine the complete migration processes of adult and juvenile Chinese sturgeons in the Yangtze River and elucidate the underlying mechanisms behind the fish migration dynamics, including their spatiotemporal distributions, aggregation behavior, and migration schedule. We discover that the Gezhouba Dam (GD) significantly impacted the breeding aggregation behavior of Chinese sturgeon during the breeding season. The GD altered the distribution of fish along their migration path and schedule. Prior to the construction of the dam, 99.9 % of the total Chinese sturgeon were able to reach the 240 km-long spawning ground. However, after the dam was built, only 36.7 % were able to reach the 30 km-long spawning ground below the GD on the day of mating. Finally, we discuss the aggregation phenomenon and its driving factors during Chinese sturgeon migration, and categorize it into three types, namely biotic-driven, abiotic-driven and dual-driven aggregation behaviors. We reveal the existence of aggregations for non-biological reasons, such as the slowdown of fish migration speed induced by natural and anthropogenic barriers and estuarine tidal effects.

Individuals of a group-living shorebird show smaller home range overlap when food availability is low

BackgroundGroup living animals, such as shorebirds foraging on intertidal mudflats, may use social information about where to find hidden food items. However, flocking also increases intraspecific competition for resources, which may be exacerbated by food scarcity. Therefore, although aggregation may bring benefits, it may also increase the intensity of intraspecific competition.MethodsWe examined this trade-off in adult great knots Calidris tenuirostris, a molluscivorous long-distance migrating shorebird species, using interannual variation based on 2 years with different levels of food availability during their northward migratory staging in the northern Yellow Sea, China. We estimated individual home ranges and the extent of spatial overlap of home ranges of individually tagged birds in 2012 and 2015, whilst discounting for possible differences in body size, body mass, sex and migration schedule between years.ResultsWe found that home range size was not associated with body mass, arrival date, body size, or sex of the individual. Despite a significant difference in food availability between the two study years, there was no significant change in the 50% and 95% home range size of great knots in the contrasting situations. However, there was a significantly smaller spatial overlap between individuals in the year when food was less available, suggesting that great knots operated more independently when food was scarce than when it was abundant.ConclusionsThese results suggest that minimizing intraspecific competition became more important when food was scarce. Where it is impossible to monitor all habitats en route, monitoring the local movements of shorebirds may offer a way to detect changes in habitat quality in real time.

Re-Scheduling IoT Services in Edge Networks

With the explosive growth of the Internet of Things (IoT) devices deployed in edge networks, the functionalities of IoT devices are typically encapsulated as IoT services, and user requests can be achieved through the composition of data and/or computation-intensive IoT services. Considering the prediction-uncertainty of forthcoming requests, certain IoT services may (i) not be hosted currently by appropriate IoT devices, or (ii) such an IoT service exists, but its non-functional properties may hardly be satisfied with respect to certain constraints prescribed by requests. To address this challenge, this paper proposes an efficiency-aware service Migration Scheduling (denoted eMS) mechanism in edge networks, in order to migrate IoT services on-demand, and thus, to optimally settle non-satisfiable constraints. Specifically, IoT services are re-scheduled, such that certain IoT services are migrated from their hosting IoT devices to neighboring ones, while minimizing the energy consumption and average delay caused by this service re-scheduling operation. We formulate this service re-scheduling as a multi-objective and multi-constraint optimization problem, which is solved through integrating the greedy algorithm into the fast non-dominated sorting and crowded-comparison operators as the hybrid genetic algorithm (G-NSGA-II). Based on real-life datasets provided by an oil pipeline monitoring project, extensive experiments are conducted, and evaluation results show that our eMS is promising in reducing the energy consumption and average delay of service re-scheduling in comparison with the state-of-art’s techniques.

Competition is a major limiting factor of refueling in migratory passerines during stopover

For an avian migrant, refueling capacity attainable during stopovers governs the entire migration schedule and, ultimately, its fitness. Specifically, timely replenishing energy stores is critical when migration involves crossing ecological barriers, within which refueling may be limited. Here, we tested the hypothesis that fuel deposition rates (FDRs) of migratory passerines within barrier‐edge stopover sites are constrained by the density of potential competitors, irrespective of migration season, phenology, and local environmental conditions. We also evaluated diverse intra‐ and inter‐specific competition scenarios and explored a potential mediation of density‐dependence by environmental factors. The analyzed data, collected by us over 13 consecutive years (2009–2022), contain information on seven species of long‐distance migratory insectivorous passerines measured within eight desert‐edge habitats throughout autumn and spring migrations. As predicted, our analyses revealed negative density‐dependence regulation of FDRs, consistent across species and migration seasons. Notably, bird density exerted its effect above and beyond the other factors known to influence FDR, such as relative ambient temperature, phenology, temporal progress of stopover, and body mass next to landfall. As expected, FDR increased at higher relative ambient temperatures and with the stopover's progress. In spring, FDR also rose as the season advanced. These findings signify the substantial impact of competition on the refueling performance of migratory passerines during their stopover on an ecological barrier's edge, acting over and above the other environmental factors. The detected importance of competition and its interrelation with other predictors provides an insight into stopover's functioning; environmentally imposed and inescapable interspecific interference is thus a significant limiting factor of FDR, a deleterious relationship potentially remediable by informed habitat restoration and planning.

Carbon Management of Multi-Datacenter Based On Spatio-Temporal Task Migration

With the massive deployment of geographically distributed data centers (DCs) and the demand surge for cloud services, their high energy consumption and carbon pollution are increasingly problematic. Therefore, mitigating the harmful effects of the carbon footprint of DCs has become a critical challenge. This paper takes the first step toward analyzing the complementary characteristics of global multi-regional renewable energy sources (RES). There is an opportunity to schedule workloads flexibly and track RES to reduce emissions. Integrating DCs and inter-DC network to form a refined emission model for the trade-off between emission cutting effects from scheduling and carbon costs of workload migration, we propose the spatio-temporal task migration mechanism to pursue low carbon in dual-dimension: This paper shifts intensive workloads to locations sufficient in RES at a coarse scale, and adjust the execution time of the workload in response to real-time RES fluctuations at a fine scale. Thus, the emission overage is shifted and offset by RES in a complementary manner; meanwhile, the acceptance of RES is enhanced. Finally, experiments with real-world data show that our method can optimally coordinate demand with RES and mitigate carbon pollution in geographically distributed DCs, and verify the performance and applicability with various-parameter scenarios.

As the Goose Flies: Migration Routes and Timing Influence Patterns of Genetic Diversity in a Circumpolar Migratory Herbivore

Migration schedules and the timing of other annual events (e.g., pair formation and molt) can affect the distribution of genetic diversity as much as where these events occur. The greater white-fronted goose (Anser albifrons) is a circumpolar goose species, exhibiting temporal and spatial variation of events among populations during the annual cycle. Previous range-wide genetic assessments of the nuclear genome based on eight microsatellite loci suggest a single, largely panmictic population despite up to five subspecies currently recognized based on phenotypic differences. We used double digest restriction-site associated DNA (ddRAD-seq) and mitochondrial DNA (mtDNA) sequence data to re-evaluate estimates of spatial genomic structure and to characterize how past and present processes have shaped the patterns of genetic diversity and connectivity across the Arctic and subarctic. We uncovered previously undetected inter-population differentiation with genetic clusters corresponding to sampling locales associated with current management groups. We further observed subtle genetic clustering within each management unit that can be at least partially explained by the timing and directionality of migration events along with other behaviors during the annual cycle. The Tule Goose (A. a. elgasi) and Greenland subspecies (A. a. flavirostris) showed the highest level of divergence among all sampling locales investigated. The recovery of previously undetected broad and fine-scale spatial structure suggests that the strong cultural transmission of migratory behavior restricts gene flow across portions of the species’ range. Our data further highlight the importance of re-evaluating previous assessments conducted based on a small number of highly variable genetic markers in phenotypically diverse species.

CAMIG: Concurrency-Aware Live Migration Management of Multiple Virtual Machines in SDN-Enabled Clouds

By integrating Software-Defined Networking and cloud computing, virtualized networking and computing resources can be dynamically reallocated through live migration of Virtual Machines (VMs). Dynamic resource management such as load balancing and energy-saving policies can request multiple migrations when the algorithms are triggered periodically. There exist notable research efforts in dynamic resource management that alleviate single migration overheads, such as single migration time and co-location interference while selecting the potential VMs and migration destinations. However, by neglecting the resource dependency among potential migration requests, the existing solutions of dynamic resource management can result in the Quality of Service (QoS) degradation and Service Level Agreement (SLA) violations during the migration schedule. Therefore, it is essential to integrate both single and multiple migration overheads into VM reallocation planning. In this paper, we propose a concurrency-aware multiple migration selector that operates based on the maximal cliques and independent sets of the resource dependency graph of multiple migration requests. Our proposed method can be integrated with existing dynamic resource management policies. The experimental results demonstrate that our solution efficiently minimizes migration interference and shortens the convergence time of reallocation by maximizing the multiple migration performance while achieving the objective of dynamic resource management.

Inter and intra-population variability of the migratory behaviour of a short-distance partial migrant, the Eurasian Stone-curlew Burhinus oedicnemus (Charadriiformes, Burhinidae)

Migratory behaviour in birds shows a remarkable variability at species, population and individual levels. Short-distance migrants often adopt a partial migratory strategy and tend to have a flexible migration schedule that allows a more effective response to extreme environmental variations. Weather seasonality and environmental heterogeneity have been reported as significant factors in the diversification of migratory behaviour for Mediterranean migrants, but relatively few studies investigated the migration patterns of non-passerine birds migrating within the Mediterranean basin. In this study, we investigated the migratory strategy of 40 Eurasian Stone-curlews Burhinus oedicnemus tagged with geolocators and GPS-GSM tags and belonging to continental and Mediterranean populations of the Italian peninsula. The proportion of migrants was higher in continental populations, but we observed a significant variability also within Mediterranean populations. All birds spent the winter within the Mediterranean basin. Continental Stone-curlews departed earlier in spring and later in autumn and covered longer distances than those from Mediterranean areas. The speed of migration did not change between seasons for continental birds, while Mediterranean individuals migrated faster in spring. The likelihood of departure for autumn migration of GPS-tagged birds increased when temperatures were near or below 0 °C suggesting that Stone-curlews tend to delay departure until weather conditions worsen abruptly. As a consequence of global warming in the Mediterranean, the frequency of migratory birds in the considered populations might decrease in the near future. This could affect the distribution of species throughout the year and should be taken into account when targeting conservation measures.

Length of stay and departure strategies of Semipalmated Sandpipers (Calidris pusilla) during post-breeding migration in the upper Bay of Fundy, Canada

The Bay of Fundy, Canada is a critical staging area for Semipalmated Sandpipers (Calidris pusilla) during post-breeding migration. Recent range-wide population declines and changes in diet and migratory timing in the Bay of Fundy prompted a re-examination of staging ecology, including length of stay (last estimated in 1981), which is used in calculating migratory population estimates. We used radio-telemetry and the Motus Wildlife Tracking System to estimate individual length of stay and departure conditions for 159 Semipalmated Sandpipers in 2013 and 2014. Using tracking data we compared two estimation methods, minimum length of stay and mark-recapture modelling. Using minimum length of stay, the mean length of stay was approximately 21 days, an increase from the previous estimate of 15 days. Mark-recapture models suggested a much longer staging period that is inconsistent with other data. Sandpipers captured early in the staging period stayed longer on average than those captured later. Departures from the staging area were correlated with north-westerly winds, moderate to high wind speeds and low but rising atmospheric pressures. We suggest that Semipalmated Sandpipers in the Bay of Fundy are not operating on a time-selected migration schedule and instead wait for favourable weather conditions to depart, which occur more often later in the migratory period. Population trends in the Bay of Fundy should be re-evaluated in light of the increased length of stay.

Revealing migration schedule and potential breeding grounds of Lined Seedeaters using citizen science data

ABSTRACT The Lined Seedeater (Sporophila lineola) is a small intra-tropical migrant songbird. However, little is known about its breeding and wintering grounds, or migratory habits. To investigate potentially distinct breeding populations and the migratory schedule of Lined Seedeaters we analysed its spatial and temporal distribution using published breeding records, museum vouchers, and data from citizen science projects (eBird and WikiAves). Our findings suggest that there are three main breeding areas: northern Argentina and north-western Paraguay, south-eastern Brazil, and north-eastern Brazil, and that the breeding season seems to be restricted to November through May, with slight differences in timing among these three areas. The species winters in the northern part of South America (mostly in grassland areas) and maybe also in the Amazonia. Moreover, rainfall predicts the latitudinal and longitudinal movements of Lined Seedeaters, with the migratory movements associated with an increase in rainfall. Taken together, these results provide a first comprehensive overview on the migration of Lined Seedeater, calling for further empirical field studies. Understanding intra-tropical migratory patterns is paramount to comprehend the potential impacts of environmental change in tropical ecosystems.

Operation optimization of data center based on multi-station integration

With the rapid development and extensive application of Internet technology, the data information grows exponentially. The proposal of the multi-station integration mode not only provides effective assistance for the development of the big data industry, but also put forward a new direction for the energy-saving operation of data centers. This paper presents a cooperative operation architecture of the fusion station covering substation, data center and energy storage power station, and establishes a mixed integer nonlinear programming model which aims at minimizing the annual total cost. The analysis of the role of data migration and energy storage scheduling are carried out by case study. The calculation results showed that, the typical daily operation cost was reduced by 10.52% and the annual total cost was reduced by 5.96% after the implementation of the data migration and the energy storage scheduling. Results demonstrate that on the premise of satisfying the delay constraint, the complementary scheduling of each fusion station can be realized through a certain data migration strategy, hence reducing the cost. Furthermore, the energy storage scheduling can transfer the peak load to the valley load, thus significantly decreasing operation costs.

Seasonal and regional differences in migration patterns and conservation status of Swan Geese (Anser cygnoides) in the East Asian Flyway

BackgroundThe Swan Goose (Anser cygnoides) breeds across Mongolia and adjacent China and Russia and winters exclusively in China. It is globally threatened, showing long-term major range contractions and declining abundance, linked to habitat loss and degradation. We remain ignorant about the biogeographical subpopulation structure of the species and potential differences in their migration timing, stopovers and schedules, information that could be vital to effective conservation of different elements of the species population, which we address here with results from a telemetry study.MethodsIn 2017–2018, we attached GPS/GSM telemetry devices to 238 Swan Geese on moulting sites in three discrete parts of their summering area (Dauria International Protected Area, Central Mongolia and Western Mongolia), generating 104 complete spring and autumn migration episodes to compare migration speed and nature between birds of different summer provenances.ResultsBirds from all three breeding areas used almost completely separate migration routes to winter sympatrically in the Yangtze River floodplain. Although many features of the spring and autumn migrations of the three groups were similar, despite the significantly longer migration routes taken by Western Mongolian tagged birds, birds from Dauria Region arrived significantly later in winter due to prolonged staging in coastal areas and took longer to reach their breeding areas in spring. Among birds of all breeding provenances, spring migration was approximately twice as fast as autumn migration. Areas used by staging Swan Geese (mainly wetlands) in autumn and spring almost never fell within national level protected areas, suggesting major site safeguard is necessary to protect these critical areas.ConclusionsThis study showed the discreteness of migration routes taken by birds of different summer provenances and differences in their migratory patterns, highlighting key staging areas (Yalu River Estuary in China/North Korea for Dauria Region breeding birds, Daihai Lake for Central Mongolian and Ordos Basin for Western Mongolian birds). Based on this new knowledge of the biogeographical subpopulation structure of the Swan Goose, we need to combine data on subpopulation size, their distribution throughout the annual life cycle and conservation status, to develop more effective conservation strategies and measures to reverse population decline throughout the range.

Timing of Breeding Site Availability Across the North-American Arctic Partly Determines Spring Migration Schedule in a Long-Distance Neotropical Migrant

Long-distance migrants are under strong selection to arrive on their breeding grounds at a time that maximizes fitness. Many arctic birds start nesting shortly after snow recedes from their breeding sites and timing of snowmelt can vary substantially over the breeding range of widespread species. We tested the hypothesis that migration schedules of individuals co-occurring at the same non-breeding areas are adapted to average local environmental conditions encountered at their specific and distant Arctic breeding locations. We predicted that timing of breeding site availability (measured here as the average snow-free date) should explain individual variation in departure time from shared non-breeding areas. We tested our prediction by tracking American Golden-Plovers (Pluvialis dominica) nesting across the North-American Arctic. These plovers use a non-breeding (wintering) area in South America and share a spring stopover area in the nearctic temperate grasslands, located >1,800 km away from their nesting locations. As plovers co-occur at the same non-breeding areas but use breeding sites segregated by latitude and longitude, we could disentangle the potential confounding effects of migration distance and timing of breeding site availability on individual migration schedule. As predicted, departure date of individuals stopping-over in sympatry was positively related to the average snow-free date at their respective breeding location, which was also related to individual onset of incubation. Departure date from the shared stopover area was not explained by the distance between the stopover and the breeding location, nor by the stopover duration of individuals. This strongly suggests that plover migration schedule is adapted to and driven by the timing of breeding site availability per se. The proximate mechanism underlying the variable migration schedule of individuals is unknown and may result from genetic differences or individual learning. Temperatures are currently changing at different speeds across the Arctic and this likely generates substantial heterogeneity in the strength of selection pressure on migratory schedule of arctic birds migrating sympatrically.

Identification of breeding grounds and annual routines of the newly discovered bohaii subspecies of Black-tailed Godwits

ABSTRACT The Bohai Black-tailed Godwit (Limosa limosa bohaii) is a newly discovered subspecies in the East Asian-Australasian Flyway. Based on satellite tracking of 21 individuals that were tagged in northern Bohai Bay, China, from 2016 to 2018, we here describe the annual cycle of this subspecies. All the birds had Thailand as their southernmost ‘winter’ destination. The spring departure was in late March during northward migration, Bohai Bay was the first stopping site where they spent on average 39 days (± SD = 6 d), followed by Inner Mongolia and Jilin province (stopping for 8 d ± 1 d). The arrival of the breeding grounds in the Russian Far East was centred in late May. Two breeding sites were detected, with average locations 1100 km apart; the eastern site was beyond the known Asian breeding distribution of the Black-tailed Godwit. Southward migration started in late June, with the godwits tending to make longer stops at the same two main stopping sites used in the spring, i.e. Inner Mongolia and Jilin province (32 ± 5 d) and Bohai Bay (44 ± 8 d), with some individuals making a third stop in the middle-lower reaches of the Yangtze River in southern China (12 ± 4 d). By the end of September, most tracked individuals had arrived in Thailand. Compared with the previously known subspecies, bohaii godwits have strikingly different schedules of migration and moult, this study thus adding to the knowledge about intraspecific diversity of black-tailed godwits in the East Asian-Australian Flyway.

Species‐specific demographic and behavioral responses to food availability during migratory stopover

AbstractUnderstanding the effects of migratory stopover site conditions on both demographic rates and migratory behaviors is critical for interpreting changes in passage population sizes at stopover sites and predicting responses to future changes and conservation actions. We used a Bayesian formulation of the open robust design model to analyze mark‐resight observations of three migratory shorebird species using Delaware Bay, USA during spring stopover from 2005 to 2018. We tested for an effect of stopover food availability and weather conditions on survival probability and the probability of returning to this site in the next year and found species differences in these relationships. After years with greater food availability, red knot Calidris canutus rufa had higher survival probability but ruddy turnstone Arenaria interpres were more likely to return to the site. Estimates of within‐year probabilities of arrival and persistence at the stopover site showed relatively consistent migration schedules for ruddy turnstone, but more interannual variation for red knot and sanderling Calidris alba. Shorebird use of this site typically peaked during May 26–28, but the estimated proportion of the population present during this period varied dramatically among years for red knot (range: 0.07–0.59) but less so for ruddy turnstone and sanderling. This demonstrates that both the proportion of the flyway population using this stopover site and the proportion present during a given sampling period vary among years, and both should be considered in analyzing and interpreting monitoring data. Stopover conditions can influence both migratory behavior and demographics, underscoring the importance of flyway‐wide monitoring.