Spring Migration Research Articles

THE TICKS <i>HYALOMMA RUFIPES</i> KOCH, 1844 IMPORTATION BY MIGRATORY BIRDS TO THE SOUTH OF RUSSIA - VECTORS OF CRIMEAN-CONGO HAEMORRHAGIC FEVER VIRUS: EPIDEMIOLOGICAL ASPECT

Koch, 1844 (Acari, Ixodidae) is the main vector of the Crimean-Congo haemorrhagic fever (CCHF) virus in southern and eastern Africa. In the spring migrations of birds, immature stages of this species are carried out beyond the range of the parasite and are often found in various countries of Europe. Finds of adult ticks in Europe are single. In June 2018, in the north of the Stavropol Territory, one male of with characteristic features was removed from a cow. Prior to this, single registrations of this species were known on the territory of the Astrakhan Region, Dagestan and the Stavropol Territory in the middle of the last century.

Continental‐scale biomass redistribution by migratory birds in response to seasonal variation in productivity

AbstractAimAnimal migration is often explained as the result of resource tracking in seasonally dynamic environments. Therefore, resource availability should influence both the distributions of migratory animals and their seasonal abundance. We examined the relationship between primary productivity and the spatio‐temporal distributions of migratory birds to assess the role of energy availability in avian migration.LocationNorth America.Time periodFull annual cycle, 2011–2016.Major taxa studiedNocturnally migrating landbirds.MethodsWe used observations of nocturnally migrating landbirds from the eBird community‐science programme to estimate weekly spatial distributions of total biomass, abundance and species richness. We related these patterns to primary productivity and seasonal productivity surplus estimated using a remotely sensed measure of vegetation greenness.ResultsAll three avian metrics showed positive spatial associations with primary productivity, and this was more pronounced with seasonal productivity surplus. Surprisingly, biomass showed a weaker association than did abundance and richness, despite being a better indicator of energetic requirements. The strength of associations varied across seasons, being the weakest during migration. During spring migration, avian biomass increased ahead of vegetation green‐up in temperate regions, a pattern also previously described for herbivorous waterfowl. In the south‐eastern USA, spring green‐up was instead associated with a net decrease in biomass, and winter biomass greatly exceeded that of summer, highlighting the region as a winter refuge for short‐distance migrants.Main conclusionsAlthough instantaneous energy availability is important in shaping the distribution of migratory birds, the stronger association of productivity with abundance and richness than with biomass suggests the role of additional drivers unrelated to energetic requirements that are nonetheless correlated with productivity. Given recent reports of widespread North American avifaunal declines, including many common species that winter in the south‐eastern USA, understanding how anthropogenic activities are impacting winter bird populations in the region should be a research priority.

Migration tactics and connectivity of a Nearctic-Neotropical migratory shorebird.

During long-distance spring migrations, birds may rest and refuel at numerous stopover sites while minimizing the time to reach the breeding grounds. If habitat is limited along the migration route, pre-breeding birds optimize flight range by having longer stopovers at higher quality sites compared to poorer quality sites. Stopover duration also depends on distance remaining to breeding grounds, ecological barriers and individual characteristics. We assessed spring migration tactics and connectivity of a Nearctic-Neotropical migratory shorebird, the semipalmated sandpiper Calidris pusilla, at two sites with known relative habitat quality on the northern Gulf of Mexico (NGOM) coast, the first land encountered after crossing the Gulf of Mexico (GOM). We used automated radio telemetry (Motus) to estimate stopover duration and probability of departure. Migration speed was estimated for individuals detected at subsequent receivers on the Motus network. To measure migratory connectivity, we used morphometrics and the Motus network to assign general breeding regions. Additionally, feather stable isotope ratios of C and N provided coarse information about overwintering regions. Stopover duration declined with higher fuel loads at capture as expected under a time-minimizing strategy. After accounting for fuel load, stopover duration was approximately 40% longer at the higher quality site. We found no detectable effect of age, sex or breeding location on stopover behaviour. The probability of departure was strongly affected by humidity and also by tailwind and weather conditions. Birds stopping at the higher quality site had earlier apparent arrival to the breeding grounds. The Louisiana coast is an apparent stopover hub for this species, since the individuals were departing to range-wide breeding regions and isotope values suggested birds were also using widespread wintering regions. Our study shows how high-quality, coastal wetlands along the NGOM coast serve a critical role in the annual cycle of a migratory shorebird. Stopover behaviour indicated that high-quality habitat may be limited for this species during spring migration. As threats to the GOM coast increase, protection of these already limited wetlands is vitally important.

Climate in Africa sequentially shapes spring passage of Willow Warbler Phylloscopus trochilus across the Baltic coast.

BackgroundMany migrant birds have been returning to Europe earlier in spring since the 1980s. This has been attributed mostly to an earlier onset of spring in Europe, but we found the timing of Willow Warblers’ passage to be influenced by climate indices for Africa as much as those for Europe. Willow Warblers’ spring passage through northern Europe involves populations from different wintering quarters in Africa. We therefore expected that migration timing in the early, middle and late periods of spring would be influenced sequentially by climate indices operating in different parts of the winter range.MethodsUsing data from daily mistnetting in 1 April–15 May over 1982–2017 at Bukowo (Poland, Baltic Sea coast), we derived an Annual Anomaly (AA, in days) of Willow Warbler spring migration. We decomposed this anomaly into three main periods (1–26 April, 27 April–5 May, 6–15 May); one-third of migrants in each period. We modelled three sequential time series of spring passage using calendar year and 15 large-scale climate indices averaged over the months of Willow Warblers’ life stages in the year preceding spring migration as explanatory variables in multiple regression models. Nine climate variables were selected in the best models. We used these nine explanatory variables and calculated their partial correlations in models for nine overlapping sub-periods of AA. The pattern of relationships between AA in these nine sub-periods of spring and the nine climate variables indicated how spring passage had responded to the climate. We recommend this method for the study of birds’ phenological responses to climate change.ResultsThe Southern Oscillation Index and Indian Ocean Dipole in Aug–Oct showed large partial correlations early in the passage, then faded in importance. For the Sahel Precipitation Index (PSAH) and Sahel Temperature Anomaly (TSAH) in Aug–Oct partial correlations occurred early then peaked in mid-passage; for PSAH (Nov–March) correlations peaked at the end of passage. NAO and local temperatures (April–May) showed low correlations till late April, which then increased. For the Scandinavian Index (Jun–Jul) partial correlations peaked in mid-passage. Year was not selected in any of the best models, indicating that the climate variables alone accounted for Willow Warblers’ multiyear trend towards an earlier spring passage.DiscussionClimate indices for southern and eastern Africa dominated relationships in early spring, but western African indices dominated in mid- and late spring. We thus concluded that Willow Warblers wintering in southern and eastern Africa dominated early arrivals, but those from western Africa dominated later. We suggest that drivers of phenological shifts in avian migration are related to changes in climate at remote wintering grounds and at stopovers, operating with climate change in the north, especially for species with complex and long-distance migration patterns.

West Nile and Usutu Virus Introduction via Migratory Birds: A Retrospective Analysis in Italy.

The actual contribution of migratory birds in spreading West Nile (WNV) and Usutu virus (USUV) across Europe and from Africa to old countries is still controversial. In this study, we reported the results of molecular and serological surveys on migrating birds sampled during peaks of spring and autumn migration at 11 Italian sites located along important flyways, from 2012 to 2014. A total of 1335 specimens made of individual or pooled sera, and organs from 275 dead birds were tested for WNV and USUV RNA by real time PCR (RT-PCR). Furthermore, sera were tested by serum neutralization assay for detecting WNV and USUV neutralizing antibodies. Molecular tests detected WNV lineage 2 RNA in a pool made of three Song Thrush (Turdus philomelos) sera sampled in autumn, and lineage 1 in kidneys of six trans-Saharan birds sampled in spring. Neutralizing antibodies against WNV and USUV were found in 5.80% (n = 72; 17 bird species) and 0.32% (n = 4; 4 bird species) of the tested sera, respectively. Our results do not exclude the role of migratory birds as potential spreaders of WNV and USUV from Africa and Central Europe to Mediterranean areas and highlight the importance of a more extensive active surveillance of zoonotic viruses.

Understanding the ecological and evolutionary function of stopover in migrating birds.

Global movement patterns of migratory birds illustrate their fascinating physical and physiological abilities to cross continents and oceans. During their voyages, most birds land multiple times to make so-called 'stopovers'. Our current knowledge on the functions of stopover is mainly based on the proximate study of departure decisions. However, such studies are insufficient to gauge fully the ecological and evolutionary functions of stopover. If we study how a focal trait, e.g. changes in energy stores, affects the decision to depart from a stopover without considering the trait(s) that actually caused the bird to land, e.g. unfavourable environmental conditions for flight, we misinterpret the function of the stopover. It is thus important to realise and acknowledge that stopovers have many different functions, and that not every migrant has the same (set of) reasons to stop-over. Additionally, we may obtain contradictory results because the significance of different traits to a migrant is context dependent. For instance, late spring migrants may be more prone to risk-taking and depart from a stopover with lower energy stores than early spring migrants. Thus, we neglect that departure decisions are subject to selection to minimise immediate (mortality risk) and/or delayed (low future reproductive output) fitness costs. To alleviate these issues, we first define stopover as an interruption of migratory endurance flight to minimise immediate and/or delayed fitness costs. Second, we review all probable functions of stopover, which include accumulating energy, various forms of physiological recovery and avoiding adverse environmental conditions for flight, and list potential other functions that are less well studied, such as minimising predation, recovery from physical exhaustion and spatiotemporal adjustments to migration. Third, derived from these aspects, we argue for a paradigm shift in stopover ecology research. This includes focusing on why an individual interrupts its migratory flight, which is more likely to identify the individual-specific function(s) of the stopover correctly than departure-decision studies. Moreover, we highlight that the selective forces acting on stopover decisions are context dependent and are expected to differ between, e.g. K-/r-selected species, the sexes and migration strategies. For example, all else being equal, r-selected species (low survival rate, high reproductive rate) should have a stronger urge to continue the migratory endurance flight or resume migration from a stopover because the potential increase in immediate fitness costs suffered from a flight is offset by the expected higher reproductive success in the subsequent breeding season. Finally, we propose to focus less on proximate mechanisms controlling landing and departure decisions, and more on ultimate mechanisms to identify the selective forces shaping stopover decisions. Our ideas are not limited to birds but can be applied to any migratory species. Our revised definition of stopover and the proposed paradigm shift has the potential to stimulate a fruitful discussion towards a better evolutionary ecological understanding of the functions of stopover. Furthermore, identifying the functions of stopover will support targeted measures to conserve and restore the functionality of stopover sites threatened by anthropogenic environmental changes. This is especially important for long-distance migrants, which currently are in alarming decline.

Within- and between-Year Variation in the Presence of Individually Marked Ruff Calidris pugnax at a Stopover Site during Northward Migration

Ruffs Calidris pugnax migrate from wintering areas in West-Africa and Europe to breeding grounds in northern Eurasia, using stopover sites along the way. At one such stopover site in southwest Friesland (53°N, The Netherlands), we studied variation in the timing of individual stopover based on 6474 Ruffs colour-ringed in 2004–2012. 43% of males and 22% of females were recorded in the study area in March–May the years following marking. Minimal stopover duration of returning individuals showed substantial within-year heterogeneity. We distinguished two classes: (1) ‘transient’ individuals were observed only on a single day in the study area within a season (51% of observed males and 79% of females), and (2) ‘staging’ individuals were observed on multiple days. We observed two seasonal peaks in the presence of transient Ruffs, typically coinciding with the peak of arrival and departure of staging birds. Males known to winter in Europe were more likely to be observed in the study area and arrived earlier than males of unknown winter origin (3.1 days and 3.7 days earlier for transient and staging males, respectively), but departure was unrelated to winter origin. Staging and transient females arrived later than males. Between-year repeatability of individual behaviour was low, and individuals did not significantly advance their arrival date over the course of years, in contrast with a pattern of shifting arrival dates at the population level. The observation that a large proportion of Ruffs visit southwest Friesland for only a short stop suggests that many individuals rely on other sites for moulting and refuelling during spring migration. Resightings of marked individuals elsewhere in western Europe indicated that these sites are largely located between 51° and 54°N. Thus, during spring migration, Ruffs marked in southwest Friesland displayed high between- and within-individual variation in minimal stopover duration.

Continental Patterns of Bird Migration Linked to Climate Variability

Abstract For ∼100 years, the continental patterns of avian migration in North America have been described in the context of three or four primary flyways. This spatial compartmentalization often fails to adequately reflect a critical characterization of migration—phenology. This shortcoming has been partly due to the lack of reliable continental-scale data, a gap filled by our current study. Here, we leveraged unique radar-based data quantifying migration phenology and used an objective regionalization approach to introduce a new spatial framework that reflects interannual variability. Therefore, the resulting spatial classification is intrinsically different from the “flyway concept.” We identified two regions with distinct interannual variability of spring migration across the contiguous United States. This data-driven framework enabled us to explore the climatic cues affecting the interannual variability of migration phenology, “specific to each region” across North America. For example, our “two-region” approach allowed us to identify an east–west dipole pattern in migratory behavior linked to atmospheric Rossby waves. Also, we revealed that migration movements over the western United States were inversely related to interannual and low-frequency variability of regional temperature. A similar link, but weaker and only for interannual variability, was evident for the eastern region. However, this region was more strongly tied to climate teleconnections, particularly to the east Pacific–North Pacific (EP–NP) pattern. The results suggest that oceanic forcing in the tropical Pacific—through a chain of processes including Rossby wave trains—controls the climatic conditions, associated with bird migration over the eastern United States. Our spatial platform would facilitate better understanding of the mechanisms responsible for broadscale migration phenology and its potential future changes.

Migratory Pathways, Stopover Locations and Wintering Grounds of Southern Spanish Eurasian Scops Owls Otus scops

Little is known about the migration and wintering distribution of Eurasian Scops Owls Otus scops. We deployed GPS-loggers on breeding Scops Owls from a southern Spanish population to analyse migratory routes and migration timing of this trans-Saharan migrant. Tag deployment had no short- or long-term effects on Scops Owls. Individuals followed rapid autumn and spring migrations along the coasts of Morocco and Western Sahara and the western edge of the Sahara desert. South Spanish breeding Scops Owls wintered across a large area of West Africa; within Mauritania, Senegal, Mali, Gambia, Guinea and Sierra Leone, where they stayed apart from one another for 4-5 months. Wintering sites were primarily in tree-covered habitats suggesting that these are important for Scops Owl conservation year-round.—Avilés, J.M., Rodríguez-Ruiz, J., Cruz-Miralles, Á., Abad-Gómez, J.M. & Parejo, D. (2022). Migratory pathways, stopover locations and wintering grounds of southern Spanish Eurasian Scops Owls Otus scops. Ardeola, 69: 129-139.

Stopover use of a large estuarine wetland by dunlins during spring and autumn migrations: Linking local refuelling conditions to migratory strategies.

Migratory strategies dictate stopover ecology, particularly concerning decisions of when, where and how long to stop, and what to do at stationary periods. In birds, individuals stop primarily to replenish energy stores, although the functions of stopover events vary among and within species, particularly between pre- and post-breeding seasons. Here, we combined plasma metabolite levels and haematological parameters to compare refuelling rates and physiological state within (early, mid, late) and between (spring, autumn) migratory periods, aiming to identify potentially different migratory strategies in a shorebird, the dunlin Calidris alpina, using a key stopover site in Iberia. Plasma triglycerides and β-hydroxybutyrate concentrations did not differ between seasons, and small differences were found in haematological profiles (higher haemoglobin and hematocrit levels in spring). Similar refuelling rates and physiological status suggests a single migratory strategy in spring and autumn. During both seasons, dunlins arrive at the Tagus estuary with medium-to-high fuel loads, indicating they do not engage in prolonged fuelling. This agrees with a skipping migratory strategy, where birds fly short-to-medium distances while fuelling at moderate rates along a network of sites. Although we may expect late spring migrants to experience stronger pressures to optimally schedule migratory events, we found no significant differences in physiological profiles among early, mid and late migrants. Unexpectedly, such differences were found in autumn: early birds showed the highest triglycerides and haemoglobin levels and lowest β-hydroxybutyrate concentrations. These results denote enhanced refuelling rates and blood oxygen-carrying capacity in early autumn migrants, which is typical of jumpers, i.e., birds travelling with larger fuel loads and performing fewer stops. Our study adds substantially to previous knowledge of stopover ecology in migratory shorebirds in the East Atlantic Flyway. Importantly, it indicates that the Tagus estuary is a high-quality stopover site for intermediate fuelling. Yet, understanding non-fuelling stopping functions is needed to ultimately inform conservation planning.

Testing the potential of streamflow data to predict spring migration of ungulate herds.

In mountainous and high latitude regions, migratory animals exploit green waves of emerging vegetation coinciding with rising daily mean temperatures initiating snowmelt across the landscape. Snowmelt also causes rivers and streams draining these regions to swell, a process referred to as to as the 'spring pulse.' Networks of streamgages measuring streamflow in these regions often have long-term and continuous periods of record available in real-time and at the daily time step, and thus produce data with potential to predict temporal migration patterns for species exploiting green waves. We tested the potential of models informed by streamflow data to predict timing of spring migration of mule deer (Odocoileus hemionus) herds in a headwater basin of the Colorado River. Models using streamflow data were compared with those informed by traditional temperature-derived measures of the onset of spring. Non-parametric linear-regression techniques were used to test for temporal stationarity in each variable, and logistic-regression models were used to produce probabilities of migration initiation. Our analysis indicates that models using daily streamflow data can perform as well as those using temperature-derived data to predict past-migration patterns, and nearly as well in potential to forecast future migrations. The best performing model was used to generate probabilities of onset of migration for mule deer herds over the 69-year period-of-record from a streamgage. That model indicated spring migration has been trending toward earlier initiations, with modeled median initiations shifting from a Julian day of 123 in the mid 20th century to Julian day 115 over the most recent two decades. The period of 1960 to 1979 had the latest modeled median initiations with Julian day of 128. The analyses demonstrate promise for merging existing hydrologic and biological data collection platforms in these regions to explore timing of past migration patterns and predict migration onsets in real-time.

The potential function of post-fledging dispersal behavior in first breeding territory selection for males of a migratory bird.

One possible hypothesis for the function of post-fledging dispersal is to locate a suitable future breeding area. This post-fledging period may be particularly important in migratory species because they have a limited period to gather information prior to autumn migration, and in protandrous species, males must quickly acquire a territory after returning from spring migration to maximize their fitness. Here we use color-ring resightings to investigate how the post-fledging dispersal movements of the Cyprus wheatear Oenanthe cypriaca, a small migratory passerine, relate to their first breeding territory the following year when they return from migration. We found that males established first breeding territories that were significantly closer to their post-fledging location than to their natal sites or to post-fledging locations of other conspecifics, but these patterns were not apparent in females. Our findings suggest that familiarity with potential breeding sites may be important for juveniles of migratory species, particularly for the sex that acquires and advertises breeding territories. Exploratory dispersal prior to a migrant's first autumn migration may contribute toward its breeding success the following year, further highlighting the importance of early seasonal breeding on fitness and population dynamics more generally.

Association of weather variables with the migration phenology and body conditions of Siberian warblers

Different elements of weather, such as wind speed, wind direction, precipitation and temperature are very important regulators of bird migration. Weather conditions also play role on the body condition such as body mass and the deposited fat. In this study we selected four warbler species to examine the impact of different weather variables on their spring and autumn migration timing and their body condition in one of the most extreme weather areas of the Earth, at Lake Baikal in Siberia. We also studied the changes in body mass and fat reserves during the spring and autumn migration periods of these species. For the analyses, we used ringing data of 2471 birds from five spring and five autumn seasons during 2015–2019. According to our results, it can be stated that the weather did not have a significant association with the migration timing of the studied warblers, perhaps due to the geographical location of the study site. However, the body mass and the fat reserves of the birds increased during unsuitable weather conditions because of the increased energy requirements. Birds generally migrate with low fat reserves, which is due to the fact that this area is not an important stopover site for these species.

A tail of plumage colouration: disentangling geographic, seasonal and dietary effects on plumage colour in a migratory songbird

Plumage ornamentation in birds serves critical inter‐ and intra‐sexual signaling functions. While carotenoid‐based plumage colouration is often viewed as a classic condition‐dependent sexually selected trait, plumage colouration can be influenced by a wide array of both intrinsic and extrinsic factors. Understanding the mechanisms underlying variation in colouration is especially important for species where the signaling function of ornamental traits is complex or when the literature is conflicting. Here, we examined variation in the yellow/orange tail feathers of American redstarts Setophaga ruticilla passing through two migratory stopover sites in eastern North America during both spring and fall migration to assess the role of geographic variation and seasonality in influencing feather colouration. In addition, we investigated whether diet during moult (inferred via stable isotope analysis of feather δ15N and δ13C) influenced plumage colouration. Our findings indicate that geographic variation, season and diet all influence individual differences in American redstart colouration, represented by both traditional and tetrahedral colour variables. The extent to which these factors influence colour expression however is largely dependent on the colour metric under study, likely because different colour metrics reflect different attributes of the feather (e.g. structural components versus pigment deposition). The effects of diet (δ15N) and season were pronounced for brightness, suggesting a strong effect of diet and feather wear/degradation on feather structure. Though hue, a metric that should strongly reflect pigment deposition, also changed from spring to fall, that effect was dependent on age, with only adults experiencing a reduction in ornamentation. Taken together, our results highlight the numerous sources of variation behind plumage coloration and underscores the difficulty of unraveling complex visual signaling systems, such as those in American redstarts.

Relationship between reproductive hormones and migration distance in a polygynous songbird, the Red-winged Blackbird (Agelaius phoeniceus)

Many bird species migrate to southern overwintering locations to avoid harsh conditions at their breeding grounds, but at the cost of an energetically demanding migration that may delay their spring reproductive development. Previous work on the relationship between migration distance and reproductive readiness has primarily focused on early season baseline testosterone in both males and females. However, for females, testosterone alone may not be the appropriate measurement of reproductive development. Estradiol, a metabolite of testosterone that is essential for breeding behaviors and reproduction, should also be measured. Furthermore, baseline testosterone varies throughout the day and may change due to social interactions that occurred prior to sampling. Injection of gonadotropin-releasing hormone (GnRH) elicits an individual’s maximum potential testosterone production, minimizing daily and social variation. We explored relationships between migration distance and reproductive status after arrival to the breeding ground in Red-winged Blackbirds (Agelaius phoeniceus). We predicted that individuals that travel a shorter distance will have higher levels of reproductive hormones upon arrival given they are able to invest less in migration and more in reproduction. This is important because individuals that breed earlier often have higher reproductive success. In females, we measured baseline estradiol and testosterone. In males, we assessed baseline and GnRH-induced testosterone. Hormone values were related to migration distance, estimated by stable isotope analysis of claw samples collected before breeding began in eastern North Dakota. We found that males with shorter inferred migration distances have higher baseline testosterone upon arrival. However, inferred migration distance was not correlated with GnRH-induced testosterone. Female inferred migration distance was not correlated with baseline testosterone, but it was correlated with baseline estradiol. Females with higher testosterone had lower estradiol, suggesting that testosterone in females is not a reliable indicator of estradiol levels, thus readiness to breed. Our observations suggest that baseline hormone levels were related to migration distance, but baseline testosterone alone may not provide a complete assessment of a male or female’s preparedness to breed following spring migration.

Investigating the phenology of juvenile potamodromous brown trout (Salmo trutta L.) in two large lake catchments.

There is growing interest in the phenology of juvenile Salmo trutta and evidence of significant downstream migration during the autumn in some anadromous populations. The present study used acoustic telemetry to examine the phenology of potamodromous trout parr across a region encompassing two large lake catchments. One hundred sixty-seven trout parr were tagged in late summer across four lake tributaries between 2018 and 2020. In total, 75 tagged parr migrated into the lakes with 67 (89%) migrating between September and December and 8 (11%) migrating between March and June. Autumn migration was highly prevalent across all the tributaries, with 16%-66% of each tagged sample exhibiting autumn migration, and 0%-15% of each tagged sample exhibiting spring migration. Autumn migrants were significantly longer and heavier than spring migrants, but condition factor was similar. Autumn migrants were associated with higher river discharge levels and lower water temperatures than spring migrants. The management challenges posed by extensive autumn migration behaviour in migratory trout stocks are examined and discussed.

Dynamics of various forms of manganese in the pond waters

The forms of migration of manganese in pond waters are suspended matter and truly dissolved forms, including free manganese cations, as well as complex compounds formed by manganese with organic substances. The aim of the work was to study the dynamics of the content of various forms of manganese in the water of fish ponds. The content of individual forms of manganese was established according to the method developed by Linnik and Nabivanets. According to the methodology of Alekin, Semenov and Skopintsev determined hydrochemical parameters. It has been established that the dynamics of the content of manganese forms in different seasons depends mainly on the concentration of dissolved oxygen, pH value, inflow from sludge waters and the content of dissolved organic complexing substances in the water. In winter, free uncomplexed ions are the dominant form of migration. In other seasons, the content of complex forms exceeds the concentration of uncomplexed manganese. The dominant form of manganese migration in spring, summer, and autumn is Mn suspended, while in some periods of the same seasons, Mn dissolved predominates, which is explained by the influence of the intensity of water exchange, where suspended particles settle under conditions of slow runoff.

Migrants employ mixed strategies to route across the Great Lakes basin

Millions of migrants encounter the Great Lakes during spring and autumn migratory movements. How migrants behave when encountering these lakes is relatively unknown at the local and basin scales. Using seven years of radar data from 33 sites along the Great Lakes coastline, we investigated three hypotheses on migrant behavior during crepuscular and nocturnal movements. First, we hypothesized migrants’ direction is driven by local geography and its relation to the destination of migration. Second, we hypothesized migrants would move toward shore at dawn. Finally, we hypothesized that the Great Lakes would have different directional movements at lakes on the outside of the basin versus the interior. We found partial support for our first hypothesis, as well as evidence of decision making when migrants first encounter the Great Lakes. We found partial support for our second hypothesis. We found that migrants moved toward land at elevated levels at dawn compared to night during fall migration, but no effect was found during spring. We found support for our final hypothesis during spring migration, but not during fall. This pattern may be because of a combination of geographical, biological, and data bias, and will require additional work to disentangle. Taken together, we found that migrants perceive and react to the Great Lakes, and attempt to decrease risk, perceived or real, as they make their way to their migratory destination. Better understanding of directional movement has conservation implications, including mitigating anthropogenic obstacle collision risk and prioritizing stopover habitat restoration.

Dynamics of pre-breeding nutrient reserves in subarctic staging Lesser Snow Geese (Anser caerulescens caerulescens) and Ross’s Geese (Anser rossii): implications for reproduction

Phenological mismatch occurs when the timing of reproductive events and seasonal availability of resources become decoupled, and is increasing in migratory birds in response to climate change. Arctic-nesting geese acquire important nutrient reserves at spring-staging areas, but advancing springs, combined with large population increases and long-term goose-mediated habitat alteration, could induce a mismatch between optimal timing of nesting and accumulation of required reserves. From 2012 to 2019, we randomly sampled Lesser Snow (<em>Anser caerulescens caerulescens</em>) and Ross’s Geese (<em>Anser rossii</em>) throughout their spring migration near Churchill, Manitoba, Canada. Our objectives were to evaluate patterns of protein and lipid accumulation, and draw comparisons to historical estimates obtained before widespread habitat changes. We found significantly reduced pre-breeding protein reserves in Lesser Snow Geese relative to their historical values, but average protein reserve size increased somewhat with declining population size during the years of our study. Lesser Snow Geese catabolized lipid reserves, and no longer increased protein reserves during spring staging. Protein reserves were on average 17–23% smaller in 2012–2019 than in the 1970s, the deficit being equivalent to the amount of protein found in two to three eggs. In contrast, Ross’s Geese maintained lipid reserves, and accumulated protein during the staging period, irrespective of annual Lesser Snow Geese abundance. Based on patterns in gizzard hypertrophy, they appeared to be using a more digestible food source than were Lesser Snow Geese. Declines in protein reserves may hinder the ability for Lesser Snow Geese to keep nutritional pace with increasingly early springs, and could be an important underlying mechanism driving mismatches between vegetation phenology and emergence of goslings. Differences in recruitment between Lesser Snow Geese and Ross’s Geese could be related to differences in nutrient-reserve dynamics during the final stages of spring migration, which can carry over to influence annual breeding probability, clutch size, nest success, and likelihood of mismatch at a population level.

Migration and wintering of vulnerable adult Chinese Egrets (Egretta eulophotes) revealed by GPS tracking

Knowledge of migratory bird requirements is critical to developing conservation plans for vulnerable migratory species. This study aimed to determine the migration routes, wintering areas, habitat uses, and mortalities of adult Chinese Egrets (Egretta eulophotata). Sixty adult Chinese Egrets (31 females and 29 males) on an uninhabited offshore breeding island in Dalian, China were tracked using GPS satellite transmitters. GPS locations recorded at 2 ​h intervals from June 2019 to August 2020 were used for analysis. A total of 44 and 17 tracked adults completed their autumn and spring migrations, respectively. Compared with autumn migration, tracked adults displayed more diverse routes, higher number of stopover sites, slower migration speed, and longer migration duration in the spring. Results indicated that migrant birds had different behavioral strategies during the two migratory seasons. The spring migration duration and stopover duration for females were significantly longer than those for males. A positive correlation existed between the spring arrival and spring departure dates, as well as between the spring arrival date and stopover duration. This finding indicated that the egrets that arrived early at the breeding grounds left the wintering areas early and had a shorter stopover duration. Adult birds preferred intertidal wetlands, woodlands, and aquaculture ponds during migration. During the wintering period, adults preferred offshore islands, intertidal wetlands, and aquaculture ponds. Adult Chinese Egrets showed a relatively low survival rate compared with most other common ardeid species. Dead specimens were found in aquaculture ponds, indicating human disturbance as the main cause of death of this vulnerable species. These results highlighted the importance of resolving conflicts between egrets and human-made aquaculture wetlands and protecting intertidal flats and offshore islands in natural wetlands through international cooperation. Our results contributed to the hitherto unknown annual spatiotemporal migration patterns of adult Chinese Egrets, thereby providing an important basis for the conservation of this vulnerable species.