Spring Migration Seasons Research Articles

Human-facilitated feeding on Date Palm Phoenix dactylifera sap by trans-Saharan warblers during spring stopover in a Tunisian oasis

ABSTRACT Capsule Some trans-Saharan warbler species feed on human-extracted Date Palm Phoenix dactylifera sap during spring migratory stopover. Aims To investigate the behaviour of birds feeding on Date Palm sap at a Tunisian oasis during the spring migration season. Methods Birds feeding on Date Palm sap were monitored during the peak of spring migratory passage of trans-Saharan birds in southern Tunisia by recording the species involved and their numbers, and noting whether there were agonistic interactions between them. Data were used to describe the assemblages of birds feeding on Date Palm sap. Results We recorded five trans-Saharan warbler species feeding on Date Palm sap, either in single- or mixed-species flocks. Aggressive conflicts were common, suggesting competition by interference within this bird assemblage. However, other abundant fruit-eating trans-Saharan warbler species were never seen feeding on Date Palm sap, possibly due to the potential inability to assimilate some of its components, or simply because they did not need to ingest it for reasons related to their migration strategy. Conclusions Our findings reveal that Date Palm sap is a food resource for some trans-Saharan warbler species, highlighting a rarely documented human-facilitated feeding behaviour in birds. They also underline the high ecological plasticity of these warbler species, capable of using different food resources to meet the needs of their challenging migratory journey.

Leveraging similarity analysis to understand variability in movement behavior

AbstractThe increasingly large volume of trajectories of moving entities obtained through GPS and cellphone tracking, telemetry, and other location‐aware technologies motivates researchers to understand the implicit patterns hidden in movement trajectories and understand how movement is influenced by the environmental context. Trajectory similarity serves as an important tool in computational movement analysis and as the foundation of revealing those patterns. However, there are various trajectory similarity measures, each of which has its own strengths and weaknesses. In this article, we present a hierarchical clustering framework that integrates five commonly used similarity measures, including Fréchet distance, dynamic time warping, Hausdorff distance, longest common subsequence, and normalized weighted edit distance, a special kind of edit distance for movement analysis. The framework aims at clustering similar patterns and identifying variability in movement. The optimal number of clusters are first obtained. Then, the clusters are characterized by environmental variables to explore the associations between variability in movement and the environmental conditions. We evaluate the proposed framework using 15 years of tracking data of turkey vultures, tracked at 1‐ to 3‐h sampling intervals, during their fall and spring migration seasons. The results suggest that, at 5% significance level, turkey vultures select their movement paths intentionally and those selections appear to be related to certain environmental context variables, including thermal uplift, vegetation state (observed indirectly through Normalized Difference Vegetation Index), temperature, precipitation, tailwind, and crosswind. And interestingly, there exist preferential differences among individuals. Although the preference of the same turkey vulture is not strictly consistent over different years, each individual tends to preserve a more similar preference over different years, compared with the preferences of other turkey vultures.

Glass eel (Anguilla anguilla L. 1758) feeding behaviour during upstream migration in an artificial waterway

The transition from marine to fresh water is a challenging task for juvenile eels. This critical step in the early eels' life is preceded by a metamorphosis from the oceanic larval to the continental glass eel stage, requiring major energy-demanding morphological, physiological and behavioural modifications during which time these animals do not feed. The success of the glass eels' inland migration after metamorphosis will largely depend on remaining energy levels, which can be supplemented only by resuming food uptake. Although it is crucial for their survival and the maintenance of the population, the feeding behaviour of glass eels is still an understudied aspect of the eels' complex life cycle. Many uncertainties about the phenology, diet, potential prey preferences and their relation with migration modus (migratory vs. sedentary) still remain. In this study, the authors analysed the stomach and gut contents of 458 European glass eels (Anguilla anguilla L. 1758) captured in a drainage canal connecting a small mesotidal estuary with an adjacent polder area during the spring migration seasons of 2016 and 2017. They demonstrated that although glass eels started feeding briefly upon arrival in the estuary, food uptake for early arrivals was restricted to a minority that sparsely feed on detritus and some worm-like benthic invertebrates. Along the season, food uptake intensified eventually engaging all glass eels and their dietary palette diversified including a wide array of planktonic and benthic organisms. Crustacean plankton (mainly cyclopoid copepods) was an important part of the glass eel diet, whereas benthic oligochaetes were less abundant as food source in spite of their high presence in the sediments. No clear differences in feeding behaviour could be observed between migratory and sedentary glass eels. This study showed that glass eels can use highly artificial and dynamic drainage canals as feeding ground during their critical marine/freshwater transition. This outcome is also a plea to improve the accessibility of alternative (unnatural) migration routes between the ocean and suitable freshwater growth habitats for the European eel.

Season, anthocyanin supplementation, and flight training have mixed effects on the antioxidant system of migratory European Starlings

Abstract Migratory birds engage in 2 periods of endurance flight annually as they travel between summer breeding and overwintering grounds, and such endurance flights likely incur oxidative costs. These costs may differ between fall and spring migration, especially for females who must prepare for breeding and egg laying in spring. The objective of this study of a migratory bird was to test proposed hypotheses about how key components of the female’s antioxidant system differ in response to flight training in the fall and spring and to dietary antioxidant supplementation. We hand raised female European Starlings (Sturnus vulgaris) and fed them either a diet supplemented with dietary anthocyanins or a diet without added anthocyanins. We flew females in a wind tunnel for 15 days during fall and spring migration seasons and measured over time oxidative lipid damage (d-ROMs) and 3 components of the antioxidant system: nonenzymatic antioxidant capacity (OXY), uric acid, and glutathione peroxidase (GPx) activity. Prior to flight training, OXY and oxidative damage were lower in females during spring compared with fall, and females fed a low-antioxidant diet had consistently higher circulating uric acid. GPx activity decreased more in spring immediately after a long-duration flight. Females fed a high-antioxidant diet had a greater decrease in OXY after the 15-day flight training. Flight-trained females had higher circulating uric acid than untrained females immediately after the longest-duration flight and decreased GPx activity after the 15-day flight training. In sum, females upregulated enzymatic and nonenzymatic endogenous antioxidants in spring, and females fed a diet with less antioxidants appear to compensate by increasing circulating uric acid. Our findings emphasize the important role of dietary antioxidants for birds during migration, and similar flights in fall and spring likely represent distinct oxidative challenges in the life history of female birds.

Songbird use of interior and edge floodplain forest sites along the Upper Mississippi River, USA, during spring migration and breeding seasons

Floodplain forests of large rivers in the midwestern United States are naturally fragmented by sloughs, backwaters, wetlands, and shrub carr. On the highly altered Upper Mississippi River (UMR), resource managers want to protect and manage floodplain forests to benefit forest “interior” bird species. To discover bird relations with interior and edge floodplain forest, we characterized bird assemblages during spring migration and breeding season in 3 forest types: habitat in the interior of forest areas > 100 m from an edge, edges associated with interior areas, and other areas of forest not associated with an interior area (random sites) on the UMR between Hastings and Red Wing, Minnesota. The random sites represent the majority of UMR floodplain forest area because only a small percentage of forest occurs >100 m from edge. Estimated habitat characteristics did not differ among interior, edge, and random sites. Bird relative abundance, species richness, diversity, assemblage composition, and detections of all but one species (in spring) did not differ among interior, edge, and random sites during both seasons. Our results suggest a homogeneous bird assemblage across UMR floodplain forest in the study area during spring migration and the breeding season, and that individual forest bird species do not seem to be more abundant in interior or edge areas as we defined them.

Consistency of spatio‐temporal patterns of avian migration across the Swiss lowlands

AbstractEach year, billions of birds migrate across the continents by day and night through airspaces increasingly altered by human activity, resulting in the deaths of millions of birds every year through collisions with man‐made structures. To reduce these negative impacts on wildlife, forecasts of high migration intensities are needed to apply mitigation actions. While existing weather radar networks offer a unique possibility to monitor and forecast bird migration at large spatial scales, forecasts at the fine spatial scale within a complex terrain, such as the mountainous Swiss landscape, require a small‐scale network of ornithological radars. Before attempting to build such a network, it is crucial to first investigate the consistency of the migratory flow across space and time. In this study, we simultaneously operated three ornithological radar systems across the Swiss lowlands to assess the spatio‐temporal consistency of diurnal and nocturnal bird movements during the spring and autumn migration season. The relative temporal course of migration intensities was generally consistent between sites during peak migration, in particular for nocturnal movements in autumn, but absolute intensities differed greatly between sites. Outside peak migration, bird movement patterns were much less consistent and, unexpectedly, some presumably non‐migratory bird activity achieved intensities close to peak migration intensities, but without spatial correlations. Only nocturnal migration intensity in autumn could be predicted with consistently high accuracy, but including parameters of atmospheric conditions in the model improved predictability of diurnal movements considerably. Predictions for spring were less reliable, probably because we missed an important part of the migration season. Our results show that reliable forecasts of bird movements within a complex terrain call for a network of year‐round bird monitoring systems, whereas accurate information of atmospheric conditions can help to limit the number of measurement points.

Urban areas affect flight altitudes of nocturnally migrating birds.

Urban areas affect terrestrial ecological processes and local weather, but we know little about their effect on aerial ecological processes. Here, we identify urban from non-urban areas based on the intensity of artificial light at night (ALAN) in the landscape, and, along with weather covariates, evaluate the effect of urbanization on flight altitudes of nocturnally migrating birds. Birds are attracted to ALAN; hence, we predicted that altitudes would be lower over urban than over non-urban areas. However, other factors associated with urbanization may also affect flight altitudes. For example, surface temperature and terrain roughness are higher in urban areas, increasing air turbulence and height of the boundary layer, and affecting local winds. We used data from nine weather surveillance radars in the eastern United States to estimate altitudes at five quantiles of the vertical distribution of birds migrating at night over urban and non-urban areas during five consecutive spring and autumn migration seasons. We fit Generalized Linear Mixed Models by season for each of the five quantiles of bird flight altitude and their differences between urban and non-urban areas. After controlling for other environmental variables and contrary to our prediction, we found that birds generally fly higher over urban areas compared to rural areas in spring, and marginally higher at the mid-layers of the vertical distribution in autumn. We also identified a small interaction effect between urbanization and crosswind speed, and between urbanization and surface air temperature, on flight altitudes. We also found that the difference in flight altitudes of nocturnally migrating birds between urban and non-urban areas varied among radars and seasons, but was consistently higher over urban areas throughout the years sampled. Our results suggest that the effects of urbanization on wildlife extend into the aerosphere and are complex, stressing the need of understanding the influence of anthropogenic factors on airspace habitat.

Avifauna of Gungdae Oreum and its seasonal changes in the Jeju Eastern Oreum Group in Jeju Island, Korea

“Oreum” is a local common name for a volcanic cone in Jeju Island, the Republic of Korea. Oreums in the Jeju Eastern Oreum Group (JEOG), located in the eastern mid-mountain region of Jeju, have been threatened by increasing tourism and associated development pressures; however, year-round monitoring activities on their ecological values have rarely been implemented. This study aimed to provide for the first time weekly monitoring information on the avifauna and its seasonal changes at Gungdae Oreum, covered by planted forest stands and located at the eastern end of the JEOG, to bridge our knowledge gap on local ecosystems of the JEOG. We surveyed the avifauna weekly for 51 weeks from July 2017 to July 2018 and documented a total of 4,763 birds from 69 species, including nine nationally protected species and 22 breeding species. Species richness and diversity indices calculated in each survey effort were not significantly changed by seasons, probably because the majority of the avifauna in the JEOG was dominated by common resident forest birds. However, seasonal rarefaction curves revealed that more frequent and repeated surveys may document more species especially in spring and autumn migration seasons, suggesting that diverse migratory birds would pass through the JEOG. The computed asymptotic richness was 83 species (95% confidence interval: 73–116), which is higher than the observed species richness (69 species) recorded over a year. This result also emphasizes the importance of long-term and multiyear monitoring programs with constant and standardized sampling efforts to better understand the local avifauna and biodiversity in forested environments.

Sandhill Crane Use of Riverine Roost Sites along the Central Platte River in Nebraska, USA

Wide channels with short bank vegetation, access to nearby foraging habitat, shallow water areas ( 5000 cranes), but the ratio was statistically similar across a wide range of maximum unobstructed channel widths. Medium-sized Sandhill Crane groups (501–5000 cranes) were less influenced by in-channel vegetated islands, and these groups selected channels based on wide total unvegetated channel widths. Our results also suggest that flows ≤39.05 m3/s (cms; 1379 cfs) in channels that are 275 m in unvegetated width maximize selection ratios for medium and large crane groups, so flows above this level may not improve Sandhill Crane roosting habitat conditions during the spring migration and staging season within the central Platte River. While Sandhill Cranes stage within the central Platte River valley for a longer time interval in the spring, Whooping Cranes (Grus americana) also use the Platte River as a stopover point. Both species share similar indices for roosting habitat, such as unobstructed channel width and shallow water depths. The results of our investigation could be used to identify a range of flows and channel width configurations expected to generate the highest amount of suitable habitat for Sandhill Cranes roosting along the central Platte River.

Oral Capillariosis Due to Eucoleus dispar in Migrating Sharp-Shinned Hawks (Accipiter striatus) in New York, USA, 2016–18

Oral lesions focused around the oral commissures were documented in several Sharp-shinned Hawks (Accipiter striatus) in the 2016-18 spring migration season at a banding station located on the southern shore of Lake Ontario, New York, US. Samples of the inflamed and caseous lesions repeatedly tested negative for Trichomonas gallinae and poxvirus; however, large numbers of capillariid eggs and embedded worms were consistently present. Morphologically, the nematodes were identified as Eucoleus dispar, which was confirmed by PCR and genetic sequencing. The affected hawks displayed no other clinical signs of illness, were in good body condition, and were released back into their migration pathway shortly after examination and testing. We report a unique clinical presentation for oral capillariosis in A. striatus.

Phenology of the avian spring migratory passage in Europe and North America: Asymmetric advancement in time and increase in duration

Climate change has been shown to shift the seasonal timing (i.e. phenology) and distribution of species. The phenological effects of climate change on living organisms have often been tested using first occurrence dates, which may be uninformative and biased. More rarely investigated is how different phases of a phenological sequence (e.g. beginning, central tendency and end) or its duration have changed over time. This type of analysis requires continuous observation throughout the phenological event over multiple years, and such data sets are rare. In this study we examined the impact of temperature on long-term change of passage timing and duration of the spring migration period in birds, and which species’ traits explain species-specific variation. Data used covered 195 species from 21 European and Canadian bird observatories from which systematic daily sampling protocols were available. Migration dates were negatively associated with early spring temperature and timings had in general advanced in 57 years. Short-distance migrants advanced the beginning of their migration more than long-distance migrants when corrected for phylogenic relatedness, but such a difference was not found in other phases of migration. The advancement of migration has generally been greater for the beginning and median phases of migration relative to the end, leading to extended spring migration seasons. Duration of the migration season increased with increasing temperature. Phenological changes have also been less noticeable in Canada even when corrected for rate of change in temperature. To visualize long-term changes in phenology, we constructed the first multi-species spring migration phenology indicator to describe general changes in median migration dates in the northern hemisphere. The indicator showed an average advancement of one week during five decades across the continents (period 1959–2015). The indicator is easy to update with new data and we therefore encourage future research to investigate whether the trend towards longer periods of occurrence or emergence in spring is also evident in other migratory populations. Such phenological changes may influence detectability in monitoring schemes, and may have broader implications on population and community dynamics.

Screening for multiple tick-borne pathogens in Ixodes ricinus ticks from birds in Denmark during spring and autumn migration seasons

Presently, it is uncertain to what extent seasonal migrating birds contribute to the introduction of ticks and tick-associated pathogens in Denmark. To quantify this phenomenon, we captured birds during the spring and autumn migration at three field sites in Denmark and screened them for ticks. Bird-derived ticks were identified to tick species and screened for 37 tick-borne pathogens using real-time PCR. Overall, 807 birds, representing 44 bird species, were captured and examined for ticks during the spring (292 birds) and autumn migrations (515 birds). 10.7% of the birds harboured a total of 179 Ixodes ricinus ticks (38 ticks in spring and 141 in the autumn) with a mean infestation intensity of 2.1 ticks per bird. The European robin (Erithacus rubecula), the common blackbird (Turdus merula), and the common redstart (Phoenicurus phoenicurus) had the highest infestation intensities. 60.9% of the ticks were PCR-positive for at least one tick-borne pathogen. Borrelia DNA was found in 36.9% of the ticks. The Borrelia species detected were B. spielmanii (15.1%), B. valaisiana (13.4%), B. garinii (12.3%), B. burgdorferi s.s. (2.2%), B. miyamotoi (1.1%), and B. afzelii (0.6%). In addition, 10.6% and 1.7% of the samples were PCR-positive for spotted fever group rickettsiae and Candidatus Neoehrlichia mikurensis. All of the tick-borne pathogens that we found in the present study are known to occur in Danish forest populations of I. ricinus. Our study indicates that migrating birds can transport ticks and their pathogens from neighboring countries to Denmark including sites in Denmark without a sustainable tick population. Thus, a tick-borne pathogen affecting human or animal health emerging at one location in Europe can rapidly be introduced to other countries by migrating birds. These movements are beyond national veterinary control. The current globalization, climatic and environmental changes affect the potential for introduction and establishment of ticks and tick-borne pathogens in Northern Europe. It is therefore important to quantify the risk for rapid spread and long distance exchange of tick-borne pathogens in Europe.

Ticks (Acari: Ixodidae) Parasitizing Passerine Birds in Turkey With New Records and New Tick–Host Associations

In 2016 spring and autumn migration seasons, 7,992 birds belonging to 83 species, 51 genera, 34 families, and 12 orders were examined for tick (Acari: Ixodidae) infestation in the Kızılırmak Delta, Samsun, Turkey. A total of 1,229 (649 larvae, 536 nymphs, 40 females, 4 males) ticks were collected from 349 (4.36%) birds belonging to 33 (39.75%) species within 16 families in the order Passeriformes. Nine tick species were identified belonging to the family Ixodidae, namely Haemaphysalis concinna Koch, Haemaphysalis punctata Canestrini & Fanzago, Haemaphysalis sulcata Canestrini & Fanzago, Hyalomma marginatum gr., Ixodes eldaricus Djaparidze, Ixodes festai Tonelli-Rondelli, Ixodes frontalis (Panzer), Ixodes redikorzevi Olenev, and Ixodes ricinus (L.). The present study also reports 78 different avian (resident, migratory or partially migratory) hosts for documented tick species; 63 (80.76%) of them were new tick-host records for Turkey. In addition, the presence of I. eldaricus and I. festai ticks were documented in Turkey for the first time.

Urban green roofs provide habitat for migrating and breeding birds and their arthropod prey.

The world is rapidly urbanizing, and many previously biodiverse areas are now mostly composed of impervious surface. This loss of natural habitat causes local bird communities to become dominated by urban dweller and urban utilizer species and reduces the amount of habitat available for migrating and breeding birds. Green roofs can increase green space in urban landscapes, potentially providing new habitat for wildlife. We surveyed birds and arthropods, an important food source for birds, on green roofs and nearby comparable conventional (non-green) roofs in New York City during spring migration and summer breeding seasons. We predicted that green roofs would have a greater abundance and richness of both birds and arthropods than conventional roofs during both migration and the breeding season for birds. Furthermore, we predicted we would find more urban avoider and urban utilizer bird species on green roofs than conventional roofs. We found that both birds and arthropods were more abundant and rich on green roofs than conventional roofs. In addition, green roofs hosted more urban avoider and utilizer bird species than conventional roofs. Our study shows that birds use green roofs as stopover habitat during migration and as foraging habitat during the breeding season. Establishing green roofs in urban landscapes increases the amount of habitat available for migrating and breeding birds and can partially mitigate the loss of habitat due to increasing urbanization.

Long-term bird ringing in Palestine

Abstract This paper reports the results of mist-netting of birds, mainly passerines, at the Talitha Kumi ringing site by the Environmental Education Center (EEC), supported by the Evangelical Lutheran Church in Jordan and the Holy Land. Bird catching/ringing has been conducted there since 2000, but the data presented here are limited to ten years of work (2004-2013), mainly for compatibility reasons. During this time 6,810 individuals of 70 species were caught, of which 16 migrants and 8 local species caught most frequently are discussed. Data on seasonal (all year) and long-term (10-year) dynamics are given. The following general conclusions were drawn: (1) Even infrequent sampling of the local population by netting provides important information on seasonal and long-term patterns and trends; (2) the same is true of migrating species, provided that the work is carried out using the same methods over a long time span; (3) in migrants, very differentiated relations are observed between numbers of individuals caught during the spring and autumn migration seasons; (4) during the ten years of the study negative trends in the number of captured birds were observed for 14 species, including significantly negative trends for 4 species, while positive trends were observed for 10, none of which was significant.

Habitat use of the Wood Warbler Phylloscopus sibilatrix during spring migration versus breeding season based on citizen science data

ABSTRACTCapsule: Citizen science data on Wood Warblers Phylloscopus sibilatrix showed that the species non-selectively used a wide variety of habitats during migration but had a tendency for settling to breed in forest and natural areas.Aims: We tested the hypothesis that habitat used during spring stopovers in Spain differed from habitat use during the breeding period in Switzerland in a year of exceptional abundance as a result of persistent easterly winds in the Mediterranean.Methods: Habitat use during spring migration 2015 was compared by using bootstrapping resampling techniques on citizen science data from Spain and Switzerland, comparing the land-cover categories between locations of observations with random pseudo-absences.Results: Wood Warblers showed no preference for habitat features during migration and covered practically all available habitat types from urbanized areas to wetlands and forests, whereas in the breeding range birds showed an increasing tendency to be present in forest habitats.Conclusions: Habitat use during spring migration covered most available habitat types from urbanized areas to wetlands and forests. Breeding habitat use was restricted to forested areas. Citizen science allowed a quick collection of biological data over a wide area to potentially identify large-scale biological patterns. This is essential to potentially manage international conservation efforts for declining species.

Day of year, temperature, wind, and precipitation predict timing of bat migration

Many temperate-climate bats migrate tens to hundreds of kilometers from hibernacula to summer habitat each spring and in the opposite direction each fall. Understanding the timing of migration can help reduce the risk of disturbance via anthropogenic activities, guide effective management, and determine future impacts of a changing climate. We examined the influence of weather and day of year on the arrival and departure of Indiana bats (Myotis sodalis) monitored at a summer maternity colony site in central Indiana from 1998 to 2014, using emergence count data to track the timing of bat presence during the spring and fall migration seasons. We used an information theoretic approach to compare 23 models that predicted bat presence as a function of weather, climate, and lunar illumination; these models predicted arrival of the first Indiana bat and the first observation of a colony in spring, and the last observation of a colony and the last bat observed in fall. Bats embarked on spring and fall migrations to the maternity colony area at approximately the same time each year (arriving ∼3 April and departing ∼7 October) and variation was accounted for by changes in weather. Spring arrival and colony formation were predicted by higher temperatures ( = 22.5°C for colony formation) and precipitation and lower wind speeds, whereas lower temperatures ( = 25.9°C for colony breakup) and precipitation and higher wind predicted colony breakup and departure in fall. Spring migration coincided with periods of increased winds and, thus, we advocate for higher cut-in speeds for wind turbines during bat migration seasons. Resource managers should consider the entire time that bats are on the summer landscape when defining regulations and implementing conservation measures.

Sandhill crane roost selection, human disturbance, and forage resources

ABSTRACTSites used for roosting represent a key habitat requirement for many species of birds because availability and quality of roost sites can influence individual fitness. Birds select roost sites based on numerous factors, requirements, and motivations, and selection of roosts can be dynamic in time and space because of various ecological and environmental influences. For sandhill cranes (Antigone canadensis) at their main spring‐staging area along the Platte River in south‐central Nebraska, USA, past investigations of roosting cranes focused on physical channel characteristics related to perceived security as motivating roost distribution. We used 6,310 roost sites selected by 313 sandhill cranes over 5 spring migration seasons (2003–2007) to quantify resource selection functions of roost sites on the central Platte River using a discrete choice analysis. Sandhill cranes generally showed stronger selection for wider channels with shorter bank vegetation situated farther from potential human disturbance features such as roads, bridges, and dwellings. Furthermore, selection for roost sites with preferable physical characteristics (wide channels with short bank vegetation) was more resilient to nearby disturbance features than more narrow channels with taller bank vegetation. The amount of cornfields surrounding sandhill crane roost sites positively influenced relative probability of use but only for more narrow channels <100 m and those with shorter bank vegetation. We confirmed key resource features that sandhill cranes selected at river channels along the Platte River, and after incorporating spatial variation due to human disturbance, our understanding of roost site selection was more robust, providing insights on how disturbance may interact with physical habitat features. Managers can use information on roost‐site selection when developing plans to increase probability of crane use at existing roost sites and to identify new areas for potential use if existing sites become limited. © 2016 The Wildlife Society.

Migrating birds reorient toward land at dawn over the Great Lakes, USA

ABSTRACT Most landbirds migrate at night and typically make landfall in suitable stopover habitat before dawn. However, when birds find themselves over large water bodies at dawn, they must continue flying into the day and either finish crossing the water body and land on the far shore or backtrack to the near (i.e. first encountered) shore to land. Their collective decisions will influence how migrants are distributed among shoreline stopover habitats on either side of the water crossing. We studied birds during 4 spring migration seasons from 2010 to 2013 in the Great Lakes region, USA. We used 3 weather surveillance radars to observe migrating landbirds' behavior at dawn and subsequent terrestrial distributions during stopover. Mean flight heights over land and water were higher and mean flight directions were more oriented toward the closest shore at dawn when compared to peak migration earlier in the night. The wider the lake crossing, the higher that birds along the lakeshore flew at dawn. Seasonal ...

Migratory restlessness increases and refuelling rate decreases over the spring migration season in northern wheatears

For migrating birds, late arrival at the breeding grounds reduces reproductive success. Hence, while en route, late migrants are expected to accelerate migration. Most time can be saved by shortening stopovers, periods of rest and fuel replenishment (refuelling) in between flight bouts. In several field studies late migrants have indeed been observed to shorten stopovers. The length of stopovers is assumed to depend, at least partly, on refuelling rate (fuel deposition rate, FDR). Therefore, shorter stopovers later in the spring migration season may be explained by a seasonal increase in FDR. We tested this idea by measuring both migratory restlessness (an accurate proxy for departure likelihood from stopover) and FDR in the same set of temporarily caged wheatears, Oenanthe oenanthe, a long-distance songbird migrant, throughout spring migration. We found that the amount of migratory restlessness increased with the progress of the season, indicating higher departure likelihood in late migrants. Clearly, however, late migrants in our sample did not accelerate migration by increasing their FDR; daily FDR was relatively constant during the season in lean birds, and even decreased over the season in fat birds. There was little seasonal variation in daily food intake in both lean and fat birds. Because we eliminated and/or corrected for environmental factors influencing departure likelihood, these results strongly indicate that an endogenous time programme is involved in the regulation of departure from stopover in spring.