Migratory Landbirds Research Articles

Spatial variation in spring arrival patterns of Afro‐Palaearctic bird migration across Europe

AbstractAimGeographical patterns of migrant species arrival have been little studied, despite their relevance to global change responses. Here, we quantify continent‐wide interspecific variation in spatiotemporal patterns of spring arrival of 30 common migrant bird species and relate these to species characteristics and environmental conditions.LocationEurope.Time Period2010–2019.Major Taxa StudiedBirds, 30 species.MethodsUsing citizen science data from EuroBirdPortal, we modelled arrival phenology for 30 Afro‐Palaearctic migrant species across Europe to extract start and duration of species arrival at a 400 km square resolution. We related inter and intraspecific variation in arrival and duration to species characteristics and temperature at the start of the growing season (green‐up).ResultsSpatial variation in start of arrival times indicates that it took, on average, 1.6 days for the leading migratory front to move northwards by 100 km (range: 0.6–2.5 days). There was a major gradient in arrival phenology, from species which arrived earlier, least synchronously, in colder temperatures and progressed slowly northwards to species which arrived later, most synchronously and in warmer temperatures and advanced quickly through Europe. The slow progress of early arrivers suggests that temperature limits their northward advance; this group included Aerial Insectivores and species wintering north of the Sahel. For the late arrivers, which included species wintering further south, seasonal resource availability in Africa may delay their arrival into Europe.Main ConclusionsWe found support for the green‐wave hypothesis applying widely to migratory landbirds. Species arrival phenologies are linked to ecological differences between taxa, such as diet, and wintering location. Understanding these differences informs predictions of species' sensitivity to global change. Publishing these arrival phenologies will facilitate further research and have additional conservation benefits such as informing designation of hunting seasons. Our methods are applicable to any taxa with repeated occurrence data across large scales.

David F. DeSante’s Birds of Cabo San Lucas, Fall 1968: A Historic Account

In preparation for his doctoral studies at Stanford University, the late David F. DeSante spent the fall of 1968 studying migratory landbirds at Cabo San Lucas. Although his hopes to capture numerous vagrant warblers were not met, he amassed an impressive list of distributional records for the Baja California Peninsula at a time when few ornithologists were working there. Among these were peninsular firsts for the Ring-necked Duck (Aythya collaris), Broad-billed Hummingbird (Cynanthus latirostris), Broad-winged Hawk (Buteo platypterus), Bobolink (Dolichonyx oryzivorus), and Painted Bunting (Passerina ciris). Another six species, and one subspecies, were found for the first time in Baja California Sur. Venturing away from the immediate confines of Cabo San Lucas, DeSante established the first peninsular record of the Gray-headed Junco (Junco hyemalis caniceps) and first state records for another five species and one subspecies. Although many of these records have been reported previously, the junior authors believe it is appropriate to synthesize them more completely with current context, in Dave’s honor.

Annual survival rates of satellite-tracked adult European honey buzzards (Pernis apivorus) based on the Kaplan-Meier estimator and its probabilistic extension

Abstract The annual survival rate of adult raptors is an important parameter in population dynamics and is needed to derive measures for population stability and conservation management. Here we studied adult European honey buzzards (Pernis apivorus), a migratory land bird, using satellite telemetry throughout the year for up to three years. We used the Kaplan-Meier method of survival estimation in combination with the distribution density function for survival. This function describes the number of survivors N as a function of time t, based on the survival rate SR. This probabilistic extension of the Kaplan-Meier estimator results in a simple method that does not require a commercial statistical program to extract survival rates from event time analysis. It can be applied to analysing any event-time data, not only telemetry results but also ring recoveries, as demonstrated using European honey buzzards as an example. The average adult survival rate in our study, based on permanent satellite telemetry monitoring, was 0.44/year (linear correlation factor f = 0.99). This implies an adult mortality rate of 0.56 per year. It seems that particularly unfavourable weather conditions during the crossing of the Sahara and the Mediterranean led to this high mortality rate of our birds during migration from 2001 to 2011, but is likely to vary greatly from year to year. However, the loss rate in the wintering area was also high, at one third of the birds. More honey buzzards need to be tracked throughout the year to assess factors affecting survival and threats to populations adequately.

Survival estimates of resident and migratory landbirds banded at a coastal managed Southeast Asian wetland

Survival estimates of resident and migratory landbirds banded at a coastal managed Southeast Asian wetland

Cuba’s first motus tower for tracking migrant land birds

Cuba’s first motus tower for tracking migrant land birds Keith Hobson, Professor and Research Scientist at Environment and Climate Change Canada and Western University, discusses updates in the expansion of tracking migratory birds in Central and South America, and the Caribbean. The conservation of migratory birds requires basic knowledge of connectivity between population-specific breeding, wintering, and stopover sites. This recognition has encouraged several government and NGO initiatives since many migratory species cross international borders during their annual travels. While the task is immensely difficult, an array of new tools is now available to track even small birds (~10g) using both intrinsic (e.g. stable isotope or genetic markers) and extrinsic (e.g. attached electronic devices) methods.

Seasonal patterns and protection status of stopover hotspots for migratory landbirds in the eastern United States.

Migratory landbirds in North America are experiencing dramatic population declines. Although considerable research and conservation attention have been directed toward these birds' breeding and wintering grounds, far less is known about the areas used as stopover sites during migration. To address this knowledge gap, we used 5 years of weather surveillance radar data to map seasonal stopover densities of landbirds across the eastern United States during spring and autumn migration. We identified stopover hotspots covering 2.47 million ha that consistently support high densities of migratory landbirds in spring or autumn. However, only 16.7% of these sites are hotspots in both seasons. The distribution of hotspots is shifted eastward in autumn compared with spring. Deciduous forest is the most important habitat type in both seasons, with deciduous forest fragments embedded in broadly deforested regions having the highest probability of being hotspots. The concentration of birds in these forest fragments is stronger in spring, especially in the agricultural Midwest. We found generally higher stopover densities in protected areas than in unprotected areas in both seasons. Nonetheless, only one-third of identified stopover hotspots have some sort of protected status, and more than half of these protected hotspots are subject to extractive uses. A well-distributed network of well-protected stopover areas, complementing conservation efforts on the breeding and wintering grounds, is essential to sustaining healthy populations of migratory landbirds in North America.

Stopover habitat quality of urban green space for migratory landbirds and the impact of urban wilding measures

Stopover habitat quality of urban green space for migratory landbirds and the impact of urban wilding measures

The evolutionary history of “suboptimal” migration routes

Migratoriness in birds is evolutionary labile, with many examples of increasing or decreasing migration distances on the timescale of modern ornithology. In contrast, shifts of migration to more nearby wintering grounds seem to be a slow process. We examine the history of how Palearctic migratory landbirds have expanded their wintering ranges to include both tropical Africa and Asia, a process that has involved major shifts in migratory routes. We found that species with shorter migration distances and with resident populations in the Palearctic more often winter in both Africa and Asia. Our results suggest that changes in wintering grounds are not by long-distance migrant populations per se, but through historic intermediate populations that were less migratory from which long-distance migration evolved secondarily. The failure of long-distance migrants to shift migration direction to more nearby winter quarters indicates that major modifications to the migratory program may be difficult to evolve.

Deforestation within breeding ranges may still drive population trends of migratory forest birds in the East Asian Flyway

The East Asian Flyway (EAF) is the most species diverse of global flyways, with deforestation in its migratory landbird’s non-breeding range suspected to be the main driver of population decline. Yet range-wide habitat loss impact assessments on EAF migratory landbirds are scarce, and seasonal variation in habitat preference of migratory species further increases the complexity for conservation strategies. In this study, we reviewed population trends of migratory forest breeding birds in the EAF along with their seasonal habitat preference from the literature and assessed the impact of forest cover change in species’ breeding and non-breeding ranges on population trends. We found that 41.3% of the bird species with trend data available are declining, and most have higher forest preference in the breeding season. Despite 93.4% of the species experienced deforestation throughout their annual cycle, forest cover change in the non-breeding range was not identified as the main driver of population trend. However, forest cover change in species’ regional breeding range interacts positively with the degree of breeding season forest preference in predicting population trends. We therefore stress that regional breeding habitat protection may still be important while following the call for cross-border collaboration to fill the information gap for flyway conservation.

Co-migration fidelity at a stopover site increases over time in African-European migratory landbirds.

Migratory species are changing their timing of departure from wintering areas and arrival to breeding sites (i.e. migration phenology) in response to climate change to exploit maximum food availability at higher latitudes and improve their fitness. Despite the impact of changing migration phenology at population and community level, the extent to which individual and species-specific response affects associations among co-migrating species has been seldom explored. By applying temporal co-occurrence network models on 15 years of standardized bird ringing data at a spring stopover site, we show that African-European migratory landbirds tend to migrate in well-defined groups of species with high temporal overlap. Such 'co-migration fidelity' significantly increased over the years and was higher in long-distance (trans-Saharan) than in short-distance (North African) migrants. Our findings suggest non-random patterns of associations in co-migrating species, possibly related to the existence of regulatory mechanisms associated with changing climate conditions and different uses of stopover sites, ultimately influencing the global economy of migration of landbirds in the Palearctic-African migration system.

Individual‐based models of avian migration for estimating behavioural traits and predicting ecological interactions

Abstract Rapid advances in the field of movement ecology have led to increasing insight into both the population‐level abundance patterns and individual‐level behaviour of migratory species. Despite this progress, research questions that require scaling individual‐level understanding of the behaviour of migrating organisms to the population level remain difficult to investigate. To bridge this gap, we introduce a generalizable framework for training full‐annual cycle individual‐based models of migratory movements by combining information from tracking studies and species occurrence records. Focusing on migratory birds, we call this method: Models of Individual Movement of Avian Species (MIMAS). We implement MIMAS to design individual‐based models of avian migration that are trained using previously published weekly occurrence maps and fit via Approximate Bayesian Computation. MIMAS models leverage individual‐ and population‐level information to faithfully represent continental‐scale migration patterns. Models can be trained successfully for species even when little existing individual‐level data is available for parameterization by relying on population‐level information. In contrast to existing mathematical models of migration, MIMAS explicitly represents and estimates behavioural attributes of migrants. MIMAS can additionally be used to simulate movement over consecutive migration seasons, and models can be easily updated or validated as new empirical data on migratory behaviours becomes available. MIMAS can be applied to a variety of research questions that require representing individual movement at large scales. We demonstrate three applied uses for MIMAS: estimating population‐specific migratory phenology, predicting the spatial patterns and magnitude of ectoparasite dispersal by migrants, and simulating the spread of a pathogen across the annual cycle of a migrant species. Currently, MIMAS can easily be used to build models for hundreds of migratory landbird species but can also be adapted in the future to build models of other types of migratory animals.

Geomagnetic disturbance associated with increased vagrancy in migratory landbirds

Rare birds known as “accidentals” or “vagrants” have long captivated birdwatchers and puzzled biologists, but the drivers of these rare occurrences remain elusive. Errors in orientation or navigation are considered one potential driver: migratory birds use the Earth’s magnetic field—sensed using specialized magnetoreceptor structures—to traverse long distances over often unfamiliar terrain. Disruption to these magnetoreceptors or to the magnetic field itself could potentially cause errors leading to vagrancy. Using data from 2 million captures of 152 landbird species in North America over 60 years, we demonstrate a strong association between disruption to the Earth’s magnetic field and avian vagrancy during fall migration. Furthermore, we find that increased solar activity—a disruptor of the avian magnetoreceptor—generally counteracts this effect, potentially mitigating misorientation by disabling the ability for birds to use the magnetic field to orient. Our results link a hypothesized cause of misorientation to the phenomenon of avian vagrancy, further demonstrating the importance of magnetoreception among the orientation mechanisms of migratory birds. Geomagnetic disturbance may have important downstream ecological consequences, as vagrants may experience increased mortality rates or facilitate range expansions of avian populations and the organisms they disperse.

Autumn stopover hotspots and multiscale habitat associations of migratory landbirds in the eastern United States

Halting the global decline of migratory birds requires a better understanding of migration ecology. Stopover sites are a crucial yet understudied aspect of bird conservation, mostly due to challenges associated with understanding broad-scale patterns of transient habitat use. Here, we use a national network of weather radar stations to identify stopover hotspots and assess multiscale habitat associations of migratory landbirds across the eastern United States during autumn migration. We mapped seasonal bird densities over 5 y (2015 to 2019) from 60 radar stations covering 63.2 million hectares. At a coarse scale, we found that landbirds migrate across a broad front with small differences in migrant density between radar domains. However, relatively more birds concentrate along the Mississippi River and Appalachian Mountains. At a finer scale, we identified radar pixels that consistently harbored high densities of migrants for all 5 y, which we classify as stopover hotspots. Hotspot probability increased with percent cover of all forest types and decreased with percent cover of pasture and cultivated crops. Moreover, we found strong concentrating effects of deciduous forest patches within deforested regions. We also found that the prairie biome in the Midwest (now mostly cropland) is likely a migration barrier, with large concentrations of migrants at the prairie-forest boundary after crossing the agricultural Midwest. Overall, the broad-front migration pattern highlights the importance of locally based conservation efforts to protect stopover habitats. Such efforts should target forests, especially deciduous forests in highly altered landscapes. These findings demonstrate the value of multiscale habitat assessments for the conservation of migratory landbirds.

Specific composition, abundances and phenology of migratory landbirds of the Comoé National Park, north-east of Ivory Coast

Specific composition, abundances and phenology of migratory landbirds of the Comoé National Park, north-east of Ivory Coast

Differences in migration phenology of warblers at two stopover sites in eastern Russia suggest a longitudinal migration pattern

Long-distance migratory birds often face major geographical barriers on their journey. While some species are able to cross them, others use longer routes to avoid such barriers. Little is known about the strategies of Siberian landbird migrants, which either cross or circumvent the deserts and mountain ranges of Central Asia en route to their non-breeding sites in Southeast Asia. Here we compare data on migration phenology and morphology from two bird ringing stations in eastern Russia, situated at similar latitudes but with a longitudinal difference of 1500 ​km, to hypothesise migration patterns. We found significant differences in timing between the two sites (birds migrated significantly earlier in spring and significantly later in autumn in the east), suggesting longitudinal migration as a result of migration detour. However, morphological differences show a less clear pattern. We argue that most Siberian landbirds might opt for a detour through the Russian Far East instead of a direct route in order to avoid unfavourable stop-over habitat in Central Asia. However, tracking studies will be necessary to prove this.

A roadmap integrating research, policy, and actions to conserve Afro‐Palearctic migratory landbirds at a flyway scale

AbstractThe populations of Afro‐Palearctic migratory landbirds (breeding in Europe and overwintering in Africa) are declining and conservation efforts to halt or reverse their decline have failed to meet their targets. Yet, most studies and conservation measures focus on migratory landbirds’ breeding grounds, whereas knowledge about threats, drivers of their decline and conservation actions in their nonbreeding grounds, where they spend most of their annual cycle, is largely limited. Here, we provide a four‐step roadmap to integrate research, policy and actions for conserving Afro‐Palearctic migratory landbirds at a flyway scale: (1) assessing and monitoring population trends and defining priority species accordingly; (2) maximizing tracking data to identify important areas for the conservation of priority species; (3) conducting ground‐based studies on the nonbreeding grounds to identify conservation challenges; (4) implementing conservation measures, for the benefit of both the avifauna and the local human communities. Alongside these steps, international conventions may facilitate new collaborations across range‐states and institutions to engage diverse stakeholders and involve local communities, with particular emphasis on evidence‐based policymaking, law enforcement in addition to capacity strengthening and knowledge transfer of new technologies. This four‐step roadmap provides guidance for future work on Afro‐Palearctic migratory landbirds and will ultimately contribute to their conservation.

Factors associated with arrival timing and condition of migrant landbird species in northeastern Pennsylvania

AbstractExtrinsic and intrinsic factors operating during and prior to the passerine spring migratory period have been associated with both migratory timing and condition. Here we take advantage of a long-term data set to answer questions about how extrinsic factors encountered on the wintering grounds (El Niño Southern Oscillation, ENSO) anden route(temperatures south of our study site) along with intrinsic factors (age, sex if possible) influenced both arrival timing and condition at our site in northeastern Pennsylvania. Older birds preceded younger, male Common Yellowthroats (Geothlypis trichas) preceded females and within a year later arriving Gray Cat-birds (Dumetella carolinensis) and Common Yellowthroats were in better condition. We found that Gray Catbirds and Common Yellowthroats migrating during warmer years arrived in better condition. Finally, we found evidence that ENSO, likely via influencing weather and food availability during the winter, was associated with arrival timing in Veery (Catharus fuscescens), Common Yellowthroats and possibly Gray Catbirds. Our results support the hypothesis that events experienced earlier, either between (wintering to migratory periods) or within (earlier vs. later in migration) phases of the avian annual cycle may carry over, influencing fitness later in time or in subsequent phases of the annual cycle.

Opportunities for the conservation of migratory birds to benefit threatened resident vertebrates in the Neotropics

Neotropical countries receive financing and effort from temperate nations to aid the conservation of migratory species that move between temperate and tropical regions. If allocated strategically, these resources could simultaneously contribute to other conservation initiatives. In this study, we use novel distribution maps to show how those resources could aid planning for the recovery of threatened resident vertebrates.Using eBird‐based relative abundance estimates, we first identified areas with high richness of Neotropical migrant landbirds of conservation concern (23 species) during the stationary non‐breeding period. Within these areas, we then identified threatened species richness, projected forest loss and conducted a prioritization for 1,261 red‐listed vertebrates using Terrestrial Area‐of‐Habitat maps.Richness for migrants was greatest along a corridor from the Yucatan peninsula south to the northern Andes but also included south‐west Mexico and Hispaniola. Protected areas account for 22% of this region while 21% is at risk of forest loss. Within this focal region for migrants, all four vertebrate groups showed hotspots of threatened species richness along the west and east Andean slopes. Taxa‐specific hotspots included montane areas of southern Mexico and central Guatemala (amphibians/reptiles) and the entire east slope of the Colombian East Andes (mammals).Our prioritization highlighted several areas of importance for conservation due to high threatened species richness and projected forest loss including (a) the Pacific dry forests of south‐west Mexico, (b) montane regions of northern Central America and (c) the west Andean slope of Colombia and Ecuador. At a landscape scale in southern Colombia, we show how conservation efforts for six Neotropical migrants could benefit 56 threatened residents that share a similar elevational range. Synthesis and applications. Funding and effort for migratory bird conservation also has potential to benefit threatened resident vertebrates in the Neotropics. Our study highlights how novel, high‐resolution information on species distributions and risk of forest loss can be integrated to identify priority areas for the two groups at regional and landscape scales. The approach and data can be further modified for more specific goals, such as within‐country initiatives.

Community modeling reveals the importance of elevation and land cover in shaping migratory bird abundance in the Andes.

The tropical Andes are characterized by extreme topographic and climatic complexity, which has likely contributed to their outstanding current species diversity, composed of many range‐restricted species. However, little is known about how the distribution and abundance of highly mobile organisms, like long‐distance migratory birds, varies across different land covers, elevations, and climatic conditions within the Andes. We conducted 1,606 distance‐sampling point counts across the Colombian Andes, spanning elevations from 253 to 3,708 m, a range of precipitation regimes and representative land covers. We then employed a novel application of a multispecies hierarchical modeling approach to evaluate how elevation, local land cover, aboveground woody biomass, cloud cover, precipitation, and seasonality in precipitation shape the abundance of the migratory land bird community in the Andes. We detected 1,824 individuals of 29 species of migratory land birds, six of which were considered incidental in our study region. We modeled the abundance of the remaining 23 species, while considering observer and time of day effects on detectability. We found that both elevation and land cover had an overriding influence on the abundance of migratory species across the Andes, with strong evidence for a mid‐elevation peak in abundance, and species‐specific responses to both variables. As a community, migratory birds had the highest mean abundance in shade coffee plantations, secondary forest, and mature forest. Aboveground woody biomass did not affect the abundance of all species as a group, but a few showed strong responses to this variable. Contrary to predictions of a positive correlation between abundance and precipitation, we found no evidence for community‐level responses to precipitation, aside for a weak tendency for birds to select areas with intermediate levels of precipitation. This novel use of a multispecies model sheds new light on the mechanisms shaping the winter distribution of migratory birds and highlights the importance of elevation and land cover types over climatic variables in the context of the Colombian Andes.

Habitat associations of landbirds in southern Texas during migration

It is estimated that about 80% of North American avian migrants travel along the southern coast of Texas. Quality of stopover habitat for landbirds in southern Texas is a concern, however, due to agricultural and wind energy development and increasing urbanization. Since little regional research has been conducted on stopover habitat use, we investigated habitat associations of migratory birds to identify important factors driving density along the southern Texas coast. We did this using data from landbird surveys, which took place during spring and autumn migrations from 1991 to 1993 and 2006 to 2008, within 6 land-cover types common in southern Texas. We found that oak motte had the highest density among most bird guilds. A total of 125 species of birds were detected over the course of our study and species richness was highest in oak motte and lowest in grassland. In general, land-cover types with more woody vegetation cover tended to have higher species richness and diversity than those with minimal to no woody vegetation. Although grassland ranked lowest in other metrics of bird use, it ranked highest in habitat conservation value, which accounts for species of concern. At the time of this study, Golden-winged Warbler (Vermivora chrysoptera) was the only species on Partners in Flight's Red Watch List (highly vulnerable and in need of special attention) that we observed, with recorded observations occurring in oak motte and woodland exclusively. Oak mottes are likely a prime location for species to land after flying over the Gulf of Mexico during their journey north to their breeding grounds, thus land managers that wish to provide high-quality stopover sites for migratory landbirds should preserve them.