Search

Waterfowl migrations are large‐scale events that involve millions of birds moving over broad geographic extents, which make them difficult to quantify and study. Historically, wildlife managers have relied mostly on field surveys, such as visual counts from the ground or air that sample at small spatial or temporal extents, or both. Combining field surveys with remote sensing data comprehensively collected over large spatial extents at high temporal frequency may improve the study of migrating waterfowl distributions. We tested the strength of the relationship between broad‐scale weather surveillance radar data and fine‐scale field surveys of waterfowl abundance at wetlands within the Rainwater Basin of Nebraska, USA, from 2017–2019. Radar reflectivity of waterfowl at the peak exodus of evening flights was positively correlated with diurnal waterfowl count data, although there was unexplained variation in the relationship. The association was also very similar across various time scales ranging from daily to monthly averages of waterfowl abundance. We suggest that human‐based ground surveys can calibrate and leverage more comprehensive remote sensing data to get a broad understanding of waterfowl distributions during migration. Several confounding factors, such as spatial displacement between radar and survey observation, individual variation in orientation and body size, and identification of avian species sampled by radar, remain on the path to improving radar‐based waterfowl estimates. [ABSTRACT FROM AUTHOR]

As wind energy rapidly expands worldwide, information to minimize impacts of this development on biodiversity is urgently needed. Here we demonstrate how data collected by weather radar networks can inform placement and operation of wind facilities to reduce collisions and minimize habitat‐related impacts on nocturnally migrating birds. We found over a third of nocturnal migrants flew through altitudes within the rotor‐swept zone surrounding the North American Great Lakes, a continentally important migration corridor. Migrating birds concentrated in terrestrial stopover habitats within 20‐km from shorelines, a distance well beyond the current guidelines for construction of new land‐based facilities, and their distributions varied seasonally and at local and regional scales, creating predictable opportunities to minimize impacts from wind energy development and operation. Networked radar data are available across the United States and other countries and broad application of this approach could provide information critical to bird‐friendly expansion of this globally important energy source. [ABSTRACT FROM AUTHOR]

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. • Weather radar can map seasonal stopover hotspots for landbirds in the eastern US • There is little spatial overlap between spring and autumn hotspots • Birds concentrate in deciduous forest fragments at stopover, especially in spring • Only one-third of identified hotspots are in protected areas Using weather radar, Guo et al. map the seasonal stopover density of migratory landbirds and identify stopover hotspots across the eastern United States. They find little overlap in the distribution of spring versus autumn hotspots. Most of these hotspots do not fall within protected areas, especially for deciduous forest fragments where birds concentrate. [ABSTRACT FROM AUTHOR]

Migrating birds require en route habitats to rest and refuel. Yet, habitat use has never been integrated with passage to understand the factors that determine where and when birds stopover during spring and autumn migration. Here, we introduce the stopover‐to‐passage ratio (SPR), the percentage of passage migrants that stop in an area, and use 8 years of data from 12 weather surveillance radars to estimate over 50% SPR during spring and autumn through the Gulf of Mexico and Atlantic coasts of the south‐eastern US, the most prominent corridor for North America's migratory birds. During stopovers, birds concentrated close to the coast during spring and inland in forested landscapes during autumn, suggesting seasonal differences in habitat function and highlighting the vital role of stopover habitats in sustaining migratory communities. Beyond advancing understanding of migration ecology, SPR will facilitate conservation through identification of sites that are disproportionally selected for stopover by migrating birds. [ABSTRACT FROM AUTHOR]

Operational weather surveillance radars (WSRs) are permanent radars that constantly detect precipitation at regular intervals (approx. every 4–10 min) for the purpose of weather reporting and are often part of a larger network of radars. Ecological studies using WSR to detect flying animals within the airspace have been on the rise since the early 2000s. However, the vast majority of published ecological studies (>300) have occurred in the Northern Hemisphere with only two published studies occurring in the Southern Hemisphere, both on insects. The lag in uptake of the technique in the Southern hemisphere is likely due to limited WSR coverage and the challenges of data acquisition and interpretation. However, we argue that WSRs are numerous enough in the Southern Hemisphere to offer equal opportunity to understand the movement of flying animals there. Here, we explore why that might be and present a road map so that ecological researchers in the Southern Hemisphere may take advantage of this valuable data resource. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Condor: Ornithological Applications is the property of Oxford University Press / USA and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Context: Annual migration of landbirds across the Gulf of Mexico (GOM) presents a unique opportunity to examine extrinsic processes operating at various spatial scales in determining animal distributions. Objectives: Our objectives were to comprehensively quantify bird stopover densities across the northern GOM coast and model broad-scale factors explaining distributional patterns. Methods: We used weather surveillance radars to measure reflectivity of birds aloft at onset of nocturnal migratory flights and estimate bird stopover densities during four springs (2009-2012) for 6.7 million ha along the GOM. We aggregated bird densities to one longitudinal degree and 3 km of proximity to coast. Results: Boosted Regression Tree models revealed that stopover density was related to year, longitude, proximity to coast, and amount of hardwood forest cover in the landscape. Average longitudinal patterns supported previous studies of broad-scale trans-Gulf migrant arrivals with highest density in Louisiana (92-93°W) and lowest in Alabama (88-89°W). Florida (83-84°W) supported a second peak in migrant density, suggesting an eastern trans-Gulf route or contribution from trans-Caribbean migrants. Longitudinal patterns in migrant distributions varied strongly between years and appear generally related to variability in GOM wind patterns. Densities increased with proximity to coast, highlighting constraints on migrants to travel inland, especially in Florida's panhandle. Despite this, density was positively related to amount of forest cover more steeply along the immediate coast. Conclusions: Broad-scale stopover distributions of migrating landbirds along the GOM coast are heavily influenced by geographic constraints in the context of the GOM acting as a barrier to landbird migration. [ABSTRACT FROM AUTHOR]

The dynamic weather conditions that migrating birds experience during flight likely influence where they stop to rest and refuel, particularly after navigating inhospitable terrain or large water bodies, but effects of weather on stopover patterns remain poorly studied. We examined the influence of broad-scale weather conditions encountered by nocturnally migrating Nearctic-Neotropical birds during northward flight over the Gulf of Mexico (GOM) on subsequent coastal stopover distributions. We categorized nightly weather patterns using historic maps and quantified region-wide densities of birds in stopover habitat with data collected by 10 weather surveillance radars from 2008 to 2015. We found spring weather patterns over the GOM were most often favorable for migrating birds, with winds assisting northward flight, and document regional stopover patterns in response to specific unfavorable weather conditions. For example, Midwest Continental High is characterized by strong northerly winds over the western GOM, resulting in high-density concentrations of migrants along the immediate coastlines of Texas and Louisiana. We show, for the first time, that broad-scale weather experienced during flight influences when and where birds stop to rest and refuel. Linking synoptic weather patterns encountered during flight with stopover distributions contributes to the emerging macro-ecological understanding of bird migration, which is critical to consider in systems undergoing rapid human-induced changes. [ABSTRACT FROM AUTHOR]