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.

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.

Migratory animals are affected by various factors during their journeys, and the study of animal movement by radars has been instrumental in revealing key influences of the environment on flying migrants. Radars enable the simultaneous tracking of many individuals of almost all sizes within the radar range during day and night, and under low visibility conditions. We review how atmospheric conditions, geographic features and human development affect the behavior of migrating insects and birds as recorded by radars. We focus on flight initiation and termination, as well as in-flight behavior that includes changes in animal flight direction, speed and altitude. Several similarities and differences in the behavioral responses of different aerial migrants include an overlooked similarity in the use of thermal updrafts by very small (e.g., aphids) and very large (e.g., vultures) migrants. We propose that many aerial migrants modulate their migratory flights in relation to the interaction between atmospheric conditions and geographic features. For example, aerial migrants that encounter crosswind during flight may terminate their flight or continue their migration and may also drift or compensate for lateral displacement depending on their position (over land, near the coast or over sea). We propose several promising directions for future research, including the development and application of algorithms for tracking insects, bats and large aggregations of animals in weather radars. Additionally, an important contribution will be the spatial expansion of aeroecological radar studies to Africa, most of Asia and South America where no such studies have been undertaken. Quantifying the role of migrants in ecosystems and specifically estimating the number of departing birds from stopover sites using low-elevation radar scans is important for quantifying migrant-habitat relationships. This information, together with estimates of population demographics and migrant abundance, can help resolve the long-term dynamics of migrant populations that face large-scale environmental changes.

Quantifying the timing and intensity of migratory movements is imperative for understanding impacts of changing landscapes and climates on migratory bird populations. Billions of birds migrate in the Western Hemisphere, but accurately estimating the population size of one migratory species, let alone hundreds, presents numerous obstacles. Here, we quantify the timing, intensity, and distribution of bird migration through one of the largest migration corridors in the Western Hemisphere, the Gulf of Mexico (the Gulf). We further assess whether there have been changes in migration timing or intensity through the Gulf. To achieve this, we integrate citizen science (eBird) observations with 21 years of weather surveillance radar data (1995–2015). We predicted no change in migration timing and a decline in migration intensity across the time series. We estimate that an average of 2.1 billion birds pass through this region each spring en route to Nearctic breeding grounds. Annually, half of these individuals pass through the region in just 18 days, between April 19 and May 7. The western region of the Gulf showed a mean rate of passage 5.4 times higher than the central and eastern regions. We did not detect an overall change in the annual numbers of migrants (2007–2015) or the annual timing of peak migration (1995–2015). However, we found that the earliest seasonal movements through the region occurred significantly earlier over time (1.6 days decade⁻¹). Additionally, body mass and migration distance explained the magnitude of phenological changes, with the most rapid advances occurring with an assemblage of larger‐bodied shorter‐distance migrants. Our results provide baseline information that can be used to advance our understanding of the developing implications of climate change, urbanization, and energy development for migratory bird populations in North America.