Aeroecology
What is aeroecology?
The United States upgraded the NEXRAD network to dual-polarization in 2013, providing new radar products for the description of migrant flight strategies.
Aeroecology is the study of airborne organisms and their utilization of the lower atmosphere (i.e. aerosphere). Like any other habitat or ecosystem, organisms use the aerosphere in a multitude of ways. Whether for foraging or migrating, breeding or roosting, there is no debating that the aerosphere plays a critical role in the life histories of airborne organisms. However, our understanding of these uses is incomplete at best.
Studying the aerosphere requires a unique suite of tools, naturally linking multiple disciplines together. Sensor systems like radar, thermal imaging, and acoustics are regularly employed by aeroecologists, particularly for describing nocturnal movements. Radar remote sensing offers an invaluable tool for quantifying large-scale animal movements, whereas acoustics provide fine-scale, species-specific records of migrant activity. Each of these tools provide a unique perspective to answer questions that improve our understanding of migratory systems and their association with abiotic and biotic phenomena.
“Aeroecology is a discipline that embraces and integrates the domains of atmospheric science, ecology, earth science, geography, computer science, computational biology, and engineering. ”
Radar aeroecology
Radar, since it’s advent, has undergone numerous advances, prominently in hardware development. The use of radars in biology dates back to the 1940s when David Lack, arguably the father of what we today call radar ornithology (or radar aeroecology), championed the use of radar for understanding large-scale nocturnal movements of birds. In aeroecology, radar is used for a multitude of uses: monitoring of migratory bird stopover sites, identification of species-specific bird and bat roosts, and tracking of broad-front migrations.
In 1988 the United States began a massive upgrade to its ageing radar network, installing what is known more commonly today as the NEXRAD (Next Generation Radar) network. Today the United States operates 143 WSR-88D (Weather Surveillance Radar 1988-Dopper) radars in the continental US. These 10-cm wavelength radars possess a typical biological range of 80-120 km, and provide rapid updates of migration intensity, migration track, and more recently orientation direction.
Radar correlation coefficient revealing large-scale orientation fields of nocturnal migrants.
Until about 2013, WSR-88Ds collected three primary radar moments: reflectivity, radial velocity, and spectrum width. In 2013 the US upgraded the NEXRAD network to dual-polarization, an update that resulted in the collection of three additional data products: differential reflectivity, correlation coefficient, and differential phase. The incorporation of this second plane of polarization added another “dimension” for describing precipitation, atmospheric debris, and biological scatterers. Although the use of polarimetric weather surveillance radar data are relatively new in aeroecology, they have proven useful for describing migratory behaviors and characterizing biological scatters. This upgrade has allowed for a direct measure of migrant orientation, an important feature for determining migrant flight strategies regarding wind drift compensation. I am interested in how migratory birds cope with crosswinds and how these strategies may differ at large geographic scales.
Nocturnal Flight Calls
Wood-warblers of eastern North American and their corresponding nocturnal flight calls spectrogram. Underlying flight call audio from Evans and O'Brien (2002).
Nocturnal flight calls are unique species-specific vocalizations given by many birds. Like the name entails, these calls are largely given during flight, particularly migratory flights. Because these calls are unique at the species level, they provide one of the few methods for documenting species-specifc nocturnal movements. From a monitoring standpoint the utility of these calls seems obvious, however the underlying function of these calls remains unknown. I am interested in the role these calls play in migratory flights and the cues that stimulate flight-calling. Additionally, I am interested in the interpretation of flight calls as a measure of migration intensity and the dependence of bird behavior and atmospheric properties on the detection of these calls from ground-based recorders.