BirdCast takes flight in Alaska:
New research expands the footprint of US aeroecology
For more than 50 years US radar aeroecology has largely been restricted to the lower 48 states — until now. Just out in the Proceedings of the Royal Society B, the BirdCast team publishes the first weather surveillance radar studies of Alaskan bird migration. This research builds on earlier studies at smaller scales using marine and tracking radars (e.g. Cooper and Ritchie 1985, Flock 1972, Flock 1973), hopefully representing advances into a new frontier of Arctic radar studies!
Monitoring avian migration occurring in and over subarctic regions of the globe is at once critically important and logistically challenging, with a primary need to fill a gap in available research tools and science necessary to develop conservation strategies for these regions. The seasonal productivity of these areas, with dramatic and enormous emergences of invaluable food sources for breeding birds, is especially important in supporting bird populations – in fact it is likely to be one of the primary factors relating to the evolution of bird migration to these areas. Moreover, bird populations in these regions are perhaps the most likely to encounter the most rapid effects of changing climates.
To fill this gap, our team leveraged the untapped potential of weather surveillance radar data to quantify active migration through the airspaces of Alaska. Using over 400,000 NEXRAD radar scans from seven stations across Alaska between 1995 and 2018 (86% of samples derived from 2013 to 2018), the team measured spring and fall migration intensity, phenology, and directionality.
Whereas the peak spring migration window may have already passed some areas of the lower 48 states, the period for Alaskan peak migration is just beginning. A breeding destination for tens of millions of waterfowl, shorebirds, and songbirds, Alaska’s bird community is dominated by those species that are migratory. On average, peak spring migration ranged from May 3rdto May 30th, and peak fall migration occurred from August 18thand September 12th, with timing across the state predicted by longitude, rather than latitude. Across all radar stations, the intensity of migration was greatest during the fall as compared to spring, highlighting the opportunity to measure seasonal indices of net breeding productivity for this important system as additional years of radar measurements are amassed.
The team is excited to see what other valuable information these data may hold! Like many research endeavors, this study is spawning a flood of new questions. For instance, is the seasonal timing of Alaskan migration changing, particularly under the dramatic and rapid impacts the region is now experiencing because of climate change? Additionally, when do “nocturnal” migrants fly when there’s no nocturnal period? Alaska’s unique, high latitude location, position as a bridge between North American and Asian flyways, and radar coverage all contribute to its enormous potential for bird migration studies. We hope this is the first of many studies using these radar data and that our findings enhance future studies while complementing and supplementing past studies in there state.
As we begin to unravel the drivers of Alaskan migration, the BirdCast team is examining on the possibility of extending our forecast models to include Alaska. And furthermore, with each passing season, BirdCast will continue to collect radar data to extend and to improve our abilities to understand bird migration in a changing world, in and beyond the contiguous United States!
Photos, courtesy of Kyle Horton | Colorado State University
