Migration Alerts

Besides providing curious birders information on migration and where and when to go birding, these alerts serve an important conservation need.

They can provide timely information about nights of high intensity migration (otherwise referred to as peak migration), only a handful of which occur throughout a given season (approximately 10% of a season’s migration nights account for approximately 50% of the migration traffic). This allows effective targeting of the most important migration nights in a season, helping determine when to act for maximal effect of conservation actions such as turning off lights when birds are flying at night to avoid luring them towards artificial light and potentially fatal hazards.

Purdue University and Cornell Lab of Ornithology currently produce and maintain these alerts.

Migration alerts are expressed in units of birds/km/night, indicating the cumulative number of birds that fly within a night across a 1-km line transect on the Earth’s surface oriented perpendicular to the direction of movement of the birds.

Whether migration is low, medium, or high is determined from the predicted density of birds for your area, and a comparison to the historic migration intensities for that same area. The alert levels aim to predict what is high or low migration for your local region of interest, not for the U.S. as a whole. A high alert is given when the density is predicted to be within the top 10% of migration nights for a season. A medium alert is given when the density is predicted to be within the top 70-90% of nights for a season.

The primary reason we do not display data from Alaska and Hawaii is about the map graphics we use and the challenge of making a good, concise visualization. The current projection for displaying bird migration data is the contiguous 48 states of the U.S., and although we are seeking a map visual that captures these other areas, this has been a low priority given a very small team of people developing and maintaining the project. Moreover, although there is excellent, and diverse, movement in Alaska captured in WSR-88D data, bird migration on radar in the Hawaiian Islands is much less intense than any continental location, providing additional challenges. But, for the record, there are seven weather surveillance radars in Alaska, and another four in Hawaii, all of which detect birds and migration.

There are 32 weather surveillance radars operating in Canada, collecting data very similar to those from the contiguous U.S. already used in BirdCast observations and forecasts. The BirdCast team is actively working to study the possibility of adding Canadian weather surveillance radar data to the BirdCast project’s visualizations and tools. The addition of these data would be invaluable for studying and monitoring the large numbers of birds that breed in boreal forests, taiga, and tundra, areas where human surveys are generally infrequent and highly localized.

Mexico has 14 operational weather surveillance radars, and although access to some version of these data is free, the raw data that does not exclude biological information are not freely accessible. Filtered data remove all or almost all of the information about birds detected by the radar. So, until there is a relationship among necessary partners, we sadly will not be integrating Mexican radar data into the BirdCast system.