Review and Interpretation
Migration Forecast Maps (2018)
Migration forecasts come from models trained on the last 23 years of bird movements in the atmosphere as detected by the US NEXRAD weather surveillance radar network. In these models we use the North American Mesoscale Forecast System (NAM) to predict suitable conditions for migration occurring three hours after local sunset. Warmer colors correspond to more intense bird migration. These maps also show precipitation (outlined and shown in grayscale) forecasts. Note, areas forecast to experience precipitation and bird migration may overlap, and predictions for migration intensity may be highly variable in these locations. Support for this research comes from Leon Levy Foundation, Edward W. Rose Postdoctoral Fellowship, and the Marshall Aid Commemoration Commission. These models were made possible by additional research at University of Massachusetts Amherst and University of Oklahoma. The BirdCast project, a collaboration among Cornell Lab of Ornithology, University of Massachusetts Amherst, and Oregon State University, was funded by grants from the National Science Foundation and Leon Levy Foundation. Citation:
Van Doren, B. M. and K. G. Horton. 2018. A continental system for forecasting bird migration. bioRxiv. https://doi.org/10.1101/293092.
Live Migration Maps (2018)
Real-time analysis maps show intensities of actual nocturnal bird migration as detected by the US weather surveillance radar network between local sunset to sunrise. All graphics are relative to the Eastern time zone. The yellow line moving east to west represents the timing of local sunset. Areas with lighter colors experienced more intense bird migration. Orange arrows show directions to which birds flew. Green dots represent radar locations for which data are available; red dots represent radar locations with no data available. Note that many radars in mountainous areas (e.g. the Rockies) have obstructions that restrict radar coverage, providing the appearance of no migration where migration may be occurring. Support for this research comes from from Leon Levy Foundation, NASA, Edward W. Rose Postdoctoral Fellowship, and Amazon Web Services. The BirdCast project, a collaboration among Cornell Lab of Ornithology, University of Massachusetts Amherst, and Oregon State University, was funded by grants from the National Science Foundation and Leon Levy Foundation.
For migration forecasts and analyses, we use the following divisions to represent the continental US. We use these regions because their component states have many migration patterns in common and because their component states’ proximity make for logical groupings. Without doubt, finer scale delineation based on analyses of the details of migration patterns might yield more meaningful and representative biogeographic patterns, and our regions are not meant to replace such analyses’ findings (when we get to do them!).
West — Washington, Oregon, California, Idaho, Nevada, Utah, Arizona, Montana, Wyoming, Colorado, New Mexico
Great Plains — North Dakota, South Dakota, Nebraska, Kansas, Oklahoma
Upper Midwest and Northeast — Minnesota, Iowa, Missouri, Wisconsin, Michigan, Illinois, Indiana, Kentucky, Ohio, Pennsylvania, West Virginia, Virginia, New York, New Jersey, Delaware, Maryland, Vermont, Massachusetts, Rhode Island, Connecticut, Maine, New Hampshire
Gulf Coast and Southeast — Texas, Arkansas, Tennessee, Louisiana, Mississippi, Alabama, Georgia, Florida, North Carolina, South Carolina
Species on the Move (pre-2018)
Beginning in Spring 2015 we will be presenting more detailed information about when we expect species to pass through the four BirdCast regions in the continental United States. These are not complete lists, but they highlight many species on the move. The values below are calculated from the past 12 years of eBird data. The following are interpretations of these dates:
Noticeability — We categorized (using *,**,***,****) how likely birders are to notice a given species’ arrival or departure based on eBird reports.
Migrants Begin Arriving — We expect migrating individuals of this species’ to begin arriving around this date.
Rapid Migrant Influx — We expect migrating individuals of this species to be increasing rapidly around this date.
Peak — We expect this species’ occurrence in the region to peak around this date.
Rapid Migrant Departure — We expect migrating individuals of this species to be departing around this date. (We may show Rapid Depart dates even if some individuals of a species remain in the region, as long as there is a detectable departure from other individuals.)
Last Migrants Depart — We expect the last migrating individuals of this species to be departing the region around this date.
Note that sometimes we will not provide all dates for a given species in a given region. This may occur if arrival/departure occurs largely outside of the spring months or if a species lingers in the region before or after migration.
Migration Amounts (pre-2018)
For ease of describing bird densities and migration traffic from weather surveillance radar (WSR-88D in particular), BirdCast has chosen to divide movements among four different classes. We provide a qualitative description, a relative measure in decibels of Z (dBZ) of the energy returned to a radar, and a bird density based on previous work by Gauthreaux et al. (1999). Additionally, see this article published previously.
Little to no migration — Minimal migration: < 5 dBZ — fewer than 59 birds per cubic kilometer
Light — Light migration: 5-10 dBZ — approximating 59-71 birds per cubic kilometer
Moderate — Moderate migration: 10-20 dBZ — approximating 71-227 birds per cubic kilometer
Heavy — Heavy migration: 20-30 dBZ — approximating 227-1788 birds per cubic kilometer
Very Heavy — Extreme: >30 dBZ — more than 1788 birds per cubic kilometer (this intensity of movement occurs rarely, perhaps at certain individual radar stations a handful of times each migration season)