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
Species on the move
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.
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)