▲ ▲ ▲

A wondrous nightly event is occurring in the skies right above you. Unseen and silent, the annual spring bird migration northwards is in high gear! Millions of birds leave the Caribbean, Central America, and South America to begin the annual journey northwards to nesting grounds throughout North America. These are the songbirds and summer residents in your yard, neighborhood, and hometown you see arrive each year.

The birds normally leave within an hour or so after dark, weather and winds permitting, to continue flying northwards. Depending on where the journey started, the migration time and distance for species can be from a few weeks to a few months, from hundreds of miles to thousands of miles. Most birds migrate at night and stop during the day to rest and feed.

Spring Bird Migration 2012

Below is snapshot of the National Weather Service national radar mosaic at about 9:45 p.m. CDT on Sunday, April 15, 2012. The blue, with some green, circles around the radar sites are “bird rings”. Some humidity is undoubtedly being detected, but mostly these are birds. There are several interesting dynamics occurring on this specific night.

A line of thunderstorms stretches across the United States. To the east of the line, especially along the Mississippi River corridor, or flyway, the northern push is on ahead of the advancing storms. To the south, on the Gulf coast and inland, tremendous numbers of birds are rising up plus coming in from flying across the Gulf of Mexico. Along the Atlantic seaboard, many birds fly offshore parallel to the coast.

Behind the line of thunderstorms, to the west, an interesting effect is noted. To the north and west of Tulsa and Oklahoma City, there are very few birds detected. The central flyway, the migration path through the middle of the United States, would normally show pronounced rings. The rings are missing. Why? The backspin of a low pressure area is creating northerly and westerly winds. Migrating birds don’t fly into a side or head wind. They will stay in place and wait for a wind shift to their navigational advantage. Normally there would be large blue rings northwards into Kansas and Nebraska.

Both adverse winds and storms cause birds to “drop down”, wait for the weather to clear or winds to shift, and continue the northward migration the next permissible night. These are called “fallouts” by birders and some avidly seek these areas during the day to observe an abundance of species in a relatively small area.

For who knows how many years, centuries, eons this silent drama of the night of millions of birds flying northwards has continued. Many ultimately journey to the Boreal forest in Canada and to Alaska. The Boreal forest of Canada is extensive and critical habitat for North American birds.

National Weather Service
National Radar Mosaic (for images as presented above)

Cornell Lab of Ornithology
All About Birds

eNature.com
Following Spring Migration

Clemson University Radar Ornithology Lab
Home Page

▲ ▲ ▲