Night migration: A predator-avoidance strategy among the nation's small birds

Sharon StitelerFall migration is an exciting time whether you like to sort out confusing fall warblers, welcome redpolls to your yard, or if you are a hawk watching junkie. Depending on your location in the northern United States, you could potentially see several thousand broad-winged hawks fly over in a day. One day your yard can have a boatload of white-throated sparrows, then a big push of northwest winds overnight will sweep them away and deposit juncos in their place. Many small birds migrate at night using the stars as a navigational system and the cover of darkness to hide from aerial predators like sharp-shinned hawks as they tackle their marathon journey south.

White-throated Sparrows are a fun fall sparrow to watch for as they carbo load for their migration south.So many birds migrate at night that they actually show up on Doppler Radar. If the skies are clear and you look at radar and see a circular pattern over your city in the spring or fall, that could be thousands if not millions of warblers, vireos, thrushes, and flycatchers on the move. On those nights you can step outside and hear the eerie single-note chirps of the birds as they give contact calls in the moving flock.

The Internet makes it possible to track some of these bird movements. One great resource is Bird Cast from Cornell Lab of Ornithology (http://birdcast.info). This site uses information from user-submitted data on eBird, radar, and weather forecasts to predict when species will be on the move.

The blue circles are birds migrating at night, moving with the cold front.

Another is Bad Birds Reloaded (http://badbirdz2.wordpress.com), which can give real time shots of nighttime radar alerting users to large pushes of night migrants. Hardcore birders have used it as a resource to call in sick so they can watch for the new birds the following morning. This is an especially handy site to follow on Facebook for the most up-to-date information.

Check these sites out and on nights with a big migration push, see if you can note any new birds in your yard.

Categories: Sharon Stiteler, Social Media

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