Tuesday, August 10, 2010

Purple Martin Megaflock

Photo by Chris Barnhart- Click to enlarge
Chris Barnhart put us on to the annual pre-migratory flocking of Purple Martins which are collecting at sunset north of Division at Old Orchard Road.  This is an annual event as they prepare for their trip south to the Amazon for the winter.  They routinely gather at various sites in North Springfield, covering the skies as they swoop into the trees for the night.  They are frequently mistaken for starlings flocking, but as swallows, their distinctive graceful flight is easy to distinguish.

You commonly hear that they eat lots of mosquitoes, but unfortunately it isn't true.  According to the MDC,
"These aerial acrobats catch flying insects on the wing.  They are not major predators of mosquitoes, which fly much lower than martins do.  A martin colony, however, may catch and eat several hundred beetles, horseflies, grasshoppers, dragonflies and wasps each day. Because inclement weather can greatly reduce the availability of flying insects, an extended period of rainy or cold weather can cause massive mortality in purple martin populations."
Purple Martins are the largest North American swallow and are sometimes called "America's Bird. " Originally they were cavity nesters, but early Native Americans began providing them gourd homes and European immigrants took up the habit more formally.  Over time east of the Rockies they have become completely dependent on humans, living only in human provided martin houses.  Now there are Purple Martin Societies, blogs, clubs, magazines and a large commercial market for houses and other paraphernalia.  There is extensive information about their life at Purplemartin.org.
Pre-migratory resting- Click to enlarge
Purple Martins begin to arrive in Missouri in late March and follow the blossoming insect populations north all the way into Canada.  After monogamous mating, they raise their chicks in the summer and then fuel up for the return to the Amazon.  Their pre-migration flocks can measure in the hundreds of thousands.  Having lived in apartment houses, they are very comfortable clustering together on tree branches as they prepare for their big trip.

Currently they are filling the skies (See this map) around 8:10 and settling in around 8:30.  You can probably catch the show for another 10 to 20 days.

Thanks to Chris and Deb Barnhart for the call and the pictures.
More on Purple Martin dwellings is available at missouribirds.com
and a pdf file with house designs at mdc4.mdc.mo.gov/Documents/12199.pdf