Monday, August 1, 2011

Puttting Bands on Purple Martins

The month of July in Minnesota has been just oppressively hot and humid. Not a great combination for getting out into the field to do some birding. That's O.K. though because the first two weeks of each July are taken up with banding young Purple Martins before they can fledge. We work with several martin "landlords" in the Twin Cities metro area and this year have had a banner year for putting bands on young.

People wonder what the purpose of banding is and there are several things we're learning by doing this but in the case of Purple Martins, it is to find out more about their movements after they leave their colonies and how much movement there is between colonies of birds. After 3 years of marking birds with both federal USFWS silver bands and red alpha-numeric bands (showing a letter and numbers) we are starting to find out some cool stuff.

We head to the colonies when young birds are between 13 and 20 days old and pretty ugly. Old enough so that their legs are actually thinner than when they hatched. Baby birds have thick legs because they store fat along the bones. Bands won't fit well until the birds use some of that fat up. We put 2 bands on each bird, a silver band on their right leg and a special red band on their left leg. In Minnesota, all Purple Martins that are color marked get a red band with white letter and numbers. The 3 numbers on the red band match the last 3 numbers on the silver band so we can identify a bird without having to catch it again. Birds are placed back into the houses after they've had a good cleaning and then we just sit back and wait to see young birds soaring around eating mostly dragonflies.

In this photo you can see the bands on the birds legs. Once the birds fledge they leave the colony and head for what are called "pre-migratory" roosts before heading south for the winter. Here are some of the things we've learned so far:
-When young birds first start to fly, they will often return to a nest cavity in a martin house that is not the one they hatched in. Parent birds don't seem to care and will feed these intruders along with their own young.

-Purple Martins in Minnesota actually move north after they leave their colony and spend time in north-central Minnesota in huge flocks of up to 30,000 birds, roosting at night in cattails around the edges of large lakes.

-When arriving back in the spring, most Martins show up at the colony they were born in but some will go to a nearby colony and take up residence at a new site.

Anybody out birding and seeing Purple Martins should check their legs as they perch. We banded 535 young this year and now have over 1600 martins with bands flying around (we hope). Citizen science only requires a good pair of binoculars and some patience to help add to our understanding of Purple Martins and where they go.

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