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Outdoors: Purple martin ‘landlord’ helping scientists

For the purple martins that call Minnesota home, it's only an 11-day flight from a corn field south of Willmar to the remote wilds of the Amazon River rain forest.

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Dick Doll offers 50 housing units in his purple martin colony north of Willmar. This year, 49 of the 50 were occupied, and more than 200 chicks were fledged. Tribune file photo.

For the purple martins that call Minnesota home, it’s only an 11-day flight from a corn field south of Willmar to the remote wilds of the Amazon River rain forest.

The route there and back can vary, but the timing is generally pretty consistent.

Dick Doll’s purple martins returned right on time in April, and unfortunately so. Our late spring meant the insects that these world-class travelers rely on were yet to develop in Minnesota.

 Doll more than made up for it.

He served up more than 4,000 crickets to his returning purples martins, and dozens of scrambled eggs as well to carry them through.

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Really, the food is only part of a fair trade. The purple martins returning to the colony that Doll maintains at his home north of Willmar carry loads of information with them.

For three years now, Doll has been working with scientists with the Purple Martin Working Group to place tiny geo-locators on some of the purple martins in his colony. The geo-birds that return are trapped and the tiny devices (weighing only 3 grams) are recovered. The geo-locator provides a day-by-day account of the individual bird’s travels.

The group is also working with two other purple martin enthusiasts in Minnesota. This year they placed geo-locators on 24 birds, eight of them from Doll’s colony.

Only a small number of the geo-birds will return and be caught.

Yet already, the recovered locators are answering lots of questions for scientists. They’ve shown just how quickly the birds make their annual migration, and just how far they will go. One of Doll’s birds almost reached Bolivia.

Doll wasn’t surprised by the speed or distance, but the varied routes of the birds did catch his attention. One bird that previously was tracked crossing the Gulf of Mexico changed his flight plan the next year and followed the Mexican coastline. The dates suggest he made the diversion to avoid a hurricane headed to the Gulf at the time.

All of this information is becoming increasingly important. The population of purple martins in Minnesota has declined by 70 percent since the 1960s. The birds - a member of the swallow family - were recently listed as a species of special concern in Minnesota, said Doll.

In North America, the birds are entirely dependent on human-built housing.  They’ve proven very adaptable to living in close proximity with humans. Doll has no trouble teaching his birds to accept his hand outs of crickets and scrambled eggs in the spring.

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Surprisingly, the geo-locators show that the purple martin’s winter grounds are the remote regions of the Amazon rain forest, and far from people.

That’s helped alleviate some concerns. Until now, many had feared the birds were also migrating to agricultural areas of South America. That would have possibly made them vulnerable to pesticides used in those areas.

Minnesota’s purple martins are now gathered in large numbers on any of four main roosting sites in the state. One of the sites is located in a corn field two miles south of Willmar.

Doll has used his spotting scope to read the bands on birds at the roosting site. He’s documented that purple martins using the site come from diverse locations in the state. It indicates that there is much more inter-mixing of the bird colonies than many had realized.

Come spring, the mix up continues. Only about 10 percent of the previous year’s colony will return to the home site, said Doll. Some of his birds have shown up near Brainerd, in a colony maintained by fellow “landlord’’ and purple martin enthusiast Larry Leonard.

Doll is hoping some of the eight birds fitted with geo-locators at his colony this year will be among those returning home to Willmar. For now, he can only wait. The geo-locators have shown that for these birds, September 1 is about as late as they will wait to say adios to Minnesota for the winter.

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