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2011 loon study may contain clues to adult diving depths

This was one of the loons captured and monitored during the study. (Steve Maanum / For the Enterprise)

BY Steve Maanum


As the fall migration gets underway, our loons will be among those birds leaving for southern waters. Recently, Kevin Kenow’s research team with the U.S. Geological Survey’s Upper Midwest Environmental Sciences Center in La Crosse, Wisconsin made another visit to our area.

Their Minnesota goal was to capture a total of 15 juvenile loons (this year’s chicks) and tag them as part of their project to study loon behavior and migration. Two of the 15 were captured in Tamarac National Wildlife Refuge and three juveniles were captured on Big Mantrap Lake.

In 2011 the research team was here to capture loons as part of the project that would track migration in order to shed light on any negative effects from the Gulf oil spill and to locate the source of an avian botulism that appears in the Great Lakes food web.

That night the team captured fourteen loons on Big Mantrap – five adult males, three adult females, and six juveniles. The juveniles received colored leg bands, the adult females were given the leg bands and a geolocator tag, and the males got the colored leg bands, a geolocator tag, and an internal satellite transmitter.

The satellite transmitters send signals to receivers on-board NOAA weather satellites and location data is emailed to Kevin, whereas the geo-locators store data and must be retrieved by recapturing the loons at a later date so the data can be downloaded and studied.

When our loons leave Minnesota lakes each fall, a large percentage of them spend a few weeks on Lake Michigan before heading south. In the spring some loons visit Lake Michigan again before returning to their breeding grounds. Avian botulism has killed approximately 80,000 water birds over the past decade and loons account for almost half of those deaths.

This past August when the research team captured and banded the two juveniles in Tamarac NWR, both were given geo-locator tags and satellite transitters. Of the three juveniles captured and banded on Big Mantrap, two were given the satellite transmitters and geo-locator tags.

The botulism in Lake Michigan appears to affect adult loons more than juveniles and the data collected from the geo-locators might offer an explanation.

During feeding, adults have been documented as diving to depths of 130 feet. It is not known how deep juvenile loons forage during migration or how much time they spend on the Great Lakes.

Could the source of the poison be found in those deeper waters or is it carried by the fish inhabiting those deeper areas where the adults are feeding? Are juvenile loons at less risk of exposure to avian botulism because they spend little time there during their first migration?

These questions are only a small part of the loon research project being conducted in Minnesota, Wisconsin and Michigan.

Sometime during the next few months the juveniles will make their first flight south. They make it alone; their parents will have already left – the males usually migrating first, followed by the females.

The pair may not even see each other until they return to their nesting territory next spring. On the other hand, the juveniles will not return next spring. They will remain south for the first two and a half years of their lives.

Many of them will spend that time in the Gulf of Mexico, where they will be swimming and feeding in those waters where the oil spill occurred.

The data collected from those birds will be valuable in assessing the quality of the water and remnants of any hazardous chemicals that may negatively affect the health of our loons and other water birds.

Kevin Kenow will be a featured speaker at the North American Loon Symposium in Ashland, Wis., on Oct. 25-26.

By the end of September you should be able to follow loon migration at loons/migrations.html.