by Adele Porter
The July sun melted below the horizon. This was the signal for U.S. Geological Survey wildlife researcher Kevin Kenow and his team to fill their coffee thermoses and head to work. Under the cover of darkness, they would collaborate as loon catchers, wildlife vets, and digital techies with gizmos to transform unknowns into facts.
On this night, their worksites were Baby and McKeown lakes in north-central Minnesota. Their aim was to capture seven of the adult common loons (Gavia immer) residing on the two lakes. Over the summer the researchers would capture 42 loons, measure and assess the condition of each one, and outfit it with a geolocator tag. Then, for the next year after the loon's release, this small digital device would track and record the depth, timing, water temperature, and location of the loon's underwater dives.
The researchers were using geotags, as well as satellite transmitters implanted in previous years, to gather information for a long-term Great Lakes study of botulism. From 1999 through 2009, some 48,000 birds, including 24,000 loons, died of botulism during migratory stopovers on Lake Michigan. Kenow's role is to help identify where in the aquatic environment loons are coming into contact with the toxin. As a result of the April 2010 oil spill disaster in the Gulf of Mexico, this botulism research now serves double duty. When tagging loons, the team takes blood samples to be analyzed for contaminants the birds might have picked up in the gulf.
Loon Whisperer As the researchers' boat left the dock on Baby Lake at nearly 10 p.m., the brightest stars broke through the haze and reflected off the water.
"Send me a wail, Pete," Kenow called to wildlife biologist Pete Boma.
A recorded loon wail cried out from the rear of the boat. But there was no response from the dark, only the blinking of a distant cabin light.
Recorded calls traveled across the still lake. Silence returned. Then, the wolflike howl of an adult common loon rebounded through the humid air.
With the precision of a baseball catcher signaling a pitcher, Kenow motioned to Boma. The boat slipped through the murk on this moonless night to the opposite side of the lake. At the bow, Kenow was poised with a muskie net. Shining spotlights, the researchers scanned a 150-yard-wide circle around the boat.
The sleepy darkness over Baby Lake opened in the light. Flickering bats swooped to devour insects just above the water. Mergansers moseyed toward a cove. And a loon broke above the glassy surface, its red eyes reflecting the beam of light.
Like a loon whisperer, Kenow whistled a series of quiet peeps, which seemed to mesmerize the loon as the boat drew closer. Then, with a quicksilver stroke, Kenow scooped the loon into the net. The researchers carefully placed the adult loon in a black tub. Its muffled wails and knocks subsided by the time the boat docked.
On shore, wildlife technician Luke Fara laid out a makeshift exam station. Fara took the bird from the tub, firmly holding its spearlike bill. Working together, the team members measured the bird's bill, head, wingspan, legs, and body. They attached two leg tags: a color-coded identification tag and a geolocator, or geotag. Then, with the care of a surgeon, Kenow drew a blood sample from the loon's unbanded leg.
Migratory Stopover Loons are strong indicators of the health of their environment. In the 1960s, loons staging on Lake Michigan began dying in large numbers. The cause of death was discovered to be type-E botulism (Clostridium botulinum), which had not previously been recorded in wild birds in the United States. No one knew where the birds were contacting the deadly toxin.
In the 1980s, aquatic species from as far away as the Baltic Sea appeared in the Great Lakes. They had most likely arrived in the ballast of ships from this region. Without natural predators in their new habitat, some of these creatures multiplied. Probable players in botulism outbreaks include three of these introduced species: zebra mussel (Dreissena polymorpha), quagga mussel (Dreissena bugensis), and round goby (Neogobius melanostomus).
Zebra and quagga mussels live on lake bottoms, where the spores of type-E botulism can be found. The spores can remain dormant for years, but under the right conditions—such as nutrient-rich environments created by decaying algal mats and dead mussels—they can become active and produce botulism. The Great Lakes researchers are working to understand the path of this deadly organism through the aquatic food web. One clue: Round gobies feed on zebra and quagga mussels, and loons and other waterbirds in turn feed on round gobies.
In the 1990s, Kenow began gathering information on loon migratory movements with the aid of satellite transmitters surgically implanted. Two Minnesota loons received transmitters in 2010. In 2011 another 13 loons got transmitters. The data revealed that Minnesota common loons were among the thousands that annually gather on the Great Lakes during fall migration.
Gulf Coast Connection Soon after the BP Deepwater Horizon rig spilled some 200 million gallons of oil over nearly 600 square miles of the gulf in April 2010, biologists in the Minnesota Department of Natural Resources began asking questions about the disaster's effects on migratory Minnesota loons, which winter in ocean waters from Alabama south to the Florida Keys. They knew oil residue and dispersants, used to dissipate oil in spill recovery efforts, could linger in the gulf's aquatic habitats. To provide the USGS with funding for satellite tracking and contaminant testing in Minnesota loons, the DNR Nongame Wildlife Program sought and received a three-year grant from the Environmental and Natural Resources Trust Fund (from a portion of state lottery proceeds). The Nongame Wildlife Checkoff also contributed funds.
DNR Nongame Wildlife Program biologist Rich Baker, his staff, and a team of volunteers with the DNR's loon monitoring programs have been keeping track of common loons since 1994.
"Loons can be exposed to oil spill contaminants directly from the water or on the ocean bottom," says DNR Nongame Wildlife Program supervisor Carrol Henderson, who has been as protective as a parent and astute as an attorney in putting together the investigation. "They may ingest contaminated prey species that have fed on contaminated microorganisms. Loons exposed to the contaminants could experience reduced reproductive success or a shortened lifespan, in addition to other effects."
While adult loons winter on the Gulf Coast, young loons spend most of their first two years there. The young loons don't return to Minnesota until spring of their third year. The 1- to 2-year-old loons that were in the gulf when the oil disaster hit are at particular contamination risk, Henderson says. This coming summer, some of those birds will reach reproductive age (typically 5 years old) and should begin to nest and raise young. Although the DNR has been gathering loon blood, feather, and tissue samples during the past two years, this data does not provide information on any ripple effects on the next generation of loons. Summer 2013 will be the first year for testing loon eggs and gaining insight into generational contaminant links.
And here is where understanding our state bird's reproductive capacity is important: Common loons can live as long as 30 years, but only three or four of the young they produce will ever reach adulthood. When an adult loon dies prematurely, the young that it might have added to the population are also lost. Thus, the balance of loon population gain to loss is easily tipped.
Researchers have recently identified a tipping point. Once the number of adults lost reaches 3 percent of the total population, the losses are more than what loon reproduction can make up for. From this point, the population is in trouble.
Although Minnesota's common loon population has held stable at 12,000 loons during the past 18 years, Henderson and other experts are adding up the ecological threats to loons in their various habitats for migration, nesting, and wintering. From this broad perspective, the resilience of common loons is being put to the test.
This summer Kenow and his team will return to the 18 Minnesota lakes where they captured loons in 2012. To wrap up the study here, they will recapture as many of the 42 loons outfitted as possible, remove the geotags, and claim the data within.
New insights have already been gained from satellite transmitters and geotags. We've learned the migratory routes taken by Minnesota's loons. We know how long they spend on the Great Lakes in the fall before moving on, and that many of them have indeed perished in the botulism die-offs. We know too that loons are feeding as deeply as the bottoms of lakes where type-E botulism can exist.
Still, researchers need more time and funding to solve this complex puzzle. They need more certainties to devise and implement a plan to avert more die-offs of waterbirds on the Great Lakes.
Meanwhile, research on the effects of the 2010 gulf oil spill on Minnesota's common loon population will continue with this summer's egg tests. It will take many years of data and documentation of population trends to draw conclusions, Henderson says. Because the health of our loon populations reflects the health of our waters, every Minnesotan has a stake in long-term research and monitoring of our state bird.
Follow the movements and migrations of common loons in this study.