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Published in Autumn 2002
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On the trail of the disappearing owl
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By Jamie Bowman
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With the engine of their small plane overheating, the abandoned gravel airstrip below was a welcome sight to the biologists tracking radio signals from endangered burrowing owls.
But their relief was short-lived when Mexican combat troops swarmed out of hiding and surrounded them, weapons at the ready. "There were a few tense minutes until we could explain what we were doing," says Geoff Holroyd, a research scientist in the Canadian Wildlife Service's Species at Risk program at Environment Canada. "It turned out they had been staking out the airstrip, waiting for drug traffickers."
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Chanda Jones, US Geological Survey
Living in the sand under a concrete slab, this burrowing owl was trapped by researchers from the US Geological Survey, measured, fitted with leg bands, and released unharmed.
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The flight, one leg of a 200-hour air surveillance, was only a part of the wide-ranging effort across North America to figure out what is killing the burrowing owl. Scientists are employing tiny radio transmitters to monitor the signals from the ground and the air. They are also doing lab analyses of owl feces, building computer models to examine the battery of information gathered over the past few years, and, much more high-tech, pioneering the use of stable isotopes, which allow them to pinpoint an owl's geographic origin by examining a single tail feather at an atomic level.
It's now a race against time. Estimates of the number of burrowing owls are in the thousands, possibly as many as 10,000, but wildlife scientists stress that their census methodology is highly imprecise. What they do know for sure is that the population is dropping at an alarming 22 percent per year. They are anxious to solve the puzzle, not only to save the species, but because whatever is going wrong for the burrowing owl will likely have implications for other grasslands wildlife--and perhaps even for humans.
"It could be like peregrine falcons and DDT," says Holroyd, who has devoted himself to finding an answer. "When DDT was isolated as a problem with peregrines, people went looking and found it was a problem for merlins, some prairie falcons, cormorants, pelicans, great blue herons--a whole host of species. It just turned up first with peregrines." And, of course, the threat from DDT eventually extended to human health.
Canadian studies have indicated that a mere six percent of juvenile owls, and less than half of adults, are returning from one breeding season to the next, but until recently very little was known of their winter lives. Using radio collars (satellite transmitters are too heavy for small owls), biologists have learned that the little raptor migrates annually from nesting burrows in Canada and the northern US to winter in southern Texas and Mexico.
"Once we attach a transmitter, data is generated every moment until the final ‘beep' is heard in mid-March, when the owls migrate north again," says Enrique Valdez, a Mexican biologist working in the states of Guanajuato and Jalisco under contract to the Canadian Wildlife Service. "This is amazing, considering the little information that was available about the wintering grounds." One thing he's learned is that the owls become nocturnal in Mexico, unlike in Canada, where they are active both day and night.
Perhaps just as valuable, Valdez has learned to build a relationship with the Mexican authorities, who one night arrived to investigate reports of a masked man operating strange electronic equipment on top of his truck at 3 a.m. (The dust mask was for Valdez' asthma.) He also managed to convince Air Force generals Roberto Huicochea Alonso and Sergio Parra Estradas to allow biologists access to the restricted Zapopan Air Base near Guadalajara, a small island of grassland in a sea of urban development. That work went smoothly, except for one inky-black night when he and Holroyd accidentally bagged something bigger than expected in their bow-net traps set for owls. Fortunately, the surprised soldier who had been cycling the dark road didn't think he was under attack; he simply got up, dusted himself off, and kept going.
"We didn't even get a chance to apologize to him," says Holroyd.Valdez says he is inspired by Holroyd's devotion to the burrowing owl. That keen dedication has proven infectious elsewhere, too; the scientist's efforts played a key role in getting the burrowing owl included on the CEC's Species of Common Conservation Concern--a list of seventeen mammals and birds that the wildlife services of Canada, Mexico, and the US have agreed to work together to protect. Representatives of the CEC and many wildlife experts were present at a 1998 international symposium in Utah organized by Holroyd, where he made a convincing presentation on behalf of the burrowing owl. Later, when the CEC surveyed many of the same experts to identify species of concern, there was consensus that the burrowing owl's critical situation was high priority.
Since that conference, Holroyd has enlisted a number of Mexicans, Canadians, and Texans in the fight--something that has become easier as experts increasingly view the burrowing owl as a bellwether for the state of North America's distressed grasslands. "This ecosystem is in trouble," says Jürgen Hoth, program manager of the CEC's Conservation of Biodiversity program. "It is considered one of the most threatened environments in North America." Hoth has been leading the project for a trilateral grasslands strategy--a central focus of the first North American grasslands symposium, which the CEC co-hosted with The Wildlife Society this September in Bismarck, North Dakota, the heart of the North American prairie.
With cultivation, the grasslands have changed dramatically. Crops have replaced natural vegetation, with serious consequences: plowing affects the lives of prey, and, of course, herbicides and pesticides are another challenge for wildlife.
The heightened levels of nitrogen now showing up in the owls' tail feathers appear to be related to heavy fertilizer use on farms. Traditionally, burrowing owls have used the holes dug by prairie dogs, but that is no longer possible, since prairie dogs have been virtually exterminated in most grain-growing areas.
With a shortage of such residences, the owls sometimes choose more dangerous locations, such as road culverts. And naïve juveniles foraging on road kill are often run over by traffic. When biologist Mary Kay Skoruppa goes looking for burrowing owls in south Texas, she finds that many are using small culverts on country roads, dangerously close to traffic, humans, dogs, and cats. "We don't have mammal holes," says Skoruppa, who works for the US Geological Survey. "The major cause is that so much of the landscape here has been plowed under and we don't (naturally) have prairie dogs."
Her agency recently began a study using artificial burrows and was encouraged to note that several owls began showing a preference for one model burrow over another, using the smallest of three different sizes that were set out. "It's a management tool," says Skoruppa. "If we can find out exactly what they like, then we can provide them in safe places, away from roads and disturbances."
While that may help preserve some owls, the hunt to find the cause of their rapid decline continues on a variety of fronts, including a project by the US Geological Survey to determine whether contaminants in cotton fields are showing up in the birds.
It's painfully obvious to Holroyd that burrowing owls cannot continue to lose so many of their numbers. "Hopefully, we can determine the key causes and recommend corrective action soon, or the burrowing owl will no longer be part of Canada's grassland avifauna," he says. Holroyd's quest for an answer has caught the attention of producers at Canada's Discovery Channel, who are considering an episode on the mystery for Canadian Geographic Presents.
Even if the burrowing owl is lost before scientists find the answer, they have learned a lot that can be applied to other animals nearing extinction. Such endangered species are an important part of our natural history, he says, and hold significance for generations to come. "These are species we share the planet with and they have every right to exist."
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Species of Common Conservation Concern in North America