"You are just in time. You've caught us in the middle of an attack. This is going to be either really exciting or really boring." And so began my morning of tracking the elusive golden-winged warbler fledglings at Tamarac National Wildlife Refuge.
The golden-winged warbler is a vulnerable songbird and according to the Golden-winged Warbler Working Group, its population is declining by three percent by a year. The birds are extensive travelers that spend winters in tropical climates of northern South America and throughout Central America. In the spring they migrate to Canada and to the northeast and north central areas of the United States to breed and nest. They are distinguished by their bold yellow crown, golden patches on their wings and their signature cry, the "bee-buzz-buzz-buzz."
Over two percent of the global golden-winged warbler population finds its way to Tamarac each breeding season to mate and raise young in the refuge's aspen trees and shrubby forest floors. Tamarac maintains early successional habitat, the birds' preferred nesting environment, through forest fires, and other intense habitat management strategies.
At 6 a.m., I enter the sanctuary area on the refuge that is off limits to the public, opening a locked gate that provides access to miles of untouched wilderness as well as prime golden-winged warbler habitat. I drive the government hybrid suburban down a bumpy, dirt road through a tunnel of lush green forestation. I keep the windows down, enjoying the cool morning air and brisk spray of morning dew that hit me in the face as the Suburban brushed branches out of the way. After several miles, the narrow road opens into a field of charred stumps, young aspens and thick brush.
I slam on the brakes as John Denver stepped out into the road, or what John Denver would look like if he left the mountains to venture out into the Minnesota wilderness and needed to avoid our deer flies and wood ticks.
A lanky biologist with round glasses, wool socks tucked into his nylon zip off pants and a hat with an ear and neck guard gracefully walks over to my window. His actual name is Sean Peterson, and he is one of four University of Minnesota Twin Cities graduate students working every morning on the refuge to monitor fledglings' predation rates, behavior and their preferred habitats until they migrate as adults. Even though there are extensive studies about the conservation status of adult warblers, little is known about their first thirty days of life.
Tracking young warblers
This morning they are working on adding additional fledglings to their study group, by attempting to "herd" them into mist nets in order to place radio tracking transmitters on them. This is a timely process that involves stumbling your way through the brush like a black bear until you hear the high-pitched chirp of a fledgling, which they use to call to their parents when they are hungry or when there is a predator near.
So far, Sean has not been successful and we decide to join with the other crew members. On the drive, Sean explains that the golden-wings are disappearing fast and they are expected to be on the endangered species list soon.
"We are hoping to find out the details of their habitat needs before it is too late," he said. "Then your biologists can manage for these habitats and find ways to take out some of their predators."
As we get out of the car, Sean holds his hands up to his mouth and delivers a loud call, which sounds like a Na'vi from Avatar, that echoes throughout the area. A similar higher pitched call responds and he points through a wall of shrubs and fallen trees.
After bush whacking for several hundred yards we reach Henry Streby, the crew leader, who is watching on a hill over a mist net as the two other members from the crew are trying to scare up a sound that might have been a fledgling, or, more likely, some type of rodent.
When they reach the other side of the brush without seeing as much as a feather, no one seems too disappointed. I am told by Henry that an ornithologist's work involves patience and that the failures greatly outweigh the captures.
After several hours, falling over several times in the brush and several hundred bites from deerflies, we finally manage to ensnare a fledgling into a capture net. The bird is quickly retrieved; its weight, age and sex are recorded. A transmitter is placed on its back in front of its soft gray tail feathers.
Henry said that this study will be the first in United States to attach transmitters on such tiny birds. Miniscule transmitters are a new and useful technology to the world of songbird research. Transmitters allow the group to radio track the fledglings to see where they are living at what ages, and if they have been hunted by a bird of prey or a mammal.
"If we track a signal to a hawk's nest, obviously we can make a note of it and take it out of the study," he said.
Threats to survival
Predation is not as much of a threat as parasitism. Many of Minnesota's songbirds are threatened from the brood parasitism of the brown-headed cowbird. The cowbird does not actually raise its own young. Instead it will fly into a vacant nest while the parent songbird is feeding, push several of the eggs out, drop its own and then leave. After the eggs hatch, the cowbird fledgling is much larger than the others and will snatch most of the food the parents bring to the nest and it has been known to push the others out entirely. Henry estimates that approximately eight fledglings in his study have fallen victim to cowbird parasitism.
However, according to Tamarac Biologist, Wayne Brininger, the greatest threat to the golden-winged warbler is habitat loss. Early successional growth is being sacrificed to urban development, and lost from changes in natural resource management. For example, reducing the natural occurrence of forest fires through the "Smokey the Bear" campaign eliminates the young forests and the shrubby meadows that golden-wings require to nest.
Currently there are an estimated 210,000 breeding pairs around the globe. The goal is to eventually double this number to assure that golden-wings will be here for years to come. For a list of ways you can contribute to the golden-wing warbler conservation initiative, visit the Golden-winged Warbler Working Group