Unique forestry method created perfect habitat for golden winged warbler
WARBA — Golden-winged warblers are little birds in big trouble.
Scientists say they are declining faster than any other songbird in North America. They are under consideration for federal Endangered Species Act protections. The Cornell Laboratory of Ornithology says only about 400,000 breeding adults remain, a decline of 66 percent since the 1960s. In some eastern states, their population has crashed by 98 percent.
But in northern Minnesota, the tiny songbirds, less than half an ounce, are doing quite well. It's now believed that half of all golden-winged warblers on the continent spend their summers in Minnesota.
And on a plot of Blandin Paper Co. land in eastern Itasca County, golden-winged warblers are thriving more than anywhere else.
On Friday, bird researchers for the Natural Resources Research Institute at the University of Minnesota Duluth were conducting their annual field survey to see if the warblers were still doing well here.
Researchers bushwhacked through the forest along predetermined grids, stopping to listen to and make note of every bird they heard, pinpointing the location with GPS coordinates.
There was a cacophony of calling. Veeries, red-eyed vireos, purple finches, Nashville warblers, cedar waxwings, rose-breasted grosbeaks, yellow-bellied sapsuckers, red-winged blackbirds and more.
Among songbirds, males are the ones you hear, guarding their territory or keeping track of their mate or maybe singing just because they can. And among those noisy males, researchers Friday documented more than three dozen golden-winged warblers across the square-mile study area.
"That's the highest concentration of golden winged warblers anywhere that we know of,'' said Jerry Niemi, ornithologist and longtime NRRI forest bird researcher.
Niemi can't do the official count anymore; his hearing is failing. Even with a hearing aid, it's hard to hear quieter or more distant calls.
"But I know there are probably golden-winged warblers here because of the habitat," Niemi said as he walked through woods.
The golden-winged warbler eats insects exclusively and favors very specific kinds of young forests for nesting — seasonal wetlands, upland shrub lands such as abandoned fields, and recently burned or logged forests. They nest on the ground in grassy areas. But they also like some bigger, older trees nearby.
So in what kind of forest do the bird counters hear them most?
"Wet. Shrubby. Young stuff. We count a lot of them near ash, if not actually in ash,'' said Josh Bednar, one of four counters on this season's survey.
The problem across the golden-winged warbler's North American nesting range — which used to run from New York across Ontario and as far south as Tennessee — is believed to be an aging forest with fewer open, wet areas. But it's not as simple as logging everything off to get more warblers. Studies using tiny radio transmitters placed on female warblers show that, after nesting, the warblers move into older forests, making a mix of habitat critical.
"The key, really, is you need a mosaic. Not too much of any one age or one type of habitat," Niemi said. "But it's also clear that you need disturbances, openings, and probably bigger disturbances than we have had in recent years..."
More, bigger openings
Disturbance is forestry lingo for logging, fires or wind. In centuries past, wildfires would create the patchwork of open and forested lands that the warblers needed. In decades past, extensive logging worked to open land for the little bird. Now, with fires suppressed and logging diminished in many areas, much of that land simply grows too big, too thick and too old for the golden-winged warbler's needs.
But on this plot of Blandin land, some innovative logging methods in the early 2000s have paid off for the little bird and several other species.
Just as important for scientists, the land had been extensively surveyed in the 1990s for bird populations, so there would be "before" logging numbers to compare to the "after" logging numbers.
"Blandin asked us what we'd like to see it look like. I said let's try to mimic what a fire would do. I had no idea this was going to become a hotbed for golden-winged warblers. We weren't sure what would happen," Niemi said.
Most of the 640 acres were logged over from 2001-03, said Cheryl Adams, forest resources manager for Grand Rapids-based Blandin, part of Finnish company UPM. But there were few straight lines marking where trees were felled by loggers. Niemi calls it 'feathering," logging uneven patches into unlogged areas, creating more edge opening.
There are patches of big pine on higher ground spared from the saw. Lots of young aspen are 30 feet high already. Maple are regenerating. Alder, spruce and ash are flourishing in the low areas. Far from the usual clearcut that regenerates into a sea of same-size aspen, here there were pockets of different tree species and size everywhere. Small, wet meadows and open areas around beaver ponds abound.
"It's a big area. But we didn't flatten it. We left a lot of leave areas and leave trees and there's a real mix of forest types in there," Adams said. "We certainly got the fiber (trees for papermaking) off of there. But we tried to emulate what a fire would do, and natural disturbances are usually big ... and I think we came pretty close."
A decade after the logging Adams called Niemi to suggest he start re-surveying the area. He jumped at the chance to see how birds had responded.
The results surprised even Niemi:
- The total number of all species of birds counted increased from 31 in 1994, before the logging, to 47 in 2015.
- The total number of birds increased, too, from 582 to 779.
- Veery numbers increased from zero to 105.
- Chestnut-sided warblers jumped from 20 to 87
- And golden-winged warblers increased from just 3 in 1994 to 40 last year, with about that many counted Friday for the 2016 count.
- Of course, some species that favor older, bigger trees declined. Scarlet tanagers went from 11 in 1994 to zero last year. Ovenbirds declined from 220 to 93. Black-throated green warblers declined from 43 to zero. But none of those species is in any danger on a large scale.
Whether it's the beaver pond openings or wet meadows or the residual open areas from the logging 15 years ago — or all of the above — this chunk of land appears to be haven for golden-winged warblers even as most of the trees age beyond what experts had thought was their favorite habitat.
"We don't know if this is an anomaly or what. But the numbers aren't going down as the forest gets older. There are still enough residual openings that they (golden-winged warblers) seem to have the openings they need here," Nimei said.
Adams said the logging project wasn't revolutionary in its methods but was much larger than the trend in the 1990s — a trend to small logging plots that continues across many forested areas.
"A lot of what was happening at that time, determining the size of (logging areas), was based on aesthetics," Adams added. "If you look at it biologically, the best thing you can do might be a lot different. Bigger might be better if you are looking at diversity of species."
As scientists decide what habitat to encourage for golden-winged warblers to make a comeback across North America, and as federal agencies throw millions of dollars at habitat projects to rescue the little bird, Niemi said they might do well to come to Warba and see where golden-winged warblers are thriving.
The bird already is listed as threatened in Canada. The U.S. Fish and Wildlife Service is expected to decide by 2017 if the warbler warrants protection here. The Minnesota Department of Natural Resources has listed it a species of "greatest conservation need" mostly because of its decline in other states.
In addition to aging forests or their nesting grounds, other factors including urban sprawl, competition from other bird species and loss of habitat in their wintering grounds in Central America and South America also loom large as forests there are cleared for palm oil, cattle grazing and sun-grown coffee. (True shade coffee, grown in forest settings, provides important winter habitat for the birds.)
Golden-winged warblers also are mating with blue-winged warblers, which seem to be the dominant species. The long-term trend appears to favor the blues.
"It may not make it over the long haul," Niemi said. "But it's making it here now. And that's good news."