This article originally appeared as "Seminar Teaches About Forest Birds, Ecosystem Health" in the Friends of the Florissant Fossil Beds Newsletter, September 2006. Click on photos to view full-size images.
At the Ecotone
by Melissa Barton
Colorado College ecology professor Brian Linkhart frees a pygmy nuthatch from a mist net. All photos by Melissa Barton.
The pygmy nuthatch hangs quietly in the nearly invisible mist net, suspended in midair. The bird is unharmed; its alert black eyes follow the students as we gather around to watch Colorado College ecology professor Brian D. Linkhart free it from the net.
Biologists often use lightweight nylon mist nets like this one for catch-and-release trapping of small birds like this pygmy nuthatch. The nets are usually set up at the ecotone, the border or transition between two ecosystems. This net stretches along the transition between pine and aspen forests. Unfortunately, our seminar class, Ecology and Conservation of Forest Birds in the Pikes Peak Region, had a late start this morning at 7:00 a.m.--the best time to set up a mist net is around 5:30 a.m.
Linkhart carefully works the nuthatch free. It's thoroughly tangled in the nylon strands, so the process takes about 10 minutes--mist netting is not for the impatient. Finally he works the bird loose and cups it gently but firmly in his hands.
A female pygmy nuthatch caught in a mist net.
Nuthatches don't usually have obvious sex characteristics, but fledging season is just past, so Linkhart flips the bird over and blows lightly on its stomach feathers. The feathers spread to reveal a bright reddish-purple patch of bare skin on the belly, the brood patch. Female nuthatches, like many other birds, lose feathers from their belly area while incubating their eggs. Numerous tiny blood vessels close to the skin help keep their eggs warm.
We observe the nuthatch, examining the shape of her flight feathers, until she manages to wriggle free and fly to a nearby tree, where she chatters loudly. Linkhart would normally band the birds he captures here at the Manitou Experimental Forest, a U.S. Forest Service (USFS) research station near Woodland Park, but there's no time today. The sunny morning is growing warmer, and it's important to check mist nets frequently so birds won't injure themselves by struggling or overheating.
Unfortunately, our late start means that the nets remain empty. We examine other signs of bird activity in the aspens trees, including numerous woodpecker and flicker nest cavities. Both mountain bluebirds and flammulated owls nest in the abandoned nest cavities of other birds, but only flicker cavities are large enough for the owls.
Linkhart and students set up the first mist net.
Flammulated owls, one of the two smallest owl species in the United States, are Linkhart's speciality.
Every summer, Linkhart brings a few of his students from Colorado College to the experimental forest to collect owl data. They work from dusk until the wee hours of the morning, tracking the owl's movements, trapping the adults for blood samples, and weighing the owlets. During the day they describe habitat and perform other diurnal tasks.
"Flams," as Linkhart calls flammulated owls, are nocturnal insect-eaters that migrate in winter. Because flams are very sensitive to habitat changes, they are what biologists call an "indicator species." The health of their population provides information about the health of the whole ecosystem.
We had hoped to see owlets, but this year's unusually hot, dry spring and early summer followed by sudden heavy rains killed almost all of the owlets. Fortunately, flammulated owls are unusually long-lived for such a small raptor--the oldest Linkhart has caught was over 14 years old, and most are 6 to 8 years old. One year's nest loss will probably not be as devastating for them as it would be for a shorter-lived species.
Flammulated owls aren't the only forest animals that like flicker nest cavities--several trees show deep scars from black bears that had climbed the trees in search of eggs or nestlings. When the bears do manage to reach the nests, it usually kills the soft-wooded aspens.
As we start taking the mist nets down, we catch another bird, an iridescent blue-green broad-tailed hummingbird. The tiny female lacks the russet throat patch of the males.
A female broad-tailed hummingbird resting in a spruce tree after release. Males can be recognized by their russet throat patches, which the females lack.
Because of their high metabolisms, just flying into a mist net is exhausting for hummingbirds. This one is so tired she's barely moving, so we observe her for only a few minutes and then set her in a spruce tree to recover.
The Manitou Experimental Forest is an exceptionally good site for observing and studying forest birds like pygmy nuthatches and broad-tailed hummingbirds. A USFS research station for 70 years, it provides an excellent opportunity to study the elusive flammulated owl and other rare birds, as well as the effects of careful thinning on ponderosa pine forests and their inhabitants. The health of sensitive mountain ecosystems like this one is an increasingly important topic of study as conservation becomes an ever-greater concern.
For those who missed this bird seminar, Linkhart will also be presenting a winter seminar about flammulated owls at Colorado College.