There are two kinds of people in this world: those who know something about birds and those who don’t. Most of us belong to the latter group, educated enough to know the difference between eagles, owls, and crows but blissfully unaware of the richly variegated world of Pink-sided Juncos and Grey Catbirds, of Mountain Chickadees, Ruby-crowned Kinglets, and White-breasted Nuthatches. I’ll give us the benefit of the doubt and suggest that most of us are ignorant not because we’re uninterested, but because you have to be looking through a pair of binoculars to see the complexity. Tiny songbirds weighing as little as a quarter flit through the trees like shadows. Looking up at them silhouetted against the sky, they all look black. If we could only hold them in our hands, see them up close, we might be more aware of their subtle differences.
At a plastic picnic table against the wall of the barn in the Holmes grove, this fall’s bird banders Nancy and Aaron are doing just that.
“Is the crown shiny or dull?”
“Skull looks like a two.”
“These tail feathers are narrow though.”
Aaron holds a Wilson’s Warbler, or WIWA, in his hand, as he and Nancy try to determine its age and gender. They side step out of the shade and into the light to get a better look at one of the minute details of the plumage. Male and female birds share a reproductive opening called the cloaca (which is also the opening for the digestive and urinary tracts), so this aspect of a bird’s physical anatomy is little help in distinguishing genders. Instead, biologists have to use characteristics like coloration, wing length, and feather condition to get their answers.
The tiny, delicate bird waits patiently as a variety of instruments are used to take measurements. Special rulers are inserted under its wing, into the middle of its tail, and across the width of its beak. Aaron pulls out the wing and inspects the tail, looking for clues in the condition of its feathers. He wets his fingers and parts the feathers on the WIWA’s head to try and get a look at the degree of ossification of the skull.
Even for a “Master Bander” like Nancy, a biologist from the Bird Conservancy of the Rockies who has been running the station at the Chico for years, there are some birds that will elude easy identification. The sheer volume of the amount of data points required for these procedures is overwhelming, which is where Pyle comes in. Peter Pyle that is–a member of the highest echelons of bird expertise who authored a massive tome of technical ID data for banders, full of charts and diagrams for 395 species. Various other binders, printouts and books are strewn across the table, flipped open to pages on birds that have been giving them trouble this morning. It’s enough information to keep someone busy for a lifetime.
Aaron, a 22-year-old unpaid volunteer who’s been living in a tent 50 feet from the banding table for the past month, is something of a rarity in that he’s a young birder. During an Animal Behavior course at Middlebury College, his class conducted an experiment to observe the Black-capped Chickadee’s preference for shelled versus un-shelled seeds. He was hooked. Back in Colorado, he joined the Boulder Bird Club, where he, as he puts it, “hung out with a bunch of retirees.” In the afternoons, when the banding station closes, he heads out to the east side of the ranch or into the mountains looking for an uncommon species to add to his list for the year. Luckily he likes to go alone, because not many of his peers turn up at the ranch for birding.
“I think it’s a female–let’s call it a young female.”
After a look at Pyle’s chart on head cap length–is it 15mm or 16mm?–Nancy feels certain enough to make a call on the WIWA. With the age and gender determined, other measurements, such the fat level and weight are taken and recorded. A gentle blow on the bird’s chest reveals the pouch of milky fat under her translucent skin. She then goes head first into a piece of PVC pipe atop a digital scale, and finally, a metal band with a unique number is fitted around her leg. In case the bird is ever recaptured, she now has an official scientific identity linked to all the data points that Aaron and Nancy have now collected.
The odds of that happening, however, are rather slim. Of the roughly one million birds that are banded nationwide every year, an estimated 2% are ever recaptured outside of their original banding area. Only three birds out of the many thousands banded at the Chico have turned up elsewhere–in 2014, a Western Tanager banded in 2011 showed up in Lubbock, TX; in 2015, a Northern Flicker banded in 2013 was captured in Custer, SD; and in 2006, a Swainson’s Thrush banded earlier that year was found dead in southern British Columbia. Despite their infrequency, the recaptures that do occur are extremely valuable to scientists. Short of actually following an individual bird on it’s migratory journey, which would be next to impossible, there’s simply no other way to get the data. Compared with the prospect of walking a few thousand miles across North America while trying to keep one bird in sight, banding thousands with the hope of recapturing a couple is actually fairly efficient. One day we’ll have GPS technology small enough to attach to feather-light birds without weighing them down, but until then, banding is the best option we have.
There’s also the fact that setting up mist nets to catch birds every day simply allows us to see a sampling of what’s out there. WIWAs are reliable visitors, robins are everywhere, but every once in a while, a rare species turns up that might have otherwise gone unnoticed. There was a lot of excitement this season about two new birds that have never been seen on the ranch before–a Baltimore Oriole and a Pacific Wren (see Bill Maynard’s post on the Pacific Wren here). One young birder even spotted a Tropical Kingbird, the first ever reported in Colorado, that he was able to conclusively ID by converting an audio recording of its song into a sonogram. According to Bill Maynard, general patterns from this season reveal a higher percentage of mountain species than normal, suggesting that a failure of mountain crops drove masses of bird eastward in search of food.
Indeed, the Chico is both one of the best birding sites and most prolific banding stations in the state. This fall, over 900 birds of 60 species came through the station, including not a few noteworthy ones. The soil on the ranch has never been plowed, making it one of the best specimens of short-grass prairie anywhere, with the result that it’s a haven for native species. Riparian such as the Holmes grove where the banding station is set up host stands of cottonwoods full of forage for the hungry migrants. They hang out for a few days, filling up their fat stores for the next leg of the journey, before heading off again towards breeding or wintering grounds. The little six gram warbler in Aaron’s palm is in the midst of an epic multi-thousand mile journey that could take it as far south as Panama to spend the winter. She’s had a good stay refueling on the Chico; we can only hope that she continues to find as good of or better feed on her continuing trip south. Maybe one day, another bander will recapture her, and we’ll know that she survived her journey. Aaron loosens his grip, and in a split second she’s disappeared back into the trees. On to the next bird.