The Bird Conservancy of the Rockies in conjunction with Denver Audubon has been running the banding station at Chatfield State Park each spring at the peak of landbird migration for about thirty years.  In the fall, with a focus again on migrant landbirds, a comparable effort is conducted at Barr Lake State Park.  The process entails using mist nets strung between poles in which birds are harmlessly trapped.  They are then removed from the nets, measured, weighed, banded on a leg with a small, numbered band, and then released.  Each of these bands has a unique number so that if the bird is recaptured somewhere else, we can know where and when it was banded, thus learning a bit about the timing and route of that species’ migration.  In more recent years a single feather may be removed from a bird, or even a small blood sample taken, for DNA analysis.

Our visit to the banding station was scheduled to begin at 7:30, so after checking in at the Audubon Nature Center, we spent a nice half-an-hour enroute capturing a bit of the dawn chorus being enacted by a couple of Yellow-breasted Chats, a Spotted Towhee or two, and some House Wrens and Lesser Goldfinches.  Once at the banding station we were greeted by chief bander, Meredith McBurney and her band of volunteer assistants who immediately took us out on a net run to see what they had been able to catch.  Returning to the banding station with birds in small cotton bags, Meredith proceeded with processing and releasing this first round of birds.  She chose to immediately deal with a male Downy Woodpecker, the reason being that our bird had an obvious brood patch indicating that he and his female cohort were in the process of incubating some eggs.  For many species the female does all the incubation, but there are exceptions.  We then got to watch a number of Yellow Warblers being processed and learned that on average they weigh about 9.5 g (a third of an ounce).  A subsequent net run yielded a Western Wood-Pewee and we got nice looks at its rictal bristles – small feathers by the bill that help flycatchers catch insects, and we also noticed the bright orange of the interior of the bill which can act as an attractant for insects.

Meredith spent over an hour with us answering our many questions, but finally another group was waiting, and it was time for us to move on to some birding along the South Platte River.  Here we had several more Yellow-breasted Chats, a good number of Gray Catbirds, and a couple of Least Flycatchers.  This last is a small eastern flycatcher that occurs uncommonly in a few Colorado locations, one of these being Chatfield SP where it appears to be increasing yearly.  Moving on, a mystery bird in the highest branches of a cottonwood captured everyone’s attention for awhile leading to many thoughts as to its identification, with a few people leaning towards it being a Western Tanager.  Some saw (or thought they saw) yellow on the breast and belly, some saw a red-orange head, some saw black wings with wing bars.  When I suggested House Finch, I had a rebellion on my hands – the bill was wrong, the bird was bigger than a House Finch, etc…  Subsequent photographic evidence provided by Ron Belak eventually verified our bird as a House Finch, but not before we had had some good lively debating.

As for the highlight of the morning, we got several great looks at a pair of Red-eyed Vireos.  This is an Eastern species that occurs uncommonly in Colorado as a spring migrant and rarely as a summer resident. Overall, throughout the Rocky Mountain states it is apparently declining, though eastern populations are doing fine. Our birds observed in late May could conceivably fall into either category of either being migrants or breeders, though the breeding option is the less likely.  Nevertheless, our birds were vocalizing constantly and in close communication with one another presenting an intriguing prospect.  It would be interesting to try and keep an eye on the area they were in during the coming weeks.

Good birding!  Chuck

Chatfield SP–Audubon Center, Banding Station, & Trails, May 29, 2022
41 species (+1 other taxa)
15 participants

Canada Goose  7
Mallard  3
Common Merganser  5
Mourning Dove  3
Broad-tailed Hummingbird  11
Double-crested Cormorant  3
American White Pelican  1
Great Blue Heron  3
Turkey Vulture  8
Cooper’s Hawk  1
Downy Woodpecker  1 
Northern Flicker  5
American Kestrel  1
Western Wood-Pewee  4
Least Flycatcher  2
Say’s Phoebe  2
Red-eyed Vireo  2
Woodhouse’s Scrub-Jay  2
Black-billed Magpie  1
American Crow  4
Common Raven  1
Black-capped Chickadee  2
Tree Swallow  5
Barn Swallow  2
swallow sp.  5
White-breasted Nuthatch  2
House Wren  20
Gray Catbird  8
American Robin  4
Cedar Waxwing  15
House Finch  1
Lesser Goldfinch  5
American Goldfinch  2
Song Sparrow  2
Spotted Towhee  16
Yellow-breasted Chat  17
Western Meadowlark  2
Red-winged Blackbird  20
Brown-headed Cowbird  1
Common Grackle  2
Common Yellowthroat  2
Yellow Warbler  24