Carolina or black-capped? Telling chickadees apart near Washington

A black-capped chickadee at Monocacy National Battlefield. NPS.

Chick-a-dee-dee-dee. Anyone can name the bird. But in the hills around Washington, D.C., telling which chickadee it is — Carolina or black-capped — can defeat experienced birders, because the region sits on the line where the two species meet, interbreed, and borrow each other's songs.

Two species, one overlap

Chickadees are small songbirds of the tit family, Paridae, that move through the woods in busy little flocks and stay all year, often at backyard feeders. North America has five species; in the East the two commonest are the black-capped (Poecile atricapillus) and the Carolina (Poecile carolinensis).

A Carolina chickadee. NPS / Neal Lewis.

A black-capped chickadee. NPS.

Most of the National Capital Region is Carolina country. But Catoctin Mountain Park and the upper Chesapeake and Ohio Canal lie in or near the zone where the two ranges overlap. There the species hybridise, which lowers their breeding success and produces birds with in-between plumage and songs that mix both species' patterns — and some birds sing both species' songs perfectly. A voice, in other words, is not proof.

Why the Park Service counts them

The region's Inventory and Monitoring Network has surveyed forest-breeding birds since 2007, both to track bird populations and as a measure of forest health. Carolina chickadees turn out to be among the most abundant and densely distributed birds in the region's parks. Because they raise a single brood a year, they are one of the life-history traits in the Bird Community Index, which grades forest quality by which birds live there. Long-term counts will show how the forests — and the birds — change.

Sources

Written from Zach Ladin, "Carolina or Black-Capped Chickadee? Sometimes It's a Hard Call", National Park Service National Capital Region Inventory and Monitoring Network (first published in a 2012 newsletter), which cites Brewer (1963), Reudink and others (2007), and Ladin and Shriver (2011).