Carolina Chickadees are breeding species found year-round in Central Maryland. Black-capped Chickadees are not likely in Central Maryland except during the winter during irruption years. (The winter of 2020-2021 is an irruption year.)

There are gradations (and possible hybrids) between the two. Some observations will never be decided conclusively to the satisfaction of all.

Generally, if a Black-capped Chickadee is around, Carolina Chickadees will be present as well, and it’s useful to get photos of both species to compare them.

Do not depend on a single characteristic to distinguish between the two species.

If you believe you have a Black-capped Chickadee, take diagnostic photographs showing the following characteristics:

• >Plumage – the “hockey stick”
  Black-capped Chickadees are generally brighter and show more contrast between lighter and darker feather areas on the back and wings. The tertials, secondaries, greater coverts and tail feathers are more blackish, and the edges of these feathers are more contrastingly bright white.  The white edges of the tertials and secondaries form the “handle” of the upside-down hockey stick, and the white covert edges (especially the tips) form the “blade”.  In Carolina Chickadees the central areas of these feathers are lighter (grayer), and the edges of these feathers are duller – grayer or more silvery.
• >Size and shape
  With good photographs at the right angle, it may be apparent that Black-capped Chickadees’ heads appear relatively larger compared with those of Carolina Chickadees, and Black-capped Chickadees are larger overall—if you can compare directly.

There are other features that may be useful, but they are tricky at best.

• >Cheek patch of Black-capped Chickadees may be larger, extending further back to the nape, and the posterior portion may be whiter, as compared with Carolinas.
• >Lower margin of the bib may be straighter or “neater” on Carolinas, but this can vary with the position of the head.
• >A few authorities see the back of Black-capped Chickadees as “greener”.

Standard field guides tend to have little information regarding the subtleties of separating the two species.

Here is a useful reference by David Sibley and another by Eirik Blom:

• >https://www.sibleyguides.com/bird-info/black-capped-chickadee/black-capped-carolina-chickadee/
• >https://www.birdwatchersdigest.com/bwdsite/solve/faqs/how-to-identify-chickadees.php  (but the illustrations are perhaps less than optimal)

Note that the two authors have some differences of opinion!

This is another older reference by Sibley with two good black-and-white drawings: https://www.sibleyguides.com/wp-content/uploads/Chickadees_NJ1.pdf

The interrelationships of the two species are a subject of ongoing research.  Here’s a reference regarding the apparent northward movement of the hybrid zone, likely a consequence of climate change: https://doi.org/10.1016/j.cub.2014.01.069

Frank Witebsky
Jo Solem, editor