Carolina Chickadees

For years I thought I could tell the difference between black-capped and Carolina chickadees by their songs and calls. After all, I had heard them one winter on the mall in Washington, D.C. and they certainly sounded different from the black-cappeds I was used to. So last winter, when I heard a calling chickadee that sounded different, I wondered if it could be a Carolina chickadee.

black-capped chickadee

Photo of a black-capped chickadee taken near our house by Dave Bonta, February 15, 2006

I located the bird perched in a cedar tree outside my window. While I studied the bird, I looked at my four field guides and learned that black-capped chickadees are larger than Carolina chickadees by a quarter to half an inch with longer tails and bigger heads. In addition, black-cappeds have more white on their wing edges and their white cheek patches are entirely white while those of Carolinas blend to pale gray at the rear.

But most of my guides agreed that their songs and calls should be my guide. Carolinas’ “chick-a-dee” calls are higher pitched and more rapid than black-cappeds and their whistled “fee-bee, fee-bay” is distinct from the single “fee-bee-ee” or “fee-bee” of black-cappeds.

As I examined my singer, I noticed its white wing edges and decided it was only a black-capped. Studying the most recent Carolina chickadee range maps in the Second Atlas of Breeding Birds in Pennsylvania, it was clear that none had been reported in Blair County where I live even though if I drew a straight line from east to west across the commonwealth, our home would be at the northern edge of Carolina chickadee territory.

A Carolina chickadee in Codorus State Park

A Carolina chickadee in Codorus State Park, southwestern York County, February 9, 2013 (Image by Henry T. McLin on Flickr, Creative Commons license)

But that’s not how it works in Pennsylvania. Since 1975, Carolinas have been expanding northward at about seven-tenths of a mile per year in southeastern and south western Pennsylvania, and they now live as far north as Lehigh and Schuylkill counties in the east and Beaver County in the west. However, they are mostly absent at higher elevations in the Allegheny Mountains and southern Appalachian physiographic sections of Pennsylvania according to Robert L. Curry’s account in the atlas.

Curry, who teaches biology at Villanova University, has been conducting field studies of the population ecology and behavior in hybridizing Carolina and black-capped chickadees in southeastern Pennsylvania since 1997. That’s when his students built 450 fake nests of short lengths of sewer pipe and made them look like trees with a cavity and top entrances in an attempt to attract cavity-nesting chickadees.

They erected their fake nests in Chester County to study Carolina chickadees, Nolde Forest near Reading in southern Berks County to study both Carolina chickadees and hybrid Carolina/black-cappeds, and Hawk Mountain Sanctuary on the easternmost ridge in the Valley and Ridge province of Pennsylvania to study black-capped chickadees. (Our ridge is the westernmost in the province, incidentally.)

Even though Carolina and black-capped chickadees have been distinct species for between one and 2.5 million years, from Kansas to New Jersey these two species meet, mate and give birth to hybrid species. But Curry and students have learned that male Carolinas, which are more aggressive than male black-cappeds, mate with female black-cappeds, but female Carolinas rarely mate with male black-cappeds. Furthermore, these hybrid birds lay a large number of infertile eggs, in contrast to a 92% hatching success of an average of five eggs laid by Carolinas in 55 nests in southeastern Pennsylvania with similar fertility rates in black-capped chickadees.

Curry and other researchers don’t agree that anyone can identify Carolina and black-cappeds by their unique calls and songs in hybrid areas because hybrids can sing Carolina, black-capped and intermediate songs. Carolinas can also learn and sing black-capped songs and black-cappeds can learn Carolinas’ songs. So researchers use “diagnostic protein, nuclear DNA, and mitochondrial DNA markers” to identify species according to the life history of Carolina chickadees in The Birds of North America.

Curry and students documented over the years a northward movement of Carolina chickadees, and by 2006 he added Tuscarora State Park in Schuylkill County to his study area for black-cappeds because almost half of Hawk Mountain’s chickadees were then hybrids while Nolde Forest had only Carolinas. Curry hypothesized that Carolinas are moving northward as a result of warming winter temperatures. Hybrids, he says, live in places with an average low winter temperature of between 15 and 19 degrees Fahrenheit, while black-cappeds prefer colder winter temperatures and Carolinas are primarily southern birds and one of only four birds John James Audubon discovered and named while in coastal South Carolina.

Today they range from south-central Kansas to the Atlantic coast and south from north and southeast Texas to the Gulf Coast and central Florida. Black-cappeds persist south along the highest mountains, but even on Mount Mitchell, the highest mountain in North Carolina, Carolinas replaced black-cappeds after logging and repeated burning, but after reforestation black-cappeds did not return.

Carolina chickadee upside down

Carolina chickadee upside down on a tree snag in Georgia, July 2, 2011 (Image by Evangello Ganzalez on Flickr, Creative Commons license)

Like black-cappeds, Carolinas are acrobatic, hanging upside down from branch tips as they search for insects that make up 80 to 90% of their spring, summer, and fall diets and half their winter diet. The other half is seeds and fruit, including bird feeder seeds, which they often cache for later use, especially in the winter.

They prefer to breed at the edges of deciduous forests with a healthy shrub, midstory, and overstory canopy, but they don’t mind a high human population in the area or fragmented forests as long as there are dead trees or nest boxes for nesting. In Pennsylvania, they breed in late April, which is a week sooner than black-cappeds.

Earlier, during flock formation in late summer or in winter flocks or even as late as early spring, they pair up, forming a bond that can last as long as three years. Males feed the females during courtship and guard them during egg-laying. The feisty Carolina males chase other males away from their mates and their breeding territory and may engage in feet-kicking, bill-jabbing and wing-fluttering in the air or on the ground.

By mid-March, the pairs are excavating and building nests in cavities, natural snags, fence posts or nest boxes. While both parents take turns excavating, the females construct nests with a base of moss and a thick lining of hair or plant fiber, especially the fur of eastern cottontails, white-tailed deer, eastern fox squirrels, opossums, raccoons, or even domestic cows or cats. This fur she fashions into a flap and the nest, with the flap down, probably is an attempt to keep house wrens from destroying the eggs. Other cavity nesters, such as eastern bluebirds, tufted titmice, and house sparrows are also known to take over Carolina chickadees’ nests even those with eggs or nestlings.

Carolina females lay three to 10 white eggs spotted with reddish brown. They also incubate the eggs for 12 to 15 days while the males feed them. In one case in southeastern Pennsylvania, a brooding female was killed on her nest, and Curry suspected a southern flying squirrel was the culprit. Other mammalian predators on eggs, nestlings, and young fledglings are raccoons, opossums, domestic cats, and rat snakes. Avian predators, even on adults, are sharp-shinned and Cooper’s hawks.

Carolina chickadee feeding its young

Carolina chickadee feeding its young in the hole of a North Carolina tree, April 13, 2008 (Image by cotinis on Flickr, Creative Commons license)

Once the eggs hatch, females continue to brood their nestlings until they are eight days old. Both parents feed them for 16 to 19 days, and then they fledge, usually in the morning. The parents continue to feed them for two to three weeks, and after that they are on their own.

Parents that remain paired hold the same territory in successive years, and they remain there where they are joined by young Carolinas to form a winter flock. In these flocks and generally males dominate females and larger males dominate smaller males. Although such dominance doesn’t guarantee winter survival, it does guarantee a breeding territory. Not all Carolinas stay in a flock. Instead, they are flock-switchers or winter floaters, either joining another flock or continuing to move from flock to flock.

To survive the winter, they spend their time along stream valleys in sheltered forest interiors when it is cold and the wind is blowing. They also decrease their movements and the distance they fly between foraging sites. They can enter a state of regulated night hypothermia by dropping their body temperatures to 84 degrees Fahrenheit and pairs will roost together in tree cavities, staying there as long as 15 hours during a 24 hour period to conserve heat. They sunbathe early in the morning by perching on branches sheltered from the wind and facing into the sun with their body feathers fluffed and their wings spread. To obtain water, they drink from bird baths and natural sources and eat snow.

From the first (1984-89) to the second atlas period (2004-09), Curry estimates a 90% increase in Carolinas’ population in Pennsylvania. During the second atlasing period researchers estimated there were 105,000 singing Carolina males. However, Curry concludes that atlas results do not support upslope movement into ridgetops in Franklin and Fulton counties, so it looks like I won’t see Carolinas or hybrids here anytime soon.

Cavity-Nesting Birds

tufted titmouse at nest hole by The Natural Capital on Flicker

tufted titmouse at nest hole by The Natural Capital on Flicker (Creative Commons licence)

I’ve never thought of myself as a female Dr. Doolittle, but last June a bird “talked” to me and I understood her.

My tale began last April when our son, Dave, decided not to remove a dead oriental cherry tree trunk in his front yard. It was an eyesore, but, on the other hand, he thought it might attract cavity-nesting birds.

And so it did. Almost immediately a pair of black-capped chickadees started excavating a hole facing the woods and then deserted it and began another hole facing the guesthouse porch five feet away. Unlike most chickadees, which are secretive during the nesting period, they were exhibitionists. As Dave and I sat on the porch, they continued to dig out their nest, carrying beaks full of wood chips and dropping them nearby. Not only were they unafraid of us, but they also weren’t fazed on April 20 when several members of our Juniata Valley Audubon Society stood on the porch watching them.

Dave spent far more time on his front porch than I did and kept me informed about the chickadees’ work. Once they hollowed out an area deep in the trunk, the female started gathering material for her nest. Chickadees are supposed to use natural materials such as moss, pine needles, and possibly bark to provide a firm foundation to their nests and then they line them with finer material such as rabbit fur.

But at 2:00 p.m. on April 23, as I sat on our veranda reading several hundred feet away from and out of sight of Dave’s porch, a chickadee, presumable the female, flew in and landed on my book. By doing this, she grabbed my attention, and I watched her fly over to a piece of unraveling beige twine attached to the handle of a covered plastic bucket. She clung to the twine and pulled out strands of this material until she had crammed her beak full, and off she flew. She returned several minutes later and yanked off more, but this time her beak was only half full. She didn’t come back so I assumed she had enough lining for her nest.

 

One of the chickadee parents at the nest hole in the cherry snag

One of the chickadee parents at the nest hole in the cherry snag

The next time I saw her pulling out twine fibers was the afternoon of the Pennsylvania Migratory Bird Count on May 11. No doubt she had been back numerous times when I hadn’t seen her. According to chickadee researchers, nest-building by females can take as little as two days and as long as two weeks so this female was several days over the limit. Or maybe she was freshening her nest lining.

On the 21st, Dave and I sat and watched the chickadee male feeding the female sitting down in the nest. Neither paid any attention to us. But we were worried. Several days earlier Dave had discovered a six-and-a half-foot-long, shed black rat snake skin not far from the nest. And the previous spring he had observed a black rat snake climb up a tree at the edge of the woods and wipe out a northern flicker nest he had been watching form his porch. We hoped the chickadees would survive and raise their young, but their nest hole was much closer to the ground and the trunk much easier to climb than the mature live tree that had held the flickers.

a black rat snake in a flicker hole, just after eating the nestlings

a black rat snake in a flicker hole, just after eating the nestlings

Four days later, when I went down to check on the chickadees, one parent held a caterpillar in its beak and kept calling “dee-dee-dee” as it perched on a cherry stub above the hole, while a second chickadee flew down into the nest. Finally, it emerged and the calling bird zipped down and reappeared a few seconds later without the caterpillar. Then both parents flew off.

It looked as if they were feeding young. She must have begun incubating her eggs the day after I saw her gathering more twine because it takes 12 to 13 days for the eggs to hatch. But after the eggs hatch, according to ornithologists, the male is supposed to feed both the young and the female for several days since she is brooding the nestlings. Not only was this pair unusually bold, but they didn’t seem to be following the “rule book” either.

Day after day they continued feeding their young, most often caterpillars, which was the most common fare for chickadee nestlings, according to the work of one ornithologist in Massachusetts back in 1961. He constricted the throats of nestlings when they were fed and altogether counted 35 caterpillars, 11 spiders, 10 unidentified larvae, six termites, one white Lepidoptera, one pupa, and one fly.

On June 2 I did some more chickadee watching as they fed both caterpillars and insects to their young. Twice a parent emerged with a fecal sac and flew away with it. Sometimes parents eat these sacs, but usually they drop them far from the nest so they don’t attract predators.

After a short wait, a parent arrived with a green caterpillar, paused at the nest hole for several minutes, and finally ate the caterpillar. It flew into the nest entrance and stayed there for more than ten minutes, and I could see the nestlings below. Then the second parent arrived with another green caterpillar which it fed to a begging nestling.

Right on time, on June 8, 16 days after hatching, the chickadees fledged, but both Dave and I missed it. However, the black rat snake never found them, much to our relief, because we had gotten fond of the plucky birds. Perhaps, by building their nest close to the porch, they had gained some measure of protection from our constant surveillance.

In the meantime, the twine story developed another twist. On May 26, my husband Bruce and I sat on the veranda in the afternoon and watched a tufted titmouse fly in twice and pull out a beak full of twine strands, the second time mixing it with a little freshly cut grass. Titmice are also cavity nest builders and titmice females construct the nest, but I had no idea where her nest was. Still, I couldn’t believe how popular the twine was as nest-building material.

More than three weeks later, on June 19, as I sat on the veranda reading in early afternoon, a tufted titmouse flew in and landed on a round white table. Then she flew toward my face and over to the rim of a white chair across from me. Next she flew back to the table, then to me where she landed on my foot, which was propped on a stool, and looked up at me. This titmouse was trying even harder than the chickadee had to get my attention.

She returned to the table, hopped underneath it, and pecked a few times on the cement floor beneath her spread legs. It was then I realized that she was “asking” me to move the two large containers of potting soil I had recently placed in front of the covered bucket with the treasured twine.

“Alright,” I said to her. “I understand what you want.”

She flew off, and I moved the larger containers so the twine would be accessible. A couple minutes later, the titmouse returned and spent five minutes shredding the end of the twine and filling her beak. She looked over at me several times as if to say thank you. At least that’s how I interpreted it. Then she chirped to me as she flew away.

For the first time in my life, I felt as if I had had actual communication from a wild creature. To me it was a transcendent experience I will never forget.

A short film of the chickadees at work excavating the den hole.


Video and photos by Dave Bonta except where indicated.