BIRDWATCH: Brown thrasher, master mimic
Early last spring, I found myself wandering around the Penn State Arboretum, along the Bellefonte Central Rail Trail. Bird song filled the air. But just what birds were they that were singing? I couldn’t seem to recall.
Each spring I have to go through a short refresher period to brush up on my ability to identify birds by their songs. I usually start in late winter by playing some bird song CDs in my car. Then I spend a little time outdoors listening to the birds and trying to match them to their songs. Thankfully, the recognition comes back quickly.
At one point on my walk through the arboretum, I came upon what seemed to be a nice mixed flock of singing birds only a short distance away. As each song was belted out, I did my best to determine who the cantor was.
The first song I recognized was the tea-kettle, tee-kettle of the Carolina Wren. Next was the drink-your-tea of the Eastern Towhee, which was followed quickly in succession with the fee-bee-o of the Black-capped Chickadee. Then I heard what sounded like a car alarm followed by two gunshots. Then a red squirrel. What the…?
As I closed in on the flock, I soon realized that there was no flock at all. I had been duped by an imposter – the infamous copycat known at the brown thrasher. The thrasher was prominently perched in a hedgerow at the top of a small incline and continuously singing one song after another. I settled down at the base of a tree while the thrasher entertained me.
During the 30 minute span that I listened, the thrashed delivered over 500 songs. With few exceptions, each song was repeated twice before moving on to the next.
The brown thrasher is a member of the Mimidae – a family of birds well known for their ability to mimic the songs of other birds. The brown thrasher is a handsome bird. It is roughly about the size of a blue jay. The upper parts are a bright chestnut brown, while the underparts are a buffy white. The breast and flanks are marked with thin dark streaks.
Overall, the thrasher appears superficially similar to the more familiar wood thrush; however, it can be distinguished from the thrush by its lengthy tail, a long and slightly decurved bill, and brilliant yellow irises.
Perhaps the most distinguishing feature of the brown thrasher is its song – or more appropriately, its large repertoire of songs. Like its close relatives the catbird and the mockingbird, the thrasher is an accomplished song mimic. Popular misconception holds that the mockingbird is the champion of avian impersonation. In reality, there is no contest. The thrasher is far superior to its more diminutive cousin in the vocal arena. While the mockingbird has an impressive repertoire of 200 or so distinct songs, the thrasher has up to 3000!
As the thrasher’s reputation as a mime suggest, many of these songs are replicas of verses sung by other birds; however, the majority appear to be song improvisations, imitations of other environmental sounds (other animals, sirens, gunshots, etc), or musical phrases that are simply made-up on the fly.
This raises some obvious questions. If most birds get by with catalogs composed of a small handful of songs, why do thrashers need so many? And why do they mimic?
Unfortunately, the answers to these questions are not so obvious. Ornithologists have speculated that having large inventory of songs, be they mimicked or otherwise, is an indicator of reproductive fitness, thereby making the crooner a good choice as a mate.
Others have suggested that it serves to put males of both the same and the mimicked species on alert that a territory and its associated resources have been claimed.
Research continues in this area.
The thrasher’s habitat preference overlaps with that of Mockingbirds and Catbirds, so if you hear a bird singing the counterfeited songs of other birds, you may want to listen carefully.
With a little practice, one can readily distinguish thrashers from their kinfolk by their vocalization patterns.
The catbird song typically consists of a single phrase pilfered from another bird, followed by a meandering babble of whistles and cat-like mews. The thrasher delivers his phrases in pairs, each of which is punctuated with an attendant pause.
Mockingbirds repeat their phrases three to six times, pause briefly, and then move on to the next series.
As March advances into April, thrashers begin returning from their winter quarters.
The best local places to find them are Millbrook Marsh, Toftrees Pond, the Penn State Arboretum or any other areas with dense, tangled thickets.
The best time to go is in the morning when the birds are singing, although chances are that they will be singing late in the afternoon as well. ■
By JOE VERICA
Photo by DAN PANCAMO // Creative Commons
A brown thrasher (Toxostoma rufum). The thrasher is an accomplished mimic, and can learn hundreds of songs, improvisations, and environmental sound mimicry. Researchers continue to search for reasons.
Photo by HENRY T. MCLIN // Creative Commons
A brown thrasher (Toxostoma rufum) perches on a tree branch in Cordorus State Park in Hanover, Pa.