Midsummer dawn brings birdsong

Every experienced birder knows that bird song and activity begins well before dawn. At the peak of the nesting season in May and June, robins and cardinals may begin singing before four a.m.
As the nesting season winds down in July, however, the dawn chorus dims. I've noticed recently that by eight a.m. only a few cardinals, house wrens, and Carolina wrens are still singing. I wondered if the morning chorus had simply ended. So on July 24 - 26, I got up at 4 a.m. and sat on the back porch to monitor the mid-summer dawn chorus.
Fortunately, on each of these three mornings, the sky was clear. Light intensity triggers bird song, so on overcast mornings, the first song of the day occurs as much as an hour later than when the sky is clear.
The sun rose officially at 6:15, plus or minus a minute, on these three days. Here are the earliest times I heard each species during the three-day test:
Cardinals (5:23), robins (5:25), wood thrushes (5:28), mourning doves (5:28), and scarlet tanagers (5:29) were the early risers. The first songs were by individual birds, and it was easy to pick out each one. Within just a few minutes, however, many birds joined in. By 5:34, the woods behind the house echoed with the voices of at least a dozen cardinals, wood thrushes, and scarlet tanagers. The singers included some recently fledged young males. Their songs were recognizable, but less than perfect. All these songs overlapped, and it became impossible to count the numbers of birds singing.
This cacophony is actually an effective anti-predator strategy. When just a single bird sings, a hungry screech-owl might easily locate the singer. But when many birds sing over top of each other, a predator relying on sound is easily confused. The singing birds aren't confused because they filter out the songs of other birds and hear only their own.
Continuing songs
At 5:36, my neighbor's rooster crowed. Within four minutes, I added Acadian flycatcher (5:38), common yellowthroat (5:38), downy woodpecker (5:40), and red-eyed vireo (5:40) to the list.
Thus far, every song had come from the woods beyond the yard. At 5:41, the first yard bird, a Carolina wren, chimed in. The first eastern towhee and eastern wood pewee sang at 5:42.
By then the eastern sky was brightening, but sunrise was still 27 minutes away. And already the chorus had begun to fade. In May it would still be building, but by late July the urgency of finding a mate and defending a territory has eased. But there were still plenty of late-risers that hadn't checked in yet.
At 5:45 a great-crested flycatcher called from the edge of the woods, and the first cardinal (5:47) and a white-eyed vireo (5:48) sang from the yard. I suspect singing from a relatively open backyard is risky in dim light. Owls enjoy a distinct visual advantage at low light levels, so yard birds stay hidden in dense vegetation until the morning brightens. At least they do if they want to see the sun rise.
At 5:50 I heard the first ruby-throated hummingbird buzzing at the nectar feeders; by 5:56 at least eight hummers had begun their daylong routine of perch, drink, attack, flee.
It seemed late when I heard the first song sparrow (5:52) and house wren (5:54) because I think of them as early risers. That may be because they sing close to the bedroom window, so I hear them before the more distant birds in the woods.
At 6:04 a flock of crows chimed in, and an indigo bunting sang from the top of a dead apple tree. Finally, at 6:07, I heard the agitated alarm calls of several tufted titmice and Carolina chickadees. Perhaps they had seen a screech-owl go to roost because they were obviously upset about something.
A few cardinals, doves, and wrens would sing throughout the day, but at eight minutes before sunrise the mid-summer bird chorus was over.
That's why birders are early risers.
Send questions and comments to Dr. Scott Shalaway, R.D. 5, Cameron, W.Va. 26033 or via e-mail to sshalaway@aol.com.