Friday, May 24, 2013
By HERB WILSON
The overworn expression that there is no accounting for taste certainly applies to music. At this time of year, I thrill to the music of the birds whose concerts start well before the crack of dawn. As a reader of this column, I'm sure you share my joy of the morning chorus. On the other hand, non-birding friends and family may complain vigorously about the infernal early morning ruckus disturbing their sleep.
Locally, American robins are the first to welcome the new day with their caroled song around 4 a.m., nearly an hour before sunrise. Others join the choir and by dawn it is possible at a stationary point to hear 10 or more species singing. For the next hour, the male songbirds sing energetically and often. The frequency of singing starts to decline and by 10 a.m., the chorus is essentially over. That is why Breeding Bird Surveys and other ornithological counts relying heavily on identification by sound must be done in the early morning.
Why do birds sing with such vigor early in the morning? We don't really have a compelling explanation. Some ornithologists believe that the early morning is the best time for males to attract females that might have arrived on migration during the night. Or, perhaps singing allows a male to reassert possession of his territory to any males that might have arrived during the night. In the early dawn hours, light is too weak to permit birds to forage efficiently so singing may be a profitable use of the time. Often, weather conditions are calm in the early morning and songs can be broadcast then for maximal distance.
The singing behavior of some songbirds is quite different during the early-morning hours compared to the remainder of the day. The long, dry trill of a chipping sparrow is a familiar and easily recognized song that can be heard off and on throughout the day. A male typically sings the song from a perch at least 20 feet high.
But an early riser has the chance to witness singing behavior that has only recently been studied. For the first half hour after dawn, male chipping sparrows sing from the ground! Males in adjacent territories gather in a central arena and sing very short songs in machine-gun like fashion to each other. Presumably, males are establishing a dominance hierarchy by these social events.
The change in behavior is really quite striking. At 4:30 a.m., the chipping sparrows are singing from the ground at a rate of about 40 songs per minute. Then 45 minutes later, the males sing their longer, more familiar trills from perches in trees at a rate of three or four songs per minute.
Many warblers are known to sing two types of songs. Accented songs usually end emphatically like the "pleased-pleased-pleased-to-meetcha!" of the chestnut-sided warbler and seem to function primarily in mate attraction. Unaccented songs are used to proclaim territorial ownership to other males.
Chestnut-sided warblers in the dawn chorus sing almost entirely unaccented songs. Interestingly, every male has a distinctive song, so individual recognition is possible. Later in the day, the males switch to the more easily recognized accented song. These accented songs are nearly identical among the males in a given area.
Unaccented songs are typically given from the periphery of a bird's territory, while the accented songs are given in the middle of a territory.
The crescendo-like "tea-CHER, tea-CHER, tea_CHER tea_CHER tea_CHER" of the ovenbird is an easy song to recognize. However, during the early morning, ovenbird males fly above the canopy and sing a warbled flight song with a couple of "tea-CHER" phrases in the middle of the jumble of notes. At least 11 other warbler species sing early morning flight songs.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at: