By Patrick McShea, Carnegie Museum Of Natural History

Puppies aren’t much appreciated for the consequences of poor body control. House training involves days of quick trips outside, often at inconvenient hours. When training occurs in the fall, excursions into pre-dawn darkness sometimes deliver unexpected rewards.

A dozen years ago, while obliging 5:00 a.m. got-to-go signals from a yellow lab puppy, I learned that our backyard rambles took place beneath legions of migrating songbirds. The discovery was far from an instant revelation.

“Tree frogs,” I decided when I first heard unfamiliar sounds, one and two-syllable intermittent tweets, some faint and others remarkably distinct.  Standing half-awake amid familiar territory transformed by darkness and fog, I didn’t much wonder then about why I had never before noticed the neighborhood amphibian hoard.

Those very doubts led to more focused listening the next morning, an adjustment that revealed the source of the mysterious sounds to be both overhead and in rapid motion.

The Invisible flyers revealed their presence, numbers, and roughly north-to-south passage across the suburban Pittsburgh landscape through a cadence audible above the background buzz of crickets, but periodically drowned out by nearby road noise and the harmonica-like wail of a distant freight train. 

The puppy, more interested in ground level scent than sound above the tree tops, investigated recent rabbit wanderings while I listened to the chorus. This practice has since become our September ritual, a fall activity different from its initial sessions by my growing understanding of the flight calls and the requirement that I now wake the dog.

Researchers who study the calls explain them as the way birds in low visibility conditions maintain contact during long flights.  The abbreviated vocalizations are therefore related to covering territory, rather than claiming it.

On many mornings my ears are able to discern enough differences among the calls to know they represent several different bird species. Occasionally a tone or cluster of calls will make me guess “oriole,” or “grosbeak,” but otherwise the birds pass over my Plum Borough home in trickles and torrents, unseen and anonymous.

Some 40 miles southeast, on the western flank of Laurel Ridge, night flying birds receive a far more thorough notice when they cross Powdermill Nature Reserve. 

Since 2003 this field research station of Carnegie Museum of Natural History has been part of a network of monitoring stations that utilize microphones, recording equipment, and a sophisticated computer program to determine the both the numbers and species of birds passing unseen in the darkness.

This ongoing scientific work contributes much to our understanding of the workings and health of the world we live in. Because the birds’ seasonal journeys encompass thousands of miles, their calls create an audio pulse for the ecological health of both American continents.

In the Pittsburgh area, and in neighborhoods all across Pennsylvania, it’s a pre-dawn signal that can be listened for every September, with or without canine company.

Patrick McShea is an educator at Carnegie Museum of Natural History and can be contacted by sending email to: mcsheap@carnegiemnh.org.

More background information on bioacoustical research is available online from the Powdermill Avian Research Center as well as research articles and publications.

9/8/2014