The bullfrogs are back, at least for this summer, and I found a musical mnemonic for their song in one of Beethoven’s symphonies.

One morning each June for the past 15 years I have left the cottage around 4 a.m. to participate in the international Breeding Bird Survey. At that hour I used to always hear bullfrogs (Lithobates catesbeianus) singing along the far shore of the lake, but about 12 years ago the sound started to disappear. In the past five years we have seldom heard them at any time, anywhere on the lake.

Since the 1980s, amphibian populations around the world have been crashing. The trend is well documented but the cause poorly understood. It is thought to relate to a combination of disease, pollution, habitat loss, increasing ultraviolet radiation and other factors.

Some people have noted a decline in bullfrogs in Ontario, though it is not well-documented. Around our cottage the vanishing has been progressive, distinct – and puzzling, considering the lake is situated at the top of its watershed and shows no sign of damage from pollution or acid rain. Shoreline development has been minimal. The vast majority of the perimeter remains Crown Land, with numerous ideal shallow marshy habitats. One of the more mysterious causes seemed to blame, such as a deadly fungus.

The diversity of other amphibians around the area does not seem to be affected. Overturn an old log and you are bound to find several red-backed salamanders. The marsh behind our cottage provided a deafening chorus of spring peepers when we visited in May. Green frogs, bullfrog look-alikes with a much different call, still chortle from time to time, though they haven’t flourished as one might expect from the disappearance of a prime competitor. Tree frogs squeak in the forest throughout the summer. But for several years I hadn’t heard a single bullfrog.

Until early Saturday morning. Shortly after 4 a.m. I left the cottage equipped for the survey. I closed the cottage door and halted on the porch. A familiar, soft groan resonated across the water, where dawn brushed the first, calm hints of silver. I couldn’t spare more than a moment to listen. I had to drive to Dwight for the first stop in my survey by 4:54.

My solstice ritual was, as always, a delight. I had better than average results for the Breeding Bird Survey this year, about 58 species, including two new ones for the route: Cape May warbler and American coot. Other highlights included Eastern bluebird, olive-sided flycatcher and black duck. Birds between stops cannot be included in the data, but I saw three others that way: mallard, broad-winged hawk and wild turkey. The weather was mild and still, perfect conditions for identifying bird songs. It was an exciting and fulfilling exercise, but I was equally excited about what had happened before.

Later that evening, about 10:30 p.m., I went down on the dock to look at the stars. And there the bullfrogs were again: a soft boom in the stillness. They would fall silent for a few moments, then resume their chorus again.

Suddenly I was reminded of one of my favourite moments in music, toward the end of the last movement of Beethoven’s Symphony No. 7 when the orchestra fades into swirling chaos. There is a moment of soft, teeming darkness as a distinct, insistent throb emerges from the string basses.

“Boo-DUM! Boo-DUM! Boo-DUM!”

It is the song of the American bullfrog, a sound even nature-loving Beethoven could never have heard, except in his soul. It’s the heartbeat of the universe. The rest of the orchestra gathers itself, smiles and mounts to a radiant climax, the amphibious basses bellowing underneath. Millions of stars explode, shedding light from decades and centuries away.

Hopefully, the bullfrogs have returned to stay. Maybe they have adapted to whatever threat sent them away. Or maybe this year was an anomaly. In any case, I was grateful for their greeting. And I will never hear my favourite Beethoven symphony again without seeing the splendid night sky underlined by pounding, breeding, thriving life.

Photo courtesy of Craig Stanfill on Flickr via Creative Commons.