Intense, high-pitched trills seemed to follow me home that afternoon. The hum of my bike tires on pavement and the wind in my helmet didn’t drown them out. When I pedaled past upland areas, enjoying the warm sunshine, a brief silence would settle in. But as soon as I dipped down past a wetland again, the sound rose up from among the blooming leatherleaf, sprouting cattails, and budding water calla.
The toads were singing!
Every spring, warming temperatures and longer days trigger those warty brown critters to try their hand at romance. As with warblers, hummingbirds, and many other species, males arrive on the mating grounds well ahead of females to establish their territories. Then the “boys” commence calling. With throats inflated like balloons, they trill for 4 to 20 seconds at a time.
As with most frogs and toads, females choose a mate based on the length and strength of the male’s trill, as well as the quality of his territory. Therefore, it is worthwhile to a male frog or toad to expend a lot of energy in calling. While studying gray tree frogs (another loud calling amphibian), scientists discovered that they spend most of the night shouting aerobically at about 60% of their maximum output. But when a female is near, they bump it up to near 100% for a short time.
In order to accomplish these athletic feats of song, male frogs and toads have highly developed body-trunk muscles. Packed with mitochondria, the powerhouses of the cells, the singing muscles have the capacity for high aerobic metabolism. Frogs and toads call for such a long time that their muscles must switch from burning carbs to burning fats, just like human endurance athletes.
Those muscles are used to drive air over the vocal chords, producing the surprisingly loud calls. Some frogs and toads can be as loud as a lawn mower. Luckily, they have an internal pressure system that keeps their own ear drums from vibrating excessively and therefore prevents hearing loss in the shouter himself.
In contrast, the silent female frogs and toads have much less body–trunk muscle. Their specialization is laying eggs.
Although adult toads are mostly terrestrial, they lay their eggs in water. Their favorite breeding habitats include shallow wetlands, ponds, lakes, and slow-moving streams. Once a lady toad decides on a suitably musical mate and approaches him, the male will climb onto her back and grip around her abdomen with horny pads on this first and second toes. In this posture, called “amplexus,” the male can fertilize the strings of eggs externally as she releases them in two rows. A single female can lay 4,000 to 8,000 eggs, connected in a long, spiraling tube of jelly from 20 to 66 feet long.
About as big as a blunt pencil tip, each egg is black on top and white on the bottom. This type of camouflage, called “countershading,” makes the eggs hard to see from both above (looking down at dark water) and from below (looking up at bright sunshine.)
Just like the eggs, freshly metamorphosed toadlets and adult toads are well camouflaged in their habitats, using a technique called “background matching.” Toad skin can even change color from yellow to brown to black depending on temperature, humidity, and stress. If a predator finds a toad, the would-be killer gets a mouthful of nastiness. Glands in toads’ skin produce a poisonous fluid that is harmful if swallowed or rubbed in the eyes. Toad tadpoles have these same defensive chemicals.
A couple days after my noisy bike ride, I floated down an equally noisy river. In patches along the river banks, the toads’ trilling chorus joined with vociferous warblers, orioles, catbirds, and song sparrows, to create quite a cacophony of reproductive fever.
Even after I shut myself in a moving car, I couldn’t seem to escape the cacophony. Fiddle music played from a CD. The notes whirled and warbled with emotions every bit as powerful as the toads, and quite similar in purpose. I imagined a barn or dance hall full of people, twirling and smiling—and sizing up potential mates—all in step (or out of step as the case may be) to the lively music. In the end, maybe we are all a bit like the toads when we try our hand at the age-old, springtime music of romance.
For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! The current exhibit, “Nature’s Superheroes—Adventures with Adaptations,” opens in May 2014 and will remain open until March 2015.
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