April 1, 2008; March 18, 2009; March 22, 2010; April 3, 2011; and March 14, 2012.
You probably recognize these as the five most significant dates of the last five years. Well, OK, the most important days in the life of a wood frog. OK, OK, the most important five days in the life of a wood frog in the vernal pond near my house.
The first time I heard the wood frog (Rana sylvatica), I thought, “Oh no, someone is strangling ducks in the pond!” Alas, it was not ducks, it was the unusual call of the male wood frog announcing to the female wood frogs the start of their explosive breeding season.
For me, the call of the wood frog represents the true sign that spring has arrived. Like the spring peeper (Pseudacris crucifer) and the grey tree frog (Hyla versicolor), the wood frog is freeze tolerant, releasing glucose (sugars) to protect vital organs during Winter. When the temperature rises above freezing, the wood frogs defrost and head off to breed. The wood frog and the spring peeper are the first frogs that I hear each spring, usually within a few days of each other, but the peepers’ peeping does not peak for a few weeks, while the wood frog chorus is practically immediate.
The wood frog has many amazing characteristics, but the most amazing one that I have observed is their patience. Wood frogs are explosive breeders. This means that the breeding takes place over a very short time, from a few days to a few weeks depending on weather conditions. The females lay their eggs at the same time in the same location. This large mass of eggs contains a few hundred to a few thousand eggs. Presumably, the wood frogs do not want anyone or anything to know where their egg mass is for obvious protection. No matter how silently I approach the pool, under the cover of darkness, when I get about 50 yards from the water, the frogs all go silent. Quietly, I slip into the edge of the water, make my way to a clump of sedge and lean against a tree. There I stand, unmoving and silent. Fifteen minutes. Thirty minutes. Forty-five minutes. No matter how still I remain, the wood frogs do not make another sound. They will outwait me. Usually, I am forced to give up and leave the water without seeing a single frog.
The eggs in the mass act like tiny magnifying glasses refracting the sun’s light and heating the area around the eggs several degrees warmer than the pond water. This increases water circulation, bringing more oxygen and nutrients to the eggs. A symbiotic alga also grows on the eggs, producing oxygen in exchange for carbon dioxide and other waste the embryos want to get rid of. This alga in turn becomes food for newly hatched tadpoles. Eggs hatch in 2-4 weeks and tadpoles metamorphosize into frogs in 2-3 months
The wood frog is recognized by its brown color and distinctive raccoon-like dark mask around the eyes. Adult females are larger than males and can turn a pinkish beige during mating season, while the males turn darker brown. Adult diet includes flies, gnats, beetles, caterpillars, spiders, snails and slugs. Snakes, raccoons and waterfowl predate on wood frogs. Adult habitat is generally deciduous forests with moist shaded forest floor.
The author is a licensed NY State Hiking and Camping Guide and owner of Critter Patrol LLC, an outdoor adventure, education and environmental business. To find out more about Critter Patrol programs and our current Adopt a Forest junior forest stewardship program for students, in conjunction with the Mohawk Hudson Land Conservancy, email Paul at [email protected].