Sunday, October 12, 2008
Frogs of Metchosin
February 12, 2006
Metchosin is home to a variety of amphibians and reptiles and in this issue of the Muse, we take a look at members of the frog family, called anurans. Toads are considered to be members of the frog family but differ from frogs in having stubby bodies with short hind legs (walk instead of hop), warty, dry skin and poison glands behind their eyes. A tidbit of useless information: a congregation of these creatures is referred to as an army of frogs or a knot of toads.
One of the true signs that the grip of winter has weakened (never that strong here in the first place!) is the loud and boisterous chorus of the Pacific treefrog, as males sing together to announce their presence and availability to females. Sound familiar? The movie industry has used their resonating songs in many night scenes and to depict tropical locations.
Late winter is breeding season for these diminutive amphibians that come cloaked in a variety of colours from pale gray to bronze to a bright, almost florescent green. They are distinguished by a dark stripe that extends from nose tip to shoulders and a wandering habit that takes them from ponds to forest, meadows and your own backyard. They have evolved a waxy substance on their skin that helps prevent dehydration during their travels and they can even change their colours from light to dark.
Treefrogs prefer shallow, sometimes seasonal ponds in which they fasten their small clusters of eggs to sedges and other grass-like plants. The embryos hatch in approximately 2 weeks and the tadpoles transform into frogs in about 2 months. This hurried schedule and an aquatic nursery that often dries up during the summer mean there is less chance they will encounter fish and other aquatic predators that need a constant water supply to survive. The newly emerged froglets are the size of your pinkie nail, though the adult females (frog females are larger than the males) can reach 5 cm or 2 inches when fully grown.
The red-legged frog is slightly larger than the Pacific treefrog, reaching 10 cm (4 in). This amphibian is designated blue-listed or species of concern by the provincial government and is usually found in the vicinity of water, alongside ponds and within riparian areas. They have a light golden to dark brown back and the insides of their hind legs are a translucent red. The males call to the females from underwater during late January to February in shallow, slow-moving streams, ponds or marshes. They need 5 weeks to hatch and 3-4 months to change from tadpole to frog, so they require a more guaranteed aquatic habitat than their treefrog cousins. They also use the cool, damp refuge of rotted logs and other debris during their adult life. If you have ever tried catching them, you will know that their long, low hops keep them just out of reach!
The western toad can be found in the Victoria watershed, so they are probably in Metchosin as well. The breed in ponds and along shallow lake edges and lay long stings of eggs that can contain 12,000 eggs! Many hundreds to thousands of tiny, ½ inch toadlets stage a mass exodus from their nurseries and might congregate in a huge “knot” of toads to keep warm. After leaving their ponds, toads spend up to 90% of their time on the land where they favour dense shrub cover, perhaps because it provides protection from desiccation and predators. They are nocturnal, preferring nighttime ramblings and burrow into soil or hide out in abandoned burrows during the day. The World Conservation Union (IUCN) considers the western toad “endangered,” the only IUCN red-listed amphibian in Canada. This is mainly due to their dramatic population deterioration in the US. In BC they are considered a species of “conservation concern” and there are signs that populations around the Victoria area are declining.
All frog species feed on algae as tadpoles and small insects and slugs as adults. They are prey to many creatures including predatory fish, bullfrogs, dragonfly larvae, raccoons, birds and many small mammals.
The most serious threats to frogs are habitat loss from the development of wetlands, pollution and predation by the introduced bullfrog.
Bullfrogs were first brought here as a food item to be farmed and harvested, and when that business failed, some were released into local waters. They are very large (6 in or 15 cm), dark olive to pale green with voracious appetites that consume anything that will fit in their mouths, including snakes, birds, fish and other amphibians. Ducklings have disappeared beneath the surface of ponds infested with these invasive pests. Bullfrogs require year round persistence of water as the singularly large tadpoles overwinter for one to three years. Adults prefer remaining close to water.
Another introduced alien is the green frog, native to Eastern North America, probably brought in as pets and as fish bait. It does not appear to have caused the havoc to native species that the bullfrog has effected although they compete for the same food.
Small ponds that dry up in the summer are important habitat for many of our amphibians but are not hospitable to bullfrogs or green frogs.
Many people have childhood memories of aquariums, often cloudy and murky, where they watched tadpoles slowly produce buds that grew into arms and legs, and observed, fascinated, as tails disappeared and tadpoles or polliwogs transformed into small frogs. What happened next? The frogs were usually taken outside and released into the nearest pond or stream.
Now, however, when bullfrogs (and green frogs) are inadvertently collected and released into different areas, they can quickly expand their range. To protect our native frogs and many other species, please refrain from collecting amphibians in any stage and NEVER release them, especially into a different pond or stream.
Frogs and many other amphibians, are wonderful “pesticides” in your garden. They eat slugs, snails, mosquito larvae and many other garden pests, however, they have permeable skin which supplies them with oxygen and water but which leaves them extremely vulnerable to pollutants in the air and water. Chemical pesticides on lawns and in gardens are very harmful, especially in mixed combinations.
Frog populations have been declining throughout the world and probably from a variety of interrelated causes, including habitat loss, pollution, ozone layer depletion (increased UV), and disease. BC Frogwatch would like to know about any amphibians you hear calling during the year, but are especially interested in the time of year you hear the first calls. This will signal when the breeding season begins. They will share that information with the Ecological Monitoring and Assessment Network (EMAN), who will compare the times of first calling across Canada and over time. This will help them learn more about climate changes.
Sometimes found in flowerpots on the balcony, in long grass beside the house or maybe just glimpsed in a walk along a stream, Metchosin frogs need your help.
B. C. Frogwatch http://www.env.gov.bc.ca/wld/frogwatch/
Information gleaned from Amphibians of Oregon, Washington and British Columbia by Corkran and Thoms