Friday, March 14, 2008

Red-legged Frog? Things not so good.

By now, here in the Fraser Delta, Red-legged Frog breeding should be well underway, if not completed. These frogs breed early, even beneath the ice of ponds where it is cold enough. Sadly, though, you would be hard-pressed to find a frog, or tadpole, or egg mass these days, because most populations have disappeared, along with the gradual disappearance of wetlands and other important habitat.

In the past century, the Fraser Delta has lost 95 percent of its wetlands, causing the obliteration of most amphibian populations and fragmention of those that remain. The Oregon Spotted Frog, Rana pretiosa, a highly aquatic species that requires expanses of shallow marshy water, has in British Columbia been reduced to three known populations, and is the most endangered frog in Canada.

The other medium-sized frog once common here, the Red-legged Frog, Rana aurora, is more terrestrial. It can be found along the edges of mountain streams, or near vernal woodland pools, and if encountered will leap away through dense underbrush, leaving, it hopes, predators and herpetologists tangled up in the shrubbery. Moot plan when hillside and bottomland habitats melt away with the clearing of forests.

Hence the name.

Red-legged Frog, Rana aurora, indignant.

Red-legged Frog habitat, near Chilliwack, BC.

Both the Oregon Spotted Frog and Red-legged Frog are known in British Columbia as “peripheral species,” an artifact of a line on a map, itself an artifact of history. Their historic ranges lie between the coastal mountains and 49th parallel (the Canada-US border). Because of its mild climate, rich soil, and location, this relatively tiny scrap of Canadian territory is dearly sought for human interests -- urban, agricultural, industrial, and so on.

Red-legged Frogs live here, in scraps of forest within Fraser valley farmland. The Canada-US border runs along the hills on the south side (the narrow line cut through the trees extending up from the right side).

Conversely, perhaps perversely, two non-native frogs are doing quite well throughout the former ranges of the two native Rana species. The Green Frog, Rana clamitans is an eastern species similar in size to the Oregon Spotted Frog and Red-legged Frog, and seems to thrive in any permanent pond or ditch. Its deadened banjo-string "twang" can be heard on warm spring and summer days. The Bullfrog, Rana catesbeiana , also an easterner, has made itself at home throughout western North America and elsewhere, descendants of releases from ill-conceived farms (frogs’ legs), and other human insanity. Both species, particularly the much larger Bullfrog, may be involved in the elimination of populations of native species, through competition or predation. Introduced fish may also prey on tadpoles in permanent bodies of water. These zoological factors combine with the overriding issue of habitat loss in a way that is not fully understood. It is understood, though, that things aren't looking rosy for the Red-legged Frog.

Not so fast. Bullfrog detained.

Bullfrog at large, waiting to inhale (whatever passes by). Richmond, BC.


Adams, M.J. 1999. Correlated Factors in Amphibian Decline: Exotic Species and Habitat Change in Western Washington. Journal of Wildlife Management, Vol. 63: 1162-1171.


Anonymous said...

I have some sort of frog in my yard???I havent seen it,only hear it.There is no pond nearby and it seems to live in the plants which grow up the side of the house???!!!I live in Abbotsford,any ideas what kind of frog it could be? dee,

Hugh said...

I expect it's a Pacific Chorus Frog, formerly known as the Pacific Treefrog. They are often found away from water.