TORONTO STAR (Ontario) 19 August 06 Missing all that familiar croaking (Darryl Stewart)
If you think you haven't encountered as many frogs in recent spring and summer months than in past years, you are not mistaken. Since the early 1980s, frogs have generally become less plentiful than they once were in Ontario and in other parts of Canada.
This situation has become especially noticeable in the heavily populated urban areas around the Great Lakes, where human encroachment of natural wetlands, intensified agriculture and pesticide poisoning have taken a heavy toll on native frogs. In Ontario alone, more than 75 per cent of the pre-settlement wetlands have been modified or destroyed.
As yet, no Canadian species are known to have become extinct, although Blanchard's cricket frog, whose Canadian range is restricted solely to the extreme tip of southwestern Ontario, is now believed to be extirpated in this country (although still to be found in parts of the contiguous United States).
Dwindling frog populations have been reported in Ontario, and elsewhere in North America, for such familiar species as the leopard frog, the bullfrog and the chorus frog. Leopard frogs, although still abundant in some areas, have totally disappeared from other former localities. In addition to habitat loss and pollution, bullfrogs are also at risk through being captured and sold to restaurants where frogs legs are regarded as a culinary delicacy.
Chorus frogs, in particular, have disappeared from many areas where they were one of the most familiar of early spring calling species. While still generally common in parts of western and southwestern Ontario, in recent decades these frogs have declined from around Toronto, Eastern Ontario, the Lake Huron drainage area and in New York state. Substantial chorus frog declines have also been reported for Quebec, while they have become extirpated or very nearly so in Vermont.
Scientists have been alarmed and mystified by the many unexplained disappearances of frogs and other amphibians (toads, newts, salamanders and caecilians) occurring throughout the world. The reasons for declines in most local frog populations is generally not difficult to explain - human encroachment and other anthropogenic activities are invariably to blame.
Far more perplexing, however, is that of declining species and thriving ones occupying the same habitat. For example, in the Rocky Mountains of Alberta, the leopard frog has declined while the wood frog has remained unaffected. Does this somehow point to a physiological or ecological difference in the two species? Many frogs, and amphibians in general, have also inexplicably disappeared from some of the most protected areas on the North American continent, including national parks like Yosemite, Sequoia and Kings Canyon in California.
It has been documented that in the last decade, more than 200 species of amphibians throughout the world are in decline, and about 20 species of these are presumed to have become extinct. Most alarmingly, the species in question inhabit areas that are protected from direct human interference. When the loss of species occurs in areas removed from human exploitation, then more far-reaching causes such as acid rain, global warming, ultraviolet radiation, droughts, fungal diseases and viruses may be to blame.
Some of the more glaring examples are occurring in Australia and in the tropical rain forests of South and Central America. The golden toad of the Monteverde cloud forests of Costa Rica, that has only been known to science since the 1960s, is now extinct; this despite the fact that its habitat was protected within a vast nature reserve.
Similarly, the Monteverde harlequin frog disappeared from the area in the 1980s. At least 110 species of brightly coloured harlequin frogs once lived near streams in the tropics of Central and South America, but about two-thirds of these vanished in the 1980s and 1990s.
In Australia, numerous frog species are believed to have become extinct in the past 35 to 40 years and the continued survival of others remains uncertain. The common thread between these diminishing populations is their habitat: A significant portion inhabit northern Queensland's tropical rain forest. Upland rain forest frogs are more vulnerable to variations in climatic conditions, giving rise to scientific theories that an increase in ultraviolet radiation or a fungal disease may be at the root of the problem.
Some Australian frogs differ from their international cousins in that their young are brooded inside their bodies, eliminating the free-swimming tadpole stage. Probably the most bizarre of these is the gastric brooding frog. This shy, nocturnal species may be one of the most primitive of all frogs. Restricted to the Connondale Range in southeastern Queensland, the female gives birth by vomiting forth fully formed froglets.
Unhappily, the numbers of this frog have declined to a point where the species is now regarded as extinct.
The recent information gathered in studies on amphibian disappearances is quite compelling. According to Bob Johnson, curator of herpetology at the Toronto Zoo, "Loss of natural habitat is likely the principal cause of frog declines in Canada, although there are doubtless other factors involved, as indicated by the example of the leopard and wood frogs in Alberta. Globally, the most likely causes are due to the effects of global warming, increased ultraviolet radiation and environmental pollutants."
The increased pressure imposed on the amphibians as a result of these environmental changes has resulted in lowered immune functions in these animals, making them especially susceptible to infectious diseases such as chytrid fungus and ranavirus.
If you wish to find out what part you can play in conserving these charming little animals you can check out the Toronto Zoo website at www.torontozoo.com/adoptapond.
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