PREFACE: Since I began this post in April, there have been some signs indicating the situation with local amphibians is not quite as bad as I originally portrayed – see the Addendum at the bottom. (But it’s still bad.)
It can happen here – is happening
A typical reader of this blog will know that, worldwide, amphibians—principally frogs and toads—are being ravaged by lethal fungal diseases and diminished habitat. Some species have already gone extinct, and many are sure to follow. The foremost villain in these fungal epidemics is world trade in animals. When one thinks of trade in exotics, one usually thinks of highly visible animals—colorful birds (or uniquely gifted birds such as the African Gray parrot), big cats, rare dog breeds, snakes, lizards, and such. But amphibians, despite small size, are valued by collectors for their calls and colors. And any one of them, usually from the tropics, may carry a disease that will lay waste to the toads and frogs in your neighborhood, should it escape. Even in an absence of local release, local populations are vulnerable to the plague creeping across all populations at a rate comparable to the spread of Dutch Elm Disease 50 years ago.
Something like that may have happened in or near our neighborhood in semi-rural Virginia. For whatever reason, this year our spring nights have gone silent in the absence of calls by amphibians—primarily the Gray Treefrog and the Cope’s Gray Treefrog, whose calls you may be familiar with. You can listen to their overlapping calls in the last 15 seconds of this sweet little clip:
Of course, on YouTube you can listen to a host of frog and toad calls as varied as their physical sizes and colors. Probably more varied—the diversity is astonishing!
On many a spring and summer night, the air is continuously astir with the trilling, burbling, chattering chorus of frogs and toads—especially intense, and thrilling, after a rain. At least, on many a spring and summer night of the past—the kind of night that might never return to our neck of the woods. All this spring, I have heard only two calls, on separate nights, and they were brief.
One publicly available study of amphibian decline in the U.S.* suggests that populations may be declining by an average of 3% per year. That comes to 26% over ten years, and that’s just an overall average. There is variability among species (American bullfrogs seem to be resistant) and geographic areas. Some populations may hold steady for a series of years, while others crash to zero in a year or two.
It’s more than sad, it’s ominous. One more sign of the wreckage we are inflicting on the living Earth.
Triple whammy: disease, habitat loss, and climate change
Those fungal diseases are but one prong of the assault on amphibians. The principal others are habitat loss and climate change—both driven by human activity. Wherever bogs or wetlands are filled in, countless amphibians perish. Wherever streams and ponds run dry from climate change induced drought, countless amphibians perish. In the case of tree frogs, wherever trees are felled, countless individuals perish.
Amphibians are especially vulnerable to habitat loss and fragmentation, because, unlike birds, they can’t move around easily, and the range of habitats they can survive in is narrow. They need a lot of moisture and cover from predators. Crossing a superhighway is unthinkable. Just crossing a small parking lot is rife with danger. Acres of bare ground at building sites are totally hostile.
One piece of relatively “good” news points to the importance of intact habitat. Some frog species in Panama appear to have recently evolved resistance to the most virulent chytrid fungus strain , in 9 of the 12 species for which there are good data. See this in New Scientist (I’m not sure if you have access unless you’re a subscriber, but the takeaway is, there’s hope): Frogs rebound in Panama
Sounds promising. But, without enough intact habitat to support large numbers of individuals breeding at a high rate, the evolution of a trait such as resistance to a deadly fungus is highly improbable. Wherever we destroy and carve up habitat with roads, buildings, airports, landfills, pipelines, transmission lines, dams, walls, fences, farmland, and other artifacts, we diminish the chances that any threatened species can evolve resistance to disease, air and water pollution, and climate impacts.
Ecological role of amphibians
Most amphibians are small and, except for their mating calls, inconspicuous. They don’t get the media play that “charismatic megafauna” such as big cats, elephants, and gorillas do, and they occupy a narrow range of habitats. The result is a paucity of research dollars, and the result of all that is, there’s a whole lot about amphibians we don’t know, and don’t know we don’t know.
A quick case for the value of amphibians is made in a short piece on The Biodiversity Group website, that also summarizes the devastation from the principal chytrid fungus: Amphibians under siege. (Note the possibility that a protein in certain amphibian nests could be used in a system of artificial photosynthesis!)
A much more comprehensive treatment of amphibians’ ecological role is found in this peer reviewed paper published in 2014: Amphibian Contributions to Ecological Services This paper, as thorough as it is, reflects the current limits to knowledge of amphibians, as evidenced in such turns of phrase as “As predators . . . amphibians may support ecosystem services. . . .” [emphasis mine]
Amphibians may provide even more significant ecosystem services than the foregoing paper addresses, but by the time we figure it out, there may not be many amphibians around to continue their good work.
IMPORTANT ADDENDUM: just as I was about to wrap up this post—1:38 am, May 25th—I stuck my head out the back door to see if I was prematurely crying doom. I heard, in the distance, two tree frogs, and nearby, the call of what I’m pretty sure is a ground-dwelling toad whose call is an uninflected reepreepreepreepreep (you get the idea). This was heartening, but the calls of three individuals fall far short of the enveloping chorus I had been accustomed to.
Since May 25, more individuals have been heard, and three nights ago a surround-sound symphony occurred reminiscent of days of old. Still, the chorus has receded, and my dread of the future has hardly abated.
===============– footnote========================
* Study to be found here: Amphibian occupancy in the U.S.