Mantenerse en unas Especies resbaladizas (Boreal Toads en Colorado)

A story by Amanda Kissel

The sky turns to dusk in the Rocky Mountain backcountry as I emerge from my tent and pull on my damp rubber waders. It takes all of my will power to drag myself from my warm down sleeping bag out into the cold night. My stiff muscles protest as they have already endured a five-mile hike today, carrying about thirty-five pounds of gear. The many day hikers and tourists that frequented the trail like cars on a highway are gone, and the few backcountry campers are heading the opposite direction—into their tents. My co-worker and I, however, are just beginning our work for the day. Our job is to search the lakes of Rocky Mountain National Park meticulously for the endangered Boreal Toads (Anaxyrus boreas, formerly Bufo boreas) of Colorado. The Unites States Geological Survey (USGS) hired my co-worker and me to monitor these animals for the summer so that assessments can be made on the status of the population. Each week we take a trip to at least two sites to check on the toads. On average, this entails about twenty miles of hiking and backpacking every week.

Tonight, the evening begins with a mile-long hike from camp to the survey site. As I start off, my stomach rumbles and I regret not packing more food, even though it would have added weight to my already-too-heavy pack. About halfway up the trail my muscles loosen and fall into a familiar methodical march. The trail is still patterned with piles of snow, and the early June temperature in the high country is no more than 35oF at this time of night. Our destination is Spruce Lake, one of two or three sites where boreal toads are still known to breed in Rocky Mountain National Park, according to research by USGS biologists. It is also, from my experience, the site that we are most likely to encounter toads consistently.

It is the first trip of my second season working with boreal toads, and I am anxious to see if the toads will still be there. We trudge up the trail in our “toading gear”: several layers of warm clothes, a rain jacket, waders, a hat, and a headlamp. In a backpack we carry various pieces of survey equipment. I pay close attention to my surroundings, as the trail is unimproved and it is easy to wander off unintentionally. I hear the creaking of the dense mix of coniferous trees that line the trail as they are rocked by the wind and watch as a snowshoe hare hops hurriedly out of the trail at our approach. As we hike, I think about the work I am conducting. Who knows, perhaps these toads will provide a cure for some unknown disease in the future. And without these animals, will the ecosystems they are a part of still function efficiently? There is no doubt in my mind that these toads are important to the world, even if I don’t fully understand the role they play.

We arrive at the site as the stars emerge in the sky and it is time to begin our night’s work. Our surveys are always conducted at night, when the toads are most active. The wind has died down now and for about an hour we walk around the edge of the calm lake, searching for a sign of a toad: the reflection of an eye in our headlamp, a slight movement of the vegetation that sprouts through the water or the faint chirp of a little male toad (females do not make any sound). As we survey, my partner and I talk loudly to each other to keep away any unwanted night visitors like bears or mountain lions. When we spot a toad, our goal is to quickly snatch it before it dives under the surface of the lake, while keeping an eye out for any already-laid egg masses and trying not to go in the water over our hip waders. At times this can be difficult, as the toads tend to congregate along one bank where the water is shallow and vegetation thick. Toads tend to group in these areas because they are prime habitat for laying egg masses.

Later, we will come back and collect eggs from the one mass that we find to take to the Colorado Division of Wildlife’s native species hatchery in Alamosa, Colorado where biologists will raise toads for possible reintroduction. The toad eggs are encased in a jelly matrix, which is a tube-like structure about the consistency of slime. To collect the eggs, we count out about ten from the end of the matrix, pinch them off with a gloved hand and put them into a thermos filled to the brim with water. Since the egg masses consist of hundreds of eggs, taking ten eggs will not have a significant negative impact on the next generation of toads. Once we collect the eggs, it is vital to keep the thermos at the lowest temperature possible, since eggs develop faster in warm water than cold. On the five mile hike down, it will be important to keep the thermos very still so the eggs are not jostled, not an easy task when you are hiking down a steep, rocky trail with a thirty pound backpack.

On this particular night, we spot a total of six toads, two of which escape into the depths of the lake. We manage to catch the other four toads, though, and now it is time to start processing. We begin by taking several measurements from the squirming toads including weight, the length of the toad, and the width of its mouth. The toads do not like to hold still for these measurements and often swat at the calipers we use to measure them. The male toads chirp in protest, but as this is one of the easiest ways to tell that the toad is a male, we are glad for the noise. We record the measurements for each toad, along with the sex, and indicate whether it is a “new” toad or a “recapture.” If the toad is “new”—never having been caught before—we insert a passive integrated transponder (PIT) tag into its back. A PIT tag is about the size of a grain of rice, and we inject the tags just under the skin on the toad’s back. During subsequent surveys, we will use a hand-held scanner to search for a PIT tag in each animal. If a tag is present, the toad is considered a “recapture.” PIT tags stay permanently so this method is effective for long-term studies.

A vital part of the processing procedure is “taking a swab,” which involves swabbing the toads’ stomachs and hind feet to detect the presence or absence of amphibian chytrid fungus. This fungus is a member of a huge phylum of fungi, the Chytridiomycota. There are two schools of thought on the origin of this particular amphibian chytrid. One is that it is not native to the North America. The other hypothesis is that the fungus is native to North America and the hosts (the toads) are more at risk due to environmental changes such as increased contaminants, global climate change or stress. The amphibian chytrid fungus is thought to be a cause of boreal toad population declines in the Park, as well as other areas where these animals exist. The mobile stage of the amphibian chytrid fungus (called a zoospore) enters the toads through their permeable skin from the water. The fungus only invades skin-deep, then completes its life cycle producing more zoospores. These zoospores are released back into the water from the toad via a tiny tube that extends to the outside world from the fungal structure in the toad’s skin. The disease is generally fatal due to a thickening of the skin and the toad’s impaired ability to exchange water and oxygen with its environment.

Boreal toads are not the only amphibians experiencing declines. According to an article in Science magazine by Simon Stuart and his colleagues, the populations of at least 2,468 species of amphibians are decreasing. Causes for these declines include habitat loss, pollution, disease –including the amphibian chytrid– and other factors not yet fully understood. These and other issues about amphibian declines in the United States are addressed in recent, comprehensive book, Amphibian Declines, edited by Dr. Michael Lannoo, a scientist from The Indiana School of Medicine, Ball State University in Indiana. For example, one study shows that freshwater habitat is declining faster than any other habitat in the world, including the rainforest. Everyone has heard how quickly the rainforests of the world are being stripped, but who knew that right in our backyard the environment is degrading at an even faster rate? Boreal toad populations that are already stressed may be at increased risk as freshwater habitat in the Rocky Mountains, habitat like the lake where I search for my quarries, declines in availability or is degraded. Although the site is within the boundaries of a National Park, the lake and its inhabitants are still subject to factors such as air pollution, wind-borne contaminants such as pesticides or fertilizer, and climate change. These hazards negatively affect water quality and vegetation growth even in the most remote locations.

As the human population continues to grow, demand for natural resources and outdoor recreation increases, and more land is transformed for human use. Critical habitat for animals such as amphibians is lost as land is developed. Human activities such as energy development and natural events such as climate change compromise the integrity of the land. Introduction and spread of non-native, invasive species and disease agents like the amphibian chytrid fungus are also detrimental to vulnerable native populations of plants and animals. Mindful of this, my partner and I are careful to bleach our waders and equipment before each trip so we do not carry diseases from site to site. Fishermen are encouraged to do this as well, as anyone can be a vector for a disease.

National parks are mandated to protect native wildlife from extinction. However, even these intended sanctuaries cannot guard completely against disease, the rapid spread of invasive species or other environmental changes. These conditions and their impacts make it all the more challenging for wildlife managers to conserve resources, especially species of concern like the boreal toad. Through organizations such as the Colorado Division of Wildlife’s Boreal Toad Recovery Team and the USGS Amphibian Research and Monitoring Initiative (ARMI), scientists are generating critical information about amphibians and amphibian decline. With this information, managers and politicians can make informed decisions to help preserve amphibians as an integral part of the earth’s biodiversity.

The ultimate cost of global amphibian decline is yet to be seen. Most scientists believe that amphibians are a measure of the health of an ecosystem, making these changes consequential not only for amphibians but potentially for human health as well. Amphibians have porous skin that is sensitive to pollution, UV radiation, and other subtle changes in the environment that humans may otherwise be unable to detect. They can act as a litmus test for the environment such that the health of amphibians can give us insight into the status of the habitat we share with these small creatures. This connection makes addressing the causes of amphibian decline crucial to the health of human society and our environment at large.

Before 1995, Rocky Mountain National Park was home to approximately 16 boreal toad breeding sites. At each site, hundreds of toads could be found on a given night, a stark contrast to what we encounter on this night in June of 2006. It is hard for me to imagine a time when so many toads floated in the lake as I vigilantly search the vegetation for just one. It is even more disturbing to realize that these toads have apparently all but disappeared in only a few years. Not many people get to see first-hand the effects of such a dramatic decline. I wonder as I search, will I look back in ten or twenty years on my first few years of field experience and reminisce about how I helped save the toads? Is it possible to recover this species whose numbers have crashed so dramatically? As I muck through the shallows of the lake with my field partner on this dark night, I hold the hope that my work is playing a part—and perhaps making a difference—in these important and worthwhile efforts to keep this humble toad and its cohorts in our midst.

Reprinted with permission of Fort Collins Now.