Monday, January 9, 2017

Extinction and Saving Species

"Living wild species are like a library of books still unread. Our heedless destruction of them is akin to burning the library without ever having read the books" -John Dingell, Former Congressman and Author of the Endangered Species Act

The Tecopa Pupfish, Cyprinodon nevadensis calidae, the first organism which was removed from the Endangered Species Act due to extinction. The extinction of this fish was declared to be entirely preventable by Assistant Secretary of the Interior Robert L. Herbst. Photo by U.S. Fish and Wildlife Service.

Deserts are difficult places to live for plants and animals. High temperatures, lack of food and water, and extreme variability combine to push organisms towards the edge of their existence. Too often human disturbances and modifications in desert systems have provided a final push into extinction for many desert organisms. Biologists are aware that the idea of a species has a real temporal element as well, in other words species as we know them now are temporary. Their genetic and morphological characteristics can and do change as time goes on. Some species go extinct, some species get "re-absorbed" into their sister species through hybridization, and some survive and change due to natural selection and genetic drift. Some biologists have proposed the "ephemeral speciation model", likening species to a desert stream, in other words species are temporary and subject to change. Extinction is not a new phenomenon by any means.

What is worrying today is that humans can so quickly end the existence of so many species before we have a chance to understand them. Extinctions are happening faster today than they have in the past, this is certain. 

But what we must not forget in these times is that humans, in many cases just a single individuals or group of individuals, can save an entire lineage from almost certain demise. The last few months have been troubling for me as a biologist, a conservationist, and a person who cares about desert species and landscapes threatened by a changing climate. Perhaps you have had similar feelings given that some world leaders seem to revel in ignorance when we know that human lives and entire species are at stake. 

It is important to learn from our failures, but also to celebrate our successes in conservation. I aim to do so here by focusing on a few stories from the deserts I love so much. One story that ends in extinction, one that ends in success but uncertainty, and one that ends in recovery and hope. 

The Tecopa Pupfish: Water for soaking, but not for fish
The Tecopa Pupfish was a subspecies of pupfish native to a few spring outflows and hot spring systems outside of Tecopa, California. In the 1960s and 1970s bath houses were constructed for tourists and the spring system of the Tecopa Pupfish was heavily modified and altered. The stream course was diverted and pupfish habitats became much hotter. Modifications also allowed other pupfish to swim into the Tecopa Spring system and hybridize with the endangered Tecopa Pupfish. The introgression between the Tecopa Pupfish and other closely related species coupled with habitat modification eventually led to the Tecopa Pupfish having the distinction of being the first endangered species to be removed from the Endangered Species Act due to its extinction. More careful planning and mitigation efforts during construction of the bath houses could have entirely prevented the extinction of the Tecopa Pupfish according to the Assistant Secretary of the Interior at the time. 

The Pahrump Poolfish, Empetrichthys latos, is extinct in the wild but was saved from total extinction due to the efforts of University of Nevada, Las Vegas Biologist Dr. James Deacon. Photo by U.S. Fish and Wildlife Service.

The Pahrump Poolfish: A species in a bucket
The Pahrump Poolfish was previously found only in Manse Spring outside of Pahrump, Nevada in the Mojave Desert. The species is the only living representative of its genus and faced almost certain extinction several times during the 1960s and 1970s. Vegetation at Manse Spring was removed to construct a swimming hole for locals in addition to goldfish being introduced in the spring. The lack of cover in Manse Spring and the competition with newly introduced goldfish caused the population to crash to less than 50 individuals on two separate occasions. Finally in 1975 it seemed like the prospects for the Poolfish were nonexistent. Ground water pumping nearby led to the eventual drying of Manse Spring and would have led to the extinction of the Pahrump Poolfish if not for the efforts of Nevada biologist James Deacon. Aware of the impending demise of Manse Spring and the extinction of its poolfish, the last member of its genus, James Deacon removed every living individual poolfish from Manse Spring in a 5 gallon bucket. 

I sometimes reflect on how Dr. Deacon must have felt that day, removing an entire species from the wild, unsure if they would ever return to their native spring or if they would stave off extinction at all. I know that if I had been there, it would have been unlikely that I could have held back tears. 

The Pahrump Poolfish still exists due to the efforts of Dr. Deacon and others, but it has not yet been returned to Manse Spring. It is unclear whether suitable habitat will ever enable their reintroduction into their former home.
The Relict Leopard Frog, Lithobates onca, once thought extinct, now thriving in several locations in Arizona and Nevada. Photo by Tom Brennan

The Relict Leopard Frog: From "extinct" to "not warranted for listing as endangered"
The Relict Leopard Frog, Lithobates onca, was thought to be extinct for some time, though there were rumors that some frogs still existed in their former habitat. Biologists in the 1990s discovered frogs at former sites where Relict Leopard Frogs were known to exist in Nevada, and studies confirmed that these frogs were indeed the Relict Leopard Frogs, long thought extinct. Since the discovery multiple partners and agencies got to work and within a fairly short period of time conservation plans were in place and biologists got to work reintroducing Relict Leopard Frogs to their former habitat and collecting eggs for use in translocation experiments in an effort to save the species. 

Despite the fact that it was once thought extinct, many new populations of Relict Leopard Frog are apparently breeding and thriving. Recovery efforts have been so successful that recently the United States Fish and Wildlife Service found that the species is "not warranted" for listing as an endangered species thanks to the hard work of volunteers, scientists, and resource managers. The chirps and ribbits of the Relict Leopard Frog is now heard at night in dozens of sites which it had likely occupied historically but been extirpated (locally pushed to extinction) from.

Where next? 
The fight against extinction remains, and dozens of organisms throughout the desert southwest are still threatened due to habitat alteration, invasive species introductions, and global climate change. What happens to these species isn't in the hands of bureaucrats or pompous elected officials. It is largely in the hands of every day people. Ordinary people whose names you likely haven't heard have helped save two of these three species from extinction for now. While many other species have already become extinct or remain threatened, the future of these "libraries of knowledge" remains up to us.

The fires are burning close to the doors of these libraries. What will you do?

References and further reading:

Deacon, James E., and Joshua E. Williams. "Retrospective evaluation of the effects of human disturbance and goldfish introduction on endangered Pahrump poolfish." Western North American Naturalist 70.4 (2011): 425-436.

Bradford, David F., Jef R. Jaeger, and Randy D. Jennings. "Population status and distribution of a decimated amphibian, the relict leopard frog (Rana onca)." The Southwestern Naturalist 49.2 (2004): 218-228.

Miller, Robert R., James D. Williams, and Jack E. Williams. "Extinctions of North American fishes during the past century." Fisheries 14.6 (1989): 22-38.

Proactive conservation keeps Relict Leopard Frog off the endangered species list.

Monday, March 14, 2016


"Where there is smoke, there is fire." -Unknown

Ephedra californica, this shrub may be a a good candidate for use in post-fire restoration efforts in desert areas due to its quick growth rate. Photo by Stan Shebs

Historically in desert systems, fire has been remarkably limited. There is separation between plants which makes fire difficult to spread under historic conditions.

However, with an increase in invasive, fast growing vegetation; fires have increased in the last hundred years in desert systems.

These fires can drastically alter arid systems and kill native vegetation. Additionally, they can alter soil characteristics which make it tougher for native vegetation to re-emerge. In many cases, post fire species composition in deserts shows high dissimilarity from species compositions pre-fire. These divergences don't seem to be temporary either, with many studies suggesting that there are significant difference between before and after fire species compositions even nearly 50 years after the last time an area was burned. Fire can also change soil dynamics significantly, making it hard for cryptobiotic soil crusts to recolonize.

Fires can also result in a positive feedback loop which benefits non-native, often fire adapted plants. Making it harder for native plants to recolonize and easier for non-native ones to do so. The communities that exist after desert areas have been burned rarely bear resemblance to their former selves.

The Creosote Bush, Larrea tridentata, common in most of the North American desert region is unlikely to recolonize an area following a fire. Photo by wikimedia user Sue in az.

Invasive species management in deserts is an important way that we can reduce risk of fire in areas which often evolved without it. Removing invasive grasses such as cheatgrass, buffelgrass, and red brome is especially important to preserving intact desert plant communities which makes it an important management goal for arid land conservation.

The North American deserts have only been around for several thousand years based on climatic data, so change is not new to the region. However, the fact that seemingly small human caused changes, such as introduction of one species of non-native grass, can drastically alter plant and animal communities for half a century, may force us to answer important questions about why we value desert communities and what aspects of their biological integrity are most important to preserve.

References and further reading:

Abella, Scott R. "Post-fire plant recovery in the Mojave and Sonoran Deserts of western North America." Journal of Arid Environments 73.8 (2009): 699-707.

Brooks, Matthew L., and David A. Pyke. "Invasive plants and fire in the deserts of North America." Proceedings of the invasive species workshop: the role of fire in the control and spread of invasive species. Fire conference. 2000.

Johansen, Jeffrey R., et al. "Recovery patterns of cryptogamic soil crusts in desert rangelands following fire disturbance." Bryologist (1984): 238-243.

 Sara J. Scoles-Sciulla , Lesley A. DeFalco & Todd C. Esque (2015) Contrasting Long-Term Survival of Two Outplanted Mojave Desert Perennials for Post-Fire Revegetation, Arid Land Research and Management, 29:1, 110-124.

Tuesday, January 26, 2016

Grazing in the Deserts

"Temper tantrums, however fun they may be to throw, rarely solve whatever problem is causing them." -Lemony Snicket

A Desert Tortoise from the area where Cliven Bundy's cattle have been grazing illegally for years.

I decided to delve into this topic in part because of current events that should be startling to conservationists, resource managers, people who recreate in deserts and ranchers themselves. That is the closure of Malheur National Wildlife Refuge in Oregon. Since the refuge is located in the Great Basin Desert of Oregon, and the same family who has shut down the refuge hails from my home state I felt that it would be interesting to delve into the science behind the point the Bundy's are trying to make.

Much of their conflicts with land management agencies revolves around disputes over grazing rights in certain areas. The Bundy family famously owing over $1 million in grazing fees and fines to the federal government. They have refused to pay these fees and have now occupied an important wildlife refuge in Oregon.

A central claim that the Bundy's have raised is that grazing is good for wildlife. They have stated that wildlife on ranches and areas where grazing is allowed is more abundant than in Malheur National Wildlife Refuge itself. They famously destroyed a boundary fence between the refuge and a ranch, claiming that the Ranchers had been treated unfairly by the federal government. It should be noted that the Ranch owner, did not want the fence removed or his livestock to roam onto the wildlife refuge which encompasses 100,000 acres.

But what about the science behind these claims? Do the Bundy's have a point? Is grazing good for wildlife and wildlife habitat?

Well, like many things in nature. The answer is "it depends". In areas where plants evolved with some level of livestock grazing it is known that some levels of disturbance by grazing can promote diversity in plant communities.

It should be noted that studies on grazing can be inherently difficult. It is difficult to separate variables from each other in many of these systems. It is difficult to distinguish between certain management techniques. For instance, does season of grazing matter? How does one objectively distinguish between different grazing intensity levels?

Some studies can also become biased because certain areas, though technically open to grazing are not grazed by livestock due to other factors.

Unfortunately, some claims in this field of study are often overstated and anecdotal. One paper from  Rangelands states that Desert Tortoises are found in highest abundance where cattle are also found in highest abundance (perhaps a coincidence of both relying on similar food sources?). Other studies have found that livestock trample young tortoises, destroy burrows and remove important forage.

However, one thing is clear. Overgrazing is hardly ever beneficial, especially in deserts and riparian areas (Malheur National Wildlife is both). Cattle in riparian areas can alter stream flows and make water less available to plants, which could alter the entire riparian community. They also impact soils in these fragile areas which desert wildlife are dependent on.

Riparian habitat near where Cliven Bundy's cattle graze in Nevada

It isn't just the plants though. Overgrazing effects people too. Trout from streams where grazing is not allowed or has been eliminated tend to be much larger and more abundant, overgrazing eliminates bird species richness in riparian areas, even snakes are more abundant in areas where grazing is limited. This is bad news for the fishermen, hunters, and wildlife viewers who also own Malheur National Wildlife Refuge if the Bundy's do get their wish.

Ironically, overgrazing also reduces edible forage for cattle. So it even hurts the ranchers, which is after all why grazing is regulated in the first place. If you don't do it right you hurt ecological communities and you hurt people.

References and further reading:

Milchunas, D. G., O. E. Sala, and W_K Lauenroth. "A generalized model of the effects of grazing by large herbivores on grassland community structure." American Naturalist (1988): 87-106.

Waser, Nickolas M., and Mary V. Price. "Effects of grazing on diversity of annual plants in the Sonoran Desert." Oecologia 50.3 (1981): 407-411.

Fleischner, Thomas L. "Ecological costs of livestock grazing in western North America." Conservation biology (1994): 629-644.

Bostick, Vernon. "The desert tortoise in relation to cattle grazing."Rangelands (1990): 149-151.

Webb, Robert H. "Recovery of severely compacted soils in the Mojave Desert, California, USA." Arid Land Research and Management 16.3 (2002): 291-305.

Thursday, January 7, 2016

Side-Blotched Lizards

"Remind yourself that you don't have to do what everyone else is doing" -Rajat Dogra

A Side-blotched Lizard in the Sonoran Desert

The Side-blotched Lizard, Uta stanbursiana, is the most widespread and common lizard in the North American Deserts. One can observe them throughout the year, even during the cool winter months. Though they can be quite colorful, otherwise nothing jumps out about this typical lizard. I recall one guide book referring to them as "the popcorn of the desert", because they provide snacks to so many desert predators; snakes, birds, coyotes, and other lizards.

With this abundance, comes an increased chance that lizards of this species will cross paths and interact. This common lizard, which a seasoned herpetologist might ignore due to its abundance is part of a complex social hierarchy which lends insight into important ideas in evolution and physiology.

Males of this species are polymorphic (multiple "types" that look and behave differently). There are large males which control and defend large territories, smaller males which defend smaller territories, and males which control and defend no territories and resemble female Side-blotched Lizards. Females

Selective forces should shape evolution of males towards big, territorial males, able to control and monopolize large territories and thus female lizards. So why do the other two morphs exist?

If very large males become to abundant, they struggle. They compete with each other and have trouble defending the territory and the females in their respective territories. The smaller males are more able to defend their small territories and mate with the females there.

If either of the two males that defend territories become abundant the males that resemble females have an advantage. They are able to "sneak" into other males territories and mate with females unnoticed as the larger males fight with each other.

But when these "sneakers" become most common the large males are able to identify them and chase them away easily.

In other words, the relative fitness of each type of male is related directly to its relative abundance within the population. This is called density dependent natural selection. If one type of male becomes too abundant it increases the fitness of the other two types, and this is how all three are able to persist in the population. This is the hipster form of natural selection, you're most cool (fit) when you're doing things that no one else is doing.

Another interesting part of this social hierarchy deals with the length of each lizards tail. Recall that an important defense mechanism for many lizards is that they are able to drop their tails when threatened by a predator and that they eventually regenerate them. The predator might be then left with a tail, but no lizard.

Losing a tail appears to have social costs in Side-blotched Lizards. When a dominant lizard loses its tail, subordinate lizards recognize this and behave more aggressively towards the formerly dominant lizard, perhaps recognizing that this lizard no longer has the social status it once did due to the unfavorable encounter. The length of the tail and whether or not it was regenerated appears to be especially important for status in female lizards.

References and further reading:

Sinervo, Barry, et al. "Testosterone, endurance, and Darwinian fitness: natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards." Hormones and Behavior 38.4 (2000): 222-233.

Ferguson, Gary W. "Mating behaviour of the side-blotched lizards of the genus Uta (Sauria: Iguandidae)." Animal Behaviour 18 (1970): 65-72.

Sinervo, Barry, and Curt M. Lively. "The rock-paper-scissors game and the evolution of alternative male strategies." Nature 380.6571 (1996): 240-243.

Fox, Stanley F., Nancy A. Heger, and Linda S. Delay. "Social cost of tail loss in Uta stansburiana: lizard tails as status-signalling badges." Animal Behaviour 39.3 (1990): 549-554.

Monday, December 14, 2015

The Sonoran Desert Toad

"Bart: 'Dad, are you licking toads?'  Homer: I'm not NOT licking toads." - The Simpsons

The Sonoran Desert Toad, Bufo alvarius, note enlarged paratoid glands

The Sonoran Desert Toad is a large amphibian native to the lower Colorado River area of Arizona's Sonoran Desert. It is large, green, and can be quite aggressive if provoked. It has a special surprise for predators that try to make a meal of a what would at first glance be a feast for many a desert animal. 

Look but don't touch, and definitely don't lick this toad. 

The Sonoran Desert Toad has been made famous because of its potent toxins. Dog owners report seizures, high fevers, and rapid heart beat in their dogs following unfortunate encounters with this toad.

In fact the poison is so toxic that the Sonoran Desert Toad is responsible for more canine deaths per year than Rattlesnakes. Remember to keep an eye on your dog during summer monsoons so that you can avoid any unpleasant experiences with this amphibian. 

Because of its potent toxins the Sonoran Desert Toad has made its way into pop culture. Any references to "licking toads" are often referencing this species, which produces copious amounts of the potent neurotoxin in its enlarged paratoid glands (the fat pockets behind the ear in the first picture). So yes, this desert amphibian has even been referenced on an episode of The Simpsons, though the writers did not identify the Sonoran Desert Toad specifically as the one Homer "did not not lick". 

Some anthropologists have suggested that ancient peoples of mesoamerica used a toad as a ritualistic hallucinogen, citing mythological representations of toads. If the peoples of mesoamerica did use toads in ritualistic ways, it was likely this one due to the potent, hallucinogenic nature of its toxin. In the past some suggested that the Cane Toad, found further South, could have been used in this way, but its toxin is more a pure poison than a hallucinogen. 

 Many media outlets have reported that people have resorted to extracting this toad's toxin and smoking or ingesting it to gain a desired hallucinogenic experience. Given the high toxicity of this toxin and the contracting range of the species this action can be both illegal and stupid. 

Interestingly, the toad's toxin is not a banned substance but drug enforcement officials have prosecuted drug offenders by inciting bans on the exportation of this toad(in States where the toad is not native). The Sonoran Desert Toad is protected across some portion of its range, so officials have used the legal protection of this toad to prosecute drug offenders who would use the toxin for a cheap high.

References and Further Reading:

Musgrave, M. E., and Doris M. Cochran. "Bufo alvarius, a poisonous toad."Copeia 173 (1929): 96-99.

Hanson, Joe A., and James L. Vial. "Defensive behavior and effects of toxins in Bufo alvarius." Herpetologica (1956): 141-149.

Weil, Andrew T., and Wade Davis. "Bufo alvarius: a potent hallucinogen of animal origin." Journal of ethnopharmacology 41.1 (1994): 1-8.

Wednesday, December 2, 2015

Endangered Habitats: Joshua Tree National Park

"But those trees! Those Trees!... All my life I've been searching for trees such as these!" -Dr. Seuss, The Lorax

Lost Palms Oasis in Joshua Tree National Park

Today I'm launching a new and regular feature of this blog. A focus on habitats and special areas in desert systems which are threatened. Without complete and intact habitats we would not know much that we currently do about how the world functions. I've focused much on adaptations which desert animals possess and some ecological interactions in desert systems; but from time to time it is important to remember that without relatively undisturbed, intact habitat for these organisms we would lose so much of what we value in these unique systems.

Importantly, when it comes to conservation of intact ecosystems we must often fight many unique battles to preserve these special places. The stakes are especially high in these battles as margin for error is minimal. It is not easy to restore and ecosystem and it is impossible to undo extinction. Too many times in conservation do we forget that sometimes losing even a single battle amounts to losing the war. In this sense, conservation can be likened to evolution where the stakes are equally high for individual organisms.

I'll start this habitat spotlight with the place where I first experienced a true desert wilderness. Joshua Tree National Park in California's Mojave Desert.

Joshua Tree supports a diverse group of desert organisms, being the meeting point and melting pot for two vastly different systems, the Sonoran Desert (Colorado subsection) and the Mojave Desert. The boundary of the two is readily apparent. In the higher sections of the park in the Mojave Desert, the namesake plant dominates. In lower sections Creosote dominates the landscape.

Fan palm oases dot the park and provide unique habitats to creatures which otherwise would not be able to live in the harsh landscapes. Water bubbles to the surface and provides critical habitat to Red Spotted Toads and California Treefrogs as well as native California Fan Palm Trees.

Even a place that is formally protected such as Joshua Tree is still faced with a plethora of threats externally and internally.
The Joshua Tree, Yucca brevifolia

First and foremost is the threat of climate change which has the potential to drastically reduce the range of Joshua Trees. In fact warmer temperatures have the potential to push Joshua Trees to extinction within Joshua Tree National Park.

Ironically the people who love Joshua Tree National Park so much also have the potential to alter the systems here. The park is a geologic wonderland and is popular with rock climbers who visit from all over the world to climb here. Surveys of popular climbing routes show that ecological communities of plants and birds in and around popular climbing areas are altered compared to similar communities which are not heavily frequented. Loving a natural area to death is a very real threat, especially in fragile desert parks where footprints can mark the landscape for years.

What can be done to address these threats? Acting on climate change will be important if we hope to protect the biological feature the park was originally intended for. All of the formal protection in the world will not save a plant from a system that will no longer support it biologically. Making sure that certain critical ecological areas are subject to limited use by climbers and hikers could also be important for the future of this park which is only a two hour drive from almost 20 million people.

References and further reading:

Cole, Kenneth L., et al. "Past and ongoing shifts in Joshua tree distribution support future modeled range contraction." Ecological Applications 21.1 (2011): 137-149.

Camp, Richard J., and Richard L. Knight. "Rock climbing and cliff bird communities at Joshua Tree National Park, California." Wildlife Society Bulletin(1998): 892-898.

Camp, Richard J., and Richard L. Knight. "Effects of rock climbing on cliff plant communities at Joshua Tree National Park, California." Conservation Biology12.6 (1998): 1302-1306.

Thursday, November 5, 2015

Canyon Tree Frogs and Cryptic Species

"Trust not too much in appearances" -Virgil

A Canyon Tree Frog calling to a potential mate, photo by Jessica Phelps

What does "home" sound like? For me, the sound of home is the call of a Canyon Tree Frog. A rather odd call which could be described as a cross between the sound of a domestic sheep and a duck. I recall one night camping alone on a remote, burned over plateau in the Great Basin Desert. I went there to explore and for perspective. Sometimes nothing gives you perspective better than getting as close as possible to the natural forces that shaped us. This is probably why I love the deserts so much, as it seems here those forces are especially apparent even to casual observers. I remember the sun setting and feeling perhaps unsettled; similar to how people often do when they are alone after dark. A few minutes later I heard the call of a single frog, easily identifiable as a Canyon Tree Frog. Eventually several joined, then more, and even more. Eventually I could hear the calming call of hundreds of "Tree Frogs", though there was no living tree in site. I've since returned and camped here several times and have never found the frogs, though their incessant calls tell me they are there. Though I admittedly haven't tried very hard, perhaps worried that gazing upon frogs that no human has yet seen will somehow diminish them.

Okay. I'm getting a little too poetic and emotional for a science blog right?

You get the point. I am sentimental about these frogs. I love them. 

A "tree" frog where there are no trees, the Canyon Tree Frog has found a way to make an arboreal living in an often terrestrial landscape. These semi-aquatic frogs climb on canyon walls instead of vegetation, their coloration often varying depending on the color of the canyon they inhabit (pinkish brown if sandstone, grey if granite). These wall-climbing frogs also seem to be fairly intelligent, moving large distances between suitable bodies of water in patterns not typical of random dispersal. In other words, they KNOW where they are going.

This widespread "species" also allows us to delve into another paradox in evolution. Sometimes two species can look the same but can be quite different. These are called "cryptic species", species that look the same morphologically but cannot interbreed; hidden species. The Canyon Treefrog as we know it might actually be several cryptic species. 

Canyon Tree Frogs are widespread but their range is also choppy and intermittent in nature because of the desert springs and streams they occupy. They are found throughout the American Southwest and into Mexico but these regions have diverged quite substantially based on genetic evidence. 

In addition to this genetic differentiation, there are also subtle differences in the calls of these lineages which may not be enough for a human ear to pick up on. To a female frog though, these differences mean the world. A frog found in the southern lineages strongly prefer the calls of her own locality, and don't like the calls of other Canyon Tree Frog localities. Even something as simple as not speaking the same "language"; could be considered a barrier to reproduction and thus an example of speciation. These data are supported by the genetic data which supports strong divergence between geographical localities of Canyon Tree Frogs.

Sadly, these frogs are threatened by many of the same forces threatening amphibians worldwide. A changing climate, extreme variability and drought, and disease are all threats to this and other amphibian species. For my sake though, I hope that every time I return to that camp site I will be able to hear my frogs.

Further reading and references:

  • Kay, David W. "Movements and Homing in the Canyon Tree Frog (Hyla Cadaverina)." The Southwestern Naturalist 34.2 (1989): 293-5. Web.
  • KLYMUS, KATY E., SARAH C. HUMFELD, and H. CARL GERHARDT. "Geographical Variation in Male Advertisement Calls and Female Preference of the wide‐ranging Canyon Treefrog, Hyla Arenicolor." Biological Journal of the Linnean Society 107.1 (2012): 219-32. Web.
  • Barber, PAUL H. "Phylogeography of the Canyon Treefrog, Hyla Arenicolor (Cope) Based on Mitochondrial DNA Sequence Data." Molecular Ecology 8.4 (1999): 547-62. Web.
  • Klymus, Katy E. "Phylogenetic and Behavioral Differentiation in the Canyon Treefrog, Hyla Arenicolor." ProQuest Dissertations Publishing, 2011. Web.
  • Bradley, GA, et al. "Chytridiomycosis in Native Arizona Frogs." Journal of Wildlife Diseases 38.1 (2002): 206-12. Web.