For about eight years before coming to USC, I spent the majority of my time working at a local wildlife hospital in my community. The hospital, Lindsay Wildlife Rehabilitation Center, specializes in working with California’s endangered and threatened species. Community members bring in injured animals and the hospital staff aims to treat them and ultimately release them in the same area they were found. During my time at Lindsay, there
was one long-term hospital resident that I became particularly close with. Her name was Dandelion. She was an absolutely beautiful California Desert Tortoise who passed away right before I left to college. The Desert Tortoise (Gopherus agassizii) is an absolutely incredible species native to the southwestern part of the United States that is unfortunately in decline to due to loss of habitat largely caused by humans.
Background
This tortoise lives primarily in desert biomes, more specifically in southwestern United States (Devender, 2006). They live over 100 years and at full size are around 9-12 inches. This species reaches sexual maturity around 13-20 years old (USFWS, 2011). They are uniquely adapted to live in the hot desert temperatures. To stay cool, desert tortoises spend about 95% of their time in the burrows they dig which shield them from the hot sun (National Park Service, 2019) Their burrows are identified by their unique crescent shape. They tend to be inactive during the winter hibernating October until March (Devender, 2006). During this period of hibernation, they have very low metabolic rates which allow them to maintain inactivity using very little energy (Devender, 2006). When they are not in their burrow, desert tortoises seek water that collects in natural
depressions in the ground and forage for vegetation. Did you know that this species can actually survive up to an entire year purely on their internal fat stores (Devender, 2006)? They are able to maintain this efficiency through a unique a gut bacteria that allows them to digest cellulose in plant walls, kind of like cows (Devender, 2006).
In terms of natural threats that exist to the desert tortoise population, they are most at-risk during their early
life when their shell is soft (Grover, 1995). They may fall prey to various types of birds like ravens, eagles, and hawks in addition to coyotes and foxes (Grover, 1995). In fact, that wonderful shell tortoises are so well known for takes 5+ years to harden
(Grover, 1995). One cool fact I learned when I was working at Lindsay Wildlife was that tortoises’ shells are made up of the same material as our fingernails—cartilage. Once tortoises’ shells harden it is unlikely that they will be killed by an
-y natural predators because they can simply retreat into their shell as threatened.
PSA--Tortoises vs Turtles
Also, PSA because I think it is worth mentioning in a blog post about tortoises. Tortoises and turtles are not the same species and should not be used interchangeably. Tortoises are land-dwelling and have elephant-like feet (Langley, 2017). They are herbivores and primarily live in hot environments. Turtles, on the other hand, are sea dwelling and have flippers. They tend to feed on fish and plants (Langley, 2017).
The Human Threat
Unfortunately, the desert tortoise species is no longer thriving despite their incredible adaptations that should hypothetically allow their population to thrive in a desert biome. Humans are largely to blame for this. There are a number of factors that have contributed to the decline of this population in the southwestern United States. The most common factors are urbanization, collection by pet trade, highway mortality, and surprisingly off-roading (Berry et. al, 1997). By far the biggest threat that outweighs all the rest is habitat loss (Berry et. al, 1997). When humans move into an area, they not only displace all the species that lived there for generations, but they alter the habitat structure of that ecosystem. This is exactly what happened in the desert tortoise habitat. In the Mojave Desert specifically, there are a lot of energy development projects and military bases being built that encroach on native tortoise habitats (Nevada Fish & Wildlife Office, 2014). Desert tortoises are often unfortunately killed during the exploration and mapping of these areas (Nevada Fish & Wildlife Office, 2014).
One fairly common threat to desert tortoises that was surprising to me was the threat of off-road vehicles. Tortoises have a fairly sandy covered shell that serves as camouflage to protect themselves from birds in the sky. However, when it comes to off-roading vehicles, their camouflage works against them. Vehicles will often run over their shells damaging a key element of a tortoises’ ability to survive (Nevada Fish & Wildlife Office, 2014). In addition, a tortoises average speed is 0.2 mph, which means it is unlikely that they can run away quickly in the event that a vehicle comes very close to them (National Parks Service, 2019).
A Plan for Recovery
Due to the overwhelming habitat loss within the tortoise’s native habitat, Mojave Desert tortoises were federally listed under the Endangered Species Act of 1973 as a threatened species (Field et. al, 2007). In 2011, the USFWS came out with a comprehensive plan to increase the tortoise numbers. This recovery plan has a “50% probability of survival for the tortoise for 500 years” (Berry et. al, 1997). These were the 6 major strategic elements of this recovery plan.
1. Develop, support, and build partnerships to facilitate recovery.
2. Protect existing populations and habitat, instituting habitat restoration where necessary.
3. Augment depleted populations in a strategic manner.
4. Monitor progress toward recovery.
5. Conduct applied research and modeling in support of recovery efforts within a strategic framework.
6. Implement a formal adaptive management program.
Although they estimated that the plan would cost about $159,000,000, about $11,000,000 was spent as of 2007 (USFWS, 2011). However, in order to officially classify a species as no longer endangered the population must increase or remain stable for at least 25 years. As Desert Tortoise Recovery Coordinator Averill-Murray describes “the tortoises’ peculiar nature -- secretive and slow to breed -- means there’s a lag in seeing results from all the effort to keep them from disappearing" (Stark, 2009).
Translocation is another technique conservationists attempted. A translocation is an “intentional release into the wild as an attempts to establish, reestablish, or augment populations” (Field et. al, 2007). Although it is typically only about 19% successful, conservations were able to successfully use this method on a small population of 32 adult tortoises in an effort to prove translocation’s viability in future conservation efforts (Field et. al, 2007).
So is it worth it to save this species?
That is probably the question on every politician’s mind when they see the $159 million-dollar price tag on the desert tortoise’s conservation plan. Yet the real question we should be asking ourselves is how did we get to this place in time where we as humans are now deciding if any entire species of animals gets to live or die? How can we even morally say no, when in fact, we are the ones that are responsible for their decline in the first place.
Now after that mini rant let’s get back to the desert tortoise. They play a crucial role in the desert ecosystem ad actually known as a “bellwether species” or indicator species (Stark, 2009). This means that when their change in population numbers is as an early warning sign of environmental damage and climate change (Elizabeth, 2019). Other species use desert tortoises for burrowing and major predators rely on young tortoises for food. Their extinction would have ripple effects on the already limited biodiversity within the desert biome.
What You Can Do
We can continue to advocate for endangered species when it comes to allocating funding for their protection and stopping housing projects that encroach on their habitat. Spreading awareness is a term that is thrown around a lot, but it is truly the best possible way to be an ally for this species.
WORKS CITED
Berry, K. (1977). The Desert Tortoise Recovery Plan: An Ambitious Effort to Conserve Biodiversity in the Mojave and Colorado Deserts of the United States (Rep.). Riverside, CA: New York Turtle and Tortoise Society.
Campbell, K. (2019, March 02). Microban Toxicity. Retrieved September 21, 2020, from https://sciencing.com/microban-toxicity-22516.html
Devender, T. (2006). The Sonoran Desert Tortoise Natural History, Biology, And Conservation. Univ of Arizona Pr.
Desert Tortoise. (2019, July 1). Retrieved September 21, 2020, from https://www.nps.gov/jotr/learn/nature/tortoise.htm
Desert Tortoise Threats. (2014, April 6). Retrieved September 21, 2020, from https://www.fws.gov/nevada/desert_tortoise/dt/dt_threats.html
Grover, M., & DeFalco, L. (1995). Desert Tortoise (Gopherus agassizii): Status-of-Knowledge Outline With References (Rep.). Denver, CO: United States Department of Agriculture.
Langley, L. (2017, December 02). How to Tell a Turtle From a Tortoise. Retrieved September 21, 2020, from https://www.nationalgeographic.com/news/2017/12/shell-game--how-to-tell-a-turtle-from-a-tortoise/
Revised recovery plan for the Mojave population of the desert tortoise (Gopherus agassizii). (2011). Region 8, Pacific Southwest Region, U.S. Fish and Wildlife Service.
Stark, M. (2009, February 22). Big money for the lowly desert tortoise. Retrieved September 21, 2020, from https://www.latimes.com/archives/la-xpm-2009-feb-22-adna-tortoise22-story.html
IMAGE SOURCES:
J. Goldfarb, Crescent Burrow of Desert Tortoise. 2015, from https://lh3.googleusercontent.com/proxy/xjr34h3iac4q-tEZvba2XBoymjS--Za58Jp05M1MmwojkqQPyu3KSdjJNLVTT7Erc-dg2Dz_Qztg_WyD_KC-leWYELgOZMAX-ZgXVRe7-khpsVKEabwhDrDqjY_CYWVXltY_1BVBlA.
Turtle vs Tortoise. 2020, from https://i.redd.it/913874nz7n051.jpg.
Tortoise on Highway. 2012, from https://www.endangeredspeciesinternational.org/deserttortoise.html.
Medina Ayala-Lo. Tortoise Translocation Procedure. 2017, from https://www.dvidshub.net/news/230327/combat-center-conducts-desert-tortoise-translocation.
**NOTE: Other two images are original images from Wix and myself.