Desert Tortoise (Gopherus agassizii)

Common name: Desert Tortoise
Scientific name: Gopherus agassizii
Conservation status (IUCN Red List): Critically Endangered
Habitat: Mojave Desert: California, Nevada, Utah & Arizona
Edition: TT-30 — Desert Architect

Spends at least 95% of its life underground in burrows it digs itself, and its bladder can hold over 40% of its body weight in water. Pick one up and it may empty that store to get away from you. So please don't.

The Desert Tortoise (Gopherus agassizii) is featured in the Turtle Tuesday Club 53-week turtle art series. Its IUCN Red List conservation status is Critically Endangered and it is found in Mojave Desert: California, Nevada, Utah & Arizona.

Most of this tortoise's life happens where you can't see it. At least 95% of it, spent in burrows it digs itself, five to twenty-five of them a year, depending on the tortoise. It comes out for grass, wildflowers and new cactus growth, and it carries its own water: the bladder can hold over 40% of its body weight, enough to go a year or more without a drink. That's also why you never pick one up. A scared tortoise may empty that bladder to get away, and in the Mojave that water isn't coming back. It is Critically Endangered now. It has been digging longer than any of us. Let it keep digging.

The Mojave desert tortoise (Gopherus agassizii) is 25 to 36 cm long and weighs 8 to 15 pounds, with males slightly larger than females. It lives in the Mojave Desert of western Arizona, southeastern California, southern Nevada and southwestern Utah. In 2011 the population east of the Colorado River was split off as its own species, Gopherus morafkai, which reduced the range of G. agassizii by about 70%. It spends at least 95% of its life in burrows, using about 5 to 25 a year. Its urinary bladder can store over 40% of its body weight in water, and adults can survive a year or more without access to water, but a tortoise that is handled or frightened can empty its bladder as a defense, losing that backup supply. It eats mostly grasses, plus herbs, annual wildflowers and new growth of cacti. It reaches maturity at 15 to 20 years and can live 50 to 80 years. Eggs incubated below 31 °C (88 °F) all hatch male. It has been listed as threatened under the US Endangered Species Act since 1990, and in 2021 the IUCN Red List assessed it as Critically Endangered.

Mostly Underground

The Mojave desert tortoise lives in the hottest, driest corner of the country: western Arizona, southeastern California, southern Nevada and southwestern Utah. It handles that by not being out in it. At least 95% of its life is spent in burrows, and one tortoise uses about 5 to 25 of them a year.

It comes up to eat grasses, herbs, annual wildflowers and the new growth of cacti, and it swallows rocks and soil too, possibly to keep its gut bacteria going. Water it stores. Its urinary bladder can hold over 40% of its body weight, and adults can survive a year or more without access to water.

That reserve is also its weak spot. A tortoise that is handled or frightened can empty its bladder as a defense, and then it has no backup supply in a place where rain is rare. It is the single best reason not to pick one up, even to help.

It is slow in every way that matters. It reaches maturity at 15 to 20 years, lays four to eight eggs in a clutch, and can live 50 to 80 years. Ravens take the young, upper respiratory tract disease runs through populations, and roads, off-road vehicles and building keep eating its habitat. In 2021 the IUCN Red List assessed it as Critically Endangered.

Key Moments

1989: The Mojave population gets an emergency listing under the US Endangered Species Act
1990: It is listed as threatened under the Endangered Species Act
2011: Tortoises east of the Colorado River are recognized as a separate species, Gopherus morafkai, cutting the range of G. agassizii by about 70%
2021: The IUCN Red List assesses the Mojave desert tortoise as Critically Endangered
Today: It is the state reptile of both California and Nevada

Fun Facts

Mostly Underground: At least 95% of its life is spent in burrows, about 5 to 25 of them a year
Built-In Canteen: Its bladder can store over 40% of its body weight in water
A Year Without a Drink: Adults can survive a year or more without access to water
Temperature Decides: Eggs incubated below 31 °C (88 °F) all hatch male
Eats Rocks, Sort Of: It swallows rocks and soil, possibly to keep its gut bacteria going
Two States Claim It: It is the official state reptile of California and Nevada

Conservation Notes

The Mojave desert tortoise was assessed as Critically Endangered on the IUCN Red List in 2021 and has been listed as threatened under the US Endangered Species Act since 1990.
Ravens take many juveniles, upper respiratory tract disease affects populations, and urbanization, habitat destruction, off-road vehicles and illegal collection keep adding up. Give tortoises room, drive slowly in their habitat, and never pick one up.

Mini FAQ

Why shouldn't I pick up a desert tortoise?

Because it may empty its bladder to get away from you, and that is its water supply. Its bladder can hold over 40% of its body weight in water, the reserve that lets an adult go a year or more without drinking. Lose it in the Mojave and it may not get it back.

How does it survive the heat?

Mostly by not being in it. It spends at least 95% of its life in burrows it digs, using about 5 to 25 of them a year, and it carries stored water in its bladder.

Is it the same as the Sonoran desert tortoise?

Not anymore. In 2011 the tortoises east of the Colorado River were recognized as their own species, Gopherus morafkai, based on DNA, geographic and behavioral differences. That cut the range of the Mojave desert tortoise, Gopherus agassizii, by about 70%.

Illustration by Lee Eisenbarth for Turtle Tuesday Club. Free to use with credit under Creative Commons CC BY 4.0: how to use this art.

Sources: IUCN Red List, Wikipedia.