Skip to Main Content
It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
San Diego Zoo Wildlife Alliance logo
San Diego Zoo Wildlife Alliance Library logo

Desert Tortoises (Gopherus agassizii) Fact Sheet: Reproduction & Development

Desert Tortoise (Gopherus agassizii)

Courtship

(Ruby & Niblick 1994) (Miller & Dinkelacker 2008)

  • Courtship activity happens in any month of the tortoise's active season.
  • Courtship encounters may last 1 or more hours
  • Male trails female and exhibits
    • Nodding at female
    • Repeated circling
    • Butting
    • Ramming
    • Biting of female
    • Behavior similar to early stages of combat
  • Females lack a distinct display to discourage male attentions.
    • Such displays common in other reptiles such as lizards and snakes 
  • Females appear to be very selective in choosing a mate
  • Females usually receptive only after repeated mating attempts
  • Females may mate with several males and store sperm for many years until ready to lay eggs

Egg-laying and Nesting

(Averill-Murray et al 2002) (Curtin et al 2009) (Miller & Dinkelacker 2008 ) (Nowak et al 1999) (Wallis et al 1999)

  • Most females in Mojave Desert produced eggs every year; two, even three, clutches occasionally if resources are plentiful (Wallis et al 1999) (Curtin et al 2009)
    • Large females laid more eggs and larger eggs
  • Females dig shallow depressions near den entrances, using hind limbs
  • Sonoran desert tortoises lay single clutch in June-July when rainy season begins
  • Eggs are covered, using hind feet; front and hind limbs scrape debris over egg chamber
  • Males in managed care settings have been observed helping females dig nests. (Grover & DeFalco 1995)

Life Stages

Eggs

  • Clutch of 1-14; 4-7 normally (Ernst & Lovich 2009)
  • Eggs laid May - July; sometimes into Aug. in Sonoran Desert. (Stebbins 2003)
  • Eggs are elliptical to spherical and ping-pong ball in size. (Ernst & Lovich 2009)
  • Yolk sac remains attached to hatchling's plastron for several hours or days - provides needed nutrients.
  • Incubation period in wild: 90-120 days; if artificially incubated 82-92 days (Ernst & Lovich 2009)

Hatchlings

  • Emerge from eggs mid-August to October.(Ernst & Lovich 2009)
  • Male size at hatchling: about 45 mm (1.8 in) carapace length (Germano et al 2002) or size of silver dollar.
  • Female size at hatchling: 42 mm (1.7 in) carapace length (Germano et al 2002)
  • Young wild hatchlings defensive and "pugnacious" when disturbed (Berry 1986)
    • Lunge forward and hiss if touched near the head
    • Found in young up to 4 - 6 years and less than 60 mm (2.4 in) carapace length
    • In managed care, quickly lose this response if touched frequently
  • Very few reach maturity in the wild

Young

  • Grow slowly at about 2.5 cm/yr (1 in/yr) (Nowak 1999)
  • Until shell hardens at 5-8 years, vulnerable to ravens, roadrunners, snakes, bobcats, kit foxes, coyotes

Adults

  • Age in wild at maturity (female): 15.7 years or 190 mm (7.5 in) for length of carapace
  • Sexual maturity of females varies in wild:(Curtin et al 2009)
    • West Mojave tortoises - about 17-19 years
    • Sonoran tortoises - about 22 to 26 years
    • Western Mojave tortoises grow faster than Sonoran tortoises

 

Longevity

  • Live at least 35 years; may live 50 -100 years (Nowak 1999)
  • Tortoises in Sonoran Desert live longer than those in Mojave Desert (Curtin et al 2009)
    • 43 years for females vs. only 27 years for females in Mojave
    • More frequent droughts in Mojave Desert may add stress
  • Females in both deserts have shorter life spans than males. (Curtin et al 2009)

Mortality and Health

  • Expanding raven populations (Boarman 2002) (Woodman & Juarez 1988)
    • USFWS estimates raven populations in desert areas increased due to garbage dumps and sewage ponds
    • 250 tortoise shells found under a single raven nest (some of which had been recently seen alive and healthy)
    • When tortoises younger than 5-6 years, shell isn't fully ossified and it is easy to rip open.
    • Ravens may pose a threat to overall population numbers in this long-lived species that doesn't reproduce until 15 - 20 years.
  • Carnivores, especially coyotes and bobcats prey on tortoises.
  • Badgers, skunks, kit foxes prey on tortoises and eggs. (Luckenbach 1982)
  • Fire ants
  • Occasionally, fires
  • Mortality in wild for juveniles more than 90%
  • Gila monsters eat tortoise eggs (Nowak et al 1999)

Soft-shelled Growth Phase

two young desert tortiose

Young desert tortoises grow slowly. It take 5-8 years for their shell to harden.

Until then, they are vulnerable to predation by birds, snakes, bobcats, kit foxes, and coyotes.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Page Citations

Averill-Murray et al. (2002)
Curtin et al. (2009)
Ernst & Lovich (2009)
Germano et al. (2002)
Grover & DeFalco (1995)
Luckenbach (1982)
Miller & Dinkelacker (2008)
Nowak et al. (1999)
Ruby & Niblick (1994)
Stebbins (2003)
Woodman & Juarez (1988)

SDZWA Library Links