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Desert Tortoise (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 Global. 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)

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