Desert Tortoises (Gopherus spp.) Fact Sheet: Reproduction & Development

(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

(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)

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

Managed care

• No AZA estimates

• Respiratory tract disease
• Predation
  • 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
  • Gila monsters eat tortoise eggs (Nowak et al 1999)
• Occasionally, fires
• Humans collecting tortoises and killing recreationally
• Loss of habitat due to urban development, road construction, mining, waste disposal, etc.
• Spread of invasive plants

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.

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)