The Delicate Balance between Temperature and Gender with Reptiles in Galapagos

There are those who say that a drop of water can change the ocean. In a certain sense, the same philosophy applies to reptiles in the Galapagos Islands. Except that instead of a drop it’s a degree of temperature, and instead of an ocean its actually their gender. Science has revealed to us that temperature plays a crucial role in determining the gender of newborn reptiles. Galapagos is no exception to this rule, especially when it comes to the likes of giant tortoises (a member of the Galapagos BIG15 group of iconic species that can be viewed on all our Galapagos itineraries) and several other reptiles in the Galapagos.

Temperature-Dependent Sex Determination

As a result of laying their eggs underground (typically sand), Galapagos giant tortoises and marine iguanas do not regulate the incubation temperature of their eggs. This leaves the eggs up to the whim of the elements in terms of deciding what gender they end up as. Science has shown that warmer temperatures during the incubation period tend to display an increased number of female hatchlings. Cooler temperatures, on the other hand, show greater levels and numbers of males.

A good mnemonic for remembering the difference between the two is by simply thinking “hot babes and cool dudes.”

Galapagos Islands Breeding Center.
There Are Centers In The Galapagos Islands Specialized In Helping Giant Tortoises Breed.

The Laying of Eggs & Hatching of Galapagos Giant Tortoises

Eggs are laid via a tedious process that’s undertaken by the females as they trek many kilometers to get to their nesting areas that are found along the sandy and dry (July to November) coasts of Galapagos. Once they’ve found an adequate spot for laying their eggs, the female begins to dig its nest which take anywhere from several hours to a number of days to complete. The nest tends to be 12 in (30 cm) deep, inside of which she deposits an average of 16 spherical eggs that can weigh anywhere between 2.9 – 5.5 ounces (82 and 157 gr). After laying them, the female will top off the nest with mud that’s made from soil mixed with her own urine and will then flatten out this tortoise-made “plug” by laying down on it briefly. She’ll then stand up and walk away for good, leaving the nest to be incubated by the sun itself.  Females are known to lay around one to four clutches of eggs per season.

Galapagos Animal Species: Giant Tortoises
There Are Different Species Of Giant Tortoises In The Galapagos Islands.

Worth noting is that incubation time is also a huge factor, as clutches that are laid early on throughout the cool season have longer incubation periods which, in turn, end up producing more males. Eggs laid during the hot season, however, have shorter incubation periods and consequently produce more females.

In the Long-Run…

The implications of this in the grand scheme of things, especially when it comes to globally recognized increasing temperatures, could be a lopsided number of females versus males in the population of each respective reptile. Consequently, population sustainability might be at risk. Should the temperatures around the world continue to rise, it might very well be the case that we could see certain species of reptiles reach extinction on a long enough timeline (if they procreate out in the wild, in which case females will outnumber males).

Galapagos Giant Tortoise Walking And Eating.
The Giant Tortoise Is Protected By The Galapagos National Park.

Fortunately, scientific studies are currently underway in the Galapagos that will hopefully help to shed led light on how temperature variations will impact the sex demographics of Galapagos tortoises, specifically. Such studies would help provide a larger scale understanding of said species and will assist in developing effective conservation strategies to offset rising global temperatures.

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Updated:May 8, 2023

Published:August 29, 2017


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A Font of information, Klaus has spent decades in the field, leading tours in the Amazon, Andes and Galapagos Islands. He hung up his guiding boots a few years back and now creates itineraries for the tour operator, Metropolitan Touring. Adrift in the Pacific Ocean, hundreds of miles from mainland South America, Galapagos is one of the most biodiverse locales on Earth.

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