Desert tortoises (Gopherus agassizii) are herbivorous reptiles that come from Mexico and the southwestern United States. These sizable land-dwelling turtles often use nodding, along with several other methods, as a way to get things going in the mating process. The reproductive season for desert tortoises begins toward the closing of the spring and ends in the autumn.
Once the reproductive season for desert tortoises rolls around each year, the males start to have at it with each other. These battles are for the attentions of females that are ready to mate and breed. These scuffles involve a lot of running after each other, plowing into each other and head nodding. The objective in these rather bizarre confrontations often is to turn one's opponents upside-down. Once this happens, the defeated individual usually gets back on his feet again -- literally -- and flees the demoralizing situation. Occasionally, defeated desert tortoises die from being turned over in this manner.
Once the beaten male desert tortoise is out of the picture, the victor can begin the job of wooing the female. Strangely, a lot of these wooing signals are similar to those of the breeding battles, such as the nodding up and down of the head. Apart from nodding, the males nip the females, make whistling sounds at them, walk around them over and over, plow into them and push into their sides using their heads.
Female Reaction and Mating
When male desert tortoises nod and put on the full courtship show, they often receive little reaction from the females at first. The females often initially feign oblivion to the entire ritual. Once the males are able to assume the mating stance, however, the duration of the activity is unpredictable. In some cases, mating in desert tortoises can take mere minutes. In others, it can go on for hours at a time. The female desert tortoises determine exactly when to put an end to things, however -- and simply by leaving the scene.
Female desert tortoises are highly discerning about who they choose for mating. Despite all of the work that male desert tortoises go through in trying to impress the females, whether through nodding, plowing or anything else, it usually takes a few separate efforts before the females finally agree to mate. The gestation period for female desert tortoises lasts for between 10 and 12 months -- longer than that of human beings.
- U.S. Fish & Wildlife Service: Desert Tortoise
- Defenders of Wildlife: Desert Tortoise
- University of Michigan Animal Diversity Web: Gopherus agassizii
- San Diego Zoo Library: Desert Tortoise Fact Sheet
- University of Nevada Cooperative Extension: Behavior of the Desert Tortoise
- Arizona-Sonora Desert Museum: Care, Husbandry and Diet of the Desert Tortoise
- IUCN Red List of Threatened Species: Gopherus agassizii
- The New York Times: Science Q&A