This subject came up on another thread and I found this article by Darrell Senneke:
[Darrell Senneke] Turtles are often solitary in the wild so if they meet they usually breed. This is because if they had to wait till the perfect time many would not meet another turtle at that time. Turtles and tortoises practice what is called sperm retention. What we mean by this is that the female can hold the sperm within her for long periods (years in fact) to be used as the eggs develop. The eggs developing is triggered by environmental factors which cause hormone production which triggers the formation of the eggs. The female then uses the stored sperm to fertilize the eggs. I have had female box turtles lay fertile eggs three years after being separated from any male.
The way to tell if a female turtle or tortoise is ready to lay eggs is based on simple observation. If it is an aquatic kept in a habitat without a large land area or adequate nesting area it will usually act as if it wants out and be very persistent about it. If it is a terrestrial turtle or tortoise it will pace, sometimes even stopping to sniff the ground. This is a good indication that it is looking for a nesting site. At this point it is necessary to provide a nesting location for the turtle or tortoise. If you think the turtle may be gravid (holding eggs) and it refuses to lay when provided with a nesting location or it exhibits none of the indications noted above a veterinarian can take a radiograph (X-ray) to determine for certain if eggs are present. .
[Darrell Senneke] Turtles are often solitary in the wild so if they meet they usually breed. This is because if they had to wait till the perfect time many would not meet another turtle at that time. Turtles and tortoises practice what is called sperm retention. What we mean by this is that the female can hold the sperm within her for long periods (years in fact) to be used as the eggs develop. The eggs developing is triggered by environmental factors which cause hormone production which triggers the formation of the eggs. The female then uses the stored sperm to fertilize the eggs. I have had female box turtles lay fertile eggs three years after being separated from any male.
The way to tell if a female turtle or tortoise is ready to lay eggs is based on simple observation. If it is an aquatic kept in a habitat without a large land area or adequate nesting area it will usually act as if it wants out and be very persistent about it. If it is a terrestrial turtle or tortoise it will pace, sometimes even stopping to sniff the ground. This is a good indication that it is looking for a nesting site. At this point it is necessary to provide a nesting location for the turtle or tortoise. If you think the turtle may be gravid (holding eggs) and it refuses to lay when provided with a nesting location or it exhibits none of the indications noted above a veterinarian can take a radiograph (X-ray) to determine for certain if eggs are present. .
