Greetings to my fellow tortoise lovers!
We’ve finally finished up with our busy season here at the San Diego Zoo’s Desert Tortoise Conservation Center (DTCC) in Las Vegas, and the tortoises have gone into hibernation for the winter. Now that we have time to reflect on everything we did last season, I want to share with you one of our success stories.
We are very excited about the productive hatchling season we had this year. Many of the babies are now living in our new predator-proof hatchling enclosures. As part of our herd management plan to ensure that diseases do not get transmitted among our animals, we disinfect and sterilize the quarantine pens and then install a new artificial burrow whenever a current tortoise moves out and a new tortoise moves in. This requires a lot of digging. One day, while out preparing a burrow for a newly arrived tortoise, Daniel Essary (a research associate at the DTCC) accidentally hit a nest of eggs deep in the soil at the far end of the burrow. As careful as we are while digging new burrows, it is impossible for us to know if a previous female resident left eggs behind, especially when they are left in an unexpected location like the back of a burrow.
Daniel immediately stopped shoveling and started carefully scooping the dirt away with his hands to reveal five damaged eggs. The outer, hard part of each shell was badly cracked and missing in some places, but the inner lining was still intact. He gently scooped them up and brought them to me to see if anything could be done for the unhatched babies. The first egg he found was damaged beyond saving, but I thought maybe the others would have a chance if they were protected in the incubator. We put them in an uncovered plastic container with some soil from the burrow and placed a damp cloth over the eggs to keep them from drying out. We didn’t know if this would work since the eggs were pretty badly damaged, and we didn’t know how developed the embryos might be.
While there wasn’t anything we could do to save the first egg, we were very excited when the other four eggs all hatched naturally after a couple of days in the incubator. Three of them hatched with no problem, but the fourth had a damaged yolk sac. Since the yolk sac provides nutrients to a newly hatched tortoise and it is somewhat vascular (it has blood vessels in it), we didn’t know if this would adversely affect the hatchling’s survival. However, we didn’t give up on the baby. We soaked all four hatchlings several times a day in order to keep them hydrated and to help remove the inner egg membrane that had dried to their shell. We kept their handling time to a minimum to avoid stress and to prevent further damage to what was left of the yolk sac of the last hatchling.
Happily, after spending a few weeks in the medical pavilion, all four hatchlings made it through. The one with the damaged yolk sac developed a bit slower, and we were unsure at first if he would make it, but he survived and quickly caught up to his clutchmates. It was a very exciting day when they were finally ready to go into their own outdoor hatchling enclosure, and they took to their new home as if they had lived there forever.
You may wonder why we would allow new hatchlings to hibernate since they seem so fragile, but we have found that if you allow hatchlings to hibernate for their first winter after hatching, they become stronger and healthier adults than those that are not allowed to hibernate. I will be sure to give you an update of their condition when they wake up in the spring!
Rachel Foster is a research associate at the San Diego Zoo’s Desert Tortoise Conservation Center. Read a previous post about the DTCC, We Love Volunteers.