Eggs and incubation and hatchlings, oh my!

We have some great news to share on this #TurtleTuesday: Our Blanding’s turtle eggs have finished hatching! You can see the young hatchlings in the Americas Pavilion here at the Toronto Zoo. In case you can’t make it, our team at Adopt-A-Pond wanted to share their story – from their collection to incubation to hatch. 

The hatchlings that are in your Toronto Zoo’s Americas Pavilion are beginning their life as part of our Blanding’s turtle headstart program. Through several years of research, Adopt-A-Pond found that there was a dwindling population of Blanding’s turtles in Rouge Valley, the area that is now Rouge National Urban Park, with less than seven adults remaining. Without human intervention, it is likely that this population would go extinct. Along with our partners, the Toronto Zoo was able to start a headstarting program in 2012. Our program involves collecting eggs from sustainable populations in other parts of Ontario, incubating and hatching these eggs at the Toronto Zoo, raising them for the first two years of life, and then releasing them into Rouge National Urban Park. This process reintroduces Blanding’s turtles into their historic habitat. After 15-20 years, we hope to have released enough Blanding’s turtles that have successfully reached adulthood that they can reproduce and sustain a stable population on their own. 

Headstarting helps turtles overcome the most vulnerable stages of their lives. Turtle eggs, hatchlings, and juveniles have high mortality rates- fewer than 1% of all eggs laid will lead to a turtle surviving to adulthood! After a mother Blanding’s turtle digs a nest hole and lays her eggs, she buries them without leaving a trace on the surface. Like the eggs of other animals, they contain a yolk sac that has all the nutrients and energy the turtles will need during development. Since eggs are so nutritious, animals like raccoons, foxes, bears, crows, ravens, and skunks will seek out turtle eggs as a nutritious snack. Some predators are smart enough to figure out when turtles are going to nest and make a meal of both the mother and the eggs! 

Turtle eggshells are softer and more flexible than those of birds, so they curl up when the egg is broken. Finding eggshells above ground (as pictured here) is an indication that the nest was dug up and the eggs consumed by a predator. Had the eggs hatched successfully, the hatchlings would have dug their way out of the nest chamber, leaving their eggshells below ground (and undetectable to us!).

In addition to natural predators, due to habitat loss and fragmentation, more and more turtles are nesting on roadsides, which share the characteristics of natural nesting sites: good sun exposure and well-drained soils like gravel or sand. Unfortunately, this makes them susceptible to human destruction. Vehicles like cars and ATVs can run these nests over, compacting the soil above the nest. After the mother turtle spent hours, and sometimes multiple evenings, finding the perfect spot to lay her eggs, compacting the soil can crush the eggs, change important soil characteristics like moisture or air movement, or make it difficult for the young to escape after hatching. 

Despite facing these different challenges while developing, some of the eggs will successfully hatch! When they hatch, they young are approximately the size of a toonie and make their way from their nest to the closest wetland. At this stage, they’re perfectly bite-sized for many predators. When we collect the eggs and raise them until the age of two, we are helping to increase the survival rate of the Blanding’s turtles to a size that makes them less susceptible to predation, even in the urban environment of Rouge National Urban Park. 

Egg Collection

It was incredible for us to see the pristine wetland habitats and to witness so many nesting turtles. When forecasts predicted good nesting conditions, we would drive from Toronto to our source population, wait until just before sunset, and then begin searching for nesting turtles. Blanding’s turtles can spend a few evenings searching for the right soil conditions and dig numerous test holes before settling on the perfect spot. They also return to the same nest site every year, a phenomenon called nest site fidelity.

When we saw a turtle, we would mark her location with a GPS and give her space to find the perfect spot and begin the nesting process. After completing the route, we would loop back to the first turtles that we had marked to check in on them. We had to catch the turtles at just the right stage of nesting to successfully collect the eggs. If we disturbed them too early, then they may not return to nest that evening or to that nest site at all. If we were too late, then it would be difficult to find the exact nest spot, as they leave no trace of the nest on the ground surface. We had to catch the turtles when they were in the process of burying their eggs, as you can see here:

The female turtle carefully positions each egg using her back legs, and will completely cover the eggs up before she leaves. Once the nest is covered, there will be no visible trace that a turtle was ever here. Remember, if you ever see a turtle nesting in the wild, please give them lots of space and do not approach the turtle.

Once we identified the spot where the nest was, we carefully began removing layers of sand and dirt with our hands until we found the nest chamber. From there, we gently pulled out the eggs, nestling them into vermiculite, which we use as the nesting substrate throughout their transport and incubation. While vermiculite is traditionally used for gardening, it’s a substrate that maintains good moisture content and humidity for the eggs to develop. Once we had all the eggs from each nest, we collected data including time and date, location, if the female had previously received a unique identification mark, and the number of eggs. All egg collection was done by trained staff and under the necessary permits. 

Turtle eggs are delicate! Taking the eggs out of the nest chamber requires deep concentration and very precise movements. Please note that this was carried out by trained staff and under all required permits. In any other situation, disturbing a turtle nest would not be advised!

Incubation 

After the eggs were collected from the field site, they were carefully driven to the Toronto Zoo, where two incubators were ready and waiting! The incubators had been set up about a week prior, to make sure they were working properly before any eggs were added. The eggs are very sensitive to both temperature and humidity, and the incubators help us to closely monitor these variables while the hatchlings develop. 

The eggs are kept in Tupperware containers with holes for ventilation while in the incubator. This incubator keeps the eggs within appropriate temperature and humidity levels, so that the eggs will develop properly until they are ready to hatch!

The temperature at which the eggs incubate is particularly important, as it determines the development of each turtle’s sex. Each turtle species has unique “pivotal temperatures,” the temperatures at which the sex is determined. For Blanding’s turtles, a warmer incubator yields females and a cooler incubator yields males. In a natural setting, where eggs are incubating underground in the nest chamber, the eggs at the top may be warmer than the ones at the bottom, so there could be a mix of females and males in one nest. Also, sometimes a really cool year or a really warm year could lead to a nest hatching as all males or all females, respectively. In this regard, turtles play by the Law of Averages, and count on the environmental conditions fluctuating over time such that a population will gain both males and females, and therefore be sustainable. This is one reason why both persistently cool or warm conditions as a result of climate change are risky for turtles. If the sex distribution of a population becomes too uneven, breeding could become impossible, and this could push turtles closer to extinction! 

Hatching 

After 50-60 days, the eggs begin to hatch! Oh, happy days! Hatching is hard work, and it can take a hatchling anywhere from a couple of hours up to a whole day to completely make their way out of the egg. Once a turtle is out of the egg, it is common for the hatchling to have something round and yellow sticking out from their “belly button”. This is the yolk sac, and in fact, it’s the same yolk sac that provided nourishment to the hatchling while it was developing inside of the egg! It typically takes a few days to fully absorb, and it leaves no trace behind. If you look at the lower shell of an adult turtle, called a “plastron”, you won’t see a trace of where the yolk sac used to be. 

Hatching often starts slow, with one or two of the young “pipping” out of the egg. This is the first crack, usually made with the egg tooth, which is a sharp structure at the end of the nose that allows turtles to pierce through the eggshell. The egg tooth falls off a few days after hatching, as it is no longer needed.

Once the yolk sac is absorbed, each hatchling is delicately moved into its new home: a tank in the Toronto Zoo’s Americas Pavilion. Each turtle will live in three different tank setups while they are being cared for at the Zoo. At first, the water in the tank is shallow, and they have plenty of vegetation and a basking platform to make sure all their needs are met. The final setup are outdoor tanks, so the turtles can get used to daytime turning into night, the wind, the sunshine, and the birds singing: all  the natural sensations they would not get a chance to know while living inside! This helps to make sure they are ready to live in the wild. At the end of their two-year journey, the hatchlings are released into a suitable habitat within Rouge National Urban Park, and the Adopt-A-Pond team regularly monitors them for many years after they are released! 

We are so excited to see our this cohort of eggs successfully hatch! We look forward to continuing to track these turtles in Rouge National Urban Park until they reach adulthood, to see them find mates and nest in this habitat, and contribute to the Blanding’s turtle population. The ultimate goal is to continue collecting eggs and releasing young into the wild until the population reaches a sustainable level and no longer needs our helping hands. 

Before long, most of the eggs have hatched and the young are ready to be moved into their first tank, with shallow water and lots of vegetation to hide in.

We are happy to report on the successful hatching of 117 eggs that were incubated at the Toronto Zoo!

Thank you!!

This project would not be possible without all of our partners, both past and present. This includes Parks Canada, the Ontario Ministry of Natural Resources and Forestry, the Ontario Ministry of Environment, Conservation, and Parks, Magnetawan First Nation, Georgian Bay Biosphere Reserve, Shawanaga First Nation, Scales Nature Park, the Toronto Wildlife Centre, and the Ontario Turtle Conservation Centre. We recognize that there have been many partners involved in the headstarting and egg collection process through the years, and we apologize if we have missed anyone. 

If you would like to contribute to the success of this program, please consider making a donation here, through the Toronto Zoo Wildlife Conservancy.

This blog post was written by Donnell Gasbarrini and Megan Young.