The typical incubation for saddle-billed stork eggs averages about 31 days. We gave our saddle-billed storks an extra week of incubating beyond their due date before deciding to remove the eggs from the nest. This was done to ensure that they were not delayed in their development causing them to hatch later than expected. Earlier this week keeper staff finally removed the overdue eggs from the nest. The parents were not pleased at first, but quickly adjusted to the freedom of no longer needing to sit on eggs all of the time!
Once the eggs were removed from the nest they were transported to our Veterinary Clinic, where we first radiographed (or x-rayed) the eggs. Radiographs were done to enable staff to get a look at what was happening inside the eggs. Normally keepers would “candle” eggs to check for fertility and monitor chick development. The candling process is a method in which you shine a light through the egg shell to illuminate the interior of the egg to see what is happening inside. However, because saddle-billed stork eggs have thick shells, candling was not an option which led the staff to perform radiographs. Typically with saddle-billed storks, after about 23 days of incubation, embryonic bones have developed and are visible on a radiograph image. During the radiographing of the stork eggs, unfortunately no embryonic development was observed.
After evaluating the radiographs, staff then proceeded to immerse the eggs in water and carefully crack open the eggs to gently remove the yolks. The staff examined the egg yolks, looking specifically for any signs of embryonic development or obvious problems with the eggs. This was yet another step used to determine if the eggs were ever even fertilized since keeper staff were never able to confirm that the storks had successfully bred or copulated. After thorough examination, it was determined that the eggs were probably never fertilized.
These results now have the keepers asking if these birds are definitely copulating and if this male is capable of reproducing. The next step for the Zoo is to attempt to confirm breeding behaviors by monitoring and recording the birds’ behaviors over longer periods of time. Also, the Zoo may attempt to collect semen from the male stork to determine his breeding ability. If he proves to have viable semen, artificial insemination may be a possible alternative in the future for breeding these birds next season.
Photo Caption: Stork eggs and yolk with chicken egg as size comparison.
Saddle-Billed Stork Lays Historic Eggs for Nashville Zoo
Who delivers the babies of storks? That is hopefully a quest the Nashville Zoo Avian Department has embarked on to answer. This is the fourth time the storks have created a nest and the third time they have produced eggs since they arrived at the Zoo in 2008 from Tanzania.
Previous years they've displaced the eggs from the nest by pushing them out of the nest and onto the floor and keepers have had to artificially incubate the eggs. The eggs that have been produced in the past have been infertile and the last time the female has laid an egg was in January 2017. Since the shells are extremely thick, if an egg that was pushed out of the nest was viable, the shell wouldn’t crack and the chick would continue to grow inside.
This year the eggs have stayed in the nest.
The storks have continued to sit on the eggs and further the incubation process on their own. There has been research done, although not conclusive, about females being able to tell if the egg is viable by resting her foot on the top of the egg to feel for a heartbeat.
Right now, the Zoo does not know if the three eggs are fertile until they hatch. After 31 days of incubation, the keepers will know the answer to the question. The incubation period will end around the first week of January. This will be the first hatch of storks at the Nashville Zoo and the second hatch from a male with flight restrictions.
If the eggs are viable and the chicks hatch, they would add to the population in the United States. This species is endangered in South Africa. Nashville Zoo is part of the Species Survival Program, which carefully manages breeding in order to maintain a healthy and self-sustaining captive population that is both genetically diverse and demographically stable.
“There are very few zoos that are producing chicks,” said Sean Ployd, bird keeper. “So if they do have chicks that’s fairly significant. If the parents rear them then that’s fairly significant as well. Since the storks were from the wild, their genetics are even more important for introducing new genes into captive population and the Species Survival Program."
The storks are off exhibit right now because they are prone to frostbite under 35 degrees.
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