Cousin Ernie: Retired Zoo Keeper/ Woodland Park Zoo, Seattle
Most birds and Oviparous (egg laying) reptiles develop what is called an egg tooth prior to hatching. It is a sharp bony projection near the tip of the upper beak. It looks like a tiny rhinoceros horn. It is used to help the young break out of the shell and is usually dropped within a week after hatching. It is often flattened from side to side so can act as a knife as well as a poker.
The chicks use their neck and back muscles to push the egg tooth up and out, initially cutting their way through the inner egg membrane and then through the outer shell.
First they cut into the air cell in the broad end of the egg. This is when they first begin breathing air and when they can begin vocalizing. These calls from within the egg signal to the adults that hatching is eminent. They may also be communicating with their nest mates which may help them to synchronize their hatching.
The next step is called pipping. They push their egg tooth through the outer egg shell to create a small hole. It’s a lot of hard work and they may rest for 24 to 48 hours before proceeding on. The parents seldom help the chicks out of the egg, so it’s all up to them to get out.
After pipping they cut their way around the end of the egg using the sharp edge of their egg tooth as a knife until they’ve created an opening large enough to squirm out through.
The Peregrins in downtown Seattle are currently incubating four eggs
Nothing new. Both Lena and Spike continue to take turns incubating.
Hatching “window”. The 4th egg was laid on April 3, 2022. Peregrines sometimes begin incubating between the 3rd & 4th eggs but occasionally will wait until the 4th egg before seriously getting down to it.
Incubation can be as short as 30 days or as long as 34 days, even 35 or 36 days have been recorded, but 32 days is normal.
So … given all the variables, we can calculate a hatch window. Hatching could be as early as May 2nd or even as late as May 9th, but will most likely occur around May 4th or May 5th. Also, each egg/embryo is developing on its own timeline, so they probably won’t all hatch simultaneously. They may hatch within a few hours of each other or as much as 48 hours apart.
I’ve been wrong on most of my predictions about these guys before, but I guess we’ll see.