What do eggs, Easter, and zoos have in common? Ostriches! Well, I guess any bird... and technically rabbits... but lets just focus on ostriches for a moment. These are the world’s fastest two-legged land animals, the largest bird species, the land animals with the largest eyeballs, and, for today’s focus, they lay the largest egg of any living animal.
To get a feel for how large this egg is just picture holding a five-pin bowling ball (the norm in Canada) and you’ll be pretty close. We’re asked questions about the ostriches all the time here at the zoo and thought it might be nice to help answer some of your questions even while at home. Questions like:
- How many chicken eggs fit in an ostrich egg?
- How many do they lay?
- Why are their eggs so big?
- Do they lay them all the time?
Hopefully, we can help you find your answers and grow your love for these outrageously large birds.
How many chicken eggs fit in an ostrich egg?
On average about 24 chicken eggs fit inside an ostrich egg.
Ostrich eggs weigh about 1 360 grams, and a large chicken egg in Canada is rated at a minimum of 56 grams—so roughly 24 large chicken eggs. They also have roughly the same proportion of yolk to albumen (egg whites)!
Are ostrich eggs fragile?
No. Under the right conditions an ostrich egg can withstand about 5,000 Newtons of force, which is more than 6 times the force to break a chicken egg in the same conditions.
In general, it can take more force to break an ostrich egg than a human bone, but it is important to remember that the angle of impact, surface area of impact, and flaws in the shell can make a big difference. Eggs are strongest when upright, with even force on the pointed ends, but significantly weaker when pressed from the sides.
The egg shells GVZoo's Discovery Centre have been hollowed-out for educational purposes—so they are quite a bit more fragile.
Why are ostrich eggs so big?
Because that's how they evolved! Now that the boring answer is out of the, here’s a more detailed explanation:
Eggs are not always proportionate to the size of the animal, but, like everything, there is always a trade-off. Some birds, like kiwi’s of New Zealand, have massive eggs that are about 20% of the mother’s weight*. For any mothers reading this, a human baby is about 5% of the mother’s body weight. Picture having a baby four times bigger than that!
The upside? Kiwi chicks are practically fully-grown upon hatching and you don’t have to parent them. Downsides, they take a lot of energy to lay and you can only lay one at a time so if the egg doesn’t hatch then it was a lot of wasted energy.
Ostriches, on the other hand (or wing?), lay eggs that are only 1.5% of their body weight. They can lay more eggs at once, and if some of their eggs don’t survive then its not as big of a deal. Proportionately to their bodies, ostriches lay the smallest eggs and hold the Guinness World Record for “Smallest egg proportionate to body weight” with Emperor Penguins having an honourable mention.
The downside to having a proportionately small egg is that the babies have a long way to grow when they hatch. Ostriches take about six months to be full sized and three to four years to reach sexual maturity.
*For the curious, there isn’t a pinned down answer but current theories suggest kiwi’s evolved larger eggs because more developed babies avoided predators better.
TL;DR Ostriches have big eggs because their bodies are big and they have small eggs in proportion to their bodies.
Do ostriches lay eggs all the time?
No. They lay eggs for about 40 days during their breeding season. The breeding season is generally when the weather becomes consistently warm and would depend on the region the animals are living. The breeding season would last for a few months, with an egg laid every few days until the nest is full.
How many eggs do ostriches lay?
Good (but tricky) question. Numbers vary depending on their environment, resources available, as well as the nesting conditions!
Some ostrich farms suggest that one hen can lay a modest 20 eggs per season with others boasting 40-60 or even more than 100! We can use “more than 100” as the answer to “what is the maximum number of eggs an ostrich can lay in a year?”
Ostriches also lay eggs depending on the space available in the nest. About 20 eggs fit under a full grown ostrich so a nest typically holds about 20 eggs. The tricky part is that ostriches are polygamous and will have several female’s eggs in the nest. The dominate hen will claim the center of the nest, with other eggs towards the outside and the extras pushed away from the nest completely. Therefore, depending on the group dynamic, they may only lay 7-10 eggs to achieve a full nest. In the case that there is only one female it is possible that the female keeps laying eggs until she fills the nest with her 20 eggs.
TL;DR about 7-10 eggs in the wild but more than 100 in perfect farm conditions
What do you do with the ostrich eggs at the zoo?
Unfertilized eggs have a few different uses. When appropriate they can be used for enrichment for the animals. This can’t be frequent though because it is a lot of egg for any animal (imagine the cholesterol!).
Most other unfertilized eggs can be used for educational purposes. We can let people feel and hold them to truly appreciate their size, but we have to take a few steps before we can do that. First and foremost, we are not interested in holding a rotten egg the size of a bowling ball. No one wins there. So, we remove the insides and wash the egg in a process aptly called “blowing out”. This is an age-old practice where you put a hole in either side of the egg, break all the membranes, and then blow the insides out the bottom. With just the shell we can easily pass the eggs around a group of kids to look and learn.
Of course, by drilling holes in the egg and compromising its structural integrity, it is not as strong as a freshly laid egg. However, if the egg does happen to break then it’s not as much of a disaster to clean up either!
Traditionally, ostrich eggs are also used as decorations. This year we are hosting our very own egg decorating sessions for Easter. They will all be blown out of course, but we will have acrylic paints, stencils, and various tools available to help you translate your creativity. While there is a fee associated with booking this experience, all proceeds will be used to purchase a new enrichment toy for the animals.
While we have many different ways to enrich the animals at the zoo, durable and animal safe toys can be hard to keep in stock when grizzly bears, hippos, and jaguars are involved. Especially when the bears and hippos have ponds to sink their toys in and jaguars evolved to crush tortoise shells. Since even the most durable toys only last so long we want to directly translate your love, support, and fun energy into some special toys that may or may not last more than a week!
If you would like to book your own egg painting session, please follow the link to our zoo store.
If we missed your question or you’re looking for more opportunities to engage with the animals at the zoo, feel free to check out our website and stay tuned for more activities here and on our social media!
Please note that we do not sell ostrich eggs or any other animal product. Doing so would contribute to the illegal sale of animal products and the exploitation of animals. The ostrich eggs collected and prepared for this event were unfertilized, had no other use in the zoo, and would have otherwise been discarded.
References
Kiwi facts
https://savethekiwi.nz/about-kiwi/kiwi-facts/enormous-egg/#:~:text=By%20comparison%2C%20the%20kiwi%20egg,100%20eggs%20in%20her%20lifetime.
https://www.audubon.org/news/why-kiwis-egg-so-big
Egg laying
https://www.americanostrichfarms.com/blogs/news/all-about-ostrich-eggs-and-what-you-can-do-with-them#:~:text=An%20ostrich%20hen%20can%20lay,2%20pounds%20of%20egg%20protein.
https://www.pbs.org/wnet/nature/blog/ostrich-fact-sheet/
https://earthlife.net/how-often-ostriches-lay-eggs/
Egg composition and strength
https://royalsocietypublishing.org/doi/10.1098/rsif.2016.0804
https://pubmed.ncbi.nlm.nih.gov/12964622/#:~:text=Average%20shell%20thickness%20ranged%20from,23.3%20and%2019.6%25%2C%20respectively.
