A quick note: the science of egg development and hatching is extremely complex, and can vary quite a bit between the over 10,000 species of birds. I am simplifying many things to the basics, here, and the information is specific to emus – which hatch mechanically differently than many other birds. For instance, many birds have an ‘egg tooth’ (a sharp, horny growth on the beak that falls off soon after hatching) with which they ‘unzip’ or score a cut in the egg, then kick with both legs together to break the shell in half. Emus lack an egg tooth and have more of a ‘bull in a china shop’ approach to hatching, kicking and flailing to create a random crack in the thick shell. So take all this with a grain of salt, and if you’re interested, I’ll include some links for more reading at the end, if you’d like to know more about the science behind hatching eggs!
If you haven’t read my first article about the laying and incubation process of emu eggs, you can find it here: https://www.patreon.com/posts/everything-you-33013429
Eggs are pretty magical! An emu egg self-contains all the nutrients necessary for an embryo to go from almost nothing (a tiny clump of cells) into a feathered, breathing, walking, whole baby emu in less than two months time!
Every animal needs oxygen to live, and a chick growing inside an egg is no exception. Animals that grow inside their mothers get oxygen directly from their mom, through their bloodstream, connected via umbilical cord. They basically use their mother’s lungs to breathe until they can use their own. How does this work in an egg?
Inside an egg, through layers of membranes, is an air cell which allows the developing chick to breathe. This air cell must be replenished with oxygen (and get rid of carbon dioxide), which is done through thousands of pores in the eggshell itself. Those tiny pores in the egg also let sound through, so as soon as hearing has developed the chick can ‘hear’ its parent, who calls to it frequently. Studies have shown that developing eggs can also hear their neighbors, as well as feel their movements, so they bond with their siblings and parent while still in the shell! This also helps them synchronize their hatching as a group.
(Image credit: By KDS4444 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=59073031)
More sciencey tidbits: A network of blood vessels (called vitelline vessels) form over the surface of the egg yolk, inside the egg, connecting the growing baby to its food source. These blood vessels allow the embryo to get nutrition as well as ‘breathe’ – using the air cell and oxygen that diffuses through the egg albumin (egg ‘white’) to reach the blood vessels. Very quickly the chick needs more oxygen than this network of blood vessels can provide, so it develops another system (the allantois) through its hindgut and ‘breathes through its belly’. As this system expands it presses against the egg shell, allowing it to access outside air through the shell pores. I know I said I would keep this simple, but it’s a far from simple process!
Basically – the chick breathes through the egg shell, and its increasing need for air is important to various developmental stages and eventually, hatching.
So what happens when an egg is ready to hatch?
Right before hatching, the final stages of development happen quite quickly and the chick starts needing more oxygen than its current systems can provide. This creates a buildup of CO2, which causes involuntary muscle twitching, allowing the chick to break through the membranes, or ‘pip’ into the egg’s air cell. At this point they can be heard peeping inside the egg, and the clock starts ticking. They have about 72 hours worth of air left in that cell.
It is natural that people would want to help, to break the shell themselves and give the baby air. Doing that, though, generally causes more harm than good. This stressful hatching process looks like a struggle – and it is – but it is important to the health, development, and strengthening of the baby bird’s lungs, muscles, and circulatory system. CO2 buildup in the air cell causes the muscle spasms and kicking necessary for the baby to finish its development and be strong enough to survive outside the egg.
During these critical hours, the last of the egg yolk gets absorbed into the baby’s abdomen and the rich network of active blood vessels connecting the baby to the shell surface and membranes retreats and dries up. Breaking the egg shell early can cut through these blood vessels and cause the baby to bleed to death! Making an artificial hole can stop the CO2 process, stopping the necessary kicking and weaken or kill the baby. As much as we want to help, interfering with this natural process is something that rarely helps, and often harms. There are potential situations where a chick can be successfully aided, but they are complicated and should be left only as a last resort. Often, emu chicks that are helped out of the egg fail to thrive and die within 3 months of hatching.
Usually, though, hatching happens within 24 hours of initial pipping. You can call encouragement to the eggs and they respond. They peep back, and if you hold the egg you can feel them kicking inside (or see them rolling around if they are set on a flat surface). The babies will have periods of intense kicking and peeping, then rest and sleep for a few hours, then back to a frenzy of kicking again.
Once the external eggshell is broken, the baby takes its first breaths of outside air. Now they have more time and can rest, sometimes taking days to finish the process. Some sleep and seem cautious about leaving the egg, others seem eager to be out and pop the shell off almost right away. The baby emu comes out into the world wet, tired, and a bit dazed. Very quickly, though, they dry off and try to take their first wobbly steps. Baby emus are born fully feathered, their eyes open and are able to walk and run within a day of hatching. They need to be kept warm and protected and they do not eat or drink for the first 3-4 days after hatching. They are still living off the residual yolk in their bellies, and it is important that it gets completely absorbed or it can start to rot inside them.
Baby emus must be taught to eat and drink (something the father would do, in the wild. The father takes sole care of the babies, the mother leaves after laying eggs). Chicks will instinctively peck at things, especially bright colors, so I sometimes use large marbles in the food dish to encourage the chicks to eat. Sometimes I put in a chicken chick or two, who know instinctively how to eat, and the emu chicks will follow along. Often just picking at their food with my fingers will get them to try it, and as soon as one starts eating, the others will jealously bully in and try it, too.
Baby emu legs are very delicate. I have heard them described as the ‘thoroughbred horses of the bird world’ – their legs grow at a dizzying pace. Baby emus need to be kept on non-slip surfaces to keep their legs from splaying out sideways, and great care needs to be taken to watch for and catch early issues. Some breeders will automatically put tape braces on their legs for the first few days. I only do so as needed, but every so often emus are born with genetic leg disorders which unfortunately can’t be fixed. It is important for baby emus to be able to walk, run, and grow at an incredible pace in the wild – but it makes them very vulnerable to any slight issue in leg development, unfortunately.
As the current eggs hatch, I will follow along with their development and share lots of cute baby emu photos with you! 😊
Q: Why are some babies white/brown and some are stripey?
A: The white and brown babies are a color morph called 'blonde', which is heterozygous for leucism (a white colored emu with blue eyes - different than albino). Their father, Zal, is our white emu.
Q: Can you tell the difference between the males and females?
A: Not at this age, no, not visually. They would need to be DNA sexed - there are laboratories that specialize in this. You can send a piece of the eggshell, a drop of blood (taken from a toenail) or feathers (they can get the DNA from the feather shaft) and they can tell you the gender. Otherwise, if wait until the emus are fully adults, there are differences between the sexes then. The females have a deeper, booming call and some physical differences that are usually quite obvious, but don't show up fully until they are mature (2-4 years old).
Q: What will you do with the emus? Will you keep them all?
A: No, we plan to only add one or two of these babies to our flock. We already have seven adult emus and plan to sell the extra babies to folks who want emus as pets. They need land and space to run, as well as minimum 7-8ft fencing, and the company of other emus, so we screen homes well for their ability to care for emu.
Q: Do the chicks who are already hatched help the chicks still in the eggs get out?
A: Yes and no. They don't physically help them out of the egg, but they do call back to them and peck at the eggs (or clumsily trip over them) which helps stimulate the unhatched chicks to hatch.
Q: Why are some of the eggs muddy/dirty, why don’t you wash them off?
A: Eggs are given a final layer by the hen, directly before hatching. This layer, called a cuticle or bloom, forms a natural barrier to bacterial infection. Washing the egg will damage this delicate layer and makes it more susceptible to infection. An egg which looks dirty is often more safe than if you washed it, removing its protection and driving pathogens inside the shell through the pores. For eating eggs, it is best to wash an egg immediately before eating it (if necessary) and not before it is stored. Chicken eggs purchased commercially in a store have been washed, which is why they need to be refrigerated and are more prone to contamination.
Q: Is it ok to have those eggs outside the incubator?? Chicken eggs need to be in careful lockdown during incubation!
A: Chicken eggs develop much more quickly and are far more sensitive than emu eggs, as far as their temperature and humidity needs. Emu eggs need much more air and lower humidity than chicken eggs, and there is some evidence that mild thermal shock (short temperature changes) can help with oxygen/C02 transfer in some species. A male emu would stand up, off his eggs, many times a day to turn them, exposing them to similar elements and jostling. Chicken hens are much more careful and cautious with this process.
Do you have a question? Ask it and I can try to answer it here, if I have time 😊
For kids: An eggs-pirament to do at home: How do chicks breath inside the egg https://www.scientificamerican.com/article/bring-science-home-chick-breathe-inside-shell/
The incubation of ratite eggs: http://posc.tamu.edu/wp-content/uploads/sites/20/2012/08/Incubation-of-Ratite-Eggs1.pdf
A guide to the incubation and hatching of emu eggs: https://www.backyardchickens.com/articles/emu-hatch-2013.64737/