The dots that can be seen on baby birds’ mouths are called egg teeth. Egg teeth are small, hard, pointy bumps that form on the tip of a baby bird’s beak while it is still developing inside the egg. The egg tooth helps the baby bird chip away at the eggshell from the inside, allowing it to break out once it is fully developed.
What are egg teeth made of?
Egg teeth are made of keratin, the same material that makes up human fingernails, bird claws, and horns on animals. Keratin is very tough and durable, perfect for allowing a weak baby bird to break open its hard eggshell. However, egg teeth are only temporary – once the bird has hatched, the egg tooth falls off within days or weeks, as it is no longer needed.
When do egg teeth form?
Egg teeth start to form 2-3 days before the baby bird is ready to hatch. At this stage in development, the beak has hardened and the egg tooth starts growing as a small bulge or protuberance. Just before hatching, the egg tooth lengthens into a sharp point. The timing of the egg tooth’s formation and hardening ensures that it is ready to help the baby bird emerge from its shell right when needed.
How do egg teeth help baby birds hatch?
Egg teeth give baby birds the crucial advantage they need to break out of the egg. Here’s how they work:
- The egg tooth forms a small, hardened spike on the upper mandible (top beak) or both mandibles.
- Inside the egg, the baby bird repeatedly rubs its egg tooth against the inside of the eggshell, scraping away at it.
- The scraping motion creates small cracks and weaknesses in the shell.
- Eventually, the baby bird creates a small hole in the eggshell and continues to chip away around it to enlarge the opening.
- Finally, the hole becomes big enough for the baby bird to fully emerge from the cracked eggshell.
Without the egg tooth, baby birds would have a very difficult time breaking out of the egg on their own. Their beaks and claws are still soft and weak at this stage, useless for piercing the hard shell. But the egg tooth gives them just enough sharp force concentrated on one point to break free.
Do all baby birds have egg teeth?
The vast majority of baby birds hatch with the help of an egg tooth. However, there are a few exceptions:
- Baby megapodes (brush turkeys and mound builders) do not have egg teeth. Their parents bury the eggs and incubate them in composting vegetation, so the babies do not have to break out of a hard shell.
- Baby hoatzins of South America have claws on their wings which they use to break open the shell. They lack an egg tooth.
- Some songbirds, like crows and sparrows, hatch with an egg tooth on the top mandible only.
So while egg teeth are nearly universal in baby birds, a few species have adapted alternate strategies due to their unique nesting behaviors.
When does the egg tooth fall off?
Egg teeth are temporary structures that fall off once a baby bird has hatched. The egg tooth starts detaching within days or up to 2 weeks after hatching. The small keratin spike dries out and ultimately flakes off, leaving no trace behind on the beak.
Several factors determine how quickly the egg tooth disappears:
- Species – Egg teeth may persist longer in some species. For example, they may last 2 weeks in passerines but only 4-5 days in doves and pigeons.
- Diet – Baby birds that need to pick up food items may shed the egg tooth faster than birds fed by regurgitation.
- Hatching assistance – An egg tooth may fall off sooner if the baby bird received help emerging from the shell by a parent.
- Beak abrasion – Natural abrasion from pecking and exploring causes the dried egg tooth to shed.
Once the egg tooth drops off, it leaves behind a clean, normal beak surface with no scar or mark to indicate it was there.
Do egg teeth grow back later in life?
Egg teeth are only present in baby birds before hatching. Once the egg tooth drops off after hatching, it is gone for good – egg teeth do not regrow or reform at any later point in the bird’s life.
Egg teeth are strictly embryonic features needed for the singular task of escaping the eggshell. They serve no purpose afterward. Adult birds have hardened, fully-formed beaks and can easily crack open seeds, nuts, and prey without the need for an egg tooth.
Conclusion
Egg teeth are a remarkable adaption that gives developing baby birds the tool they need to break out of the egg and enter the world. The small keratin spike forms right before hatching and then falls off soon after, having served its purpose. While not all species use egg teeth, they are incredibly common across the avian world as a strategy to overcome the challenges of emerging from a hard-shelled egg.
Fun facts about egg teeth
- Egg teeth are found in every major group of birds, from hummingbirds to ostriches. They have evolved independently in many lineages.
- Reptiles such as snakes, lizards, turtles, crocodiles, and dinosaurs also hatch with an egg tooth that falls off afterward.
- Bird embryos start pecking from inside the egg days before hatching, exercising and sharpening the egg tooth.
- Species without egg teeth tend to have thin or soft eggshells that are easier to break.
- Emus have the most complex egg tooth, with 3-4 points for breaking through their extremely thick eggshell.
- The egg tooth forms even in birds that are hatched by humans via artificial incubation.
- Scientists can often identify bird fossils as baby birds if they have an intact egg tooth impression.
Egg tooth structure
Egg teeth have a simple conical shape, but may have some varied features between bird species:
| Feature | Details |
|---|---|
| Location | Upper mandible tip. Sometimes on both mandible tips or lower only. |
| Size | 0.5-2 mm long |
| Shape | Sharp point or cone |
| Texture | Smooth and glossy |
| Color | White or pale yellow |
| Composition | Solid keratin |
The egg tooth’s small size belies its incredible strength – that tiny keratin spike can consistently pierce through calcium carbonate shells!
Stages of egg tooth development
Egg teeth form rapidly in the final days before hatching. Their growth can be divided into three main stages:
- Initiation – Thickening of the epithelium at the upper mandible tip.
- Formation – Keratin is deposited to create the solid egg tooth point.
- Maturation – The egg tooth lengthens and hardens into its sharp, functional form.
This entire process takes only 48-72 hours. The egg tooth ruptures from the beak 24-36 hours before hatching begins. The whole developmental timeline ensures the egg tooth is hardened and ready to use just as the baby bird prepares to break free.
Behavioral development of egg teeth
Baby birds don’t hatch with robust pecking instincts – they have to practice and refine the motions needed to use the egg tooth effectively:
- Early pecks are gentle taps that gradually strengthen.
- Pecking aims at creating fractures instead of piercing through.
- The frequency and forcefulness of pecking increases close to hatching.
- Pecks become more accurate and targeted at weak points.
- The egg tooth slightly enlarges from repeated abrasion inside the shell.
This important period of activity starts as early as day 13 and continues until the shell finally cracks. The practice ensures the hatchling can efficiently break out of the egg when the time comes.
Role of the egg tooth in hatching
While baby birds use their egg teeth to pip the eggshell, hatching requires more than just the egg tooth alone. Other factors that allow the hatchling to fully emerge include:
- Hatching muscle – Bands of muscle that allow the bird to repeatedly strike the shell.
- Yolk sac – Provides nutrition needed for the strenuous process.
- Allantois – The waste sac provides room for the hatchling to move around.
- Hatching enzymes – Weaken the membranes and shell from inside.
- Hatching fluids – Cushion and lubricate the hatchling.
While not solely responsible, the egg tooth clearly plays an indispensable role. Without it, the embryo would be unable to gain that initial exit point from the egg despite its other adaptations.
Egg tooth growth across bird families
Egg teeth are widespread across modern birds, but their size and positioning can vary among taxonomic families:
| Bird Family | Egg Tooth Location | Relative Size |
|---|---|---|
| Finches | Upper mandible tip | Small |
| Pigeons | Both mandible tips | Small |
| Parrots | Upper mandible tip | Medium |
| Game birds | Upper mandible tip | Medium |
| Raptors | Upper mandible tip | Medium-large |
| Ratites | Both mandible tips | Large |
The egg tooth is largest and most robust in ratites like ostriches and emus due to their extremely thick shells. But its position at the mandible tip is nearly universal across species.
Fossil egg teeth
Egg teeth are present in not just modern birds, but also their dinosaur ancestors. Some key discoveries related to fossil egg teeth include:
- The first fossil egg tooth was identified in 1924 in a juvenile Protoceratops skull.
- Fossilized remains of perinate Oviraptor specimens clearly show an egg tooth.
- Impressions of egg teeth are found in baby dinosaur fossils too young to have hatched.
- Dinosaur egg tooth size varies from under 1 mm up to 2-3 mm.
- Fossilized dinosaur embryos are found with heads oriented toward the shells, egg tooth end poised.
These fossil discoveries prove that theropod dinosaurs, as the ancestors of modern birds, utilized egg teeth to break out of eggs just like today’s bird hatchlings.
Egg tooth abnormalities and issues
While egg teeth are a reliable evolutionary adaption, abnormalities can occur that inhibit their function:
- Double egg tooth – Extra egg tooth forms, often weaker.
- Misaligned egg tooth – Points away from optimal pecking angle.
- Fractured egg tooth – Cracks under force, rendering it unusable.
- Detached egg tooth – Partial separation from the beak.
- Microrhinus – Embryonic underdevelopment of the beak and egg tooth.
Physical damage or poor positioning reduces efficiency of the egg tooth. This can prolong the hatching process or even prevent the chick from emerging without assistance.
Assisted hatching
In rare cases where the egg tooth is abnormal, human assistance helps the baby bird successfully break out of its shell. Assisted hatching techniques include:
- Carefully prying the shell apart using fingers.
- Gently cracking the shell using tools like tweezers or a toothpick.
- Widening a pip hole initiated by the trapped hatchling.
- Moistening the shell to soften it prior to pecking.
- Removing shell fragments as the bird slowly advances.
With human help compensating for egg tooth deficiencies, chicks that would normally die in the egg can fully hatch and survive. However, the egg tooth adaption remains crucial for wild birds hatching naturally.
Egg tooth myths and misconceptions
Despite their small size, egg teeth generate some inaccurate assumptions and myths:
| Myth | Fact |
|---|---|
| Egg teeth are used to poke breathing holes. | They only hatch breakout holes. |
| Birds have extra teeth as hatchlings. | Egg teeth are not true teeth. |
| Egg teeth appear at adulthood. | Only embryos and hatchlings have them. |
| Egg teeth enable feeding after hatching. | They detach soon after hatching. |
| Egg teeth are as hard as true teeth. | Keratin is softer than dental enamel. |
While egg teeth are interesting structures, it’s important to separate facts from fiction when discussing their true nature and purpose.
Why do some birds lack egg teeth?
A small number of bird species manage to hatch without employing egg teeth. Reasons this is possible include:
- Thin, flexible shell requires less force to puncture
- Parent partially cracks shell before chick hatches
- Specialized claws, beaks or other tools compensate
- Chick has wing claws to help break shell
- Parent directly assists chick in emerging
However, most species do require egg teeth to reliably hatch. The adaption provides a fail-safe method that ensures the chick can escape the hardened eggshell when the time comes.
Conclusion
Egg teeth are a remarkable evolutionary adaption seen in nearly every bird species on earth as well as their dinosaur ancestors. These transient embryonic structures give developing chicks the means to break out of the hard eggshell and take their first breaths. While egg teeth naturally fall off soon after hatching, they provide a crucial boost during that critical transition from life inside the egg to survival in the outside world.
