I was wondering if a full aquatic bird could exist and not be on, or return to land at any developmental stage, basically, to be completely independent of land. I already know that there are some aquatic animals that can rest one side of their brain at a time, making sleep not an issue, but I can not figure out the rest:

  • Figuring out a way to explain how a bird could evolve to be completely independent from land. The best story I can come up with is that the birds evolve into the early stages of a terrestrial bird, but then that area became flooded. However, I doubt such a scenario is realistic, and it would then be easier for the to evolve into a crane or stork-like creature.

  • I am not sure what would change in their lungs that would accommodate them being submerged for such long amounts of time. More specifically, what would have to happen to keep their lungs from collapsing at great depths?

  • Also, I'm worried about the first stages of life. Perhaps carrying its eggs in its mouth like a grouper?

  • Finally, I'd prefer the bird to have some sort of mechanisms that might allow them to communicate under water , like dolphin whistles. But I cannot create a viable explanation for their nostrils moving all the away atop their heads

Any help would be greatly appreciated. Thank you

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    $\begingroup$ Note that birds, with their "hollow" bones, are very light-weight and buoyant. Imagine a duck floating in a lake; hardly any of it is submerged. You'll probably want to consider weighing them down more too, with "solid" rather than "hollow" bones. $\endgroup$ Feb 19, 2016 at 23:42
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    $\begingroup$ @BrettFromLA Most flightless birds, including penguins, have lost their hollow bones to evolution, as have diving birds like the cormorant. $\endgroup$
    – ckersch
    Feb 19, 2016 at 23:51
  • $\begingroup$ @ckersch Great point. I started envisioning penguins diving in the ocean when I was about halfway through my comment. $\endgroup$ Feb 19, 2016 at 23:54
  • $\begingroup$ When you say "bird", does this mean that you want it to fly? Or do penguinoids count? $\endgroup$ Feb 20, 2016 at 6:38
  • $\begingroup$ bird lungs don't work like mammal lungs, collapsing is not an issue. $\endgroup$
    – John
    Apr 16, 2018 at 21:12

3 Answers 3


The entirety of this problem is related to egg laying and early development of chicks, so a few things need to happen:

  1. Penguins (or similar, but penguins make the most sense) need to be born with adult feathers and/or blubber layers so that the chicks can survive in the water. Even tropical ocean temperatures are dangerous to warm blooded animals who are exposed and unprotected for long periods of time. As an alternative, the penguins' core body temperature could drop by 20°C or so and the bird could be restricted to the tropics, but that seems a bit much. The whale route is a possibility here as well, with both babies and adults losing their feathers entirely, but penguins rely heavily on their feathers creating an insulating layer between the water and their skin.
  2. The bird must evolve live birth. Shelled eggs have undergone massive amounts of evolution to function on dry land; getting a shelled egg to work underwater again would not be trivial. All sea dwelling members of formerly land-based vertebrates either give birth to live young (cetaceans, manatees, and some sea snakes) or are forced to return to land to lay eggs/have babies unsuited for ocean life (sea turtles, crocodilians, the rest of the sea snakes, flighted sea birds, penguins, and pinnipeds.) It's a lot easier to have the egg hatch out internally (or more realistically, fail to form/lay normally and continue developing without a shell internally.)
  3. For deeper diving penguins (not at all a necessity for permanent life in the water, just ask the boto) you would need greater lung capacity and perhaps larger overall size, though king penguins can already get down to 300m or so, which is comparable to dolphins. The animal's blood would also have to be vastly enriched in its oxygen carrying capacity. True deep divers like sperm whales have adaptations to prevent the bends as well as lungs that absolutely do collapse under pressure. Trying to design a biological pressure vessel that wouldn't collapse is probably a bad plan.
  4. Underwater communication - Penguins may already do this. Early tests of little penguins at the Perth Zoo were not positive, but the zoo is not a natural environment. Further, it is not at all unreasonable for penguins to evolve underwater communication. They're extremely vocal above water. Dolphin/whale blowholes are for breathing, not for vocalization. They vocalize using "lips" that are located internally, near their blowholes, but they don't blow out air when they vocalize, so you could put the nostrils/air inlet wherever you like. As far as the nostrils moving up the head for breathing purposes, that's not that big a stretch, though behind-the-head whale nostrils are pretty impressive.
  5. Regarding prey: There is something to eat at most any reasonable depth you might want your bird to inhabit. It would require a change of diet, but an unexploited food source is an enormous evolutionary driver.
  • $\begingroup$ live birth with shelled eggs is far more difficult than with normal eggs, the shell will not allow gas exchange while wet, so they need to loose shelled eggs entirely. underwater laying is just impossible otherwise one of the dozens of different marine reptiles lineages would have stumbled on it by now. $\endgroup$
    – John
    Apr 16, 2018 at 21:10
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    $\begingroup$ @John Indeed, that was my point 2. Either some sort of internal shelled birth (with a coevolved placenta-type organ?) would have to occur, or more likely, a live birth in which the egg developed internally without ever having formed a shell, never having separated from the mother. A third option would be a tough egg case instead of a calcified shell, like the cases from several species of shark. $\endgroup$ Apr 17, 2018 at 11:00
  • $\begingroup$ aquatic eggs just won't work, ammniotic species don't have the right oxygen carrying molecules or the right osmotic balance for eggs to survive underwater, bird eggs in particular are even less suitable with their strange gas exchange system. Eggs are always separate from the mother what you mean is ovovivipary holding the eggs internally, whether this is possible for birds is not know, they are the only group of vertebrates to not develop it, but it would definitely require the loss of the hard eggshell since it would prevent gas exchange when wet. $\endgroup$
    – John
    Apr 17, 2018 at 19:37
  • $\begingroup$ live birth and ovovivipary both would require the loss of the hard egg shells since it will not allow gas exchange while wet, which it would have to be while internal. $\endgroup$
    – John
    Apr 17, 2018 at 19:52
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    $\begingroup$ @John I've made it clear both in my answer and comments that bird eggs as they currently exist are not suitable for an underwater species, but for some reason you seem to want to argue against eggs in their current form, either underwater or internal, which I never proposed. In any case, you appear to feel strongly about this, and I would politely encourage you to offer an answer to the question that more fully addresses your concern. $\endgroup$ Apr 18, 2018 at 2:11

Start with a highly water-adapted bird

Namely, a penguin. These are birds that can spend long periods of time in the ocean without really needing to return to land except to breed and molt. Of course, a large portion of the reason that penguins return to land to do these things is that the land is safer for chicks where most penguins live. To get around that...

Throw in some dangerous land predators, and get rid of most of the water ones.

For penguins living in an area like the Antarctic, all of their worries live in the sea. Orcas, sharks, and leopard seals will happily snack on a wayward young penguin. Meanwhile, there are no terrestrial predators for many adult penguins, with only a few birds like petrels and skuas that might prey on their young.

Because of this, penguins don't have a strong motivation for going fully aquatic. However, if they lived in an environment that underwent catastrophic warming, killing of many of the large predators in the ocean and opening the land up to creatures like cats and wolves, penguins who spend most of their lives in the ocean would be at an advantage.

If some of the penguins build floating aquatic nests, this could further protect their young from land predators. There are already some birds that do this, like grebes, who build nests on top of floating aquatic vegetation. Penguins could evolve to build similar nests made up of buoyant kelp species. Unlike mammals, penguins don't know exactly when their eggs will hatch, so it's unlikely that they would evolve to lay eggs under water, since it would be difficult to bring chicks to the surface to breathe, even if they were fully aquatic.

Add a few million years of evolution

Without a strong need to return to land, sea-nesting penguins would slowly lose their adaptations for doing so. Feet and legs would lose their ability to bear the penguin's weight, and penguins would slowly lose and replace their feathers like most other birds instead of undergoing a single molt.

  • $\begingroup$ Read "After Man". This is they hypothetical evolution of the "Porpin" which evolves to fill the niches vacated after some unspecified disaster removes Homo Sapiens and many of the larger apex creatures form the ecosystems. $\endgroup$
    – Thucydides
    Feb 20, 2016 at 3:22

You already have the perfect example, and you mentioned it in your post. Dolphins and whales are mammals that did exactly that.

We already have a lot of sea-adapted birds, including flightless ones like penguins. All they need to do is continue that adaptation a little further so that they lay their eggs underwater and the other adaptations you suggest such as moving nostrils higher would be a natural evolutionary development with a more aquatic lifestyle. Moving the nostrils isn't needed to produce whistles underwater anyway.

The diving birds already prevent their lungs from collapsing so no further development is needed there.

  • $\begingroup$ the issue is that these bird can't go up to, say 1000 ft beneath the surface. as their prey tends not to live that deep under the sea $\endgroup$
    – user15036
    Feb 20, 2016 at 0:05
  • $\begingroup$ Adapting (re-adapting) the eggs to work underwater is a major issue. You trivialize it and mention it in passing, but really it's a dealbreaker. $\endgroup$
    – JDługosz
    Feb 20, 2016 at 3:20

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