There is no reason it couldn't evolve, but what are its limitations and niche? ---------------------------------------------------- The bird would almost certainly be **flightless**. Flight is precluded because in order for the armor to be effective it has to be strong, and dense. Stronger armor means heavier scales, and heavier scales means flight will be increasingly difficult to accomodate. This is kind of a one or the other scenario. In order for the scales to effective the flight part of this animal has to be sacrificed. If we aim for a middle ground of keeping both adaptions then neither adaption (flight, or armor) will be effective. In the scenario of having both adaptions, evolutionary pressure would probably favor reverting back to flight since it is a smaller change. See [Occam's razor][1]. This bird's wings would probably be [vestigial][2] and destined to disappear. This is because the wings would serve no practical purpose anymore, except perhaps as implements with which to manipulate objects. Since this is a flightless armored bird, the most obvious niche for it to fill is that of other flightless birds like the [chicken][3], or [Cassowary][4]. However something that has evolved the necessity for armor plating must also have an overwhelming **threat** from **predators** that would make the other two types of morphology unfeasible. Otherwise the adaption would never evolve because presumably these other two morphologies are easier to reach. All these factors will shape its [niche][5]. I surmise that you will find this kind of bird somewhere isolated, where predators are highly prevalent. It will occupy a space that other birds cant because they are killed too often for a population to survive in that place. However in this niche the armored plates of our new breed of bird will protect it from these threats. In this space, the armored bird may be the only bird around, and less armored variants struggle; otherwise the evolutionary pressure will be to lose the armor. One suitable habitat is an island infested with cats and leopards, and snakes, and bird eating spiders, and so on. Heavy armor is a necessity, rather than a luxury. This species can be [endemic][6] to that island, and so be found no where else on the planet. **Edit #1:** Isolated islands are a good contender for exotic adaptions like armored birds for the following reasons. The space is often limited; [Competition][7] is very high; and escaping unfavorable circumstances by looking for new habitats is not always possible. These limitations can lead to an [Evolutionary Arms Race][9], which is one possible cause of a highly specialized adaption like armor. In an **Evolutionary Arms Race** a predator evolves to hunt its prey more effectively, and its prey evolves survive more effectively in response. As a basic example, a predator that evolves to be faster in order to catch its prey may cause the prey, in order to survive, to evolve to be even faster to escape. Now that the prey is faster, the predator now again evolves to be even faster to catch this even faster prey. Then the prey evolves again to be faster and escape, and so on. This goes on and on in a loop until eventually both the predator and prey are absurdly and implausibly fast. Far beyond what we would expect under normal circumstances. In this way an Evolutionary Arms Race can lead to wildly exaggerated traits like very heavy armor and defense mechanisms on a bird. One real world example of an Evolutionary Arms race is this [toxic newt][10]. An isolated island is a good contender for this situation because resources are limited. The only prey available to this island's predators may be this one bird. So both species may get locked into a race that neither can escape until one species has been wiped out. For example leopards on our island may get better at cracking armor, and our armored bird may get thicker and thicker armor and or get better at killing predators. Rinse and repeat until you reach your desired level of evolution. **Edit #2:** *[RonJohn][11] makes an excellent point about the evolution of natural armors in the comments, that I would like to highlight here:* > Note … that feathers just can't evolve into armored scales unless > there's an evolutionary path. ... there is a reasonable path from feathers -- > made of keratin -- to armor made of keratin just like the [pangolin][12]. > You just need more of the same thing packed/woven closer together. [1]: https://en.wikipedia.org/wiki/Occam%27s_razor [2]: https://en.wikipedia.org/wiki/Vestigiality [3]: https://en.wikipedia.org/wiki/Red_junglefowl [4]: https://en.wikipedia.org/wiki/Cassowary [5]: https://en.wikipedia.org/wiki/Ecological_niche [6]: https://en.wikipedia.org/wiki/Endemism [7]: https://en.wikipedia.org/wiki/Competition_(biology) [8]: https://en.wikipedia.org/wiki/Red_Queen_hypothesis [9]: https://en.wikipedia.org/wiki/Evolutionary_arms_race [10]: http://www.pbs.org/wgbh/evolution/library/01/3/l_013_07.html [11]: https://worldbuilding.stackexchange.com/users/8068/ronjohn [12]: https://en.wikipedia.org/wiki/Pangolin