Externally, birds are bilaterally symmetrical. This means that you can cut a bird in half, left and right, and you'll have one wing, one eye, and one foot one each side. Internally however, birds are asymmetrical like humans, meaning they only have one heart or other internal organs. Birds reproduce sexually, with females contributing eggs and males contributing sperm. Interestingly enough, female birds have heterozygous sex-determining chromosomes, which is the opposite of humans where males exhibit this behavior. Birds also lay eggs instead of birthing live young. These organisms acquire oxygen through a circulatory system that includes lungs and a heart, similar to humans. Birds can also be omnivores, herbivores, or carnivores depending on the species. However, all birds lack teeth, and have to either use their beak to break down their food externally or swallow it whole and rely on some of the unique parts of their digestive system (like the gizzard, which grinds up food into smaller pieces) to break down food, absorb nutrients, and flush out waste. Birds are also warm-blooded, which means they regulate their own temperature. Their feathers as well as internal air sacs they have help them to keep a constant temperature.
Further Reading: Birds in Biology Reference
Further Reading: The Symmetry of Birds Emerges as the Expression of an Uninterrupted Atomic Order
Further Reading: Birds in Biology Reference
Further Reading: The Symmetry of Birds Emerges as the Expression of an Uninterrupted Atomic Order