Female birds can lay up to 2 to 3 eggs. They usually lay their eggs in spring.
Birds get most of their water from food. Water is available to small birds at shallow edges of ponds or streams.
Birds most form of individual variation is the the sexual age or seasonal variation.
Birds bones are really hollow, so it makes these birds light weighted which make them adapt to flying. Also long feathers on the wings and tail make the birds balance and steer. That also helps the birds by protecting them from ultra rays.
Birds may go to different places and start a new type of bird population.That is kind of why we have different type of bird species.