Earth is home to more than 9,000 different species of birds. Birds are warm-blooded, feathered animals of many shapes, sizes, and colors. Some birds live in large groups called flocks. They spend their entire lives with lots of other birds. Other species are solitary. They rarely interact with members of their species. Most birds can fly, and they rank as the most skilled fliers in the animal kingdom. Being warm-blooded has helped birds adapt and spread to many kinds of environments. Today, birds are found on every continent on Earth - even Antarctica where penguins live happily in temperatures that drop as low as -35°C.