Birds and mammals are warm-blooded animals because they can keep their body temperatures constant regardless of the surrounding temperatures. Birds and mammals can regulate their temperatures through different methods.
For example, in cold weather, birds can generate body heat by converting most of the foods they eat into energy. This energy helps to keep their body temperatures constant. Birds also keep warm because they have feathers. Likewise, some birds often migrate from colder to warmer areas for the winter.
Similarly, to keep body temperature constant in hot weather, birds can seek shade or a water source to cool down. Because birds do not have sweat glands like mammals, they regulate their body temperatures by panting through their mouths. Other ways they can keep cool are either to decrease their activity levels or spread their feathers to allow circulating air to reach their hot skin.