Birds defend themselves in many ways, including gathering in large groups or flocks. In a group, all of the birds keep watch for predators, and any bird that spots potential danger sounds an alarm. Individual birds foraging for food also signal the flock when they find a good food source.
To protect themselves from cold, many birds consume large amounts of food. However, eating puts them in a stationary position in which they are vulnerable to predators, so they frequently scan their environment as they eat. During the winter months, birds instinctively regulate their intake to maintain a body mass that protects them from the cold while still allowing them to escape quickly when danger appears.
Another way birds protect themselves is to fluff up their feathers to stay warm. Birds of the order Passeriformes, which make up over half of all bird species, have downy coats that trap body heat, while their outer feathers protect them from wind and cold. Alternatively, some birds, including kinglets and chickadees, drop their body temperatures in response to extreme cold, entering a state of controlled hibernation when temperatures dip overnight.
Birds also seek shelter to hide from predators and protect themselves from the elements. They roost in tree holes in trees or eaves, and even tunnel into the snow, often choosing hiding places that match their coloring as a form of camouflage. Additionally, songbirds seem to protect and defend their territory and foraging grounds by singing, despite the fact that making noise leaves them vulnerable to attack.