During calving season, it's very common to see a lone cow surrounded by a bunch of the young calves sleeping or playing around her. She's babysitting the group while the calves' mothers are out grazing. Cows are very social animals. The herd has a distinct social hierarchy of dominant to submissive animals that has evolved through the eons to protect the herd from predators. Another function of a dominant hierarchy is that it allows the animals to live in social peace, without constant fighting.
Dominant animals are generally the biggest and strongest, the first to eat at the feed trough or drink at the waterer. However, they won't be the lone animal to baby-sit the calves, says Temple Grandin, Colorado State University Animal Sciences Professor, who specializes in animal handling.
"Dominant animals are the first to get a limited resource, but they aren't leaders within a cow herd. Dominant animals will go to the middle of a herd if danger threatens," says Grandin.
The "babysitters" are usually cows that rank lower than the dominant individuals, but are often leaders. They may be more curious or social and like to get out front and lead. Leaders will take risks and are better suited to protect subordinates such as calves.
"Cows take turns 'babysitting' so individuals can maintain good condition and conception rates," says Grandin. This behavior is not unique to cattle. Many herd communities share day care responsibilities including wild pigs.