India, Nov. 9 -- Like people, birds have fewer friends as they age, but the reasons why are unclear. New research suggests they may just have no drive to.

In humans, it's often been assumed that older people have fewer friends because they're pickier about who they spend their time with. There's also the issue that there are fewer people of their own age around.

Combined with fewer same-age potential friends available, this could be a factor in the loneliness crisis among older peopleDr Julia Schroeder

But it's hard to pick apart the various potential causes for humans, so researchers have turned to animals. The team behind the new research, led by Imperial College London, studied an isolated population of sparrows on the island of Lun...