Birds are forgetting singing

 It is habitual of birds to singing. But Now a days a research have been published that a specific types of birds are forgetting singing. They do not tends to sing. 

What should be cause of forgetting of singing. Previous research explored the cause of singing of bird for colonization. Birds usually, occupied the region by singing. Birds song usually signals other birds the region is occupied by other birds.

That restricts other birds to enter in this region. Birds singing basically a colonizing behaviour of birds. 

Forgetting singing may be birds becoming more social. It may be for the region that it have not any obligation of entering other birds in this area.