Birds placing sticks on train tracks?
There is a large population of birds that look like crows or ravens,
  yet fatter. They seem to be quite social and move around in large
  groups.


First of all, this seems like a crow. Crows are very social birds, they live in flocks or murder.


  Theory: It may be a Mating Ritual?


No! The have a very spectacular mating ritual!.


  Theory: It's Making a nest


Obviously No! Crows nests are always way hidden at 18-60 feet above ground(mostly) in the tree trunk.

My Theory

Crows are very curious birds. What you saw, might be a new play the young crows found. It's common that crows will do unusual thing when spectated by the elders and siblings.