A large wild dog that roams Greenvale between 0:00 and 07:00. They drop from the sky and viciously attack intruders that enter their territory. During the day these dogs are much smaller and harmless you see them standing near the bone locations.
Strategy
These dogs are tough to take down with normal weapons but it is possible if you have a lot of time and ammo. The best advice is to just not engage in combat with one and run away. If York is in his car be sure to swerve to avoid them when they drop down into the road as hitting them will make the car take damage.
If you really want to take out one of these I suggest waiting until you have the RPG as one shot will kill them!