The House Crow (Corvus splendens) is native to the Indian Subcontinent but has been introduced to various countries including Oman. 
Although it is usually described as an entirely black bird, it has a greyish collar. 
These birds are often observed in flocks around urban areas.

1st & 2nd photo: Salalah Beach, Dhofar Region, Oman, 2 February 2017
3rd photo: Raysut Waste Disposal Site, Dhofar Region, Oman, 5 February 2017