Air carrier Captain reported performing a high speed rejected takeoff after seeing a large flock of birds on the runway. The Captain taxied back to the gate where 2 main gear fuse plugs failed and the tires flattened. The post flight inspection did not reveal an indication of a bird strike on the aircraft.

Narrative

Taxiing out at ZZZ; everything was normal. Reaching the runway we were cleared to take off ahead of Aircraft Y holding short stating they needed a few minutes. After 100 knots I realized there was a large flock of birds on the runway; and made the decision; at approximately 110-120 knots; to reject the takeoff. After the First Officer had already informed the tower that we were rejecting the takeoff; I heard them clear Aircraft Y for take off; so I felt pressure to clear the runway and come to a stop; as we were clearing the runway tower again clear Aircraft Y to takeoff and they declined the clearance; wanting to know the status of the birds that we had narrowly missed; though at that time we were still unsure. After coordinating with ops; maintenance; and dispatch; we proceeded back to the gate for a maintenance check as the brake temperatures peaked on our screen around 750-760 deg C. Airport operations stated that they did not see any birds from a strike on or near the runway and that was confirmed when we arrived to the gate that we did not hit any after inspection; though 2 fuse plugs had blown; both outer main landing gear wheels were flat; numbers 1 and 4. I spoke with the Chief Pilot on Duty; they did not [discuss fitness to fly procedures]; nor discuss the duty time issues if we were to try and operate the flight again. They simply asked if everyone was okay; and if we needed anything to let them know.