Flocks of birds seen on the runway can be lethal and the decision to abort or press on becomes a critical choice. Well below V1 is not a problem but depending on surface conditions and length of runway an abort can produce it's own hazards especially in jet aircraft.
In another life I lined up at Edinburgh RAAF, South Australia, runway. It was a long runway and there had been recent heavy rain which had cleared. I was flying a RAAF Viscount. We could see flocks of sea gulls on the runway pecking away at thousands of what seemed to be tiny worms.
We asked ATC to have the duty fire tender to squirt water at the sea gulls (after all that is how rioting crowds in some countries are dispersed). The sea gulls didn't like this too much and flocked off.
Shortly before V1 we observed a mass of sea gulls getting airborne from the grass adjoining the runway and it was clear we were going to run into them as they flew across the runway at cockpit height. We aborted the take off at the same time we felt numerous bird strikes and due to the long runway we stayed off the brakes and coasted to stop using the full length. We saw no point in risking hot brakes when excess runway was available. The ground fine position of the props was very effective at high speed.
There was hardly any damage to the aircraft despite about 25 dead seagulls being found by the fire tender crew.