A very common note in Italian NOTAMS for nearly every airfield I've flown into in the summer is "caution, grass cutting in operation." Never seen it!
It used to be that Schiphol was Holland's biggest farm. I don't know if it still is, but some years ago it produced mega tonnes of hay. That, and the nice wet warm runways on a damp summer's day attracted seagulls like moths, but bigger.
Water on the runway on a summer's day is common danger. Usually the flocks will launch as you are about 100-150'. Hopefully you will go under them and miss. If the wind is too strong you might collect some as they are blown towards you. They are nigh impossible to see until you are very low, and IMHO a G/A might climb you into them. It happened to me at Riga. We were the frst a/c for 30mins and the TDZ was covered in them. Invisible into the sun. I only realised it at about 50' as they launched. ATC had done a lousy job of checking the Rwy and actioning scare procedures. A comment to them, and a report to company safety committee, sadly produced the square root of f'all.