There was no requirement of 250 below 10000 in those days and no TAA or Ansett DC-9 to my knowledge had a windscreen taken out by a bird. However at about that time , I recall tragically, there was an F-111 that was and of course recent events have proved how aircraft and birds don't mix. To be honest, I thought the 250 below 10000 was imported from the US as an ATC measure to process traffic. Never thought of it in bird impact terms - you never stop learning in this game. Of course no sensible bird would have been up flying in the fog...... and in those days "poltically correct risk assesment" was in the future...