BIRDS STRIKE PLANES?

Why are birds numbers increasing on strikes on airplanes .Is it man ignoring the birds mitigation habits?arnithologists    are baffled .The most common birds to strike planes  are-HERRING GULLS,SKYLARKS,WOOD PIGEONS ,COMMON GULL ,SWIFT,SWALLOW.A study in AMERCIA showed that nearly half of bird strikes happen shortly before landing or just after takeoff.