Also in the early summer months the airport policy was always to let the grass grow between the runways for harvesting in August, its this long grass that birds apparently like, and which also causes problems in the Spring/Summer but not the autumn/winter when the grass is short.
The grass is kept short nowadays, and the roosting birds possibly are due to the lakes not mere puddles in the taxiways!
The tress will be kept short due to the proximity of the radar. So the trees will be routinely clipped thus disturbing any potential residents!