Lets not forget that in some parts of the country, Oystercatchers nest on the flat roofs of buildings. My own experience of them in Aberdeen over a number of years included birds hatching on the roofs of buildings 6 stories high, from which they often make their way to the ground a long time before they can fly by the simple trick of plummeting.
We did occasionally encounter birds with broken and healed legs, which may well have been a result of this leap of faith. I think they probably reach terminal velocity pretty quickly; after that it doesn't really matter how high up they are.
http://www.the-soc.org.uk/docs/scottish-birds/sb-vol22-no01.pdf
