Most sycamores are by older buildings. There are so few I can name every one/group on the isle! c. 22 sites but some are tiny like our own (one of two) in photo which is 12-15 yo next to a Hooker’s Willow which is c.7 yo. Newer plantings pretty much all Hooker’s which is useless - see alt text.
Have you got a quoteable reference link for Orkney Council discoraging Hooker's Willow? I can add it to the (very skimpy!) wikipedia page on the species.
Surprising about the willow - I'd never have thought that insects would discriminate between the different species like that. Worth comparing street view pics of islands off W Norway like Utsira, or Faroes, far more trees planted, though just as exposed to gales. Admittedly mostly Sitka Spruce...
Just going back to YBWs, in five autumns I’ve found probably 30 or so here. Only two were out of sycamores - one in a clump of willows (not Hooker’s) and the other was in long roadside grass. Same goes for all Wood Warblers, etc. never found in Hooker’s and predominantly found in sycamores.
Just remembered three more sites, one private and the other two I rarely get to as both tiny trees that have never held owt.