There's an article in the Guardian today describing the losses in the sparrow population in Britain. The decline is attributed to a complex of situations - the removal of trees, conversion of gardens for parking, the presence of a lot of evergreen hedge and screen plant material - in particular chamaecyparis leylandii, or "leylandii", and use of pesticides, resulting in too few insects to keep the birds going.
I quickly looked up "leylandii", since I planted a swath of those in my own northern california yard, and have specified them for clients as.. yes, hedges and screens. Turns out they're a mix of Cupressus macrocarpa, Monterey Cypress, and Callitropsis leylandii (well, I sort of knew that but, hey) - both CA natives. Plus, the sparrows aren't CA natives. Still, I feel badly about the loss of much of the sparrow population in Britain.
Article here ---
Guardian article on sparrows
More about Leyland Cypress here -- http://en.wikipedia.org/wiki/Leyland_Cypress