Swifts, house martins and greenfinches are now considered endangered species. Swifts migrate from central Africa, typically arriving here in May. You can make specialised nest boxes for them, or buy them and install them under the eaves. A good source of information is the swift conservation web site.
An excellent book that is both informative and a delight to read is "English Pastoral" by James Rebanks. It describes how his life in farming has taken him through the industrialisation of farming, and then his increasing desire to return to older ways that are more sustainable. You may be able to buy a second hand copy from ethical bookseller, World of Books.