House martins traditionally built their mud nests on cliff faces, but traditional nest sites were all but abandoned by the early 1900s in favour of a close association with people. These days, house martins build their nests on the outer walls of buildings, under the eaves. They are colonial nesters, with an average group size of four to five nests, although large colonies with groups of tens or even hundreds of nests are sometimes reported! 💙 #conservation #ukwildlife #uknaturecollective #rspb