House martins build cup nests under house eaves and are declining as modern buildings and householder intolerance remove traditional nest sites.
House martins denied access to traditional nest sites by renovation or hostile householders lose breeding opportunities they may have used for multiple generations. Nest destruction during active use containing eggs or chicks is an offence under the Wildlife and Countryside Act. Persistent wet spring conditions prevent mud collection for nest construction causing breeding failure. Loss of mud sources from drainage and paving eliminates the construction material martins require. Adults that cannot find nest sites lose their breeding season entirely.