Bird species data from the UK Environmental Change Network (ECN) terrestrial sites. Counts of individual bird species are recorded. These data are collected, using the British Trust for Ornithology (BTO)'s Breeding Bird Survey methodology, at all of ECN's terrestrial sites using a standard protocol. They represent continuous records from 1995 to 2015 (the transects are walked twice each year). ECN is the UK's long-term environmental monitoring programme. It is a multi-agency programme sponsored by a consortium of fourteen government departments and agencies. These organisations contribute to the programme through funding either site monitoring and/or network co-ordination activities. These organisations are: Agri-Food and Biosciences Institute, Biotechnology and Biological Sciences Research Council, Cyfoeth Naturiol Cymru - Natural Resources Wales, Defence Science & Technology Laboratory, Department for Environment, Food and Rural Affairs, Environment Agency, Forestry Commission, Llywodraeth Cymru - Welsh Government, Natural England, Natural Environment Research Council, Northern Ireland Environment Agency, Scottish Environment Protection Agency, Scottish Government and Scottish Natural Heritage.