What problems do local habitat change represent for the constant effort site ringing scheme?

Abstract

A mist‐netting site at Cow Lane Gravel Pits, Cambridgeshire, contributes to the British Trust for Ornithology's (BTO) Constant Effort Site (CES) ringing scheme. Standard net sites are located in relatively stable osier scrub Salix, but the nearby habitat is subject to rapid change which has resulted from the restoration of a gravel pit. This study addresses the question of whether this local habitat change results in fluctuations in the CES catch at Cow Lane which deviate from the national trends. CES catches of passerines in mist‐nets from 1989 to 1996 at Cow Lane are compared to the national trends as identified by the BTO. Most species have experienced increases and decreases at Cow Lane in accordance with the national trends, and appear to be relatively insensitive to local habitat changes. Sedge Warblers Acrocephalus schoenobaenus and Reed Warblers A. scirpaceus are the notable exceptions. Mist‐netting with additional nets in the adjacent habitat suggests that these species are responding to local expansion of wetland vegetation, and changes in the catch reflect localized changes in habitat use.