143 Irish Birds 9: 143-154 (2011) Introduction Previous research and monitoring of Merlin Falco columbarius in Ireland has been limited, resulting in an absence of comprehensive data on distribution, abundance and ecological requirements of the species. Evidence from the Breeding Bird Atlases suggested a moderate decline in the breeding range of the Irish population (Sharrock 1976, Gibbons et al. 1993), while preliminary results from the latest Breeding Bird Atlas (2007-2011) highlights a continuation of this downward trend (B. Caffrey, pers. comm.). The population fluctuations detected by the Breeding Birds Atlases (Sharrock 1976, Gibbons et al. 1993) have been the primary sources used to determine the categorisation of Merlin on the Amber list of Birds of Conservation Concern in Ireland (Lynas et al. 2007). However, due to difficulties associated with detecting breeding Merlin, the survey methods employed by Assessing the effectiveness of monitoring methods for Merlin Falco columbarius in Ireland: the Pilot Merlin Survey 2010 John Lusby* 1 , Darío Fernández-Bellon 1 , David Norriss 2 and Alan Lauder 3 1 BirdWatch Ireland, Midlands Office, Crank House, Banagher, Co. Offaly 2 National Parks and Wildlife Service, 7 Ely Place, Dublin 2 3 BirdWatch Ireland, Unit 20, Block D, Bullford Business Campus, Kilcoole, Co. Wicklow * Correspondence author: jlusby@birdwatchireland.ie Previous research and monitoring of Merlin Falco columbarius in Ireland has been limited. This has resulted in a lack of understanding of the status, trends and ecology of the population. A Pilot Survey was initiated in 2010 to assess the effectiveness of standard survey methods applied to the Irish population, and to inform an appropriate protocol for future monitoring. Similar to a trial of methods conducted for the 1993-94 Merlin Survey in Britain, two survey elements were undertaken simultaneously. Ten 3 x 3km squares were independently surveyed between April and July 2010. One group of surveyors (BWI) had no prior knowledge of Merlin within the squares, whereas another group (NPWS) possessed previous information on Merlin occupancy. Results for both surveys were similar for six squares. BWI recorded a higher level of breeding in two squares, while NPWS obtained more accurate detail on breeding status in two squares. Combined results confirmed all squares to be occupied. Successful breeding was confirmed in two squares. The findings emphasise considerable difficulties with monitoring Merlin in Ireland. A high degree of variation in detection rates, plucking behaviour and mobbing response was recorded, which affected the success of the methods employed. The average number of Merlin signs located per square was 20.2, but ranged from 0-79. From 40 potential mobbing events, only 12.5% resulted in responses from resident Merlin. A series of recommen- dations for future research and monitoring are outlined. Plate 61. Merlin (Shay Connolly).