Survey protocol for the Little Owl Athene noctua

Abstract

We offer a protocol for conducting standardized nocturnal broadcast (playback) surveys on Little Owls Athene noctua across the range of the species. Based on differing objectives of researchers, two intensity levels of survey efforts are outlined: (1) demographic and density studies, and (2) presence and general distribution surveys. Both survey programs utilize the same field method, but vary in the number of visits required across the survey area. Objectives and definitions for these survey programs, and criteria for determining occupancy, reproduction, and turnover rates to support demographic and monitoring studies are given. The recommended survey period coincides with the breeding season, and depending on the latitude (and elevation), is approximately from 1 February - 30 April in western-Europe, and 1 March - 31 May in eastern Europe, Middle East, and Asia. Surveys are to be conducted from sunset to midnight and from two hours before sunrise to sunrise. Survey stations are located 500 m apart from one another along transects, or in a grid network. The tape-recorded call sequence consists of a 2-min track played three times, with each broadcast track separated by silent periods of 1 min each. The observer listens for 5 min after the last sequence. Thus a maximum of 13 min is spent at each survey station. Positions of all responding owls are recorded on a field map. While Little Owls have a repertoire of 22 vocalizations, two calls, the hoot ("ghuk") and the "chewing" call, are used by males in territorial contests and are the calls recommended for use in this protocol. Broadcast vocalizations should be played at volume and clarity levels consistent with that of wild owls. For demographic and density studies, we recommend 4 visits across each of the survey routes (and associated survey stations) to gain responses from >95% of the territorial owls. For nest-box programs where the objectives are demographic status and trends, and where the majority of owl territories are already known, survey efforts described in this protocol are used to fill in gaps and offer thorough and systematic coverage of the entire study area. For presence and general distributional surveys, we suggest a 1-visit survey be conducted. While a 1-visit strategy will not detect some of the owls actually present, the outcome of these surveys will illuminate general distributions of owls and highlight areas for further study. We anticipate that this protocol will be updated occasionally, following a normal scientific peer-review process. In particular, we urge additional research on the detection probability of territorial owls to provide clarification as to the number of visits needed to accurately determine the numbers of owls present in a given area. Prior observations have indicated a potential for differential responses from owls in high density populations (higher response rates) compared to owls residing in low density situations, and this needs further research.