Figure 1

Maps of the study site showing the sampling quadrants, and phases of recruitment. a Construction of sampling grid and identification of building structures using aerial maps; b Survey of sampling grid to identify and exclude quadrants without breeding sites or with fewer than four houses; c Randomization of houses within the remaining quadrants and sequential recruitment of four houses per quadrant; d An example of a typical night of sampling, with six quadrants active and six quadrants deactivated.