Post-breeding census at roosts

In NW Italy, from the end of October, sacred ibises roost for the night in a few habitual sites, both colony sites of the previous breeding season or other suitable wood patches. We performed coordinated post-breeding censuses within a single week in November, from 2016 to 2019. The observers monitored each roost from a vantage point about 100 m distance, from 1 h before sunset to 30 min after the last sacred ibis had landed. The arriving birds could be easily counted as they arrived from the foraging areas in the open, cultivated landscape surrounding the roost. They usually fly towards the roost in groups of a few tens to some hundreds. The number of roosts checked each year varied between 13 and 19. As the sacred ibises tend to utilize the same location for several years, our census was repeated all along the study period in the first detected roost sites, while the remaining sites were added when they were discovered after the first year. In order to check for the presence of undetected roosts and to ensure the representativeness of the roosts we had monitored, we repeatedly inspected the landscape up to 15 km away from each site, during both the month before and after the post-breeding census.