2.3. Tracing honey-buzzard nests and installation of trail-cameras in the nests
The forest patches at the study area have been surveyed systematically for four years (2018-2021) to find all honey-buzzard nests (Rebolloet al. 2023). We installed trail-cameras in 24 nests of honey-buzzards: 5 in 2018, 4 in 2019, 6 in 2020 and 9 in 2021. The cameras (Browning SPEC OPS and SPEC OPS EDGE) were connected to an extra battery to ensure they could cover the whole breeding period. Cameras were placed in the surrounding branches at 1.5–2 m from the nest and programmed to take only one picture when triggered, with a delay of 20 seconds between pictures. Accessing to the nest and installation of trail-cameras was performed once the nestlings were 16 days old, moment in which they can thermoregulate by themselves.
At the time of trail-camera installation we estimated the breeding phenology from the age of nestlings, based on the length of the wing and body mass (Bijlsma 1997). Laying dates were estimated by subtracting the incubation time of a single egg (35 days) from the hatching date of the oldest nestling in each nest (Roberts et al . 1999). Laying phenology was estimated in julian days, with January 1st defined as day 1.