Breeding biology and nestling development of the Grasshopper Buzzard

Breeding Performance of the Grasshopper Buzzard (Butastur rufipennis) in a Natural and a Human-Modified West African Savanna

“…To determine potential covariates of reproductive output, we examined characteristics of the nest site and its direct surroundings and the distance to conspecifics or sources of human disturbance. Since the habitat may influence raptors' reproduction at multiple spatial scales (Penteriani and Faivre 1997), we sampled nest-site characteristics at <200 m from the nest, representing about half the mean distance to the nearest nest (NND) and core foraging area, and at <1 km, corresponding with the longest observed flight from a nest for foraging (Buij et al 2012). For each nest, we determined the species of tree (Arbonnier 2004), its diameter at breast height (DBH), and the height of the nest and the nest tree.…”

“…Nests for which DSR was modeled to vary with age included only those with nestlings for which body measurements were taken early in the nestling phase. A 30-day incubation period from egg laying to hatching of the last nestling and a 36-day nestling period (Buij et al 2012) were the basis of calculations of overall nest success. We assumed nests failed at the midpoint between the date of the last visit in which eggs or young were recorded in the nest and the date of the next visit when the nest was empty and considered eggs infertile if older than 38 days, irrespective of the presence of a breeding female.…”

“…Clutch size and nestling number refer to the number of eggs and nestlings recorded at a nest, respectively. Date of laying we calculated by subtracting 28 days from the date of hatching of the first hatchling, corresponding with the incubation period to hatching of the first egg (Buij et al 2012). We estimated the date of hatching from nestlings' stage of feather development (Buij et al 2012).…”

“…Date of laying we calculated by subtracting 28 days from the date of hatching of the first hatchling, corresponding with the incubation period to hatching of the first egg (Buij et al 2012). We estimated the date of hatching from nestlings' stage of feather development (Buij et al 2012). Fledgling number was the number of nestlings that reached 80% of the mean age at fledging (compare Steenhof and Newton 2007), i.e., ≥29 days (Buij et al 2012), and calculated separately for all pairs and for successful pairs only.…”

“…Although in the North Temperate Zone Sergio et al (2003) found that raptors' response to the presence of important avian predators varied, nest dispersion may be driven by spatial avoidance of centers of activity (i.e., nest sites) of the most important avian predators . The Grasshopper Buzzard, however, establishes territories at the end of the dry season (Buij et al 2012), which precedes a seasonal influx of migratory raptors capable of killing nestlings and adults (Thiollay 1976(Thiollay , 1977, limiting options for spatial avoidance of avian predators. Therefore, we expected nest density to be positively associated with tree density and food availability and negatively with increasing human populations and cultivation.…”