0000000000222332
AUTHOR
Tanja Caprano
Calibrating the Operational Beam Width and Maximum Range of a Ship Radar Used for Bird Observations
In order to analyse quantitative radar observations of bird movements, one needs to know the dimensions of the air space surveyed by the radar. The present study shows how to calibrate the operational beam width and the maximum range of any radar for cross sections for different body sizes of songbirds. The trial used an X-band fan beam ship radar of 25 KW (Furuno Fr-2125) and a captive balloon. Metal spheres of different diameters, fastened to the bottom of the balloon at defined distances, corresponding to the radar cross sections of song birds, were moved in all three dimensions of the air space. Simultaneously to the location by radar, the position of the suspended sphere was measured b…
Evolution of avian clutch size along latitudinal gradients: do seasonality, nest predation or breeding season length matter?
Birds display a latitudinal gradient in clutch size with smaller clutches in the tropics and larger in the temperate region. Three factors have been proposed to affect this pattern: seasonality of resources (SR), nest predation and length of the breeding season (LBS). Here, we test the importance of these factors by modelling clutch size evolution within bird populations under different environmental settings. We use an individual-based ecogenetic simulation model that combines principles from population ecology and life history theory. Results suggest that increasing SR from the tropics to the poles by itself or in combination with a decreasing predation rate and LBS can generate the latit…
Seed-dispersal distributions by trumpeter hornbills in fragmented landscapes.
Frugivorous birds provide important ecosystem services by transporting seeds of fleshy fruited plants. It has been assumed that seed-dispersal kernels generated by these animals are generally leptokurtic, resulting in little dispersal among habitat fragments. However, little is known about the seed-dispersal distribution generated by large frugivorous birds in fragmented landscapes. We investigated movement and seed-dispersal patterns of trumpeter hornbills ( Bycanistes bucinator ) in a fragmented landscape in South Africa. Novel GPS loggers provide high-quality location data without bias against recording long-distance movements. We found a very weakly bimodal seed-dispersal distribution …
Range size: Disentangling Current Traits and Phylogenetic and Biogeographic Factors
The range size of a species can be determined by its current traits and by phylogenetic and biogeographic factors. However, only rarely have these factors been studied in combination. We use data on the geographic range sizes of all 26 Sylvia warblers to explicitly test whether range size was determined by current species-specific traits (e.g., body size, dispersal ability), phylogenetic factors (e.g., age of the lineage), or environmental, biogeographic factors (e.g., latitudinal position of the range). The results demonstrated that current traits and phylogenetic and biogeographic factors were interrelated. While a number of factors were significant in simple regression analyses, only one…