Investigation on how the combination of heat and humidity affect forest hornbill thermoregulation

Twenty eight trumpeter hornbills (Bycanistes bucinator) using mist nets (Avinet Nylon 100-mm mesh, Denier/ply 210/4, 5 shelves, 3 m height) in the lowland coastal forests of KwaZulu-Natal province, South Africa, in the towns of St Lucia, Richard’s Bay and Mtunzini (28.3726° S, 32.4142° E – 28.9597° S, 31.7501° E) within the Indian Ocean coastal belt biome (Rutherford et al., 2006). Once caught, birds were transported in clean large cotton pillowcases (for ≤ 1 h) to temporary outdoor aviaries (2 x 2 x 2 m) where they were housed in family groups when >1 individual was kept at a time. The researcher obtained data for 16 males and 12 females.

Average surface temperature measurements of the beak and skin regions were extracted from thermal images using the ThermaCam software (ThermaCAM Researcher Pro 2.9, FLIR Systems Inc, Wilsonville). The polygon and line functions were used to specify the region where surface temperature was to be measured. Mean temperatures across the beak were extracted. I tested whether surface temperatures of the distal, proximal, upper, lower and casque sections of the beak differed significantly at increasing Tair, and found no significant difference. As such, all surface temperature measurements of the beak and casque were pooled and averaged for every 1°C of Tair for each bird. Values of Tbeak consist of a mean ± SD of these Ts readings from across the beak and were used in further analyses.