Meeting Abstract
The exaggerated morphological traits that appear in either sex in the breeding season (ornaments) have long been considered to have evolved by sexual selection. Acc ordingly, these would increase the success rate of mating. However, in some cases, it has been observed that these ornament-like traits are not likely to be related to sexual selection. One such example is the horn of the rhinoceros auklet Cerorhinca monocerata, a seabird species. The horn appears on the upper side of the beak in both males and females only in breeding season. Also, it has been reported that there are no differences between the sexes in the size of the horn. Hence, the horn may have a function besides affecting mating success. However, till date, no plausible function of the horn has been suggested. During the breeding season, in order to feed their chicks, both sexes of auklets fly with fish in their beaks, which would cause a substantially large drag. Thus, a preliminary computational fluid dynamics simulation study was performed, to examine the effect of the horn and prey fish on the energy cost of transport. According to the simulation, the horn negligibly increases drag during flight compared to the model without the horn. Meanwhile, with the prey in their beaks, the drag of the model with the horn was slightly less than the no-horn model. Although the mechanism of the drag reduction remains unclear, it has been hypothesized that the horn of the auklet may have a fluid dynamics function, particularly when the bird flies with fish in its beak, which potentially causes a large drag. To test this hypothesis, water tunnel experiments were conducted using 3D printed bird models, to measure the effect of the horn and prey fish on the rhinoceros auklets’ flying/swimming cost of transport. The results of the drag force measurement of the models across the evaluated range of body angles and flow speeds will be reported shortly.
