Non-invasive unmanned aerial vehicle provides estimates of
the energetic cost of reproduction in humpback whales
Full citation details (open access – freely available):
Christiansen, F., Dujon, A.M., Sprogis, K.R., Arnould, J.P.Y. and Bejder, L. 2016. Non-invasive Unmanned Aerial Vehicle provides estimates of the energetic cost of reproduction in humpback whales. Ecosphere. 7(10). Doi: e0146810.1002/ecs2.1468
An animal’s body condition will affect its survival and reproductive success, which in turn influences population dynamics. Despite its importance, relatively little is known about the body condition of large whales and its relationship to reproduction. We assessed the body condition of humpback whales (Megaptera novaeangliae) at a breeding/resting ground (Exmouth, Figure 1) from aerial photographs recorded using an non-invasive unmanned aerial vehicle (UAV). Photogrammetry methods were used to measure the surface area of individual whales, which was used as an index for body condition. Repeated measurements of the same individuals were not possible; hence this study represents a cross-sectional sample of the body condition of the population. Intra-seasonal changes in body condition of four reproductive classes (calves, immature, mature and lactating) were investigated to infer the relative energetic cost that each class faces during the breeding season. To better understand the costs of reproduction, we investigated the relationship between female body conditions (FBC) and the linear growth and condition of their dependent calves (CBC). We documented a linear decline in the body condition of mature (0.027m2 day-1; n=20) and lactating females (0.032m2 day-1; n=31) throughout the breeding season, while immature whales (n=51) and calves (n=32) did not change in body condition. The significant decline in mature and lactating female’s body condition implies substantial energetic costs for these reproductive classes. In support of this, we report on a positive linear relationship between FBC and CBC. This finding suggests that females in poorer body condition may not have sufficient energy stores to invest as much energy into their offspring as better conditioned females without jeopardizing their own body condition and survival probability. Measurement precision was investigated by making repeated measurements of the same animals both from the same and different photographs, and also by looking at residual errors in relation to the positioning of the whales in the photographs. The resulting errors were included in a sensitive analysis to demonstrate that model parameters were robust to measurement errors. Overall, our findings provide strong support for the use of UAVs as a non-invasive tool to measure body condition of baleen whales and other free-ranging mammals.
Above YouTube video provides background to the study that was published in Ecosphere.
This research project was carried out under a research permit from the WA Department of Parks and Wildlife (DPaW), and with approval from the Murdoch University Animal Ethics Committee. The UAV was operated under a UAV Operator Certificate and a Remotely Piloted Aircraft System License in accordance with Australian Civil Aviation Safety Authority regulations.
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