Moving animals can estimate the distance of visual objects from image shift on their retina (optic flow) created during translational, but not rotational movements. To facilitate this distance estimation, many terrestrial and flying animals perform saccadic movements, thereby temporally separating translational and rotational movements, keeping rotation times short. In this study, we analysed whether a semiaquatic mammal, the harbour seal, also adopts a saccadic movement strategy. We recorded the seals' normal swimming pattern with video cameras and analysed head and body movements. The swimming seals indeed minimized rotation times by saccadic head and body turns, with top rotation speeds exceeding 350 deg s−1 which leads to an increase of translational movements. Saccades occurred during both types of locomotion of the seals' intermittent swimming mode: active propulsion and gliding. In conclusion, harbour seals share the saccadic movement strategy of terrestrial animals. Whether this movement strategy is adopted to facilitate distance estimation from optic flow or serves a different function will be a topic of future research.
The authors declare no competing or financial interests.
All authors designed the study, B.R.H.G., B.N. and F.D.H. recorded the videos, B.R.H.G. and F.D.H. analysed the data, B.R.H.G. and F.D.H. wrote the manuscript, all authors edited the manuscript and gave final approval for publication.
This work was financially supported by a grant from the Volkswagen Foundation to G.D.
The data can be downloaded from http://cellneuro.uni-goettingen.de/downloads/sealsRawData.zip
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.150763.supplemental
- Received September 30, 2016.
- Accepted January 31, 2017.
- © 2017. Published by The Company of Biologists Ltd