Shearwaters know the direction and distance home but fail to encode intervening obstacles after free-ranging foraging trips
- aDepartment of Zoology, Oxford University, OX1 3SZ Oxford, United Kingdom;
- bDepartment of Physics, Oxford University, OX1 3PJ Oxford, United Kingdom;
- cBritish Geological Survey, OX10 8ED Wallingford, United Kingdom;
- dGraduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan;
- eZoological Society of London, Institute of Zoology, NW1 4RY London, United Kingdom;
- fCentre for Conservation Science, Royal Society for the Protection of Birds, SG19 2DL Sandy, United Kingdom
See allHide authors and affiliations
Edited by Carol A. Barnes, University of Arizona, Tucson, AZ, and approved September 10, 2019 (received for review March 6, 2019)

Significance
Procellariiform seabirds homing from distant foraging locations present a natural situation in which the homing route can become obstructed by islands or peninsulas because birds will not travel long distances over land. By measuring initial orientation from Global Positioning System (GPS) tracks during homing, we found that the Manx shearwater fails to encode such obstacles while homing, implying a navigation system that encodes the direction of home rather than a learned route. Nonetheless, shearwaters timed their journeys home, implying that their navigational system provides them with information about both direction and distance home, providing evidence that for routine, yet long-distance navigation, seabirds probably ascertain homeward direction by comparing their current position and the location of home with 2 or more intersecting field gradients.
Abstract
While displacement experiments have been powerful for determining the sensory basis of homing navigation in birds, they have left unresolved important cognitive aspects of navigation such as what birds know about their location relative to home and the anticipated route. Here, we analyze the free-ranging Global Positioning System (GPS) tracks of a large sample (n = 707) of Manx shearwater, Puffinus puffinus, foraging trips to investigate, from a cognitive perspective, what a wild, pelagic seabird knows as it begins to home naturally. By exploiting a kind of natural experimental contrast (journeys with or without intervening obstacles) we first show that, at the start of homing, sometimes hundreds of kilometers from the colony, shearwaters are well oriented in the homeward direction, but often fail to encode intervening barriers over which they will not fly (islands or peninsulas), constrained to flying farther as a result. Second, shearwaters time their homing journeys, leaving earlier in the day when they have farther to go, and this ability to judge distance home also apparently ignores intervening obstacles. Thus, at the start of homing, shearwaters appear to be making navigational decisions using both geographic direction and distance to the goal. Since we find no decrease in orientation accuracy with trip length, duration, or tortuosity, path integration mechanisms cannot account for these findings. Instead, our results imply that a navigational mechanism used to direct natural large-scale movements in wild pelagic seabirds has map-like properties and is probably based on large-scale gradients.
Footnotes
- ↵1To whom correspondence may be addressed. Email: oliver.padget{at}zoo.ox.ac.uk or tim.guilford{at}zoo.ox.ac.uk.
↵2Present address: School of Mathematics and Statistics, University of New South Wales, Sydney, NSW 2052, Australia.
Author contributions: O.P., S.B., L.M., and T.G. designed research; O.P., A.L.F., S.B., A.S., B.D., H.K., I.J.-M., R.F., M.B., and T.G. performed research; O.P., G.S., J.K.W., and T.G. analyzed data; and O.P., G.S., S.B., L.M., and T.G. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
Data deposition: Tracking data are deposited in Movebank, https://doi.org/10.5441/001/1.k20j58qt.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1903829116/-/DCSupplemental.
- Copyright © 2019 the Author(s). Published by PNAS.
This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY).
Citation Manager Formats
Article Classifications
- Biological Sciences
- Evolution