In Situ Clock Shift Reveals that the Sun Compass Contributes to Orientation in a Pelagic Seabird

Compass orientation is central to the control of animal movement from the scale of local food-caching movements around a familiar area in parids and corvids to the first autumn vector navigation of songbirds embarking on long-distance migration. In the study of diurnal birds, where the homing pigeon, Columba livia, has been the main model, a time-compensated sun compass is central to the two-step map-and-compass process of navigation from unfamiliar places, as well as guiding movement via a representation of familiar area landmarks. However, its use by an actively navigating wild bird is yet to be shown. By phase shifting an animal's endogenous clock, known as clock-shifting, sun-compass use can be demonstrated when the animal incorrectly consults the sun's azimuthal position while homing after experimental displacement. By applying clock-shift techniques at the nest of a wild bird during natural incubation, we show here that an oceanic navigator—the Manx shearwater, Puffinus puffinus—incorporates information from a time-compensated sun compass during homeward guidance to the breeding colony after displacement. Consistently with homing pigeons navigating within their familiar area, we find that the effect of clock shift, while statistically robust, is partial in nature, possibly indicating the incorporation of guidance from landmarks into movement decisions. Padget et al. show that a wild bird makes use of a time-compensated sun compass during active navigation. By measuring the minute-by-minute orientation of GPS-tracked Manx shearwaters homing under clock shift from distant release sites, the authors demonstrate that a sun compass is fundamental even once visual landmarks are available.