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How the viewing of familiar landscapes prior to release allows pigeons to home faster: evidence from GPS tracking

Dora Biro^1,*, Tim Guilford¹, Giacomo Dell'Omo² and Hans-Peter Lipp²

¹ Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
² Division of Neuroanatomy and Behavior, Institute of Anatomy, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland

View larger version (86K): [in a new window]   Fig. 1. (A) Homing pigeon inside release apparatus. Depending on the experimental treatment, the vertical sides of the release box either remained transparent (VIS+) or were made opaque (VIS-). (B) Homing pigeon fitted with a GPS tracker. The device is held in a plastic casing and is attached to the back by Velcro.

View larger version (56K): [in a new window]   Fig. 2. Flight tracks of 12 subjects (A-L) reconstructed using GPS data. Position fixes were taken every second. The panels show, for each subject, two releases from each of four sites (locations indicated on first panel were the same for all panels; H, home). Lines in blue, VIS+ tracks; lines in red, VIS- tracks. Map grid, 1 km2.

View larger version (16K): [in a new window]   Fig. 3. Mean difference in homing speeds of individual birds following a 5 min pre-release phase, during which they were either allowed to view the landscape (VIS+) or were denied visual access (VIS-). Bars show within-bird differences under the two treatments, calculated as speedVIS+—speedVIS- and averaged across all four sites.

View larger version (17K): [in a new window]   Fig. 4. Average difference in track efficiency (beeline distance/distance travelled) following release under VIS+ and VIS- conditions. Bars show within-bird differences under the two treatments, calculated as efficiencyVIS+—efficiencyVIS- and averaged across all four sites.

View larger version (15K): [in a new window]   Fig. 5. Effect of visual treatment on the length of track flown by birds (N=12) before passing the 500 m, 1000 m and 1500 m boundaries, measured from the release site. Dots show, for each bird, differences in the length of track flown to cross each of the three segments, calculated as track lengthVIS-—track lengthVIS+, and averaged across the four release sites.

View larger version (36K): [in a new window]   Fig. 6. Orientation of VIS+ (black lines) and VIS- groups (grey lines) at 1 s intervals after release. Thick lines show r-values (thick broken line indicates critical value for Rayleigh test, 0.5 for N=12 and P=0.050), thin lines show U-test statistic for V-test (thin broken line indicates critical value, 1.64 for P=0.050). For any given group, data are shown until the second when the first bird in that group reaches home.

View larger version (14K): [in a new window]   Fig. 7. Average difference in the number of full circles flown per minute following release under the VIS+ and VIS- treatments. Bars show within-bird differences under the two conditions, calculated as number of full circlesVIS-—number of full circlesVIS+ and averaged across all four sites.

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