Title: Bottoms up: great bustards use the sun to maximise signal efficacy

Journal: Behavioral Ecology and Sociobiology

Authors: Pedro P. Olea1, Fabián Casas2,3, Steve Redpath4, 2, Javier Viñuela2.

1.- School of Biology, IE University, Campus Santa Cruz la Real, 12, 40003, Segovia, Spain.

2.- Instituto de Investigación en Recursos Cinegéticos, IREC (CSIC, UCLM, JCCM) Ronda de Toledo s/n., 13071, Ciudad Real, Spain.

3.- School of Biological Sciences, University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, UK

4.- Current address: Aberdeen Centre for Environmental Sustainability, Aberdeen University and The Macaulay Institute, The School of Biological Sciences, Zoology Building, Tillydrone Avenue, Aberdeen. AB24 2TZ, UK.

S1. Analyses of orientation of displaying males of great bustard performed for data from an only day (27 March).

Orientations of male tail analysed by circular statitical

In early morning, the distribution of tail orientationwas significantly different from random (Rayleigh test, Z = 8.73; p<0.001, n=39). Males orientated their tales significantly towards the expected mean direction of the sun position, i.e. 100.5º (orientation mean angle ± SE: 98.658º ± 12.9º; V-Test, V= 0.47, u = 4.18, p <0.001; Fig S1). In late morning males tended to pointed their tails towards east (Fig. S1), but there was not a significantly predominant direction (mean ± SE: 90.9° ± 31.9°; Rayleigh test, Z = 1.59; p = 0.20, n = 42). In early evening, orientation of males was not significantly different from random (mean± SE: 206.1º±38.7º; Rayleigh test, Z = 1.08; p = 0.34, n =37). In late evening, males orientated their tails in a western direction although not signifcantly (250.6° ± 41.1º; Rayleigh test, Z = 0.95; p = 0.39, n = 20)., and close to the expected mean direction of 262.7º (V-Test, V= 0.21, u = 0.1.35, p = 0.09; n = 20; Fig S1).

Figure S1. Orientation of displaying males (percentage of observations) through an only day (from early morning to late evening) relative to the sun. Mean angle of orientation (black solid line from centre to edge of the circle) and 95% confidence interval (bars) are shown (computed in ORIANA 3.0 software). Mean positions of the sun for that day (27 March 2007) were: early morning=100.5º; late morning=110.3º; early evening=249.9º; late evening=262.7º.

Table1.- Minimal adequate models for whether or not male bustard displays were orientated towards the sun, considering an angle of 45º or 135º (see methods for details, N=138). LEK and SAMPLING DAY were included as random effects. SUN: sun visible or not; SKYCOVER: percentage of sky covered by clouds, DAY PERIOD: early morning: 8.00-10.00H, late morning: 10-12.00H; early evening: 17.00-19.00, late evening: 19.00-21.00).

“Tail to sun ” 45º model / Parameter estimate / SE / z-value / P
Intercept / -1.1992 / 0.4605 / -2.604 / 0.00921
DAY PERIOD / -0.5175 / 0.1329 / -3.893 / 0.00009
SUN / 0.6088 / 0.2831 / 2.150 / 0.03152
“Tail to sun ” 135º model
Intercept / 0.628375 / 0.2328 / 2.699 / 0.00696
DAY PERIOD / -0.234222 / 0.1335 / -1.755 / 0.07929
SKYCOVER / -0.006577 / 0.0042 / -1.572 / 0.11586