Table 1. Statistical properties of signed differences between the right and left sides of female yellow-legged gulls for the four measured morphological traits and results of tests of normality and mean difference with zero. Sample size = 18.

Trait	Mean±SE	Skewness	Kurtosis	Student t-test for «mean = 0»		Shapiro-Wilk normality test
				t	P	W	P
Lower mandible length (mm)	0.09±0.18	−0.29	−0.65	0.50	0.6218	0.97	0.7045
Nalospi length (mm)	0.13±0.07	−1.02	3.02	1.80	0.0899	0.91	0.0648
Tarsus length (mm)	−0.11±0.22	−0.34	1.10	−0.50	0.6243	0.95	0.4818
Middle toe length (mm)	−0.58±0.30	1.12	2.99	−1.96	0.0661	0.92	0.1135