Assortative mating for carotenoid colouration but not size in the Yellow-legged Gull Larus michahellis

Figures & data

Figure 1. Within-pair correlations of the principal components derived from the colouration features of Yellow-legged Gulls. Dashed lines indicate equality within mated pairs.

Table 1. Statistics for the morphometric traits and colouration features of Yellow-legged Gulls, and the results of the within-pair comparisons.

	Females			Males			Within-pair difference (Male–Female)
	Min	Max	Mean ± se	Min	Max	Mean ± se	Mean ± se	t-Test	P
Morphometric traits (n = 16)
Head length (mm)	118.90	125.71	121.43 ± 0.56	124.93	135.40	131.47 ± 0.61	10.03 ± 0.79	12.78	<0.0001
Bill length (mm)	48.93	58.41	54.03 ± 0.59	56.22	61.73	58.96 ± 0.48	4.93 ± 0.67	7.40	<0.0001
Bill depth (mm)	16.07	17.91	16.76 ± 0.13	17.90	19.76	18.83 ± 0.14	2.07 ± 0.16	12.58	<0.0001
Tarsus length (mm)	66.58	76.39	70.77 ± 0.81	66.46	80.70	75.39 ± 0.97	4.62 ± 1.29	3.59	0.0027
Foot length (mm)	53.71	61.77	57.53 ± 0.67	55.45	68.07	60.96 ± 0.79	3.43 ± 0.87	3.93	0.0013
Wing length (cm)	43.00	46.00	44.35 ± 0.19	42.50	56.37	46.74 ± 0.70	2.38 ± 0.68	3.50	0.0032
Mass (g)	900	1100	995 ± 14	1050	1300	1192 ± 15	196 ± 19	10.54	<0.0001
Scaled mass index (g)	845	1226	998 ± 24	912	1345	1195 ± 27	197 ± 35	5.62	<0.0001
Colouration features (n = 12)
Relative hue of red bill spot	0.003	2.143	0.495 ± 0.201	0.023	2.083	0.474 ± 0.209	−0.021 ± 0.068	−0.30	0.7681
Relative hue of bill	0.110	0.164	0.131 ± 0.005	0.090	0.178	0.132 ± 0.007	0.002 ± 0.005	0.35	0.736
Relative hue of gape	0.023	1.571	0.484 ± 0.160	0.006	3.333	0.691 ± 0.294	0.207 ± 0.155	1.33	0.2098
Relative hue of orbital ring	0.003	5.000	0.811 ± 0.398	0.020	3.750	0.627 ± 0.033	−0.185 ± 0.147	−1.26	0.2346
PC1	−0.731	2.558	−0.016 ± 0.271	−0.734	2.953	0.016 ± 0.317	0.031 ± 0.085	0.37	0.7170
PC2	−1.106	1.809	−0.019 ± 0.234	−2.147	2.497	0.019 ± 0.345	0.039 ± 0.237	0.16	0.8731

Table 2. Within-pair correlations of morphometric traits and colouration features of Yellow-legged Gulls.

Variable	r	P
Morphometric traits (n = 16)
Head length	0.092	0.7345
Bill length	0.241	0.3686
Bill depth	0.212	0.4306
Tarsus length	−0.030	0.9124
Foot length	0.297	0.2637
Wing length	0.250	0.3506
Mass	0.198	0.4630
Scaled mass index	0.049	0.8572
Colouration features (n = 12)
Relative hue of red bill spot	0.946	<0.0001
Relative hue of bill	0.678	0.0154
Relative hue of gape	0.934	<0.0001
Relative hue of orbital ring	0.934	<0.0001
PC1	0.971	<0.0001
PC2	0.728	0.0072