Table 3. Statistical models examining the causes of the change in bib colour.

(A) Results of the linear models examining the effect of treatment, change in uropygial gland size ($\mathrm{\Delta }$UGS), body condition, and the interaction treatment × $\mathrm{\Delta }$UGS on the change in colour parameters (lightness, saturation, and hue) of bib. Degree of freedom of error term were one less for lightness, as an outlier (Fig. S1) was removed (see Table S2 for the results including the outlier). (B) Linear models examining the effect of treatment, change in body condition (not included in the previous model), $\mathrm{\Delta }$UGS, initial body condition, and the interaction treatment × $\mathrm{\Delta }$UGS on changes in colour parameters (lightness, saturation, and hue) of bib. (C) Linear models examining the effect of treatment, bib size (not included in models in A and B), $\mathrm{\Delta }$UGS, body condition, and the interaction treatment × $\mathrm{\Delta }$UGS on colour parameters (lightness, saturation, and hue) of bib. For every effect, standardised coefficients (β ± SE), F- and P-value are indicated. Significant results (P < 0.05) in bold. For every model, Adjusted R² and AIC is indicated.

(A) Model excluding change in body condition and bib size
	Change bib lightness Adj. R2 = 0.11; AIC = 152.0			Change bib saturation Adj. R2 = 0.53; AIC = 49.1			Change bib hue Adj. R2 = 0.45; AIC = 21.1
	β ± SE	F1,15	P	β ± SE	F1,16	P	β ± SE	F1,16	P
Treatment	130 ± 95	1.880	0.191	170 ± 62	7.501	0.015	−135 ± 67	4.043	0.062
Body condition	0.33 ± 0.25	1.703	0.212	0.57 ± 0.17	11.530	0.004	−0.35 ± 0.18	3.783	0.070
$\mathrm{\Delta }$UGS	0.01 ± 0.27	0.001	0.977	−0.15 ± 0.18	0.740	0.402	0.42 ± 0.19	4.774	0.044
Treatment*$\mathrm{\Delta }$UGS	−130 ± 95	1.875	0.191	−170 ± 62	7.550	0.014	135 ± 67	4.052	0.061