Table 1.

List of variables selected for the description of four syndromes, with their loadings (= Spearman's rank correlation coefficients) along the first PCA component (one separate analysis per syndrome)

Ecological specialization syndrome	PC1spec	r‐K gradient syndrome	PC1rK
Disturbance tolerance	−0.39	Clutch size	−0.76
Cold tolerance	−0.17	Metabolic rate per unit body mass	−0.31
Shy	0.03	Life duration	−0.24
Drought tolerance	0.22	Broods per season	0.41
Altitudinal specialization	0.30	Incubation	0.68
Nest height specialization	0.48	Breeding season	0.70
Food specialization	0.55	Nesting stage	0.81
Habitat specialization	0.63
Foraging height specialization	0.74

Sexual dimorphism syndrome	PC1sex	Dispersal/social behavior syndrome	PC1beh
Wing relative length	−0.63	Gregariousness	−0.80
Song length	−0.62	Breeding dispersion plasticity	−0.75
Female plumage brightness	−0.60	Migration plasticity	−0.69
Frequency range	−0.56	Migration	−0.57
% melanin	−0.45	Mixed parties	−0.23
Tail relative length	−0.41	Gregariousness plasticity	0.26
Number of notes	−0.36	Territorial	0.40
Nest building by males	−0.32	Nests dispersed	0.64
Juvenile plumage distinctness	−0.27	Breeding dispersion	0.76
Monogamy	−0.27
Song mimicry	−0.23
Feeding of youngs by males	−0.06
Incubation by males	0.26
Bill relative length	0.27
Male plumage brightness	0.28
Tarsus relative length	0.32
Female plumage drabness	0.53
Weight	0.58
Sexual dimorphism present	0.59
Size	0.62
Duration of juvenile plumage	0.71
Head dichromatism	0.72
Breast dichromatism	0.75
Nest outer diameter	0.78
% carotenoid	0.79
Rump dichromatism	0.81