Table 1.

Parental cooperation in relation to sexual selection, social environment, and climate in birds

Model and predictorsEstimate (SE)F (P)
Sexual selection (R2 = 0.17, λ = 0.76, df = 4,221)
 Sexual size dimorphism−0.258 (0.057)20.62 (<0.001)
 Extrapair paternity−0.264 (0.061)18.55 (<0.001)
 Body mass0.299 (0.115)6.83 (0.011)
 Chick development−0.157 (0.151)1.12 (0.308)
Social environment (R2 = 0.07, λ = 0.91, df = 3,161)
 Adult sex ratio−0.186 (0.056)11.05 (0.001)
 Body mass0.087 (0.135)0.43 (0.524)
 Chick development−0.084 (0.261)0.12 (0.750)
Climate (R2 = 0.01, λ = 0.90, df = 4,654)
 Temperature0.041 (0.033)1.60 (0.214)
 Rainfall0.037 (0.031)1.47 (0.233)
 Body mass−0.019 (0.074)0.09 (0.795)
 Chick development−0.084 (0.145)0.35 (0.564)
Full model (R2 = 0.29, λ = 0.82, df = 7,72)
 Sexual size dimorphism−0.168 (0.098)2.93 (0.093)
 Extrapair paternity−0.230 (0.106)4.70 (0.034)
 Adult sex ratio−0.234 (0.083)7.88 (0.007)
 Temperature0.027 (0.105)0.08 (0.796)
 Rainfall0.034 (0.087)0.16 (0.696)
 Body mass0.334 (0.178)3.54 (0.066)
 Chick development0.020 (0.223)0.03 (0.900)
  • In all models, parental cooperation was the response variable and predictors included: sexual size dimorphism (log absolute size dimorphism index), extrapair paternity (sqrt EPP), adult sex ratio (sqrt ASR bias), temperature (first axis from PCA on climatic variables: higher values mean hot environments with low temperature variability; factor loadings available in SI Appendix, Table S4), rainfall (second axis from PCA on climatic variables: higher values mean dry environments with high rainfall variability; factor loadings available in SI Appendix, Table S4), body mass (log-transformed), and chick development (altricial vs. precocial). We use phylogenetic generalized least squares approach and present means from 500 analyses using different phylogenetic trees (see detailed results in SI Appendix, Table S1). Estimates are standardized regression coefficients and λ indicates the strength of the phylogenetic signal.