Results from GLMM analysis for North and South group.

Models evaluated included an index of El Niño Southern Oscillation ‘mei’; for each model evaluated the ‘lag/window’ are given in months; the number of parameters ‘par’ including both fixed (i.e. MEI) and random effects (i.e. offspring mother): AIC; the parameter estimates for the intercept ‘int’, ‘mei’(* indicates significance on 0.05 level, ** on 0.01 level, *** on 0.001 level). A negative ‘mei’ parameter estimate indicates a higher probability of male birth at high MEI values. Please note that the AIC values are derived from restricted maximum likelihood estimation and represent therefore only approximations. The ‘null’ model has no additional parameter. As the time lag of seven months with an average MEI value (window) of two months is shared by both groups, the GLMM results for the analysis combining both groups are shown as well.