Figure 4. Brood reduction likelihood determines whether low or high condition chicks signal more.

Data points represent each species' mean correlation coefficient (effect size) of offspring condition on signal intensity in that environment. Positive correlations indicate chicks in better condition signal at a higher intensity, and negative correlations indicate chicks in worse condition signal more. This is a graphical simplification; analyses were run on the full data set per effect size reported, not species' means. (a) Chicks in worse condition were more likely to beg the most in good environments (MCMCglmm, pMCMC=0.001), and in species which tend to raise the whole brood (MCMCglmm, pMCMC=0.02, N=56 species). This represents the scenario where brood reduction is least likely. (b) Chicks in better condition were more likely produce more intense structural signals in brood-reducing species in poor environments (MCMCglmm, pMCMC=0.003, N=18 species). This represents the scenario where brood reduction is most likely.