Alarm Calling by male fowl reflects judicious investment in mates

Studying the evolution of apparently altruistic alarm signals is complicated by the challenge of controlling the presence and proximity of kin, individual experience, and recent mating history. Among male fowl, the rate of alarm calling is highly correlated with mating success. This suggests that calling, like other costly traits, may be attractive to females. Calling might also reflect judicious risk-taking by males that have likely achieved paternity. We tested the latter hypothesis by pairing male and female fowl together and manipulating male mating success. After one week of viewing a hen, but not mating with her (baseline), a divider separating each male and female was either removed to permit mating, or left in place. This treatment continued for the following two weeks. During week four, we returned birds to baseline conditions. Throughout the study, we monitored male calling behavior and mating success. Males permitted to mate increased their calling effort by more than 25% compared to control males that were prevented from mating. These results are consistent with the male investment model and provide the first such demonstration for any system of alarm signals.