Species identity cues in animal communication.

Researchers have suggested that animals should respond more strongly to conspecific than to heterospecific communication signals used in territorial or courtship contexts. We tested this prediction by reviewing studies that appeared in six prominent journals over the past 10 years. A meta-analysis based on these empirical studies revealed that overall support for this hypothesis was weaker than anticipated. To help clarify the extent to which experimental design might contribute to equivocal findings, we performed playback experiments in the field, using robotic lizards. We examined whether male tropical lizards, Anolis gundlachi, responded more strongly to robots producing conspecific territorial advertisement displays than to robots producing equivalent displays of a novel heterospecific. Although this experiment was conducted under natural conditions in the field, at signaler-receiver distances typical for animals at this locality, and with high statistical power, we found that lizards responded just as aggressively to a simulated rival performing a display they had never seen before as to the same rival performing a conspecific display. Our findings suggest that predicting how animals will respond to conspecific versus heterospecific signals is more complicated than has generally been anticipated.