Three sets of experiments to test for enemy recognition and mimicry hypotheses (see Introduction). Response (aggression measured as number of contact attacks per 1 min.) is presented as a difference (mean ± s.e.) between aggression levels towards two dummies within a simultaneously presented dyad (see Methods). For sample sizes see Table 1. (a) “Specific aggression” is the aggression to cuckoo/predator dummy minus baseline aggression to control (dove), i.e., specific response to the dangerous enemy above the background aggression shown to any, even innocuous, intruders near the nest (see ). (b) Difference between responses to paired gray vs. rufous cuckoo female morph. (c) “Mimicry” is the aggression towards a particular cuckoo morph minus aggression towards its respective model (i.e., sparrowhawk for gray morph, kestrel for rufous morph). Different letters indicate statistical differences between groups according to GLMM (Tukey HSD, α = 0.05).