“…In non-Passeriformes, vocalizations are often simple and stereotyped, but messages can also be encoded in different call types. For examples, adult African penguin (Spheniscus demersus) employ four vocal categories for the use in different circumstances (Favaro, Ozella, & Pessani, 2014); male corncrakes (Crex crex) are known to express low or high levels of aggressive motivation in broadcast calls and soft calls, respectively (Rek & Osiejuk, 2011); and male ural owls (Strix uralensis) use different call types for territorial advertisement and for duetting with female (Lundberg, 1980). For cuckoos, a well-studied brood parasitic avian species, the temporal and frequency variables of male "cu-coo" calls ( Figure 1a) are well-known (Lei, Zhao, Wang, Yin, & Payne, 2005).…”