To honk or to hiss: uncovering call complexity in the Egyptian Goose Alopochen aegyptiaca

Abstract

Egyptian Geese Alopochen aegyptiaca are distributed across most of Africa. Their calls dominate the soundscape of many urban areas, yet their acoustic behaviour is poorly documented or understood. Using acoustic recordings made across a range of behavioural contexts, groups sizes and compositions, we identified a repertoire of eight distinct call types (loud, honk, short honk, hiss, soft, short soft, flight and noisy). Call classification was well supported by a supervised random forest analysis conducted on six robust time-frequency explanatory factors. Our results support a sexually dimorphic call repertoire, where both sexes produce a long, intermediate and short call type with energy distributions and structure (diffuse vs strongly pulsed) varying between types. All call types were produced in bouts. Honk bouts were longer and contained more calls when simultaneous calling by conspecifics was present, in particular when honk matching occurred. When matching or distant calls were found, honk bouts were more likely to continue. Our results document hidden complexity in the acoustic signalling of Egyptian Geese and highlight avenues for future investigation into the behaviour of this urban adapted species.