Kleptoparasitism of Shoebills Balaeniceps rex by African Fish Eagles Haliaeetus vocifer in Western Tanzania

Abstract

Kleptoparasitism is a specialised form of foraging interference occurring throughout the animal kingdom and especially is well documented among birds including African fish eagle Haliaeetus vocifer. However, only one record is reported between fish eagle and shoebill Balaeniceps rex despite their habitat overlap and it remains undescribed. This paper documents kleptoparasitism of shoebills by fish eagles in Malagarasi wetlands, western Tanzania. Kleptoparasitism was highly seasonal occurring in the dry season, especially at low floods. Both adults and non-adult eagles stole prey from shoebills, with non-adults initiating attacks at shorter distances than adults perhaps because of the lack of experience. The shoebill preys were comparatively larger than those from fish eagle own fishing and required long preparation time which provided the opportunities to kleptoparasites. Shoebill’s long prey handling time (6.90 ± 4.48 min) may have provided benefits to fish eagles as all kleptoparasitism attempts (n = 138) were successful. Moreover, it seemed likely that an attacking fish eagle posed significant danger to the shoebill and given the fact that shoebill lacks structures such as pointed bill to defend from kleptoparasitic attack it opted not to retaliate. Perch availability and habitat openness in the study sites could also have facilitated kleptoparasitic behaviours.

Keywords: Balaeniceps rex; Haliaeetus vocifer; handling time; kleptoparasitism; Malagarasi-Muyovozi Ramsar Site