Abstract
The most virulent avian brood parasites obligately kill host young soon after hatching, thus ensuring their monopoly of host parental care. While the host eviction behaviour of cuckoos (Cuculidae) is well documented, the host killing behaviour of honeyguide (Indicatoridae) chicks has been witnessed only once, 60 years ago, and never in situ in host nests. Here, we report from the Afrotropical greater honeyguide the first detailed observations of honeyguides killing host chicks with their specially adapted bill hooks, based on repeated video recordings (available in the electronic supplementary material). Adult greater honeyguides puncture host eggs when they lay their own, but in about half of host nests at least one host egg survived, precipitating chick killing by the honeyguide hatchling. Hosts always hatched after honeyguide chicks, and were killed within hours. Despite being blind and in total darkness, honeyguides attacked host young with sustained biting, grasping and shaking motions. Attack time of 1–5 min was sufficient to cause host death, which took from 9 min to over 7 h from first attack. Honeyguides also bit unhatched eggs and human hands, but only rarely bit the host parents feeding them.
Highlights
Avian brood parasites vary greatly in virulence among species [1]
While many brood parasites are raised alongside host chicks and can be relatively benign, three independently evolved brood parasitic groups have evolved extremely high degrees of virulence: the young parasite actively kills its foster siblings, ensuring that it monopolises the parental care provided by the host parents
Chick killing has never been witnessed in the striped cuckoo, but rather surmised from the presence of bill hooks and dead host young [3]
Summary
Avian brood parasites vary greatly in virulence among species [1]. While many brood parasites are raised alongside host chicks and can be relatively benign, three independently evolved brood parasitic groups have evolved extremely high degrees of virulence: the young parasite actively kills its foster siblings, ensuring that it monopolises the parental care provided by the host parents. In the striped cuckoo Tapera naevia of the Neotropics [3] and the honeyguides (Indicatoridae) of Africa and Asia [4], the parasitic chick kills host young by attacking them with specially. Chick killing has never been witnessed in the striped cuckoo, but rather surmised from the presence of bill hooks and dead host young [3]. The reproductive biology of honeyguides has remained very poorly known, despite these intriguing morphological and behavioural adaptations that are absent in their non-parasitic relatives, the woodpeckers (Picidae) and barbets (Capitonidae) [4] ( a single maxillary hook is sometimes used in intraspecific sibling aggression in at least one species of bee-eater (Meropidae) and kingfisher (Halcyonidae) [5])
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