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Conflict & Communication: Consequences Of Female Nest Confinement In Yellow-Billed Hornbills



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The most striking feature of hornbills (Bucerotiformes) is their unusual nesting behaviour. Before laying, a female hornbill enters the nest in a tree cavity. Uniquely among birds, she then seals the nest entrance using her faeces and locally available materials, leaving a narrow gap only 1 cm wide. Through this tiny slit, the female is totally dependent on her mate for between 40 days in the smallest hornbills and up to 130 days in the largest. Once walled in the nest, the female will lay her eggs and shed all of her wing and tail feathers. The male then becomes completely responsible for provisioning his mate and a few weeks later, the chicks. When her feathers have regrown, the female breaks out of the nest, often before the chicks are fully grown. The chicks then reseal the entrance until they too are ready to fledge. This thesis describes attempts to better understand the nesting behaviour of hornbills. The first chapter introduces hornbill ecology and behaviour and highlights their potential as model systems for studying conflict and communication. Chapter 2 describes the methods used to set up a study population of Southern Yellow-Billed Hornbill (Tockus leucomelas) consisting of 47 occupied nest boxes, over 35km2 in the Southern Kalahari Desert, South Africa. Chapter 3 summarises behaviour over three breeding seasons from October 2008 to April 2011. Female feather moult followed a precise staggered pattern, unlike other populations. Widespread filial cannibalism by females of both eggs and chicks was observed for the first time. The possible proximate causes of cannibalism are explored. Egg cannibalism allowed females to recoup some of their energetic investment, while cannibalism of chicks served as an efficient mechanism of brood reduction for nests with low paternal feeding rate. Chapter 4 investigates how females communicate need for nesting materials to males. Females altered the rate and structure of their begging calls when experimentally deprived of nest lining and males in turn delivered more nest materials. Chapter 5 examines the factors that determine how long females remain in the nest. Females with larger broods stayed in the nest longer, irrespective of their own or their chicks’ condition or male feeding rates. This raises questions about the role of mothers in the nest. Chapter 6 addresses this issue, demonstrating that females controlled sibling competition in the nest. Experimental temporary removal of mothers led to increased intrabrood aggression and more uneven food distribution in the brood, with larger chicks taking a greater share. The final chapter draws these findings together and the potential for future research is discussed.


This thesis was originally submitted in 2012 via the Graduate Union. Unfortunately it never made it to the UL so has been resubmitted in 2018.




Davies, Nick


Hornbill, Behavioural Ecology, Intrafamilial Conflict, Communication, Zoology


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge