The secret life of wild brown kiwi: studying behaviour of a cryptic species by direct observation

Kiwi possess many unusual features that make them interesting subjects for behavioural study. However, their nocturnal, cryptic nature has meant that studies to date rely on data collected indirectly. Infrared technology has enabled us to observe kiwi directly and here we present the first study of wild brown kiwi (Apteryx mantelli) behaviour by direct observation. We used handheld infrared video cameras to obtain c. 6 hours of video footage of kiwi over 19 months. Kiwi used native forest and exotic pasture habitats while active at night and spent most of their time foraging (75%). Prey capture rates were significantly higher in pasture than forest. The remaining 25% of time was spent walking, vigilant, engaged in comfort behaviours, escaping disturbance, and investigating obstacles. Direct social and courtship interactions were observed rarely. The senses of hearing, olfaction and touch seemed most important to kiwi. Touch was used for investigating terrain and negotiating obstacles. Hearing was used in response to sounds made by observers, conspecifics and other sources. Olfactory search behaviours (OSBs) were used in the direction of these sounds, and olfaction was also apparently used to assess odours on the ground. We observed no behaviours that appeared to be guided by vision. Behavioural repertoire size and diversity increased in winter, due to increases in OSBs towards conspecifics and other odour sources, and rarely observed behaviours. Prey capture rates also increased near-significantly in winter and microhabitat use was more diverse. Female kiwi at our study site had 30% longer bills than males, and probed into soil substrates on average 30% deeper. No other fine-scale behaviours that might reduce competition between kiwi sexes were observed.