16 Sep 2013
Whistling in the dark: an acoustic study of little spotted kiwi

BRANTA — Andrew Digby

Whistling in the dark: an acoustic study of little spotted kiwi

Institution: Victoria University of Wellington, New Zealand
Supervisors: Ben Ball, Paul Teal
Details: PhD 2013 (Completed)


Subject Keywords: Bioacoustics, communication, Apterygidae
Species Keywords: Little spotted kiwi, Apteryx owenii

Thesis Online here



Song function and evolution are two central topics of avian bioacoustic research. Discerning why birds sing and why they have such diversity of song can yield rich information on behaviour and speciation, and can provide important tools for conservation. Knowledge of vocal behaviour of a wide range of bird groups is necessary, yet avian bioacoustic studies have been hampered by a bias towards male song birds, with many species and even whole groups relatively unstudied.
The New Zealand kiwi (Apterygidae) are vocal and threatened taxa, and calls play an important part in their conservation. Yet kiwi acoustic behaviour is poorly understood, and although the five species differ significantly in their ecology, only one has been subject to detailed acoustic study. This thesis addresses this gap in knowledge of kiwi ecology with the first acoustic study of the little spotted kiwi (LSK). The principal aims are to improve understanding of kiwi calling behaviour, and to provide further acoustic tools for kiwi conservation. On a broader scale, enhanced knowledge of the acoustic ecology of the taxonomically and ecologically distinct kiwi will provide insight into song function and signal evolution in all birds.
Sexual call dimorphism in LSK is shown to be unrelated to size differences, and instead has likely functional significance, with male calls more suited for territorial defence. There is striking 'acoustic cooperation' between the sexes which constrains the function of duets in LSK. Analysis of complex vocal features, the first in any ratite, reveals that two-voicing is unexpectedly rare in this species, but that non-linear phenomena are common. Their association with territorial calls and high frequencies indicates that these features provide acoustic emphasis to enhance resource de- fence or convey aggression or fitness information. Non-linear phenomena are very common in nestling LSK calls, in accordance with the hypothesis that they add un-predictability to prevent habituation. LSK have surprisingly low inter-individual call variability, suggesting that this species may not use calls for individual identification. This lack of variability may be a result of the low genetic diversity in this species.
A long-term dataset reveals significant fluctuations in calling rates with temporal and environmental factors. These trends indicate that calls serve an important function for reproduction and pair contact, and that calls may reflect foraging activity.
They also provide evidence that kiwi are adversely affected by light pollution. A comparison of automated acoustic methods with manual call counts shows that while they have different biases, autonomous techniques are highly effective for kiwi conservation monitoring. Microphone array methods have great potential for enhancing conservation and behavioural information through spatial monitoring of kiwi, but are demonstrated not to be suitable with currently available equipment.


Digby, A., Bell, B. D. & Teal, P. D. 2013. Vocal cooperation between the sexes in Little Spotted Kiwi Apteryx owenii. Ibis, 155: 229-245.
Digby, A., Towsey, M., Bell, B. D. & Teal, P. D. 2013. A practical comparison of manual and autonomous methods for acoustic monitoring. Methods in Ecology and Evolution: doi: 10.1111/2041-210X.12060

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