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Female Scarcity and Natal Dispersal Differences Between Sexes Among Bellbirds (Anthornis melanura)

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posted on 10.11.2021, 08:09 by Cresko, Hilary Misha

Sex ratio imbalances in wild bird populations have been a challenge for wildlife managers for decades. Differences between sexes during natal dispersal has long been thought to promote sex ratio imbalances. Natal dispersal distances may differ between sexes because of competition for food and space, or intrasexual competition and aggression. I investigated natal dispersal and intrasexual competition as mechanisms for a sex ratio imbalance in a small, translocated population of a New Zealand honeyeater, the bellbird (Anthornis melanura) in the Karori Wildlife Sanctuary- Zealandia, Wellington, New Zealand. I analysed long term records of population size and structure to document annual variation in sex ratios since the reintroduction of bellbirds to Zealandia. Radio telemetry was used to track the 2008/2009 cohort of bellbirds for five months after fledging to observe movements and distances travelled from their hatching location. Observations at a supplemental food source that was used by both adults and fledglings, were used to study intrasexual competition and aggression. Dispersal distances did not differ between the sexes for any of the measurement types used. Males did however significantly dominate the use of a supplemental food source and were significantly more aggressive around this food source, which is most likely responsible for the lower feeding rate among females. Therefore, I conclude that the sex ratio imbalance in the bellbird population in Zealandia may not result from a difference in natal dispersal, but from males dominating a supplemental food source, raising their population and fitness over that of females.


Copyright Date


Date of Award



Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline

Conservation Biology

Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level


Degree Name

Master of Conservation Biology

Victoria University of Wellington Item Type

Awarded Research Masters Thesis



Victoria University of Wellington School

School of Biological Sciences


Burns, Kevin