Inter-Research > ESR > v39 > p293-302  

ESR 39:293-302 (2019)  -  DOI: https://doi.org/10.3354/esr00970

Sexual and geographic dimorphism in northern rockhopper penguins breeding in the South Atlantic Ocean

Antje Steinfurth1,2,*,**, Jenny M. Booth3,**, Jeff White4, Alexander L. Bond5,6, Christopher D. McQuaid3

1FitzPatrick Institute of African Ornithology, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch 7700, South Africa
2RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, David Attenborough Building, Cambridge, Cambridgeshire CB2 3QZ, UK
3Coastal Research Group, Department of Zoology and Entomology, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
4Marshall University, Huntington, WV 25755, USA
5RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK
6Bird Group, Department of Life Sciences, The Natural History Museum, Tring, Hertfordshire HP23 6AP, UK
*Corresponding author:
**These authors equally contributed to this work

ABSTRACT: The Endangered northern rockhopper penguin Eudyptes moseleyi, like all penguins, is monomorphic, making sex determination of individuals in the field challenging. We examined the degree of sexual size dimorphism of adult birds across the species’ breeding range in the Atlantic Ocean and developed discriminant functions (DF) to predict individuals’ sex using morphometric measurements. We found significant site-specific differences in both bill length and bill depth, with males being the larger sex on each island. Across all islands, bill length contributed 78% to dissimilarity between sexes. Penguins on Gough Island had significantly longer bills, whilst those from Tristan da Cunha had the deepest. Island-specific DFs correctly classified 82-94% of individuals, and all functions performed significantly better than chance. The model for Nightingale Island correctly classified the greatest proportion of individuals (94-95%), while that for Tristan da Cunha performed the poorest (80-82%). A discriminant function derived from all sites accurately sexed 86-88% of northern rockhopper penguins achieving similar accuracy to island-specific functions. While molecular techniques conclusively determine an individual’s sex, morphometric measurements can provide a reliable estimate with close to 90% accuracy using a method that is less invasive and requires little technical expertise. Sexing is an important tool for meaningful interpretation of ecological data. Consideration of sex-specific differences in future studies will aid investigation of a potential sex-dependent vulnerability in this Endangered species.


KEY WORDS: Northern rockhopper penguin · Eudyptes moseleyi · Sexual dimorphism · Discriminant function analysis · Morphological sexing · Morphometrics


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Cite this article as: Steinfurth A, Booth JM, White J, Bond AL, McQuaid CD (2019) Sexual and geographic dimorphism in northern rockhopper penguins breeding in the South Atlantic Ocean. Endang Species Res 39:293-302. https://doi.org/10.3354/esr00970

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