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Masaki Shirai (Graduate School of Environmental Studies, Nagoya University, Japan) and colleagues have published in the journal Ornithological Science on sexual size dimorphism in Streaked Shearwaters Calonectris leucomelas.

The paper’s abstract follows:

“We collected fresh Streaked Shearwater Calonectris leucomelas carcasses and describe sex differences in external measurements following sex identification using reproductive organs.  Males had significantly deeper bills, longer bills, longer heads, longer tarsi, greater wingspans and greater wing areas than females, but overall wing and tail lengths and aspect ratios did not differ between sexes.  Streaked Shearwaters showed a greater degree of sexual dimorphism in bill size than other Puffinus species.  Comparing the wing loadings of male and female Streaked Shearwaters, the mass increase required for females to have the same wing loading as males is 0.036 kg.  Females could feed to increase their body mass during a foraging trip to have similar wing loading to males.”

Reference:

Shirai, M., Niizuma, Y., Tsuchiya, K., Yamamoto, M. & Nariko, O. 2013.  Sexual size dimorphism in Streaked Shearwaters Calonectris leucomelas. Ornithological Science 12: 57-62.

John Cooper, ACAP Information Officer, 17 August 2013