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title: "UPDATED.  Who’s your father? Extra-pair paternity and cuckoldry in Streaked Shearwaters"
---

# UPDATED.  Who’s your father? Extra-pair paternity and cuckoldry in Streaked Shearwaters

UPDATE:  Read a popular article on the study [here](https://www.u-tokyo.ac.jp/focus/en/articles/z0508_00002.html).

 Miho Sakao ([Atmosphere and Ocean Research Institute](http://www.aori.u-tokyo.ac.jp/english/), The University of Tokyo, Kashiwa, Japan) and colleagues have published in the [*Journal of Ornithology*](https://link.springer.com/journal/10336) on extra-pair paternity in the [globally Near Threatened](http://datazone.birdlife.org/species/factsheet/streaked-shearwater-calonectris-leucomelas) Streaked Shearwater *Calonectris leucomelas.*

 The paper’s abstract follows:

 “Seabirds are long-lived birds that invest in offspring at very high levels, for which male parental care is indispensable. These characteristics are thought to explain seabirds’ generally low level of extra-pair paternity (EPP). Although the Streaked Shearwater (*Calonectris leucomelas*) is a socially monogamous seabird, it is known to copulate outside its social pair bond, which implies the frequent occurrence of EPP. In the closely related Cory’s Shearwater *Calonectris borealis*, cuckoldry is related to body size of the social male. To determine whether body-size-related EPP occurs among Streaked Shearwaters, we established 39 new microsatellite markers for parentage analysis and compared body size between cuckolded and non-cuckolded males. With the new markers, we found that extra-pair males sired 17 (15.0%) of 113 offspring during the 2014–2016 study period, which included three 1.5-month chick-rearing periods. This percentage is among the highest recorded for seabirds. We also found the bill and wing length of cuckolded males to be significantly shorter than those of non-cuckolded males, and that females can reject attempted copulations. These observations imply that EPP in this species is size related and involves female acceptance.”

  ![](https://www.acap.aq/images/stories/acap/Birds/Shearwaters/Shearwaters/Streaked_Shearwater.jpg)

 Streaked Shearwater

 **Reference:**

 Sakao, M., Takeshima, H. Inoue, K. & Sato, K. 2018.  Journal of Ornithology Extra-pair paternity in socially monogamous Streaked Shearwaters: forced copulation or female solicitation?  [*Journal of Ornithology*doi.org/10.1007/s10336-018-1587-3](https://link.springer.com/article/10.1007/s10336-018-1587-3).

 *John Cooper, ACAP Information Officer, 20 August 2018, updated 10 September 2018*