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title: "Hybridization between Northern and Southern Giant Petrels"
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# Hybridization between Northern and Southern Giant Petrels

Ruth Brown (Ecosystems Programme, [British Antarctic Survey](http://www.antarctica.ac.uk/), Cambridge, United Kingdom) and colleagues discuss hybridization in giant petrels *Macronectes* spp. in the open-access online journal [*PLoS ONE*](http://www.plosone.org/).

 The paper’s abstract follows:

 “Hybridization in natural populations provides an opportunity to study the evolutionary processes that shape divergence and genetic isolation of species. The emergence of pre-mating barriers is often the precursor to complete reproductive isolation.  However, in recently diverged species, pre-mating barriers may be incomplete, leading to hybridization between seemingly distinct taxa.  Here we report results of a long-term study at Bird Island, South Georgia, of the extent of hybridization, mate fidelity, timing of breeding and breeding success in mixed and conspecific pairs of the sibling species,*Macronectes halli* (northern giant petrel) and *M.giganteus* (southern giant petrel).  The proportion of mixed-species pairs varied annually from 0.4–2.4% (mean of 1.5%), and showed no linear trend with time.  Mean laying date in mixed-species pairs tended to be later than in northern giant petrel, and always earlier than in southern giant petrel pairs, and their breeding success (15.6%) was lower than that of conspecific pairs.  By comparison, mixed-species pairs at both Marion and Macquarie islands always failed before hatching.  Histories of birds in mixed-species pairs at Bird Island were variable; some bred previously or subsequently with a conspecific partner, others subsequently with a different allospecific partner, and some mixed-species pairs remained together for multiple seasons.  We also report the first verified back-crossing of a hybrid giant petrel with a female northern giant petrel.  We discuss the potential causes and evolutionary consequences of hybridization and back-crossing in giant petrels and summarize the incidence of back-crossing in other seabird species.”

 ![](https://www.acap.aq/images/stories/acap/Birds/Petrels/N/Northern_Giant/Northern_Giant_Petrel_by_Marienne_de_Villiers.jpg)

 Northern Giant Petrel on Marion Island, photograph by Marienne de Villiers

 With thanks to Richard Phillips for information.

 **Reference:**

 Brown, R.M., Techow, N.M.S.M., Wood, A.G. & Phillips, R.A. 2015.  Hybridization and back-crossing in giant petrels (*Macronectes giganteus* and *M. halli*) at Bird Island, South Georgia, and a summary of hybridization in seabirds.  [*PLoS ONE* 10(3): e0121688. doi:10.1371/journal.pone.0121688](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0121688).

 *John Cooper, ACAP Information Officer, 11 April 2015*