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title: "Can Southern Giant Petrels lay two-egg clutches?  Evidence from white-phase birds on Macquarie"
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# Can Southern Giant Petrels lay two-egg clutches?  Evidence from white-phase birds on Macquarie

Peter Shaughnessy ([South Australian Museum](https://www.samuseum.sa.gov.au/), North Terrace, Adelaide, Australia) has published in the open-access journal [*Marine Ornithology*](http://www.marineornithology.org/) on evidence suggesting Southern Giant Petrels *Macronectes giganteus* are able to lay a two-egg clutch.

 The paper's abstract follows:

 “Females of the order Procellariiformes most often produce single-egg clutches. At Macquarie Island (54°S, 159°E) in 1959 during a field study of Southern Giant Petrels *Macronectes giganteus*, four or five nests (0.14–0.18% of all nests) contained two eggs or two chicks (Warham 1962). This species occurs in two plumage forms, a dark phase and a white phase. Inheritance of these forms is controlled by a single autosomal gene with two alleles, with white phase dominant to dark phase. At Macquarie Island in 1959, one nest contained two white phase chicks brooded by a white-phase adult, which Warham (1962) believed resulted from a two-egg clutch rather than from polygyny. Analyses using probabilities based on the inheritance pattern of plumage phases in Southern Giant Petrels and the frequency of white-phase birds at Macquarie Island in 1959 indicate that it was almost seven times more likely that the two white-phase chicks in the nest brooded by a white-phase adult resulted from a clutch of two eggs rather than from polygyny.”

 [http://www.marineornithology.org/](http://www.marineornithology.org/)

  ![](https://acap.aq/images/stories/acap/Birds/Petrels/S/Southern_Giant/southern_giant_petrel_king_george_island_markus_ritz.jpg)

 White-phase Southern Giant Petrel, photograph by Markus Ritz 

 **Reference:**

 Shaughnessy, P.D. 2017. A two-egg clutch or polygyny?  Two white-phase chicks in the nest of a Southern Giant Petrel*Macronectes giganteus* at Macquarie Island.  [*Marine Ornithology* 45: 43-46](http://www.marineornithology.org/PDF/45_1/45_1_43-46.pdf).

 *John Cooper, ACAP Information Officer, 13 February 2017*