Two-egg clutches among albatrosses
Peter G. Ryan A D , Richard Cuthbert B and John Cooper C
A DST/NRF Centre of Excellence at the Percy FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa.
B Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK.
C Avian Demography Unit, University of Cape Town, Rondebosch 7701, South Africa.
D Corresponding author. Email: email@example.com
Emu 107(3) 210-213 http://dx.doi.org/10.1071/MU07018
Submitted: 13 March 2007 Accepted: 27 July 2007 Published: 7 September 2007
Albatrosses typically lay clutches of one, but nests with two eggs are observed occasionally. We report a relatively high incidence (0.1–1.0%) of such clutches among Atlantic Yellow-nosed Albatrosses (Thalassarche chlororhynchos) compared with Grey-headed (T. chrysostoma), Wandering (Diomedea exulans) and Tristan (D. dabbenena) Albatrosses studied at Marion and Gough Islands (no records of nests with two eggs). In at least some cases, two pairs attempted to breed in the same nest, but in other cases a single male may have consorted with two females. Egg-dumping may have accounted for some records. Our observations support the hypothesis that apparent clutches of two typically occur among inexperienced breeders, possibly because they spend less time at the nest before laying or are more easily displaced from their nests, or both. Two-egg clutches rarely, if ever, increased parental fitness, and appear to be mistakes. The flexible mating strategy of Atlantic Yellow-nosed Albatrosses may contribute to the relatively high frequency of two-egg clutches in this species. Their incidence does not appear to be linked to high nesting density.
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