[First record of the runt eggs of the Imperial Cormorant Phalacrocorax atriceps and the Rock Shag P. magellanicus in the San Jorge Gulf, Argentina]

  • Gabriel Punta Instituto de Investigaciones en Hidrobiología, Universidad Nacional de la Patagonia San Juan Bosco, Facultad de Ciencias Naturales y Ciencias de la Salud, Chubut; Secretaría de Pesca y Acuicultura de la Provincia del Chubut, Argentina.
  • Anabella Covazzi Harriague | anabella7@hotmail.com Università degli Studi di Genova, DiSTAV, Italy.


[The present study describes for the first time the abnormally small (runt) eggs of the Imperial Cormorant (IC) and Rock Shag (RS) observed during the breeding seasons of 1990/91, 1992/93, 1993/1994, 1994/95 and 1996/97 on the Isabel Island (45°07’S, 66°30’W) and the Galiano Island (45°06’S, 66°25’W), located in the northern San Jorge Gulf, Argentina. The frequency of occurrence of IC runt eggs was 0.2% (n = 995) and their average volume was significantly lower than normal eggs (t = 17.4, P< 0.0001, n = 824). The runt eggs were more spherical than those of normal size (Shape Index: 70.6 vs 64.5 for CI and 74.9 vs 63.9 for RS). The volume of the RS runt egg was 21.1 cm3. The cutoff between normal and runt eggs is between 30 and 35 cm3 for the IC and between 24 and 30 cm3 for the RS. The volume of the runt egg was 42.1% and 53.4% the average volume of the two remaining eggs of the clutch for CI and RS, respectively. None of the consistently observed IC runt eggs hatched and it seems that none of the eggs showing a volume lower than the proposed cutoff is destined to hatch].


[Article in Italian]



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runt eggs, hatching failure, Imperial Cormorant, Rock Shag, San Jorge Gulf, Argentine
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How to Cite
Punta, G., & Covazzi Harriague, A. (2021). [First record of the runt eggs of the Imperial Cormorant <em>Phalacrocorax atriceps</em> and the Rock Shag <em>P. magellanicus</em&gt; in the San Jorge Gulf, Argentina]. Rivista Italiana Di Ornitologia, 90(2). https://doi.org/10.4081/rio.2020.460