Twinning and embryonic mortality in a free-living kaka (Nestor meridionalis)

Authors: Berry R, Alley MR
Publication: New Zealand Veterinary Journal, Volume 50, Issue 1, pp 39, Feb 2002
Publisher: Taylor and Francis

Animal type: Avian, Wildlife
Subject Terms: Embryo/fetus, Reproduction, Reproduction - female, Disease/defect, Twinning/parity
Article class: Correspondence

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Abstract: Compared to mammals, twinning in birds is rare. The reported incidence in domestic chickens (Gallus gallus) is 0.11% (Byerly and Olsen 1934) and in pigeons (Columba livia) only 0.07% (Riddle 1923). Monozygotic twins occur following the fission of an early embryo and may or may not share the same yolk. Dizygotic twins are thought to occur following 2 simultaneous ovulations or perhaps by the slow passage of an ovum down the oviduct, resulting in it being caught by a succeeding yolk and then being incorporated into the same membrane and shell (Harrison 1986). Regardless of their origin most avian twins do not survive beyond hatching. Kaka (Nestor meridionalis) lay from September to January, producing clutches of 1-5 eggs. The female incubates for 23-25 days and the eggs hatch over several days (Heather and Robertson 1996). Between 1996-2001, 26 North Island kaka (N. meridionalis septentrionalis) have been released into a reserve of indigenous forest in the Mount Bruce region of the Wairarapa district, on the east coast of the North Island. All released kaka were fitted with radio transmitters and their survival and productivity have been closely monitored. Breeding first occurred during the spring and summer of 1998, 2 pairs nesting successfully. These pairs produced a total of 6 fledglings. During the 2000/01 breeding season….

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