New Zealand Journal of Zoology abstracts
Further evidence for Emlen’s hypothesis from two parrot species
Markus Neuhäuser
Department of Mathematics and Statistics
University of Otago
P.O. Box 56, Dunedin, New Zealand
email: mneuhauser@maths.otago.ac.nz
Abstract Recent studies have demonstrated that chromosomal
sex determination does not necessarily prevent facultative sex ratio adjustment
in birds. However, it is not known how the sex ratio adjustment is achieved.
One hypothesis states that birds might adjust the sex of the first-laid egg
only, but published data from Eclectus parrots indicated that the sex ratio
of second-laid eggs was also biased. In broods where two young were fledged
together, the two nestlings were often of the same sex. According to a re-analysis,
this finding, however, was not significant. In addition, new data from German
breeders are presented and, according to these data, there is no evidence
for a biased sex ratio in second-laid eggs either. Furthermore, I analyse
recently published data from kakapo. In this species there is a significantly
biased sex ratio for the first eggs, but again not for later eggs. Thus,
the sex ratio adjustment in both parrot species could arise through post-ovulation
adjustment according to Emlen’s hypothesis.
Keywords Eclectus parrot; exact statistical test; kakapo;
post-ovulation control; sex ratio adjustment
Z02029 Received 24 September 2002; accepted 7 February 2003; Online publication
date 8 September 2003
New Zealand Journal of Zoology, 2003, Vol. 30: 221-225
0301-4223/03/3003-0221 $7.00/0 © The Royal Society of New Zealand
2003
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