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Counts of the black and pied morphs (or forms) of the New Zealand fantail (Rhipidura fuliginosa) in east Otago in 1969 gave a total of 824 pied (88.22%) and 110 black (11.78%). These proportions do not differ significantly from those established by other workers for the South Island. However, morph frequency was found to vary in relation to the type of vegetation, the feeding station, and possibly also to altitude. Of the three vegetation types sampled, native hardwood forest had the highest frequency of the black morph (21%) and kanuka-manuka the lowest (5%). Introduced conifer forest had an intermediate value (14%). More pied birds were observed feeding in the canopy than in the ground to shrub layer, while the black morph showed the opposite trend. Only a restricted altitude range was sampled, but the data indicate that the black morph may be more common at higher than at lower altitudes.

Breeding data reported up to September 1970, are analysed and shown to fit the hypothesis (Caughley 1969) that the difference between pied and black is controlled by a single genetic locus with pied birds homozygous for a recessive allele. Allele frequencies are estimated as p₁ (black) 0.06 and p₂ (pied) 0.94 and morph frequencies overall agree well with those expected on the basis of Hardy-Weinberg equilibrium. There is no evidence, therefore, to implicate heterosis as a mechanism for maintaining the polymorphism. Differential habitat utilization may be such a mechanism but is unlikely to be the only one. Much work remains to be done in analysing the fantail polymorphism.