During 1967, rooks at West Melton and Banks Peninsula rookeries selected mainly Pinus radiata for nesting and chose the highest safe sites. Nest construction periods varied from 5 to 20 days, the last nests being completed most rapidly. Eggs were laid between 30 August and 6 November. Rookeries showed significant differences in laying date, apparently resulting from differences in food availability. The size of eggs varied with laying sequence. The mean clutch size was different at each rookery, ranging between 2.9 and 3.8 eggs, a similar value to that obtained by past workers in Canterbury but smaller than that of rooks in Britain. Nestling periods were directly related to brood size. Growth rates of nestlings varied with brood size, hatching sequence, partial brood loss and season. Parental feeding visits were largely independent of brood size and ranged from 1.4 to 3.3 visits per hour. Failure of the embryo to develop accounted for most egg losses. Most nestling mortality resulted from parents killing the smallest nestling before it died of starvation. Breeding success varied seasonally and ranged from 38 to 12.7%. Three and four egg clutches occurred most frequently, but larger clutches produced more fledglings.
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.
The field characters of both the thin-billed prion (Pachyptila belcheri (Mathews, 1912) ) and the Antarctic prion (P. desolata banksi (Smith, 1840) and P.d. alter (Mathews, 1912)) are described and a discussion of the differing feeding habits and food is given. The food of Pachyptila belcheri chiefly consists of the amphipod Parathemisto gaudichaudii which is taken nocturnally, while the “krill” Euphausia superba is the primary food source of P. desolata and is mainly captured by day. The thin-billed prion ranges far from its known breeding grounds at the Falkland Islands and Kerguelen, and is the most frequently encountered Pachyptila in the southernmost waters of the central Pacific. Birds of the year reach the Bellingshausen Sea from the Falkland Islands by mid-April, and disperse over much of the South Pacific during May. In early November, sub-mature birds gather in substantial numbers south of the Antarctic Convergence to take advantage of a rich food supply and undergo an early moult in December and January. The adults apparently begin the moult cycle in early February and are through by May. The distribution of both species of prion is discussed on the basis of field work and specimen records, and an attempt has been made to correlate this data with published information. A tentative distributional pattern for both species is presented.