The number of Black-backed Gulls (Larus dominicanus) between the Otaki and Ohau Rivers, on the southwest coast of the North Island, has more than doubled in the last 25 years. There was a significantly larger proportion of subadults in 1961 than now, indicating that the population may have been in a growth phase in the early 1960s. The number of Red-billed Gulls (L. novaehollandiae) was about one-third of the 1961 level; this coincides with a sharp fall in the number of Red-billed Gulls nesting on nearby Kapiti Island. Numbers of other coastal birds were recorded and are discussed.
A genetic model is presented to explain plumage polymorphism in the Little Shag (Phalacrocorax melanoleucos brevirostris). Parent-offspring data from an Auckland colony show that expression of the three morphs (white-throated, smudgy and pied) is primarily controlled by two alleles at a single genetic locus. The allele specifying ‘dark’ (D) shows incomplete dominance over that specifying ‘pied’ (6). Comparison of morph frequencies with calculated genotype frequencies reveals that about 40% of white-throated birds are homozygous dominant (DD), the rest of the white-throated birds and all smudgy birds are heterozygous (Dd), and pied birds are homozygous recessive (dd). The population mates non-assortively and the Hardy-Weinberg law correctly predicts the frequencies of black and pied offspring from crosses. Morph frequencies (and allele ratios) show a gradient from north to south in New Zealand, dark birds being more common in the south. The main factor maintaining this cline may be climatic.
In 1985, 5,967 kilometres of coast were patrolled and 28,304 dead seabirds were found, both new records for the Beach Patrol Scheme. A new species for the Scheme was a White-bellied Storm Petrel (Fregetta grallaria). Ten
species were found in greater numbers in 1985 than in any previous year: Little Blue Penguin (Eudyptula minor), Buller’s Mollymawk (Diomedea bulleri), White-headed Petrel (Pterodroma lessonii), Fairy Prion (Pachyptila turtur), Fulmar Prion (P. crassirostris). Fluttering Shearwater (Puffinus gavia), Australasian Gannet (Sula bassana), Pied Shag (Phalacrocorax varius), Redbilled Gull (Larus novaehollandiae scopulinus) and White-fronted Tern (Sterna striata). The record numbers of Fairy Prions, Fulmar Prions and Fluttering Shearwaters were the result of wrecks of these species in August-September, mainly along the western and southern coasts of the North Island. A summary is given of the coastal and monthly distributions for most Pterodroma species found during the 1960-1984 period. The most frequently found species was the White-headed Petrel, a result of 30-100 being found in spring of most years.