Distribution and numbers of the rook (Corvus frugilegus l.) in the north island of new zealand

Abstract

Historical data, and surveys of rookeries during 1956-69, document the increase and spread of rooks since their introduction near Auckland and Napier during the early 1870s to control insects. The Auckland rooks disappeared after 30 years, but the Napier ones had increased by 1969 to at least 20 000 breeding adults in 128 rookeries distributed over some 6000 km2 of farm land in central and southern Hawkes Bay; small colonies have appeared in several widely separated North Island localities, including the Auckland district. Compared with other European birds in New Zealand, rooks have spread very slowly, probably because of their strong attachment to traditional breeding and roosting places. The death of nesting trees and disturbance of birds by control measures probably accelerate spread, which is of two kinds: a progressive colonisation of new territory just beyond that already occupied and, less commonly, the establishment of small, remote groups. The breeding population in Hawkes Bay appears from nest counts to have doubled during 1965-69, when rook control was relaxed and crop acreages were increased. The greatest density of nests was in areas occupied for over 30 years, but even after the number of nests had doubled they averaged only 3/km2, much less than in Britain. Rookeries less than 3 years old averaged 17 (range 3-74) nests, compared with 149 (range 3-901) in rookeries more than 20 years old; 65% of the rookeries were less than 12 years old. In established rookeries, there was a small but consistent change in nest-site preference from eucalypts to pines during 1965-69. The numbers and distribution of rooks in the North Island will probably increase still further, though periodical poisoning may achieve local reductions in agricultural areas. South Island rook populations are here discussed only incidentally. © 1975 Taylor & Francis Group, LLC.