Only two representatives of the hawklike birds of prey (order Falconiformes) are native to this country, the New Zealand falcon or bush hawk, Falco novaeseelandiae, and the harrier, Circus approximans. The former is found only in New Zealand, is now relatively rare, and has a rather restricted distribution. The harrier is not confined to our shores; other subspecies occur elsewhere and our particular one is also native to Australia and New Guinea.
Within New Zealand harriers are a common sight in almost any stretch of open country at any time of year. Usually their powered flight is slow but sustained and they are much given to soaring on ascending currents of warm air. To accomplish this their broad (or low aspect-ratio) wings are outstretched in a shallow “V” and the birds are then carried aloft. By pursuing a spiral path they remain within the rising thermal and, whilst gliding in this way, scan the ground for prey.
Harriers eat a variety of food and, although they hunt other birds, hares, rabbits, rats, mice, lizards, frogs, fish, and insects, they rely heavily on material already dead (i.e., carrion) and are themselves often killed by being struck by vehicles whilst feeding on the corpses of the various species of wildlife (especially rabbits, hedgehogs, and opossums) that are so regularly run over on the roads. Though persecuted as “vermin” by the uncritical, harriers, like other native predatory animals, play an essential part in natural communities.
Mating occurs in early spring and is accompanied by spectacular courtship aerobatics and shrill yelping cries. Nests are made on the ground amidst such cover as toetoe, flax, raupo, grain crops, and lucerne. The untidy nest bowl is about 3 ft in diameter and is made of surrounding vegetation. The usual clutch is of four white eggs and the weakest young may eventually serve as food for the strongest. Parents, when disturbed, may readily desert eggs or young.
As is the rule among Falconiformes, females are larger than males, though the difference is not a good guide to the sexes in the field. Young, fully fledged harriers are mainly dark brown above and reddish brown below. Plumage becomes progressively paler with age.
by Gordon Roy Williams, B.SC.(HONS.)(SYDNEY), Lecturer in Agricultural Zoology, Lincoln Agricultural College.