The swamp harrier (Circus approximans), also known as the kāhu, harrier hawk or Australasian harrier, is a bird of the open country. It is often seen soaring and looking for prey, or eating dead rabbits or possums on the road.
The swamp harrier also occurs in Australia, New Guinea and many islands of the southern Pacific. In New Zealand harriers are found from the Kermadec Islands in the far north, to the Chatham Islands, and they occasionally stray as far as the chilly subantarctic islands.
Fossil records show that it came across the Tasman Sea from Australia, and became established in New Zealand less than 1,000 years ago. At that time Eyles’s harrier (Circus eylesi), four times larger, was also present.
At 850 grams, fully grown females are 200 grams heavier than males. Both sexes are the same length, about 55 centimetres. The oldest known age for a harrier in New Zealand is 18 years.
Habitat and food
Swamp harriers hunt in open country. After Europeans arrived in New Zealand and cleared land for farming, the birds’ numbers increased. They catch small birds and mammals up to the size of rabbits, as well as lizards, frogs, fish and large insects. They also eat carrion, including road kill and dead lambs, and spend much time hunting for birds' nests. Since the 1950s, successful rabbit control has meant less food for harriers, and their numbers have fallen.
The harrier is an adept hunter when flying, as ornithologist Edgar F. Stead observed:
One day I watched a Harrier beating over a stubble field, when it flushed a Skylark, which flew away some distance and settled. The Harrier carefully marked the spot, and flew swift and low towards it; saw the Lark, and struck at it on the ground. The Lark dodged the blow, ducked out from beneath the Hawk, and settled again about two yards away; but the Hawk, with a rapidity of movement with which one could scarcely have credited it, rose and swept back on its victim and flew off with it in its talons. 1
When looking for food, harriers hold their large straight wings in a shallow V to soar on thermal winds, circling effortlessly until they dive for prey. In their courtship ritual, the male performs steep dives and loops, and the female turns on her back in mid-air to greet him.
The breeding season starts in June, when males establish territories of several square kilometres. Females build nests in tall grass-like plants such as toetoe. They usually lay three to five off-white eggs between September and December. The male does not feed the chicks, but delivers food to his mate while both are flying. Chicks are able to leave the nest at 45 days.
Signs of age
Māori knew older harriers as kāhu-kōrako, a reference to their pale feathers. As harriers grow older, they lose the dark plumage of youth, and some very old birds appear almost grey.
Believing harriers posed a threat to introduced game birds such as partridges, pheasant and quail, Acclimatisation Societies offered a bounty until the 1940s. Hundreds of thousands were killed between 1860 and 1950. Naturalist Walter Buller reported that ‘upwards of a thousand’ were killed each year on one Canterbury sheep run – yet they remained abundant.
The harrier has been protected by law since 1986.
To Māori, the harrier was a symbol of victory and chieftainship. Its effortless flight inspired a chant used by East Coast Māori when performing a difficult task like moving a heavy log:
Te kāhu i runga whakaaorangi ana e rā,
Te pērā koia tōku rite, inawa ē!
The hawk up above moves like clouds in the sky.
Let me do the same! 2