Written by Neil Hetherington (Lincoln University)
Edited by Michael Hudson, Lincoln University, September 2006
- Scientific name: Circus approximans Gouldi (Bonaparte, 1850)
- Popular Common names: Australasian Harrier, harrier hawk, kahu, keranga
- Other common names: swamp harrier, marsh harrier
- Kingdom: Animalia
- Phylum: Chordata
- Class: Aves (the birds)
- Order: Falconiformes (the diurnal birds of prey)
- Family: Accipitridae (the hawks, eagles, and old world vultures)
- New Zealand Status: Indigenous
- Taxonomy sources: Checklist of New Zealand Birds (1953); Heather and Robertson (1996); Baker-Gabb (1979).
Heather and Robertson (1996) understand that the harriers colouring differs with age. Colours start out with very dark browns. These fade into paler dark browns as the harrier matures and gets older. The colour of a harriers eyes can be used as an indication of age. A juvenile male harrier has brown coloured eyes. The eye colouring changes as the bird matures, first to a speckled yellow then through to a full yellow by the age of two years old (Heather and Robertson, 1996). The female harrier also goes through a similar eye colour change; apart from the adult eye colouring is a paler yellow than that of the male (Robertson and Heather, 1999).
The colour of the plumage on the harrier can also be an indication of age. Where juvenile harriers start off with a dark, mostly brown plumage, this later transforms into lighter browns and can sometimes end up resembling shades of grey (Heather and Robertson, 1996).
When determining gender of the harrier it is quite easy to judge male or female based on the size of the particular harrier. Female harriers are on average bigger than their male counterparts. Females weigh in at around 850 grams and have an average length of around 60 centimetres. The male harrier averages only 650 grams and is only around 55 centimetres long (Robertson and Heather, 1999).
Full natural and naturalised range
Heather and Robertson (1996) describe the Circus approximans as breeding in Australia, South eastern New Guinea, and widely through the South Pacific; including New Caledonia, Tonga, Fiji, Vanuatu, Wallis Island, French Polynesia, New Zealand and also vagrants are found in Samoa and the Cook Islands.
New Zealand range
The Australasian harrier is abundant throughout New Zealand. The harrier also reaches as far as the Chatham, Kermadec, Snares, Auckland and Campbell Islands (Heather and Robertson, 1996). Rarely found in dense forest, kahu are not found in Fiordland or along the centre of both the North and South Islands where the National Parks and forests are.
The Australasian harrier is common throughout the Canterbury region due to an abundance of preferred habitat. With its flat open area Canterbury is ideal for the harrier.
Natural History in Canterbury
The kahu can be found naturally in wetlands, farmland, tussock land, scrubland, along coasts and river banks (Heather and Robertson, 1996). The harrier likes open areas where it has room to move and also has room to hunt. So by the early settlers converting the Canterbury area into what it resembles today has made the area more habitable for the harrier.
Although at home in the habitats previously mentioned, the Australasian harrier prefers a different habitat when it is breeding. Harrier chicks are raised and feed in a nest. These nests are commonly found in raupo swamp or dune hollow swamp (Baker-Gabb, 1981a). The female harrier, who builds the nest, gathers material from the nearby swampland with most of that material consisting of flax, thistle and leaves. Long grasses form the soft base in which the female will lay her eggs and feed the chicks after they have hatched (Baker-Gabb, 1981a).
The location of the kahu nest in swampy areas surrounded by tall reeds and other vegetation, provide an element of protection against both predators and the weather (Baker-Gabb, 1981a). These two elements are illustrated in Figure 3; the picture clearly shows the tall vegetation and the material of the birds nest.
The Australasian Harrier likes to display its power and authority. These traits can be seen throughout the breeding cycle by the male harrier performing territorial flights or border – patrols (Baker-Gabb, 1981a). Patrolling harriers were seen to evict intruders by escorting them out of their territories. In the lead up to the breeding season these sorts of flights have been seen to happen up to six times a day leading up to the breeding season (Baker-Gabb, 1981a). “Display-flights were preformed by the male, accompanied by the males short ‘kee-a’ courtship call” (Baker-Gabb, 1981a). The response from a female harrier would be the female’s courtship call of ‘kee-o’ (Baker-Gabb, 1981a).
Breeding occurs between September and February (Robertson and Heather, 1999). Harriers normally lay between three to five eggs (Heather and Robertson, 1996). Care of the chicks is predominately by the female who looks after the chicks until they fledge (develop flight feathers) six to seven weeks after hatching. Once fledged the chicks gradually leave the nest area and go alone into the world (Heather and Robertson, 1996).
Exhibiting flexibility in their diet (Baker-Gabb, 1981; cited in Pierce and Maloney, 1989) the kahu frequently change their diet to suit the available food source around its habitat.
From researching harrier in the Mackenzie Basin Pierce and Maloney (1989) found that the harrier targeted rabbit as its main prey item. Their conclusion was that this was due to the abundance of rabbit in the area. This helps to support the idea of harriers adapting to the most abundant food source. Whether it is live prey or carrion (dead animals), harriers will eat it (Heather and Robertson, 1996). The carrion that harriers are most accustomed to eating is that of road killed animals (Robertson and Heather, 1999); the road is probably the most likely place to come in contact with an Australasian harrier.
Harriers are a very territorial raptor (bird of prey). They establish their boundaries and defend them with their display flights and border patrols. The Circus approximans is usually a solitary creature only forming pairs for the breeding season (Heather and Robertson, 1996). With this solitary existence comes also the preference of harriers to remain silent, emitting only brief whistles from time to time (Heather and Robertson, 1996).
How to find the Australasian Harrier
Due to their abundance in our environment’s and natural landscapes, harriers are most likely to be seen near their preferred habitats the kahu can be found in swamps, forest edges, open farmland, all places where there is a chance that they will find prey to be caught. A killed animal on the road is also another likely spot where you might find a harrier nearby (Personal Observation). Due to their ability to eat either dead or alive animals; if it is there they will eat it. Alternatively during their breeding season you might sight their border-patrols or display flights.
Abundance and Conservation Status
- New Zealand: abundant
- Canterbury: abundant
Along with the conversion of the majority of New Zealand into farmland and wide open spaces, the harrier has been able to breed and occupy these spaces to the point where it has adapted to the habitats it lives in. The harrier can now move around New Zealand with relative ease.
Harriers are spread right across New Zealand. They are in no short supply either in Canterbury or New Zealand.
Significance for people
Traditional Maori significance and uses
Kahu (or kerangi) was according to Maori traditions originally one of the several things that was brought down form the heavens by Tane Matua; Tane the Parent. Because of this connection with the heavens the kahu is regarded by Maori people as being a messenger to and from the goods, (Murdoch and riley, 2001). The harrier is valued with significance by the Maori people.
Being bird of prey the harrier are useful for decreasing or controlling the rabbit population. Unfortunately at the same time they also pose a risk to native birds (Baker-Gabb, 1981b), thereby resulting in the need to watch and protect our native birds. The harrier are also useful for cleaning up the road kill and other dead animals.
The Australasian harrier, as the name implies, has connections all over the pacific. Found throughout New Zealand the kohu has adapted to the modern transformation of the country to open habitat, forming part of the ecology and playing a part in how it works. Whether it is cleaning our roads, keeping our rabbit populations down, or just adding a different aspect to our bird life, the Harrier has a role to play.
Baker-Gabb, D.J. (1981). Breeding Behaviour and ecology of the Australasian Harrier (Circus approximans) in the Manawatu – Rangitiki Sand Country, New Zealand. Notornis, 28, 103–119
Baker-Gabb, D.J. (1981). The diet of the Australasian Harrier (Circus approximans) in the Manawatu – Rangitiki Sand Country, New Zealand. Notornis, 28, 241–254
Bull, P.C., Gaze, P.D., Robertson, C.J.R. (1985). The Atlas of Bird Distribution in New Zealand. Ornithological society of New Zealand, Auckland, New Zealand
Checklist Committee of the Ornithological Society of New Zealand (1953). Checklist of New Zealand Birds. A. H. and A.W. Reed in conjunction with the Ornithological society of New Zealand, Inc., Auckland, New Zealand
Heather, B. & Robertson, H. (1996). The field guide to the birds of New Zealand. Penguin Books, Auckland , New Zealand.
Moon, G. (1979). The birds around us – New Zealand Birds, their habits and habitats. Heinemann, Auckland , New Zealand
Pierce, R.J. & Maloney, R.F. (1989). Responses of harriers in the Mackenzie basin to the abundance of rabbits. Notornis, 36, 1–12
Riley, M. (2001). Maori Bird Lore - An Introduction. Viking Sevenseas NZ Ltd, Paraparaumu, New Zealand
Robertson, H. & Heather, B. (1999). The hand guide to the birds of New Zealand. Penguin Books, Auckland, New Zealand.