The swamp harrier, so long the victim of persecution on farms along with other birds of prey, is now being billed as the “farmer’s friend”.
As farmers prepare for a new season of planting and reaping, the value of the harriers in rodent control is being promoted by the Agricultural Contractors’ Association of Tasmania. It is advising farmers that if they want to increase their yields, they should exercise “due care and protection” when dealing with the harriers.
Since the early 1800s when European farm settlement begin in Tasmania, birds of prey, along with forest ravens, have been killed in rural areas, mainly because of the threat they are seen to pose to domestic stock, including chickens.
In the harrier’s case it has been largely a case of mistaken identify. Although similarly-sized goshawks and brown falcons might target chooks round farm dwellings, the harrier is largely a creature of open paddock where it is more interested in putting the masked lapwing – or plover, as it is known in Tasmania – on the menu.
The migratory swamp harrier actually times its early arrival in the state to coincide with the plover breeding season, which begins at the end of winter going into early spring.
A swamp harrier is ground-nesting raptor built for vertical take-off and stall-speed flying. It soars in its hunt for rodents on distinctive v-shaped wings and also has a white patch on the rump, which easily separates it from other birds of prey.
Before European settlement, the harriers hunted and nested in wet grasslands and marshes but much of this habitat has now been drained to create farmland.
The harriers have been forced to breed in areas that have now become paddock and this brings them into conflict with farmers and, especially, farm machinery.
But it is only recently that fields and paddocks have become large-scale killing grounds. Agriculture was once carried out at a more leisurely pace, giving the harriers time to rear young.
Mechanisation and more intensive farming methods have in the 21st century put the harriers and their eggs and young in danger.
What’s in the harriers’ favour, however, is a growing understanding of what role avian predators play in the farmland environment, and how they can actually aid farmers instead of being viewed as the enemy.
Farmers are now being urged by the contractors’ association to identify harriers on their properties and watch out for signs of breeding and then nesting sites among crops. Once these have been identified, farmers can create buffer zones around the nests as the paddock is being harvested. Five metres – or two tractors’ lengths – is recommended.
Even after crops have been harvested and cover around nests has been left standing, a delay in post-harvest grazing by cattle or the erection of a temporary fence is also recommended until after the chicks have flown. This saves the nestlings being trampled by cows.
I wrote a few years ago of a nesting pair of harriers saved by a sympathetic land-owner on the outskirts of Hobart, who had discovered a nest just before he had started to mow and bail a paddock of hay.
The property owner left a little more than the required buffer zone around the nest because he was concerned that inquisitive forest ravens, who had watched his movements, would find the young. He was also worried about feral cats in the neighbourhood, another threat to harrier breeding success.
It was a great thrill for me to be invited out to Cambridge to view the nest with its rapidly-growing young. The harrier parents continued to feed their offspring after they had flown from the nest, and the whole family departed for the mainland at the end of summer. Harriers – possibly the parents or their young – have returned to the property in recent summers.