Black future for rooks
Clare Wishart says she is a ‘‘rook enthusiast’’. New Zealand has many of the black birds, but regional councils plan to exterminate them. Farm reporter Jill Galloway reports.
One collective noun for rooks is a ‘‘storytelling of rooks’’. They are noisy with their distinctive ‘‘kaah’’ call. The collective noun for crows is a ‘murder of crows’ and if regional councils have their way – it could be a murder of rooks.
That is because regional councils and many farmers see the rooks as pests. Horizons, the Manawatu/Wanganui regional council, says most serious is the damage they cause to farms by eating and destroying newly sown cereals, walnuts, acorns, pumpkin seeds and occasionally potatoes and fruit.
The environmental manager biosecurity and response, Bill Martyn says it has gone from wanting to limit rook numbers – to eradication.
‘‘They’re known to be destructive of crops, and we can now look at eradicating them, because it is now possible with modern techniques.
It’s the change from controlling rook numbers to eradication that has upset Clare Wishart.
‘‘I’m a rook enthusiast. While I don’t have a problem with controlling the numbers, I do with killing all the rooks.’’
She says many New Zealanders have no idea this is home to rooks. They are members of the corvidae family, along with crows and ravens. They are about the same size as a large magpie and have glossy black plumage, with a slightly purple tint.
The corvidae family are the most intelligent birds on Earth – their brain to body ratio is the same as dolphins and humans.
They’re smart – the Einsteins of the avain world. In the journal, Current Biology, researchers say crows in New Caledonia used tools (a short stick), to get at other tools (a long stick), which they can then use to get food. And they appear to solve problems with reasoning, rather than brute force.
Unlike others in the corvidae family, rooks are gregarious. They roost together in colonies called rookeries. They nest in high trees and usually feed in flocks.
They are too smart to lose many birds to shooting or ground poisoning, and after they became ‘‘bait shy’’, regional councils have used helicopter poisoning of the rookeries instead.
Poison is dropped – it includes a petroleum jelly sticky ingredient to carry the poison DAC 1339 and it is sprayed, as the applicator dangles uder a helicopter – straight into the rooks’ nests.
The birds preen themselves and die, but after several days of agony and failing organs Ms Wishart says. The poison hits the females, who stay in the nest with their young, and the chicks. Because of that, it is thought there are more male rooks than females in Hawke’s Bay.
Rooks were introduced to New Zealand in 1862 to control insects. There were liberations in Auckland and Nelson, which failed, as well as the successes of Hawke’s Bay and Canterbury.
‘‘Fifty years after their introduction, rooks in Hawke’s Bay had spread only 30 kilometres, while 100 years after their introduction in Canterbury, they had spread only 50 kilometres,’’ Ms Wishart says.
They were introduced to eat insects, and she says that is exactly what they do.
‘‘A rook diet includes a whole host of pasture pests, including weevils, striped dung flies, grass grubs and blow fly larvae as well as wasps, moths and mosquitoes.’’
They also kill and eat mice – the good they do has never been calculated against the damage.
She says research shows the rooks only turn to newly sown crops when their beaks can’t probe the ground because of winter frosts or summer drought – and in nature, that is called survival.
But humans see that differently and for some of the time, the birds compete for the same food source.
‘‘So the rooks have been labelled pests. Even though the majority of time, they are killing unwanted insects.’’
A rook damage survey was carried out in Hawke’s Bay in 1969 and of the 400 replies, 46 percent said they had suffered crop damage. ‘‘This was said to be $823 for each of these 187 ratepayers. But it included their estimated time spent on bird scaring and control, the cost of guns, ammunition, poison and scareguns.’’
As a direct result of the survey paper, Ms Wishart says ‘‘a rook holocaust began and 86,000 rooks were shot or poisoned in Hawke’s Bay’’.
Then the remaining 5000 birds spread their wings, and many moved out of the region.
She says far wider dispersement meant rooks have been seen over much of the North Island, as well as Otago and even on the Chathams and Stewart Island. A rookery has even set up base on Waiouru Military Camp land.
Their dispersal meant the Tararua district, which had been rook-free until the 1970s, became home to some.
Horizons puts it this way. Mr Martyn says a survey of active nests shows they are spread between Palmerston North and Taihape, but there is a cluster in Tararua and that is the hot spot, the council says.
‘‘Rooks are a particular pest in Tararua District, although they are widespread throughout the region. We are always keen to hear of new rookeries establishing, so please let us know.
‘‘Rooks are considered a regionally undesirable animal, based on the impact these birds can, and do have on our environment. Therefore Horizons carries out control operations and monitoring of rook populations at no cost to affected landowners.’’
Mr Martin says there are 1272 active nests in Horizons’ area.
‘‘You have to evaluate if harm is being caused. Then can you control it?v Or can you eradicate it at a responsible cost?’’
He says rooks are mainly a rural problem, which is reflected in the rating formula for rook control, with a targeted rate of 90 percent on all properties over 4 hectares and 10 percent coming from general rates.
Horizons’ Proposed Regional Pest Management Strategy is currently under review. The strategy highlights the path that Horizons thinks is the best direction for pest control into the future. The opportunity to have your say is now.
However, the ‘‘rook problem’’, which Horizons believes exists, does not wash with Ms Wishart.
‘‘I have no problem with the control of rooks, but eradication, which is openly publicised on regional council websites, that’s different.’’
She says Christchurch’s rook population has already been wiped out and currently the Hawke’s Bay Regional Council plans to eradicate all rooks by 2013. Horizons is planning to follow suit, eradicating all rooks by 2020.
This action is not necessary, Ms Wishart says, and it is years since there has been a problem with the number of rooks.
Richard Porter, who is retired from the DSIR and Landcare Research, has researched rook populations.
‘‘The rook population changed over from the dense population centred in large rookeries in a small area, to a less dense population, in small rookeries scattered over a much larger area,’’ he wrote.
By the mid 1980s, estimated rook damage went to almost nothing as indicated by complaints received by the DSIR and pest destruction Board, Mr Porter said.
Low rookery numbers means the birds do not pose an economic threat any more, he said.
A rook census is done by counting known nests and multiplying by 3.5, but Ms Wishart believes the birds are overcounted.
‘‘Rooks are not prolific breeders. An average of only 1-2 chicks survive per nest each year and only one usually makes it to fledge a few months later. There are heavy losses of both eggs and chicks.’’
She doubts all nests are used, so she says the birds are overcounted by regional councils.
Despite that, because there are fewer of the birds and they are widely dispersed, the economic threat of rooks has gone, Ms Wishart believes. ‘‘Rooks can now be regarded as part of the the large birds of the countryside. At present and in the foreseeable future, rook control is probably not warranted in most parts of the North Island.’’
Ms Wishart believes that due to heavy poisonings, the rooks’ days are now numbered in New Zealand.
‘‘This is no longer control of rooks. Eradication is on the lips of most regional councils.
‘‘But the New Zealand rook has been living here for more than 135 years and has earned its right to be here. Let’s not forget most of the humans living here – are all originally imports. There is no case for posoining them, simply because they are there.’’
On rook intelligence, here’s what the Reverend Henry Ward Beecher, 1813-87, preacher, orator, and lecturer, said.
‘‘If Man had wings and bore black feathers – few of them would be clever enough to be rooks or crows.’’
Rook enthusiast Clare Wishart. She wants to see rook populations controlled in New Zealand, but she does not want to see the birds wiped out entirely. Picture:
Young rooks in a nest. Regional councils plan on eradicating all rooks.
An adult female rook sits on eggs in her nest.
Rook poisoning from a helicopter.
Horizons environmental manager biosecurity and response, Bill Martin. Picture