Lake Taupō's black swans' upopular migration north

The new grass beside the footpath at Two Mile Bay is a summer feast for Lake Taupo's black swans. Photo / Rachel Canning

A summer family feud.

It's people versus the black swans at Lake Taupō's Two Mile Bay as our friends with webbed feet are tucking into new grass shoots growing beside the renovated Great Lake Walkway.

New Zealand Fish & Game senior officer Matthew McDougall had two recent complaints from the public about the swans and their poo and is keen to pass on some key messages to the public. A Taupō District Council spokesperson said they had also received eight complaints in the past two months.

Walking into any type of poo is an unpleasant experience and the council spokesperson said they have initiated a footpath cleaning programme since swans from Tokaanu have temporarily migrated to the northern end of the lake to eat the fresh new grass shoots.

Swans play an important role in keeping lake weed down and Matthew says this is why there are a large number of black swans at Tokaanu.

"Thank goodness they are there as the weed would be out of control if they weren't eating it.

"The swans predominately have a low fibre diet and will move from the new grass once it hardens up as it becomes unpalatable to them," says Matthew.

He says swans are rotational feeders and says there really is no way of keeping them off the new grass.

The other complaint relates to the health of the lake from swan poo being washed into Lake Taupō after it rains. The Waikato Regional Council controls the amount of nutrient discharge into the lake from farming and has standards about faecal coliform levels where people are swimming.

Matthew says the swans' impact on the water quality of the lake is negligible in that the nitrogen output is neutral and the faecal coliform count is extremely low.

"Fish & Game did a study and found the faecal coliform count from swans didn't hit any radar at all."

Swan Lake at Five Mile Bay. Photo / Gordon Collier

For the last 20 years New Zealand Fish & Game Easter Region has carried out an aerial survey of all birds on Lake Taupō. Matthew reports the swan population is consistently stable at 1000 birds.

"It takes 11 hours for us to count all the types of birds on the lake. We are up in the air for four hours at a time before the pilot comes down to refuel," says Matthew.

He says Fish & Game would not be interested in taking any action on the black swans around Lake Taupō while their population was below 3000 birds.

"The swans can be harvested, within the duck shooting period. But if you shoot them, more will come back."

For people who think 1000 swans is a big population, Matthew says there are 2000 to 3000 swans on Lake Rotorua.

And then there is the question of who was here first with fossils being found at Lake Waikaremoana of the Australian black swan cygnus atratus and fossils from the New Zealand swan cygnus sumnerensis found in Christchurch.

The fossils date back to before the Lake Taupō eruption, however both species were extinct by the 19th century. Matthew says the Otago Acclimatisation Society re-introduced the Australian black swan in 1863, but their population rose to a disproportionate number given their breeding ability and it was concluded more swans flew in from Australia to join an existing bevy of swans.

Admired while on the water, a black swan on Lake Taupō. Photo / NZ Fish & Game

"Birds blowing in from the east coast of Australia is not a new thing. The pukeko, the takahe and the pārera (grey duck) also blew in."

Known for being vicious, Matthew says just for a change a New Zealand bird species is doing well.

"And if people didn't feed them then they wouldn't snap for food."

The increased numbers of black swans at Two Mile Bay are not expected to last, and Matthew hopes visitors to the lake over summer will choose to have a positive experience.

"If humans go and build a walkway through the middle of a swan's native habitat then we shouldn't be surprised that the swans are still there."