KEY POINTS:
Roadkill has been identified as a contributor to the declining populations of blue penguins in some parts of New Zealand.
The national population of blue penguins, estimated at about 50,000, is overall in decline, especially on the mainland.
A study recently published in the New Zealand Journal of Zoology on the breeding success of the blue penguins on the west coast of the South Island identified roadkill as a significant threat to the population.
The study said the total population of blue penguins on the West Coast was thought to be in the hundreds rather than the thousands, and many residents believed the decline began a decade ago or longer.
While predators such as mustelids were generally thought to be the main cause of the declining populations of blue penguins nationally, the researchers found that on the West Coast, roadkill was a factor.
The researchers learned of 15 blue penguin roadkills within the study area, 60km of coast between Westport and Punakaiki, over just a five month period to the end of 2006.
A total of 30 road-killed penguins were counted in the Buller region during the study.
The study said since non-breeding blue penguins spent most of the year at sea, they were at greatest risk of being killed on the road during the breeding season.
"Each road-killed penguin might be incubating up to two eggs or rearing up to two chicks at the time of death."
Since both parents were required to rear the chicks, the death of one penguin on the road could remove up to three more individuals from the population.
The study said steps should be taken to identify the most hazardous road crossing points and to raise public awareness.
Other factors contributing to the declining penguin population on the coast included mortality at sea, dog kills, and habitat loss or damage.
David Housten, Department of Conservation technical support officer, told the Herald that coastal subdivisions harmed blue penguin populations by increasing risk factors like vehicles and dogs.
Mr Housten said two dogs had killed 72 penguins in Oamaru in 2001.
Ferrets and stoats were also a major problem, he said.
Ferrets were specialised burrow predators and very efficient at killing even adult penguins.
Mr Housten said where efforts were made to control predators, the penguin populations improved.
WHAT MAKES THEM SPECIAL
* The blue penguin is the world's smallest and the only penguin species that is nocturnal on land.
* Although quite common, its size and unusual habits make it rarely seen.
* The penguins come ashore only in darkness and live in burrows.
* They breed in burrows, under trees and other vegetation, in piles of driftwood, in rock crevices, under buildings and in caves.
* Blue penguins usually breed for the first time at 2-3 years of age.
* Their ability to fledge chicks from more than one clutch during a single breeding season makes them unique among penguin species.
* The core egg-laying period for most of NZ is September to November.
* Eggs are incubated for 36 days.
* Both parents share incubation and feeding duties; at least one adult will stay in the burrow all day throughout incubation and guard periods.
* The chicks are guarded for the first 2-3 weeks, after which both parents must go to sea to keep up the supply of fish.
* Chick growth is rapid, with adult weight (1kg) being achieved in 4-5 weeks.
* Chicks usually fledge at 8 weeks and are independent from then on.
* There is a high rate of juvenile mortality, but individuals can reach up to 25 years of age.
