Pukeko's game of angry birds

Pukeko respond to changes in the size of their red beak shield. Photo / Amos Chapple

New Zealand's cute pukeko, known for its colour both in plumage and personality, has been shown to have a power-hungry, aggressive streak - quite literally.

A new study shows the lanky birds, often spied on our wetlands and roadsides, vaunt their macho dominance with the size of the bright red frontal shields extending from their beaks.

As with other species, scientists have long suspected the bigger their shield, the more aggressive and dominating they were among their peers.

Canadian and New Zealand researchers confirmed this by using paint to reduce the size of the shields, and watching as the feathered ring-leaders instantly lost their tough-guy status.

Massey University ecologist Dr James Dale, who supervised the study by McMaster University PhD student Cody Dey, likened the birds' badges to the number of stars on a general's uniform, or the colour of karate belt.

"What we found was that the size of the red shield in pukeko correlates very strongly to social dominance."

When the bird's shield was made to look smaller, they observed two changes. The birds were challenged more by other members of their group.

"And the birds actually shrank the size of their true shield, probably in response to hormonal changes brought about by the increased challenges by other members of the group," Dr Dale said.

"The bottom line is that it pays to signal your dominance honestly or else you're likely to get into more conflict - much like it might be dangerous to enter a karate competition wearing a belt colour that is not an accurate reflection of your skills."

Dr Dale said the birds physically changed their status, signalling they were less willing to fight, if they became sick.

Researchers had found the time a species spent developing its badge spoke of its status, but less was known about its social interaction. "The big picture is what keeps a signal honest, and how is this communication kept free of cheaters?"

The findings, published in the renowned Proceedings of the Royal Society B, may lead researchers investigating "badges of status" around the world to adopt the same approach.

See the pukeko footage here.

"Badges of status" aren't just seen in pukeko.

They might be the bright tails of peacocks, or the facial markings of wasps, but the classic examples are those used to settle minor dominance contests in flocks of foraging birds.

The size of the black throat patch in male house sparrows, for example, reflects aggression during feeding - but it's not clearly understood how these signals are kept reliable.

Researchers believe one important possibility is badges are kept honest through social punishment.

It's held that if an individual sends "mixed signals" - its badge reflecting a status lower than its actual dominance - the bird's peers will act aggressively toward it to figure out how tough it really is.