Size matters a lot — or at least it does to a type of winged critter living in the South Pacific, a scientist at McMaster University says.

Cody Dey spoke on CBC Radio One’s Quirks & Quarks last week about his experiences studying the Pukeko, a species of bird in New Zealand with distinct social patterns. 

A doctoral candidate in McMaster’s department of biology, Dey told CBC host Bob McDonald that the size of each Pukeko’s “shield” or "badge" — the red, fleshy mound protruding from its forehead — helps determine that particular bird’s position in the hierarchy of its social group.

“Individuals with very large shields were much more likely to be dominant, and individuals with small shields were more likely to be subordinate,” he said. 

McMaster biologist Cody Dey

McMaster University biologist Cody Dey holds a Pukeko, a bird native to New Zealand and other island nations in the South Pacific. (Cody Dey's website)

Just how important is shield size for the Pukeko? Pretty important, said Dey, who, along with McMaster prof Jim Quinn and New Zealander James Dale, wrote about their findings in a paper recently published in the scientific journal Proceedings of the Royal Society B.

Well-endowed Pukeko, said Dey, tend to nest at the top of the pecking order when it comes to access to the best food. 

And shield size had more than a little impact on a group member's reproductive prowess, he noted. 

“Especially for females, dominant individuals are more likely to get to breed,” he said. “Subordinate females almost never breed within these Pukeko groups, whereas dominant females, the top one or two females is going to do all of the reproduction."

To expand on their findings, Dey and his team played a prank on a group of unlucky Pukeko, giving some of them makeovers (or rather, "make-unders") to observe what effect the changes would have on the birds’ social standing.

“We trapped them, we used a small amount of black paint that matched the colour of the black feathers around the shield, and we would paint the rim of the shield with that black paint,” said Dey. “So the individuals would appear that they had a really small shield when they actually had their normal shield size.”

How did the ruse affect social dynamics in Pukeko-land? To find out, click on the audio button in the top left-hand corner of the page to listen to Dey’s interview on Quirks and Quarks.

(Spoiler alert: Let’s just say a few Big Birds on Campus fell from their perches of power and prestige.) 

Dey produced a short documentary about his research. To view it, click on the video below:

Badge of Status from Cody Dey on Vimeo.