The animals are often sold for traditional reasons, for personal consumption or for use in ceremonial costumes.
Most Papua New Guineans do not see any problems with this, but conservation groups said it was starting to put many of the country's iconic species at risk.
The highlands city of Goroka is buzzing with people from all over the region who have come to show off their traditional dances and costumes at the annual Goroka Show.
The famous event attracts so-called "sing-sing" groups who compete to have the best performances and best traditional dress.
It also attracts people like Saifa Kaupa, who is selling a dead bird of paradise for about $40.
"I shot seven down. I had enough of my children getting them so I will sell three, and four I cooked," he said.
Mr Kaupa is from a rural part of the highlands and has come to Goroka to sell the bird to people who will use its feathers in their traditional costumes.
"It's going to be the Goroka Show soon and people will buy it for traditional costumes and sing-sings," he said.
The bird of paradise is the national emblem of PNG and it is illegal to sell them, although the law dates back to Australian colonial times and does not account for traditional practice.
There is plenty of demand and Mr Kaupa soon sells the bird to a young woman, Stephanie Hero.
"When we go to the dance we put the bird's feathers on our head and some others, like parrot [feathers]," she said.
"The parrot's feathers go first, but the main part of that headdress is the bird of paradise."
The killing and trading of wildlife for costumes is a longstanding practice in PNG, but it is particularly notable around the time of cultural shows.
Animals seen as 'spare parts'
Nathan Whitmore, a scientific support officer with the Wildlife Conservation Society in Goroka, said many animals get brought in as "spare parts" for the cultural shows.
"Birds of paradise, vulturine parrots and a lot of tree kangaroos," he said.
"So these are replacement parts for the feathers and the pelts which get used in their traditional attire."
Birds are sold dead, while mammals like the tree kangaroo and the possum-like cuscus are sold alive.
"The mammals have a dual purpose, they are brought in both for their pelts and for their meat," Mr Whitmore said.
"And so most people in PNG don't have access to electricity, and even more people don't have access to any type of refrigeration or freezing.
"So the animals have to be brought in live in order to have any value as meat."
PNG's cultural practices have remained important as the country modernises, but that has been putting more pressure on its wildlife as the population grows.
The Wildlife Conservation Society has been studying the use of vulturine parrot feathers in traditional headdresses in Simbu Province, also in the highlands.
Mr Whitmore said his colleague found there were more dead parrots in Simbu costumes than live ones in the wild.
"So our kind of strategy has been to recognise that the dead vulturine parrot resource is much bigger than the live vulturine parrot resource," he said.
Mr Whitmore and his colleague, researcher Grace Nugi, assessed the number of headdresses containing vulturine parrot feathers, and how many parrots would be needed to make one headdress.
She found that each headdress contained feathers from an average eight parrots, and that roughly 50,000 people in the province had this type of headdress, meaning the provincial costumes held the feathers of about 400,000 dead parrots.
Mr Whitmore said there are only estimated to be 44,000 vulturine parrots remaining in the wild, so the research found there were more dead parrots in Simbu costumes than live ones in the forest.
"Rather than try to spend our time as a conservation organisation trying to go to these remote areas, we've focused on trying to conserve the dead parrots by extending the life-span of the headdresses," he said.
The society is now giving preservation kits to people in Simbu to help them protect their costumes from mice and insects and reduce the demand for new animals.
'It's a friendly animal, it's easy to catch it'
Wildlife trading is not just prevalent at cultural shows in the PNG highlands, it is a growing feature of life in PNG's cities.
Jerry Are is selling a tree kangaroo, another protected species, outside a supermarket in Port Moresby.
"It's easy to find them, it's a friendly animal, it's easy to catch it," he said.
"If you go close, if you go near to it, it will just come. It won't run away."
Many people take wildlife they have caught to the Port Moresby Nature Park, but staff there will not buy them because they do not want to encourage the trade.
Brett Smith, the park's curator, said the types of animals they received depended on the time of the year.
"During the spring season or end of wet season/dry season, when there's lots of babies around, you'll see lots of eclectus parrots coming in, eagles, whistling kites, owls," he said.
"And then in other times of year you'll see a lot more increase coming up to Christmas and also the school year.
"So people coming down from the village selling [different animals] to try to source an income to send their children to school, or even maybe buy presents leading up to Christmas."
This kind of wildlife trading has been going on for a long time and is seen as culturally acceptable to Papua New Guineans.
Many of them tend to see wildlife as a resource to be exploited, not something to be appreciated.
Overseas demand adds pressure
But Mr Smith said there was also increasing overseas demand for many PNG species.
He said they were seeing a lot of people travelling between the borders of Indonesia or West Papua over to PNG and taking animals.
"We're seeing a lot pig-nosed turtles on the border disappearing, they're coming over taking fish species," he said.
"And we're now starting to see a lot of bird of paradise species turning up in Europe and south-east Asia, so I think the demand for the animal trade is going to continue, particularly in Papua New Guinea.
"It's been very isolated for a number of years and now the smugglers are starting to come in.
"We are seeing an increase, I think it's going to get more worse as the years continue."
That is a new threat to wildlife on top of growing domestic demand.
When you combine such things with other pressures, like land clearing, urbanisation and new extractive projects in their habitat, the prospects for PNG's unique and beautiful species do not look very bright.