Unusually warm seas have been blamed for the deaths of large numbers of penguins washing up along the Far North coast.
The latest "die-off" has experts fearing rising temperatures could make Northland too hot for little blue penguins or kororā, with the birds dying out locally while expanding in colder areas further south.
Fourteen-year-old Ruben Trimble was visiting Tauranga Bay, about 15km north of Kāeo, with his family last week when he discovered a dead penguin. A few metres further he found another, then another.
It didn't take long to gather up the bodies of six kororā and three petrels.
At first, Ruben, who lives in Ōkaihau, suspected they had been killed by dogs because of the number of pets he saw running loose on the beach.
Just as he made the grisly discovery a couple turned up and let their dog off the leash, ironically waiting until they reached a "dogs on leash" sign to do so. The dog headed straight to the carcasses.
However, the absence of obvious injuries, plus his own research, led him to suspect climate was the culprit.
"It was quite upsetting, especially because penguins are declining," he said.
He delivered the dead birds to the Department of Conservation in Kerikeri to establish the cause of death.
DoC Northland spokeswoman Abigail Monteith said Ruben's discovery was sadly not the first this month.
The first report of kororā deaths came on May 2. On that occasion, more than 20 birds were found.
Seven were sent to experts at the Ministry for Primary Industries, who found the birds' gastrointestinal tracts were empty and their body condition was poor.
They had most likely died of starvation and hypothermia because they lacked blubber to keep themselves warm in the water.
On May 8 another 22 dead birds were found.
MPI did not examine the second lot of penguins because the results from the first were so clear-cut.
Those birds were reported by Carol Parker, who found them scattered along Tokerau Beach in Doubtless Bay.
A day earlier she found a weak and apparently exhausted kororā by itself on another beach. She sought a vet's advice and tried in vain to save it.
Parker told RNZ she had found 10 dead penguins about five years ago but she had never seen so many at once, despite living in the area for more than 20 years.
DoC seabird expert and principal science advisor Graeme Taylor said the dead birds were likely to be juveniles from the last breeding season.
Older penguins had learned where to forage when food was scarce but not the younger ones.
"They have no relationship with their parents once they head to sea so they're on their own. When food is available and abundant it's no problem but when they're struggling to find food and don't know where to go, they just get hungrier and hungrier until they get too weak to swim. They either perish at sea or they come up on beaches looking very sad, and unfortunately that's where they die," Taylor said.
Previous die-offs had also occurred in La Nina years when an influx of water from the tropics made the sea around Northland substantially warmer than usual, and the fish penguins ate became harder to find.
It was thought fish either moved into deeper water — penguins did most of their feeding in the top 20m — or shifted south to cooler waters.
Climate change meant die-offs could become more frequent, Taylor said.
"The oceans absorb 90 per cent of the excess heat locked up in the atmosphere by carbon. That's a lot of extra heat going into the ocean so events that might have happened once a decade or once every 15 years are starting to happen more frequently. That's what's really worrying us."
Taylor said penguins were basically a cold-adapted species living in Northland.
"With these warmer conditions becoming more frequent, and the recovery periods between warm periods becoming shorter, it may be that the penguins are not going to be able to persist in the North."
Taylor said penguins preferred to spend their days at sea. By the time they came ashore during daytime they were in such poor condition that they were hard to save.
There were, however, long-term actions people could take.
"The best thing humans can do is try to change their habits around activities that add more carbon to the atmosphere. Trying to avoid plastic getting into the marine environment is definitely something else people can do. These birds do eat plastic and it gets stuck in their stomachs."
Taylor was surprised by Ruben's discovery of dead petrels in the same area.
Unlike penguins, which were limited by the distance they could swim, petrels were "very, very mobile" birds that could travel as far as the south Tasman Sea in search of food.