Forest and Bird says it will delay revealing which bird has won the Bird of The Century campaign after a "massive influx" of votes.
In a statement on their website on Friday morning, it said the email authentication team has been stretched by thousands of votes coming in.
The winner will be announced on the morning of Wednesday, November 15 - it had been planned for Monday, November 13.
However, Forest and Bird said voting still closes at 5pm Sunday, November 12.
"The sheer volume of votes has been unprecedented, with the Bird of the Century email vote verification system stretched more than ever before," it said.
"We know many people have had trouble receiving their vote verification email, but please be assured we have captured all submitted votes.
"Our small team have been working around the clock to troubleshoot and now just need a couple of days to make sure every vote from a valid email address is counted."
Forest and Bird normally run a Bird of the Year competition, but this year it's taking a step up as the organisation seeks to find the Bird of the Century to celebrate its 100th year.
There are 75 bird species up for the title.
The announcement the winner will be delayed comes just days after John Oliver launched an "alarmingly aggressive" campaign for the pūteketeke to win Bird of the Century.
"We are hereby announcing ourselves as the official campaign manager for the best candidate of New Zealand's bird of the century. I am of course talking about the pūteketeke."
"The point is we are going all out for this thing," he said.
"I don't just want the pūteketeke to win, I want it to win in the biggest landslide in the history of this magnificent competition. I want it to do to other Bird of the Century candidates what the pūteketeke does to fish in New Zealand's lakes – that is eat them alive and then throw them back up in a ball of feathers."
Campaigning in Mumbai, Tokyo and Brazil, Oliver demanded his fans flood the website with votes for the bird. So many votes came in overnight after the campaign's announcement on US channel HBO that the website crashed.
"We're all pretty chuffed, it's fair to say," Forest and Bird chief executive Nicola Toki told Newshub after the campaign came to light.
But while Forest and Bird have been impressed by the surge in voting, not everyone in New Zealand is amused by a "B-grade American celeb" meddling in Aotearoa's vote, with some getting ruffled feathers from his global involvement.
On Tuesday, the Vote Kiwi campaign issued a tongue-in-cheek statement expressing concern over the extent Oliver had gone to to secure the win.
"It's shocking, to be honest. New Zealand politics haven't been too flash lately and everyone campaigning in Bird of the Century was hoping to have a break from all that palaver," Vote Kiwi campaign manager Erin Reilly said.
"We're here to have a little fun. On behalf of all bird species campaigning in Bird of the Century, the last thing we want to deal with is a random B-grade American celeb swooping in and hijacking this iconic competition."
Air New Zealand, meanwhile, has extended an offer for Oliver to come to Aotearoa to meet a pūteketeke in person.
On Friday afternoon, the company posted a note on its social media telling the Last Week Tonight host to "consider this your invitation to jump on board one of our birds in the sky (on us) and migrate south to New Zealand.
"We've even teed up an exclusive pūteketeke meet and greet."
"What say you John? Are you ready to swoop in to back your feathered friend?" the post said.
There has been no word from Oliver about the offer, or the reaction in New Zealand to his campaign.
