Mabin spends most days working along the Waikato River, and he knows it's a dangerous place for birdlife.
"When I saw the pelicans, I thought they were running a big risk being on the river. There's injured birds out there all the time. If you're working on the river you get to see a lot of carcasses.
"But you'd have to be pretty dumb to do what [the shooter] did. I was sad and pissed off because I knew it couldn't be an accident. It's so different to any bird that you're allowed to shoot," Mabin, himself a recreational hunter, said.
He found the pelican, sex as yet unknown, curled up close to the river's edge about 1km upstream of the Rangiriri Bridge.
It looked like it was sleeping, but the multiple pellet wounds in its body told a different story, Mabin said.
"It had gone there to die, it didn't die straight away."
Pelicans have been seen in New Zealand just five times since 1890, and never in such large numbers, Miskelly said.
Department of Conservation Waikato conservancy spokesman Des Williams said pelicans were protected and the person responsible for the death could be prosecuted.
"Yes it is duck shooting season, but there are still many native species flying about our wetlands that are absolutely protected, and for good reason. Let's hope this incident serves as a timely reminder for all game-bird hunters about the need to positively identify their targets.
"It is particularly disappointing that such a rare visitor to our country should meet its end that way."
• If you have information about the shooting, email: news@hos.co.nz.