Calder and his wife, Heather, knew there were limestone caves on their small farm next to Abbey Caves, but no-one dreamed in a million years - or even just a millennium - they would be the last resting place of moa, possibly holding the biggest single cache of relics found in Northland.
This winter, four skeletons were removed from that ancient vault and are now in the care of Kiwi North, the Whangarei Museum.
They are thought to be bush moa, genus Anomalopteryx, and the excitement of their find is heightened by the fact that one of them, the largest, is near perfectly intact.
Calder found the fissure that eventually led him to the moa mausoleum in 2011, while checking possum and rat stations.It took him a week to clear away a natural cairn of rocks and tree debris at the base of the cleft, but he was reluctant to go too far into the entrance.
His initial attempts were defeated by another prehistoric New Zealand giant, cave weta.Curiosity got the better of Calder in May.
"You could look down between three or four big boulders, it looked like it went down about three or four metres and I thought 'I could get down there'.
"Only a slim, agile person like Calder could wriggle into the tight-mouthed, steep funnel.
He waited until he had a mate with him so there was someone above ground should anything go wrong.Calder crawled down the sloping passage, squirmed around boulders almost blocking the way and found himself in what thousands of years ago would have been a smallish chamber.
Sitting among fallen rocks and shining his torch around the rubble and dried-mud of the cave floor, he nearly jumped out of his skin when he saw what looked like human femur.
A closer inspection indicated the half buried bone wasn't human at all so Calder carefully pulled it free of its earthy bed, took it home and washed it.An easy computer search showed the Calders they had a moa leg in hand.
Next time he went there, Calder removed many bones out, trip by trip with an icecream carton (a bucket was too big to get inside the opening).
While the three smaller skeletons were jumbled and broken up under rocks, laid out on one side, sheltered by a wall, was a full skeleton.
It was only missing a few toes, obviously sliced off by a rock fall, and with part of its skull gone.
"It was under about 150mm of loose dirt. I just gently scratched it away. I was worried about getting all the little throat bones, they're like little rings of bone.
"I sat there and saw light further on so I knew there was another opening. I could see the direction where the moa had came in and out of the cave.
"When you're in there looking toward the other end it's higgledy piggledy and built up with dirt, it's not a continuous chamber, but you can see moa would have been able to walk walk around in there before the roof collapsed.
"A short way through the regenerating bush is another tiny opening Calder has cleared.
What appears to be a blocked cave entrance now sits 1.5m higher than what would once have been ground level, the ground having shifted or built up over millennia.
"A thousand years ago they could have just walked in through this opening on the side of the hill," says Calder. It's a phenomenal thought - we are standing where giants once stood. We are peering at rocky outcrops shaped when the past was another country.
Inside the cave large stalactites have fallen with earth movements, but new crops are well formed.It takes a long, long time for these hanging coronets of calcite to grow, so just how long ago did these birds live?
Were they a family? Were they adults or juveniles; male or female; which species?
Did they die at the same time, trapped in the cave after a natural event? Had all the bones always lain there or been dumped by the waters of a long gone underground stream?But the first question everyone asks is how old are they?
The guess is so wide it's meaningless. We can not tell you if these birds lived 100, 1000 or 10,000 years before Maori arrived, so their lifetime is not anchored in a relative historical time frame.
There are no signs of Maori habitation in the immediate area and no local oral history about moa, but the site and the bones have been blessed by iwi.
Ian and Heather Calder thought long and hard before putting them in the public arena. Their property will not be opened to moa hunters, other than authorised researchers.Te Papa Tongarewa (Museum of New Zealand), NZ Historic Places Trust and Department of Conservation have been told of the discovery, and specialist advice sought.
Kiwi North collections registrar Natalie Brookland never knows what will come out of the bag when she comes to work.But one day a toe bone connected to the foot bone, the foot bone connected to the leg bone, the leg bone connected to the ... and Brookland found herself reconstructing an almost perfectly preserved moa skeleton.
The skeleton has been taking shape for weeks now, based on drawings, information from Te Papa and the bird anatomy expertise of a Whangarei vet.
"It's been a real team effort, we've all played our part," Brookland says, "but I'm absolutely ecstatic about this project. It certainly is the highlight of my career.
"Dating and DNA tests are expensive, beyond the immediate wherewithal of a provincial museum which is only minimally bankrolled by local governments and visitor numbers.
Those visitors will be able to see the prehistoric Whareora giants from September 21.
Kiwi North director Stewart Bowden says the moa will be a great drawcard and eventually pay their own way toward the desired scientific rigour.
"But the ageing and sexing will have to wait. The important thing is the skeletons are here," Mr Bowden says.
