Islands, especially the ones that haven’t been in contact with the mainland for a very long time, come as close to being alternate histories as you can get in the real world.

What would have happened if the primitive lemur relatives of monkeys and apes had become the dominant primates instead of monkeys and apes? Go to Madagascar and you can get a pretty good idea. What would happen if a fairly large island was populated almost exclusively by rats? Some of the Philippine islands still have the fading remnants of that experiment.

This book talks about the results of a different experiment. What would happen if a fair-sized land mass lost all of its land mammals and most of its land creatures and had to be repopulated from the sea and the air? Go to New Zealand and you’ll see the remnants of a once spectacular experiment in that direction.

Moas were giant flightless birds of New Zealand. They were far heavier than ostriches. The largest ones weighed over four hundred pounds. They were herbivores, bird equivalents of deer, horses and bison. The last of the Moas probably died out shortly before Europeans started settling New Zealand. Like many island birds they appear to have been very vulnerable to human activities and quickly died out after the Polynesian Maori settled the islands.

Moas weren’t the only unique creatures of New Zealand, or even the most interesting. The island apparently broke loose from Gondwana, the southern super-continent of the Cretaceous around 82 million years ago. It probably carried a typical Cretaceous group of plants and animals, a few of which still survive there and nowhere else on earth.

More of those plants and animals might have survived, but New Zealand probably got hit hard by the indirect effects of the end-of-Cretaceous meteor strike. It also went through a fairly long period around 27 million years ago where over eighty percent of the current land area was under the ocean. There is no evidence one way or the other on whether land mammals existed in New Zealand before that bottleneck, but probably any land mammals that might have existed on New Zealand before that bottleneck didn’t survive past it. That gives us some interesting alternate history or alternate biology potential: what if the bottleneck hadn’t been as severe and New Zealand had greeted the Maori with its own collection of primitive mammals? They could be marsupials, multiberculates, distant relatives of the platypus and echidna, or even the kind of small mammal-like crocodiles that were once common in Africa.

I suppose it might even be possible that small dinosaurs could have survived there. That could have been interesting, though they probably wouldn’t have done much better at survival than the Moas did.

In reality, as I mentioned earlier, New Zealand was repopulated mainly from the sea and the air. The dominant animals were birds and insects, with a few species of bats and lizards playing odd but subsidiary roles.

One of the most spectacular birds was Haast’s Eagle, the largest known eagle. A large Haast’s Eagle probably weighed close to thirty pounds. This was not a flightless bird, just a very large and formidable one. It was apparently the top predator of New Zealand and preyed on Moas, typically ones in the one hundred to two hundred pound range, but it sometimes tackled Moas weighing more than four hundred pounds.

According to the book, very large eagles apparently were the top predators on a number of islands or groups of islands, including Hawaii and Cuba, but Haast’s Eagle was top predator in a very complex eco-system, and it tackled prey that were enormously larger than itself.

According to the book, over a dozen Moa skeletons have been found with evidence of having been attacked by Haast’s eagles. The eagles apparently used their extremely powerful claws to attack the hindquarters of Moas, crushing bones and causing massive bleeding.

The large living eagles can take prey up to about forty pounds, and they have trouble with something that big, so Haast’s eagle was an impressive animal. It may not have preyed mainly on Moas, but it was quite capable of doing so.

The book mentions in passing that while Haast’s Eagle was the largest known eagle, it wasn’t the largest raptor. The terratorns of Pleistocene North and South America ranged from about the size of Haast’s eagle up to 80 kilograms for one Argentine species.

Haast’s eagle didn’t have some of the worries that eagles on a continent have. In Africa, if an eagle actually managed to kill a two-hundred pound antelope, what would it do with it? It couldn’t fly off with the carcass, and it couldn’t defend that carcass against lions and hyenas, or even jackals. On a continent there isn’t much point in a raptor killing animals too heavy for them to fly off with. In New Zealand it was advantageous to do so because the eagle could guard the carcass and feed on it for an extended period of time.

The authors speculate on how the first Maori and Haast’s Eagle interacted. They suspect that the eagle actually did go after people. After all it was used to hunting bipeds much larger than this strange new one. They also speculate that a few Haast’s Eagle may have survived into the 1860’s, when an explorer and surveyor reported killing two large “hawks” with wingspans of up to 9 feet in a remote corner of New Zealand.

That leads to an interesting minor what-if. What would have happened if Haast’s eagle had survived long enough for Europeans to capture a few and them back to zoos? Would they have been able to breed in zoos? If so, how would Europeans have reacted to them? (Nightmare thought: Hitler or some other Nazi turns people from “undesirable races” loose in a fenced in field and turns an eagle loose to hunt them down.)

New Zealand had a lot of other interesting critters, and if you can wade through the jargon this book will tell you about most of them, from a flightless distant relative of cranes that may have been a predator to giant relatives of the cricket that act like rats and mice, and bats that scamper around in tree like miniature squirrels.

Unfortunately some of the most interesting of those animals are either extinct or close to it. I wonder if they would have fared better if the Polynesians hadn’t colonized the island. Probably not. Europeans of the early 1800s were quite capable of ripping through a naïve and vulnerable fauna like a buzz saw.

The animals of New Zealand would have faced a much larger set of threats in a very short time, rather than having a few centuries to adapt to Maori, dogs, pigs, and rats before they had to face Europeans, foxes, feral cats, rabbits, ferrets, sheep, wallabies, possums, goats, sheep, and deer.