It was on a hike to Mauna Ulu, many years ago. The path from the Pu’u Huluhulu trail head had been easy to follow – at first. It quickly left the shrubby vegetation near the road behind, and the scenery became one of total devastation. The markings of the path became fewer and fewer. Once, when I briefly lost the trail, I found myself on area of deceptively weak rock, sometimes a thin cover over a hole, clearly left by outgassing. A quick backtrack was needed. Perhaps the hole I left in one rock is still there. But the main memory is from the way back. As I re-entered the shrubs at the trail head, a group of geese suddenly walked out in front of me. It was a surreal experience. Geese, on a desolate, bone-dry volcanic tourist trail on Hawai’i? What on earth were they doing here? Were they too here as a touristic outing? The area was about as far removed from their natural environment as was possible, both in distance and ecology. Later I found out that I had disturbed a group of wild nene, the native geese of Hawai’i, once near-extinct but now protected (as far as possible on an active volcano) and doing better. They were clearly used to people and perhaps the human visitors were (illegally) feeding them – two endangered species helping each other. Amidst the otherworldly scenery of the trail, what I remember most is the shock of seeing those geese.
Nene geese (the word is pronouced as two syllables) are endemic to Hawai’i. In the 1950’s their population was down to some 30 birds, but stringent protection has helped and there are now around 2800 nene across the Hawaiian archipelago. The park has around 200 nene, which is probably close to the carrying capacity as this number has been stable (with fluctuations) for several decades. The rangers take pride in their nene, and will happily close trails and camp sites if nene are nesting nearby.
But why was this protection needed? A study of dead adult nene has shown that over half died of just three causes: interaction with cars, attacks by dogs and mongoose, and a disease called toxoplasmosis which is caused by a parasite associated with feral cats. Nene do best on Kauaʻi, an island where mongoose were never introduced. The cause of the nene’s decline was, without a doubt, the human invader: us.
This is the usual way. We know from prehistory that humanity and large animals don’t go together: wherever humanity arrived, in Australia, America or New Zealand, the mega fauna disappeared within a few centuries. But the precise cause is not known and in fact some dispute our role in the extinctions. And we don’t know how the smaller animals and birds were affected. To know that, volcanic islands provide the perfect case studies. They form far from anywhere, with a clean slate, and evolve in isolation with unique species. Our arrival at these islands was recent and sudden, and often well documented. We can see directly how we affected their ecology.
Bird watchers visiting isolated volcanic islands often come away with some vague disappointment. Yes, they saw some unique species and added to their life lists. (I prefer to let the world surprise me rather than tick off a list, but it is all about personal preference.) But they find rather fewer species than they had expected, and rather more familiar birds which were recently introduced. To them, these islands appear impoverished. Is that normal, or is it due to us? Are we perhaps seeing an ecosystem on life support? When we tell our children about the birds and the bees (for younger readers, this was in the pre-internet era), do we focus too much on birth and not enough on death?
Us and the birds
Living with humanity can bring benefits. Many species of birds have already discovered this. We have created environments which they recognize: our gardens resemble savannas, and our cities recreate rocky mountains and cliffs. Birds adapted to these environments found their world expand. An example is the house sparrow which had its original environment duplicated all over the world, and followed us everywhere. The ibis has recently expanded worldwide, as did the collared dove: both found our world suitable to them. Some birds even changed their niche completely. The european blackbird used to be a denizen of the dark, dense forests where it blended in almost invisibly and where its piercing call is at home. But in the past few centuries it has emigrated to our gardens where it is prospering but conspicuously out of place. European robins will fight each other to the death for ownership of the inexhaustable food supply of our gardens. The eastern bluebird, which from one of the most numerous birds in the eastern US was going the way of the passenger pigeon, was rescued from oblivion by our nest boxes: in many areas, the majority of the bluebird population now breeds in these artificial holes. Tree swallows discovered that those bluebird boxes were perfect for them too, and their decline too was stemmed (for a while: numbers in the east and west are decreasing as our insecticides become ever more powerful). We have become the shapers of their world. Birds that can manage humanity can do well.
But we also bring dangers. Our garden birds are in mortal danger of those lethal predators we bring with us in great, overfed numbers, the house cats. (Arguably, dogs do more damage to our wild life than cats, but we can legally banish our neighbour’s dog from our gardens and homes. Cats do not accept such boundaries.) In the US, between 100 and 150 million cats (about half feral) kill 2 billion birds per year. Those birds in your garden are living in an unbelievably stressful environment, never sure whether they will live to see the morning. They are the ultimate survivors in a home-made wild west. There are no ground nesting birds in our city environments – you may blame the supreme predator which purred its way into our houses. The wooden boxes we put up for nesting are so popular because they are the only place safe from our cats. Birds that can manage humanity can do well, but I am greatly concerned about their mental health.
Birds that instead prefer their independence still have to live with us. Their environments are changing too, as their forests fragments, insects are terminated and climate is warming. They face competition from birds that spread with humanities, and cats and dogs encroach on them too. Wherever we come, we bring change. Much of this change is hidden from us: we are very poor at noticing gradual change. But in the volcanic deep-sea islands (all deep-sea islands are volcanic) the change is radical. When people bring goats to the Galapagos, rats to Reunion, mice to Gough and snakes to Guam, it completely destabilizes the ecology. Mass extinction follows.
And some of the creatures we bring aren’t of our choosing. Among the most successful is the most despised and feared: the rat. They too have learned to follow us. There are three main species which attached themselves to humanity: the black rat, the Norway rat and the Pacific rat. The Pacific rat is the main one found on Pacific islands. It came from Flores and spread with the Polynesians across their realm, reaching New Zealand around the year 1000. Norway rats, in spite of the name, originated in southern China: they spread to Europe after 1400 AD (surprisingly late, perhaps) and from there joined in with the European invasions of the world. Black rats came from southern India and spread to Europe 6000 years ago with previous human migrations. The changes the rats brought to Europe are undocumented. The damage they did to the distant islands are much better known. Rat eradication programs have become a common part of the regeneration of islands. Where this was done, numbers of creatures as varied as arthropods, crabs and iguanas quickly began to increase.
One reason (among many) that rats are so destructive is their need to drink. On islands, especially volcanic ones, water may be in short supply. The rats get their water by stripping the bark of shrubs and trees and by eating bird eggs. So they affect not just birds, but degrade the vegetation as well. In some cases rats have caused the collapse of the local forest. The well documented disappearance of trees from Easter Island, which isolated the community when they lost the possibility to build canoes, is commonly attributed to the local need to build and transport large statues; but perhaps rats carry some of the blame. Rats have changed the world. And birds were always the first to suffer as their eggs are so vulnerable. On many islands, there were waves of extinctions. The oldest, undocumented extinctions were when the Polynesians brought the Pacific rat. A second wave followed when black rats came, twice the size and more agile climbers, affecting birds (and mammals and reptiles) large enough to fight off Pacific rats. Last of all came the Norway rat but this is now mainly found in agricultural areas where few native bird species had survived. The rats are the cats of the oceanic islands.
But what made these communities so susceptible to collapse? And some of the islands had native rats. For instance, the Galapagos supported rice rats, but these too went extinct when our rats came. Why were the rats brought by us so much more devastating?
I don’t know. But let’s look at two case studies, to see what we can learn.
Like all deep-sea islands, Mauritius is volcanic in origin, although there is no longer any activity. It rose above the waters 8 million years ago. All its land animals and birds are accidental arrivals, blown across 1000 kilometers of sea by winds of chance. (I am excluding sea birds from this post.) These included one mammal (a bat), some reptiles (geckos and a non-venomous boa), and several species of birds including pigeons, a flightless rail, and parakeets.
One of those winds brought us the dodo. The dodo became a byword for obsolence, a creature unable to fend for itself while being highly edible – a bad combination. ‘Dodo’ became synonymous with ‘dumb’. It was seen as a prehistoric creature that had outlived its world. Alice in Wonderland depicts it as such.
The island was claimed by the Dutch in 1598, abandoned in 1710 and became French in the 1720’s. The Dutch report in 1598 describes dodos as the size of swans with a large head furnished with a kind of hood; no wings but in place of them 3 or 4 small black quills. The tail consisted of 4 or 5 curled plumes of a grey colour. The Dutch named it ‘walgvogel’ which translates as ‘disgusting bird’: they found the flesh too hard to eat. They preferred eating the smaller birds. It is thought that a living dodo was brought to the Netherlands at this time. The best description we have is second hand from van Neck’s report: it describes a thick long beak with a hook on the upper mandible and a yellow colour close to the naked head of the bird, a black tip and a blue spot in between. The dodo was covered in thin, short feathers; the back was fat and fleshy. The legs were yellowish, thick, and covered halfway down with black feathers. There were three forward pointing toes and one backward pointing. The bird had fist-sized stones in its gizzards.
The hooked beak on a naked, vulture-like face is the most recognized feature of the dodo. The purpose of the beak is not known. The size of the bird suggests it was a plant eater and the beak may have been useful in pulling leaves of reluctant trees. Neither do we know where the name dodo came from: the best bet is that it came from the Dutch word ‘dodaars’ (a combination literally meaning ‘tufted arse’..), and refers to those 4 of 5 plumes pretending to be a tail. The word is also the Dutch name for the little grebe (dabchick) which has a similar tuft at its back end. The dodo was a bird of the low-land forest, mainly found near the coast. Its habitat no longer exists on Mauritius – remnants of the type of coastal forest are now found only near the mountain tops.
Dodo were clearly very common in 1598. But that quickly changed. The last report of a dodo is commonly stated to be from 1662, when Volkert Evertsz, a Dutch sailor, saw several on nearby Ile d’Ambre. However, there are in fact two later records. One is from an escaped slave who said that he saw two dodo’s during his time at large, from 1663 to 1674. The other comes from hunting records maintained by the island’s governor Isaac Joan Lamotius. These detail dodo among their prey twelve times between 1685 and 1688. After 1688, only deer, sheep and goats were listed with a very occasional Mauritian giant tortoise (now extinct). His last record of a killed dodo was on 25 November 1688. The actual extinction must have been after this. The best estimate is that the last dodo died around 1693, with a 10% chance it was as late as 1715. However, others have argued that the name dodo (given as dodaersen in the later manuscripts) had been bestowed on a different bird, and that the dodo had become extinct on the Mauritius itself already by 1640.
Many dodo fossils have since been found on Mauritius, almost all inside an ancient lava tunnel. Several hundred individuals have contributed to the fossils found there. 90% of the fossils here come from the extinct giant tortoise – this island must have been tortoise heaven. Dodo accounts for 7% of all bird fossils. DNA retrieval has been limited to one specimen in Oxford which is in very poor condition. The poor quality data suggests that the dodo was an oversized pigeon, most closely related to the Nicobar pigeon.
The dodo is often depicted as defenceless, a flightless bird that people could just walk up to and kill. But the painting show a claw-like beak, and this was a usable weapon. There are mentions of sailors receiving bad cuts from the dodo’s beak. But in spite of this weapon, the dodo disappeared within a century, and possibly within decades, of humanity’s arrival. The cause of this collapse is not known. Mystery still surrounds the dodo.
Different possibilities have been proposed. The sailors may have eaten their way through the population. Their habitat may have been destroyed. A natural disaster, such as a tropical cyclone, may have pushed the bird to near-extinction. None of these really explain the rapidity of the collapse, by a human colony that occupied only a small part of an oft-inaccessible island. This leaves the other agents of death that the humans brought: rats, pigs and goats. Of these, rats fit the bill. They would have eaten the eggs, and large birds tend to reproduce slowly: the dodo was reported to lay just a single egg. Animals survive against excessive predation by excessive reproduction. The dodo was not equipped for that. It was a sitting duck.
This leaves the question where the dodo came from. The DNA puts the evolutionary split with the Nicobar pigeon at 30 million years ago. But Mauritius has existed for only 8 million years. The island formed from the same hot spot that brought us Reunion – and the Deccan traps. If the DNA is right, there were intermediate steps, perhaps older islands formed by the hot spot. But these left us no trace, and no similar birds exist on the other islands of the hot spot. There is a mystery here: the origin of the dodo is understood as poorly as its demise.
The Hawaiian chain of islands is even more isolated than Mauritius. The nearest main land is (perhaps surprisingly) Alaska, at a little over 3500 kilometers. California is marginally further away. Kamchatka is 5000 kilometers, Japan 6500 kilometers and Australia 7500 kilometers away. It is a perfect place for a virgin hot spot. The archipelago has one more advantage over Mauritius, in that the hot spot is very active and continuously forms new islands. Species can island-hop in the archipelago, moving to new one while the islands behind them sink below the waves. But the distance is a killer. Birds still managed to get there, as did insects. But there are no endemic reptiles or amphibians, and only two land mammals made the jump, both bats (one extinct).
The birds are the outstanding feature of Hawai’i. There are 63 endemic bird species, and a further 88 are known to have become extinct. They have been joined by others: 57 species of birds on Hawai’i have been introduced by us. These include such well-known cultural assets as the house sparrow, the java sparrow, the japanese white eye and the house finch.
The iconic nene has already been mentioned, now numbering around 2800 individuals. When Cook arrived, it is estimated there were 25,000 of them. And there used to be several related goose species. The “nene-nui,” an extinct fossil species from Maui, was a heavier bird, probably mainly terrestrial and a weak flier. The giant Hawaii goose, found only on the main island, was fully incapable of flight. It was four times the size of the nene, with a more robust skull and bill. The nene, in contrast, was the smallest Hawaiian goose and has a good flying ability (albeit with some reluctance to use it). These goose species probably went extinct when the Polynesians arrived 1500 years ago.
The islands also had several species of moa-nalo, looking very similar to the geese but which derived from ducks which had evolved to become goose-size. Moa-nalo were the main herbivores on the islands, and are are the reason why the native vegetation on Hawai’i is often spiky, a defence against grazers. But the grazers are no longer there. They too went the way of the dodo with the arrival of the Polynesians.
Other endemic Hawaiian land birds include thrushes (of which two species remain and three are extinct), warblers (1 species remains, 1 is extinct), monarchs (3 species), Hawaiian crow (extinct in the wild but attempts are made at re-introduction), pueo owl (a short-eared owl which arrived within the last millennium), rails and coots (2 remain, 2 extinct), hawaiian honeyeaters also called called mohoidae which are a family of waxwing relatives (the entire family has been extinct since the 1980’s: they provided the famous yellow feathers of the Hawaiian chiefs), and the most diverse, the hawaiian honeycreepers (42 species in total, of which 17 or 18 remain).
The honeycreepers fully deserve their place in history (hopefully they will also have a place in the future but that is not assured). They are small to medium-sized birds, not as flamboyant as the (extinct) honeyeaters but not bad looking. The sheer number of species, as compared to the other families, already suggests there is something special about this family. It is the beak. The shape of the beak turned out to be quite malleable, and this provided the family with a unique possibility. A whole series of beaks evolved, each adapted to a different food source. Some have bills adapted to insects, some to particular flowers, some to fruit and some to snails. One family member, the akiapōlāʻau, even became a woodpecker. Some of the bill shapes are found nowhere else in the world. The honeycreepers became to Hawai’i what the finches were to the Galapagos. In fact this is an apt comparison, as the honeycreepers evolved from these most adaptable of birds, the finches.
An example was the Kona grosbeak, with a cross beak adapted to the hard seeds of the sandalwood tree, found on the lava slopes of Kona. This turned out to be a less successful adaptation as the seeds are tiny and the bird needed to eat all day to survive. It went extinct in the 1890’s. Other variations were more successful: the scarlet honeycreeper, better known under its native name of of I’iwi, is endangered but survives. When its food tree disappeared, it managed to move on to a new source, the ʻōhiʻa lehua trees. However, their new food tree is now itself attacked by a disease.
The list given above of extant and extinct species shows that the birds of Hawai’i did not do well in recent times. There were two waves of extinction, one after the arrival of the Polynesians and one after the arrival of the western world. These extinctions had notable differences. In the first wave, most birds more than 50 grams in weight went extinct, while birds less than 20 grams were mostly unaffected. Ground-nesting birds almost completely disappeared, which included the flightless birds. Many insect eaters died out, but nectar drinkers were almost unaffected. But in the second extinction, the nectar drinkers were very heavily affected. The impact on nectar drinkers suggests that habitat loss is a very important contributor in the second extinction wave.
The impact on ground-nesting birds suggests predation as the main factor in the first extinction. In the second extinction, these birds had already gone so we don’t know how they would have done. Pacific rats would have been the main predator in Polynesian times, whilst mongoose are the dominant killers in the last two centuries. But in recent times there has been a new factor: the mosquitos that were introduced have brought avian malaria, to which many of the endemic birds had no resistance. A third extinction wave may be in progress.
The post started with the impacts of rats. That they are among the dominant causes is not disputed, although in the past 200 years mongoose have been more damaging. But it can be hard to prove that rats are responsible for a particular decline. For the o’ahu ‘elepaio (a flycatcher), it was found that a third of all nests and half of all nestlings failed because of rat predation. Where rats were controlled, populations were stable; where not, the population declined by a quarter per generation. Another case where rats were linked to the disappearance of a Hawaiian bird from much of its previous range is the ʻakiapōlāʻau.
Many other causes have played a role in Hawai’i. New plants were introduced, displacing the ones the birds depended on. Over 60 species of birds were introduced, already adjusted to the new vegetation. But Hawai’i never had a real local predator, and introducing rats and mongoose caused havoc in paradise. And the impact of the mosquitos and their gift of avian malaria is clear from the fact that the native birds have now largely withdrawn to higher altitudes, beyond the climatic reach of the mosquitos.
A fascinating question is where the endemic birds came from. There are a variety of origins. The goose species have been found to have evolved from the large-bodied canada goose. Genetic studies suggest they arrived as a single population from the north less than 1 million years ago, and split into separate species after that. The giant goose has been dated to 0.5 million years ago: this is very close to the age of the island of Hawai’i where it was found. The moa-nalo are related to dabbling ducks (such as the mallard) but are not close to any existing species: they diverged 3 to 4 million years ago. (Interestingly, they are not related to sea ducks). The hoary bat arrived from the east: it came from North America over the past million years, in multiple migrations. The honeycreepers evolved from the rose finch, present in Asia – they came from the west. To complete the compass, the Polynesians themselves arrived from the south. Hawai’i has had contributions from all directions.
The most surprising perhaps is the Asian contribution, both because of the larger distance and because the direction is against the trade winds. Sea currents can reach from Asia, but take far too long to benefit a small bird. Continental drift is too slow to make a difference over a few million years. Perhaps the most likely explanation is that the finch arrived at a time of lowering sea level, which happened around 5 million years ago. Some islands of the Emperor seamount chain may have resurfaced at this time, giving it a series of stepping stones. Later, wave erosion took the island back to the usual tens of meter below the new sea level, and the stepping stones disappeared again.
A whole new world
There are patterns that repeat among volcanic islands in the deep ocean. It takes time to convert hell into paradise. Colonization of new volcanic islands is agonizingly slow: very few travellers make it, and those that arrive will be in poor condition. They need to be very lucky to find an instantly available food source, and it needs to bring a mate. There may be half a million year between arrivals. This allows new arrivals enough time to evolve before any competitor arrives. The birds that do best are those that are adaptable and evolve quickly. Finches do particularly well on both accounts. Pigeons are also widespread. Volcanic islands tend to have unreliable water supplies: this is probably why ducks evolve into land dwellers. Predators don’t seem to travel well, and if they do they probably starve on arrival. The island communities are too small to support large predators and evolution into hunters seems rare. But this also means that the animals evolve few defence mechanisms.
The communities that develop become hotbeds for evolution. With many niches unoccupied, the first bird to explore a new resource has time to improve. The early bird gets the worm. Diversification is rapid and explores things that are not possible in more competitive environments. But this means that extinctions rates are also high. On the other extreme, a small advantage can lead to a rapid expansion and population growth. Volcanic islands will have quite unstable communities for a while. What may look like a stable ecology is in fact fluid and fast changing. A new entrant can push the whole system out of equilibrium. And it may be an unexpected one. Among all the possible causes for the dodo’s rapid decline, no one has suggested the one devastating Hawai’i at the moment. Perhaps the invaders brought a new disease to which the dodo had no immunity.
In such small communities, symbiotic relations can quickly develop. One tree on Mauritius depended completely on the digestive system of the dodo, and its seeds can no longer germinate. This tree will follow the dodo into extinction.
One may wonder whether volcanic activity itself may be a risk factor to the local evolution. The islands discussed here are large enough that no single eruption will devastate more than a small area. But small islands could be unsafe. Krakatoa was probably too close to the main lands of Indonesia to evolve its own species, but if it did they are now left in the past. Nothing there survived. However, we are looking at time scales of millions of years. Old volcanoes tend to become extinct themselves and are therefore unlikely to endanger their cargo.
But that inactivity becomes a danger in itself. All volcanic islands are ephemeral: they form from the rising heat and magma pushing up and building up the ocean floor, and they sink back under the sea when that supply is lost. The islands don’t last and at some point the inhabitants will have to migrate to a new island in the chain. All arrive as long-distance migrants, but the ability to travel is not used after arrival, and evolution tends to discard what is not used. Not all evolution is beneficial over the longer term. Birds which lose flight are unable to leave their sinking home. All volcanic islands eventually suffer complete extinction of their biological cargo, and much of the cargo may not escape. We may have lost many previous incarnations of the dodo – we will never know.
And finally we arrive and the floodgates open to new arrivals. Migrants soon outnumber the locals and a battle for survival begins. A new ecological equilibrium will eventually evolve on these islands, which merges the surviving entrants with a few survivors of the local evolution. But much will have been lost.
We remember the iconic dodo with sadness and the flamboyant Hawaiian honeyeaters with regret. If we now loose the Hawaiian honeycreepers as well, a regretful and sad elegy would seem insufficient. Anger is more appropriate. After all, we should by now know better. Volcanoes are destructive by nature, not by choice. We don’t have that excuse. The future of these endemic, volcanic species is a matter of our choice. We can’t go back to the past, but we can choose not to lose the future as well.
Those geese on Kilauea are worth a memory. The nene survived thanks to action taken by the local people. I was just an accidental tourist, a long distance arrival able to appreciate their effort. This story is a salutation to their effort.
Albert, April 2020