Last week I wrote of my visit to an Echo Parakeet Psitticula eques research field-station in the Black River Gorges National Park in Mauritius with Lone Raffray of the Mauritian Wildlife Foundation.

As I wrote at the time being granted access to this highly-restricted and historically important station - and getting close to wild Echo Parakeets and Pink Pigeons Nesoenas mayeri (both Endangered and desperately close to extinction just a few decades ago) - was exciting enough, but when Dennis Hansen (who along with Anna Reuleaux, the leader of the Echo Recovery Programme Team, had met me at the field-station) suggested that we all visit one of the nearby Conservation Management Areas (CMAs) in the forest what fatigue I was feeling from my overnight flight dropped away immediately.

As Lone had already explained to me the CMAs were highly-managed sites and fundamental to restoring forest habitat. Relatively small, fenced areas a huge amount of work has taken place within them to clear out the island’s numerous invasive plants - especially Guava Psidium cattleianum, a Brazilian species which is abundant in Mauritian [and Hawaiian] forests, is fast-growing and shades out native plants. In some respects therefore the upland forest inside the CMAs is more or less like it would have been when European settlers first arrived. Few non-scientists have ever walked around inside Mauritius’s CMAs and to be taken around by one of the world’s leading experts on Mauritius’s biodiversity promised to be an unforgettable experience…

It was of course.

Dennis, who has worked in Mauritius on and off for the last 10 years (first as a conservation volunteer, then on studying plant-animal interactions for his BSc, MSc & then PhD), is in the middle of a 3-year post-doc project on investigating the impact of the loss of almost all large-bodied vertebrate frugivores in Mauritius, and is a remarkable ‘guide’ with sharp eyes and the slightly unnerving habit of pointing to a tree and saying “Hmm, new for Science” before striding on with a wistful and determined look.

Restored native Mauritian forest. Note the numerous (slow-growing) native seedlings that are emerging. Undescribed or incredibly rare species of trees are being found in these cleared areas as the forest regenerates.

A strangler fig Ficus sp. Starting life as a tiny seed in the canopy, the fig’s roots grow down to the forest floor where they take root and begin to take nutrients from the soil. They gradually wrap around the host tree, slowly forming a lattice-work that surrounds the host’s trunk. The host tree usually dies, leaving the strangler’s now-hollow lattice, but in this case the host - an Ebony (probably Diospyros tesselaria) - can still be seen (photo right) and appears to be alive and well.

 

Two native orchids: Calanthe sylvatica (upper photo) and Cynorkis sp

I have to admit I felt a little like a bewildered child following a Pied Piper as Dennis danced along the forest floor throwing out complex scientific names in his wake (like the ones in this post which all come via Dennis), but it is spell-binding spending time with someone who can explain the interactions and ecology of one of the rarest forest systems in the world so completely. Ferns, epiphytes, orchids, trees - Dennis seems to know all of them. As importantly he knows - and can explain simply and brilliantly - what is missing…

I chose my words carefully when I said that “In some respects therefore the forest was more or less like it would have been when European settlers first arrived”, because there have been changes made to it that are irreversible. Like far too many once-isolated islands in the Indian Ocean Mauritius has lost not only huge areas of native forest but also the majority of its large-bodied vertebrate seed-dispersing fauna. In Mauritius’s case the list of extinctions includes the Dodo (which was a large, flightless pigeon), two species of giant tortoises, two parrots, pigeons, fruitbats, and giant lizards.

This loss is fairly recent and is still being widely felt. It has left many Mauritian fleshy-fruited plant species ’stranded’ without any way to disperse their seeds. Without seed dispersal there is no efficient way for trees and plants to reach new areas - even to reach soils newly cleansed of non-native plants which are no more than a few metres from the parent tree. If mature trees can’t replace themselves inevitably they will grow old and fall, and - in a worst-case scenario - will eventually die out completely.

As Dennis himself wrote in a recent paper (http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0002111):

Recent work has highlighted how it is not species diversity per se, which breathes life into ecosystems, but rather the networks of interactions between organisms. Thus, the real ghosts in Mauritius are not as much the extinct animals themselves, but more importantly the extinct networks of interactions between the species…

Many authors have written about feeling Mauritius’s ‘ghosts’ when they’re describing what it’s like to walk in the island’s forests, and much as I’d like to be original ‘walking with ghosts’ is exactly how it feels. Europeans only arrived in Mauritius in large numbers in the seventeenth century, and what they found was an island clothed in forest, and plants and animals that were unfamiliar, exotic, and undescribed. Within a few hundred years they’d ripped up the forests, hunted many species to extinction, and introduced non-native predators like cats and rats which tore through populations of many of the ground-nesting native birds and ate native reptiles. In doing so they’d permanently altered a system of interactions that had evolved over hundreds of thousands of years and what’s left now are small pockets of forests stripped bare of its vertebrate fauna. Inside the CMAs are trees that are old enough to have had Dodos foraging on the forest floor around them, to have had giant tortoises lumbering around their roots, and extinct frugivorous pigeons descending into their canopies searching for ripe fruits. The trees still develop fruits but the animals are gone and the forests are almost silent and motionless. There is a tangible sense of loss, of broken partnerships, of the presence of ‘ghosts’ inside the CMAs that is immensely affecting…

Research using Aldabran Giant Tortoises as a stand-in for native tortoise species has shown that seeds that pass through animal guts grow taller, have more leaves, and suffer less damage from natural enemies than other seedlings. These hard, large seeds are from the endangered Sideroxylon grandiflorum - the Tambalacoque or so-called ‘Dodo tree’. Whilst some seeds do germinate, with the recent loss of so many frugivores many of the Tambalacoque fruits are left to rot uselessly on the forest floor.

Dodo reconstruction reflecting new research at Oxford University Museum of Natural History.
Wikipedia image at http://en.wikipedia.org/wiki/File:Dodo_1.JPG

Whilst many of us probably think of the Dodo as a rather fat, stupid bird it was neither: many early paintings were of obese specimens held in captivity, and many isolated island species to this day have no fear of humans - that doesn’t make them stupid just unfortunate. The interpretation that the Tambalacoque relied on Dodos to break open and disperse their seeds does appear to be wrong though. Research by scientists like Dennis suggest that Dodos were likely very poor seed dispersers, as they had a powerful gizzard and swallowed large stones which pretty much ground everything but the largest & hardest seeds to dust. It was - like many pigeons - a seed predator, rather than a disperser. Giant tortoises, fruitbats & giant skinks would have been much better. It’s also unlikely that one species of plant would rely on one species of animal as a disperser, as that goes against all that’s now known about the highly generalised nature of plant/animal interactions on islands. Lastly, the Tambalacoque seeds germinate perfectly well (albeit in fairly low numbers) without being abraded: the seeds have a well-defined line along which they split open once the embryo inside swells. The thickness of some seeds in Mauritius is more likely to be an adaptation to survive the attentions of seed predators such as parrots and dodos instead.

Not all the forest’s frugivorous species are gone though, and this is where the work that has been done to save the Echo Parakeet, the Pink Pigeon, and now the Vulnerable and endemic Mauritius Black Bulbul Hypsipetes olivaceus (known locally as the merle, it has a global population of around 560) is now doubly paying off. As the numbers of all three species are either growing (the parakeet and the pigeon) or no longer declining and remaining stable (the bulbul) evidence that they are coming back into the small pockets of native forest and feeding partly on native fruits is being gathered.

It helps if you’re an expert in interpreting the subtle signs of avian visitation but in the photo below are the leaves and seed pods of a native tree that have been nibbled by Echo Parakeets. Historically of course this would have been a commonplace find - with the Echos down to just 12 individuals as recently as the 1970s it’s far rarer (and encouraging) to see it now. How much of an impact on seed dispersal the still tiny numbers of parakeets and pigeons - which are perhaps more seed predators than dispersal agents anyway, as the discarded unripe fruits in the photo above suggest - will have on the consequent regeneration of the forest is something Dennis is working to discover, but small or not it is extremely heartening to see that at least a few of the ghosts are being laid to rest…

The seeds of Tabernamontana persicarifolia

As the afternoon wore on the rainclouds gathered and it became darker inside the forest. About an hour after we’d entered the CMA the rain started falling. There is something indescribably magical about standing in a forest in a place like Mauritius hearing the hiss of rain falling and the splattering of raindrops on the canopies of rare and endangered trees above your head. Imagine adding into that soundscape the soft moaning of Pink Pigeons and the chattering of Black Bulbuls, the occasional ‘kek-kek-kek’ of overflying Echo Parakeets and it becomes impossible not to become emotionally altered, impossible not to understand what it is that brings people like Dennis, Anna, and Lone back time after time to do all they can in their power to reverse the losses, to turn back time in effect, and to dedicate themselves to restoring this unique and wondrous place…

If you would like to help support the fantastic work being done by the Mauritian Wildlife Foundation - and without the researchers and volunteers either working for or affiliated with the MWF there would be no Echos, Pink Pigeons, or native forest remember - please go to their website at www.mauritian-wildlife.org where you can make a donation on-line or contact the Fundraising Manager: lraffray@mauritian-wildlife.org. Thanks.

All photos copyright Charlie Moores, 2009.
I am heavily indebted to Dr Dennis Hansen for most - if not all - of the information in this post (certainly for the interesting stuff on seeds and Dodos anyway), and my thanks go to him.