The plight of tropical migratory species

So much remains unknown about the tropics, including the extent to which species living in these environments migrate seasonally.  Dr Lisa Davenport has worked for many years in the tropics, especially the Peruvian Amazon.  Here she tells us about her intriguing work on a particular migrator, and its broader implications for nature conservation:

A foraging Black Skimmer

A foraging Black Skimmer

An unknown number of tropical species, such as certain birds, bats, and moths, migrate up and down elevational gradients over the year, tracking seasonal changes in the abundance of fruits, nectar, or insect prey. 

Others, notably birds such as warblers and some raptors, undertake much longer-distance migrations, wintering in the tropics while breeding in far-away temperate regions.

Manu National Park in Peru, where I have long worked, also has its share of migrators, along with being one of the most biologically stunning places on Earth.  Certain fish, birds, and mammals at Manu appear to move large distances during the course of the year. 

But as we begin to learn more about these migratory species, we increasingly suspect they could be vulnerable to escalating human pressures in this region.

Growing pressures

For instance, just downstream of Manu, on the Madre de Dios River, huge areas of river and riparian forest are being devastated by illegal gold mining.  Among these impacts is contamination of the rivers by toxic mercury, which is used by miners to separate gold from river sediments.

An illegal gold miner scours the forest soil (photo by William Laurance)

An illegal gold miner scours the forest soil (photo by William Laurance)

Since 2010, biologists at Cocha Cashu Biological Station at Manu have used cutting-edge satellite telemetry to track some of the park’s rare and endangered birds -- many of which are very poorly known.  One key reason to do this is to learn where these species go when they move outside the park, where they may be highly vulnerable.

In a new study, I and my colleagues report our research on Black Skimmers (Rynchops niger), an elegant bird that skims over water surfaces while flying, in order to catch unwary fish.  To do this it uses its uniquely elongated lower beak, which it drags through the water and which instantly snaps shut when it contacts a fish. 

We found that Skimmers tagged in Manu move extremely long distances both during and outside their breeding season. 

A Black Skimmer feeds its chick

A Black Skimmer feeds its chick

'Albatrosses of the Amazon'

I would liken our Black Skimmers to “Albatrosses of the Amazon" -- they fly surprisingly long distances, even in the breeding season, and seem to soar effortlessly. 

We found that some Black Skimmers move not only to other watersheds in Peru but even to other nations, including Brazil and Bolivia, during their breeding season.  Unfortunately, some of these areas are being severely degraded by illegal gold mining. 

Remarkably, some of the birds tagged inside Manu even crossed the Peruvian Andes -- flying above 5,000 meters in altitude to cross the towering Andes mountains -- in order to spend their non-breeding season along the Pacific coasts of Peru and Chile. 

But the Skimmers face hazards on the Pacific coast as well.  Many of the natural wetlands they need for feeding are being severely depleted by the extraction of freshwater for agriculture

Some Skimmers may go even farther afield.  One bird radio-tagged in Manu moved not to the Pacific but southeast to Bolivia and then even further to Paraguay.  Its transmitter stopped at that point but it may have been heading to Argentina’s Atlantic coast, where large numbers of Skimmers are known to summer.

New threats on the horizon

With rising development pressures, threats to large-distance migrators like Black Skimmers will only increase.  Both Peru and Brazil plan to dramatically increasing the damming of wild rivers in the Amazon and Andean headwaters.   Agriculture and mining activities are also expanding apace.

Scores of new dams are being planned (yellow) in the Amazon-Andes region (blue symbols indicate existing dams).

Scores of new dams are being planned (yellow) in the Amazon-Andes region (blue symbols indicate existing dams).

Species that need freshwater for survival and migration, and the ecological processes that sustain such species, will be intensely vulnerable

The recent collapse of a poorly constructed mining dam on the Doce River in Brazil devastated aquatic wildlife across a vast area that stretched for more than 500 kilometers to the sea. 

The lax environmental standards that allowed this catastrophe to occur should give us all pause, as we consider the avalanche of new development projects slated for the greater Amazon region.

Especially alarming is how little we know about the ecology of the Amazon and its many natural denizens -- some of which evidently traverse and require vast areas of habitat for survival.

 

Stealing the Rain from a Rainforest

ALERT’s Susan Laurance, from James Cook University in Australia, is leading an ambitious, million-dollar study to understand how droughts affect tropical rainforests.  Here she tells us about this challenging project and why it is so important:

Right now, much of the world is struggling to cope with a ‘Godzilla’ El Niño drought

The drought has been merciless, causing catastrophic fires and haze across much of Southeast Asia, unprecedented droughts and wildfires in western North America, and mass starvation from crop failure in New Guinea

Fiery future?

And there’s good reason to think future droughts might even be worse. 

First, leading computer simulations suggest global warming could strengthen future El Niño events and increase the frequency of serious heat waves.

Second, apparently new climate dynamics are appearing on Earth that could threaten large areas of rainforest.  Most notable among these are the unprecedented Amazon droughts – driven by exceptionally high sea-surface temperatures in the Atlantic Ocean – that occurred in 2005 and again in 2010.

Finally, human land-uses are making rainforests far more vulnerable to droughts and fire.  For instance, forests that have been logged or fragmented are drier and have much heavier loads of flammable slash than do pristine forests.

And as new roads proliferate almost everywhere, so do the number of human-caused ignition sources.  Even ecosystems where fire was once foreign — such as the world’s deep rainforests — now burn with increasing regularity.

All this means that it’s vital to understand how droughts will affect rainforests – the world’s most biologically diverse and carbon-rich ecosystems.

Big science for a big problem

As I detail in a recent article in Australasian Science (which you can download here), my colleagues and I have recently set up some 3,000 clear plastic panels to create a ‘raincoat for a rainforest’ – inducing an artificial drought over several thousand square meters of the famous Daintree region in north Queensland, Australia.

A big advantage of our experiment – one of the few ever to study rainforest droughts in this way – is that we have a 47-meter-tall canopy crane at the site, so we can assess plant and animal responses at all vertical levels of the forest, from the ground to the tops of the most towering trees.

Our study is comparative: we want to understand how different groups of plants, such as various functional groups of trees, vines, shrubs, forbs, and epiphytes, are affected by drought.

We are looking at the survival, growth, and physiology of these plants in a variety of ways, as well as at the forest soil and microclimate.  Others are studying how insects and other fauna are affected by the drought.

Among our key goals is determining whether big trees are especially vulnerable to droughts, as suggested by recent research.   If so, then this could have profound implications – because big trees store huge amounts of carbon and provide food and shelter for an entire zoo of animal species.

We also want to learn whether certain kinds of plants have strategies – such as special water-carrying vessels in their tissues or other physiological tricks – that allow them to better survive droughts.  If so, these ‘drought winners’ could increasingly dominate forests if droughts become more intense in the future.

Not easy – but worth it

This study has not been easy – in truth it’s been a logistical nightmare to steal the rain from a rainforest.  But the study is now fully set up, and in the end we think it will be worth all the sweat and hard work. 

Rainforests are the biologically richest environments on Earth.  And if we’re going to subject them to more Godzilla-like droughts, then we need to know how they’ll respond – and whether they can sustain their stunning biodiversity into the future.

Wildife struggle in an increasingly noisy world

We live on an ever more-populous planet, pulsating with human-generated noises of every description.  As the din of humanity grows ever louder, what will this mean for wildlife?

White-crowned sparrow: stressed-out by noise

White-crowned sparrow: stressed-out by noise

It's an important question.  Across the U.S.A., for example, nearly nine-tenths of the population experiences artificially elevated sound levels.  In the world's oceans, noises from commercial shipping alone have risen an estimated 16-fold in recent decades.

The most ubiquitous noise-making structures humans create are traffic-laden roads, which already crisscross the Earth and are projected to increase in length by some 25 million kilometers by mid-century—enough to encircle the planet more than 600 times.

A recent study by Heidi Ware and colleagues used an innovative ‘phantom road’ to assess how road noise affects migrating bird species.

Working in Idaho, USA, the authors laid out an array of loudspeakers to mimic road sounds, which they turned on and off periodically to judge the birds' responses.  They also captured birds using mist-nets to assess their overall body condition.

The authors found that bird abundance declined by about a third near the phantom road, with some some noise-sensitive species avoiding the area.

In addition, even birds that remained near the phantom road often fared poorly, having lower body weight and worse overall condition than birds captured elsewhere. 

The authors attributed this to the fact that the birds were often startled by sudden road noises -- and so spent more time looking around for predators and less time feeding. 

A graph (sonogram) of road noises, above a logging truck.

A graph (sonogram) of road noises, above a logging truck.

This is particularly bad news for migratory birds, which are already stressed out by the huge exertions of migrating vast distances.  More noise disturbance could mean that more birds will starve to death while trying to migrate.

In an independent perspective piece on this article, ALERT director Bill Laurance emphasizes that the rapidly expanding footprint of roads and other infrastructure across the planet is invisibly degrading habitat quality for noise-sensitive species.

Laurance suggests that many kinds of species could be affected by human-generated noises. 

For instance, might sensitive marine species, such as echolocating whales or migratory fish, avoid noisy regions such as high-volume shipping lanes or areas where naval vessels regularly pierce the oceans with high-intensity sonar?

Could echolocating bats be distressed by roaring airplanes or even by the steady whine of wind farms or other infrastructure? 

For that matter, might even hiking trails frequented by ecotourists or researchers reduce local wildlife activity, as has been observed in protected areas in California and Indonesia?

The oceans are getting noisier too.

The oceans are getting noisier too.

The findings of Ware et al. suggest that human-generated noises can be serious stressors for some wildlife.  This is an alarming prospect in a world ever more beset by human-induced noises.

For instance, nowhere in Costa Rica’s iconic La Selva Biological Reserve can one avoid hearing the incessant thrum of a nearby highway.  Many other nature reserves are suffering a similar fate, underscoring the urgency of limiting new roads in protected areas and devising strategies to limit noise disturbances where roads already exist.

For wildlife and for humans too, quiet places on the Earth are becoming increasingly rare and precious.

Could disease be driving extinctions of Australian mammals?

Across the vast savannas of northern Australia, mammal populations are collapsing.  Areas that once sustained healthy populations of native mammals are now ecological deserts, virtually devoid of life.  Three researchers from James Cook University, Sandra Abell, Penny van Oosterzee, and Noel Preece, believe that deadly pathogens might be partly responsible for this ongoing calamity:

Brush-tailed bettong -- a critter we don't want to lose.

Brush-tailed bettong -- a critter we don't want to lose.

One third of all mammal extinctions worldwide have occurred in Australia.  Here, 24 mammal species have been wiped out since European arrival -- and that number is still rising.

Loss of habitat, altered fire regimes, and predation by feral cats are all implicated in the recent mammal declines. The role of disease, however, is an understudied but likely contributing factor.

Disease can be deadly for wildlife.  For instance, facial tumor disease is rapidly killing off populations of the Tasmanian Devil.  Trypanosomiasis, introduced by black rats brought by sailing ships, drove the demise of two native species of rainforest rats on Christmas Island, in the Indian Ocean.

Tasmanian Devil with facial tumors -- not a pleasant way to go.

Tasmanian Devil with facial tumors -- not a pleasant way to go.

Now key populations of the Northern Bettong, an attractive wallaby-like animal endemic to north Queensland, is crashing possibly to extinction.

And just this week, endangered Saiga antelopes in Uzbekistan in Asia were reported to have suddenly collapsed, due to the combined effects of climate change and normally harmless bacteria that have evidently become lethal pathogens to the stressed animals.

Saiga Antelope -- another victim of catastrophic disease?

Saiga Antelope -- another victim of catastrophic disease?

We and colleagues have formed a multi-disciplinary group to tackle these declines.  We call ourselves the North Australia Wildlife Decline Disease Investigators.  Our acronym, NAWDDI, rhymes with "naughty".

Our group combines top wildlife ecologists and experts in wildlife disease, including one of the world’s leading experts in wildlife pathogens, Dr Peter Daszak, Director of the EcoHealth Alliance.

NAWDDI is being guided by hard-won lessons learned from the front line of the battle to save imperiled species.

One example is the Brush-tailed Bettong.  Thought to be secure in southwestern Australia, 90 percent of its population has vanished alarmingly over the last decade.  Valiant attempts to understand and halt its decline are providing valuable new insights for conservationists.

NAWDDI is working on a variety of fronts -- from advising on global policy to developing field protocols to make disease investigation a standard practice in researching declines of wild populations.

Disease must be considered early as a potential cause of the rapid and severe mammal declines in northern Australia.  We know that virulent pathogens have caused widespread extinctions or declines of many species worldwide -- from frogs, to Hawaiian birds, to African ungulates and apes, to North American bats.

Pathogens such as the chytrid fungus have driven at least 200 frog species to extinction.

Pathogens such as the chytrid fungus have driven at least 200 frog species to extinction.

Early detection saves money and time -- and could help us avoid the anguish of having to watch helplessly as charismatic mammals like the Brush-tailed Bettong follow the path of three of its sister species to extinction.