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Something was happening to the birds at Tiputini. The biodiversity research centre, buried deep in the Ecuadorian Amazon, has always been special. It is astonishingly remote: a tiny scattering of research cabins in 1.7m hectares (4.2m acres) of virgin forest. For scientists, it comes about as close as you can to observing rainforest wildlife in a world untouched by human industry.
Almost every year since his arrival in 2000, ecologist John G Blake had been there to count the birds. Rising before the sun, he would record the density and variety of the dawn chorus. Slowly walking the perimeter of the plots, he noted every species he saw. And for one day every year, he and other researchers would cast huge “mist” nets that caught flying birds in their weave, where they would be counted, untangled and freed.
For years, these counts captured birds’ annual fluctuations; they had good and bad years, seasons in which nests were disrupted by storms and others when they boomed. But by about 2012, Blake and his collaborators could see something was shifting. The birds were dying: not in masses at once, struck down by a plague, but generation by generation. The yearly fluctuations he had spent a decade recording slowly stopped their upward leaps, the trend line transforming into an unyielding downward slope. By 2022, their numbers had almost halved. Blake did not need the graph to tell him something was wrong; when he rose to listen to the dawn chorus, he could hear that it was muted. Songs were missing. Some species simply vanished.
“A number of them I have not heard for quite a few years now,” he says, over a broken video connection from the research centre; far from the outside world, it has intermittent power and relies on a satellite connection. “There are definitely some species that, for whatever reason, do not seem to be here any more.”
In North America and Europe, scientists have long warned bird numbers are falling, but mostly that has been explained by their contact with humans. As cities and farms expand, forests around them become fragments, animal habitats shrink, pollution contaminates rivers, pesticides and fertilisers kill off insects. Even pets are a factor – in the US, domestic cats are killing up to an estimated 4 billion birds a year. Tiputini, however, is one of the few patches of the planet not directly feeling those pressures: no nearby farms, no polluting factories, no encroaching loggers, no roads in. Yet, their birds were dying.
At other remote sites around the world, scientists had been starting to observe similar trends. In Brazil, the Biological Dynamics of Forest Fragments Project (BDFFP) is an ecological study located deep in primary Amazon forest, unreachable by road. These regions hold some of the oldest living forests on the planet – they evaded the ice age events that remade forests in the US and Europe with the growth and retreat of glaciers. “In the Amazon, we’ve had pockets of stable forests over millions of years,” says ecologist Jared Wolfe, one of the project’s research scientists. “The site is truly amazing.”
But in 2020, when researchers there compared bird numbers with the 1980s, they found a number of species in deep decline. At another site in Panama, scientists working in a 22,000-hectare (54,000-acre) stretch of intact forest had been gathering bird data since the mid-1970s. By 2020, their numbers had gone off a cliff: 70% of species had declined, most of them severely; 88% had lost more than half their population. At some sites, scientists are beginning to observe “almost complete community collapse”, says Wolfe. “This is occurring in pristine environments, which is really unsettling.”
For decades scientists have been trying to understand what is going on. Blake and collaborator ornithologist Bette A Loiselle published their first paper documenting the declines in 2015, but could not definitively say what was causing them. They tested birds for disease and parasites, and found no clear links. They considered the possibility that an unknown toxin or pollutant had seeped in – but there was no evidence of that. “I suspect whatever is causing these declines is something much more widespread,” Blake says. “It would not be something specific to the Tiputini area.”
The most likely answer, they concluded, was the climate crisis. “There’s very little else – at least that I know of – that has such large scale worldwide impacts,” says Blake.
A decade later, their instincts are proving correct. This week, Wolfe and collaborators published new work directly linking rising temperatures to bird declines. Their research, published in Science Advances, tracked birds living in the forest understory at the BDFFP against detailed climate data. They found that harsher dry seasons significantly reduced the survival of 83% of species. A 1C increase in dry season temperature would reduce the average survival of birds by 63%.
Exactly how the heat is causing bird numbers to decline is tricky to pinpoint, Wolfe says, but “these birds are intrinsically linked to small, small changes in temperature and precipitation”. One of the most immediate ways a heating planet hurts wildlife is by putting them out of step with their food sources: when fewer insects survive dry seasons, or leaves bloom and fruit ripens at different times, birds find themselves unable to forage and feed their young. Their nests begin to fail. Within a few generations, their numbers fall.
The losses documented in these remote stations have implications far beyond birds. “The idea has always been that if you have huge expanses of forest, then that’s going to protect everything,” Blake says. “And, well, it does protect a lot of things. But apparently not everything.”
Most western conservation works by sectioning off wilderness, as national parks or reserves. These places are like arks: reservoirs of wildlife that we hope will be saved, even as people transform the land around them. But what the researchers were seeing with birds suggested that these arks are far more fragile than first thought.
Wolfe likens the problem to pollution in a large body of water. When scientists measure water quality, they think about pollution in two ways. “Point source” pollution might be a gushing oil pipe: it’s doing huge damage, but by shutting it off you fix the problem. “Nonpoint source” would be the small dribbles of oil coming from every car in the area, washed down off the roads and into the waterways: each contribution might be tiny, but the cumulative effect can be huge – and hard to shut off. “It’s very difficult to combat,” Wolfe says. What is happening to the birds “feels like a nonpoint source; a wicked complex problem where you have breakdowns in biological interactions that are causing these declines.”
But realising what is happening is necessary to developing solutions, Wolfe says. “One thing I am becoming particularly tired of as a professional researcher, is writing these obituaries for birds,” he says. The research on pristine regions can also reveal potential solutions: early data suggests some forests are bucking the declines. Identifying why – and protecting them – is crucial.
For the scientists who are seeing birds disappear, there is grief in watching some of the most beautiful, ecologically rich places in the world fall into decline. “It is depressing,” Blake says. “When we first got here and started looking, we were just totally amazed at how many birds there were, and their diversity. We keep doing the work – but it’s harder to get excited about doing it because there’s so little.”
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