For years, these counts captured birds\u2019 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.<\/p>\n
\u201cA number of them I have not heard for quite a few years now,\u201d 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. \u201cThere are definitely some species that, for whatever reason, do not seem to be here any more.\u201d<\/p>\n 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 \u2013 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.<\/p>\n 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 \u2013 they evaded the ice age events that remade forests in the US and Europe with the growth and retreat of glaciers. \u201cIn the Amazon, we\u2019ve had pockets of stable forests over millions of years,\u201d says ecologist Jared Wolfe, one of the project\u2019s research scientists. \u201cThe site is truly amazing.\u201d<\/p>\n The idea was that if you have huge expanses of forest, that\u2019s going to protect everything \u2026 it does protect a lot of things. But apparently not everything 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 \u201calmost complete community collapse\u201d, says Wolfe. \u201cThis is occurring in pristine environments, which is really unsettling.\u201d<\/p>\n 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 \u2013 but there was no evidence of that. \u201cI suspect whatever is causing these declines is something much more widespread,\u201d Blake says. \u201cIt would not be something specific to the Tiputini area.\u201d<\/p>\n The most likely answer, they concluded, was the climate crisis. \u201cThere\u2019s very little else \u2013 at least that I know of \u2013 that has such large scale worldwide impacts,\u201d says Blake.<\/p>\n 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%.<\/p>\n Exactly how the heat is causing bird numbers to decline is tricky to pinpoint, Wolfe says, but \u201cthese birds are intrinsically linked to small, small changes in temperature and precipitation\u201d. 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.<\/p>\n The losses documented in these remote stations have implications far beyond birds. \u201cThe idea has always been that if you have huge expanses of forest, then that\u2019s going to protect everything,\u201d Blake says. \u201cAnd, well, it does protect a lot of things. But apparently not everything.\u201d<\/p>\n 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.<\/p>\n Wolfe likens the problem to pollution in a large body of water. When scientists measure water quality, they think about pollution in two ways. \u201cPoint source\u201d pollution might be a gushing oil pipe: it\u2019s doing huge damage, but by shutting it off you fix the problem. \u201cNonpoint source\u201d 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 \u2013 and hard to shut off. \u201cIt\u2019s very difficult to combat,\u201d Wolfe says. What is happening to the birds \u201cfeels like a nonpoint source; a wicked complex problem where you have breakdowns in biological interactions that are causing these declines.\u201d<\/p>\n But realising what is happening is necessary to developing solutions, Wolfe says. \u201cOne thing I am becoming particularly tired of as a professional researcher, is writing these obituaries for birds,\u201d he says. The research on pristine regions can also reveal potential solutions: early data suggests some forests are bucking the declines. Identifying why \u2013 and protecting them \u2013 is crucial.<\/p>\n 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. \u201cIt is depressing,\u201d Blake says. \u201cWhen 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 \u2013 but it\u2019s harder to get excited about doing it because there\u2019s so little.\u201d<\/p>\n
\nJohn G Blake, ecologist<\/p><\/blockquote>\n