Tropical birds in freefall: Study finds some species living in a protected Panamanian rainforest have declined by 90% in just over 40 years
- Biologists studied 44 years of bird population data at Parque Nacional Soberanía
- Panama’s 55,000-acre park is about 15 miles from Panama’s capital Panama City
- Out of 57 bird species, nine have seen numbers decline by 90 per cent or more
Some species of birds living in a protected rainforest in Panama have declined by 90 per cent in more than 40 years, a shock new study reveals.
Researchers have studied long-term bird population numbers at Parque Nacional Soberanía, a 55,000-acre national park about 15 miles from Panama City.
Data was taken from annual bird surveys at the national park by University of Illinois researchers between 1977 and 2020.
Out of 57 bird species, they found 35 have seen numbers decline by half or more, while nine species have declined by 90 per cent or more.
The researchers can’t definitively point to causes for the declines, but they’ve called it ‘a concerning trend’.
Possible explanations – such as changing amounts of rainfall, food availability and reproductive rates – may be tied to climate change, they say.
Over a 44-year study, University of Illinois researchers observed significant declines in common tropical bird species, including the Ocellated antbird (Phaenostictus mcleannani, pictured), in a protected area in Panama’s Parque Nacional Soberanía
Panama’s Parque Nacional Soberanía is around 15 miles from the country’s capital, Panama City
Over 44 years, researchers gathered sufficient data to track 57 bird species.
The researchers noted declines in 40 species, or 70 per cent.
Out of the 57 species, 35 (61 per cent) have numbers that have fallen by half or more.
Nine species (15 per cent) declined by 90 per cent or more.
Only two species (3.5 per cent) increased over the 44-year period.
‘It was very surprising,’ said study author Henry Pollock at the Department of Natural Resources and Environmental Sciences (NRES) of the University of Illinois.
‘Many of these are species you would expect to be doing fine in a 22,000-hectare national park that has experienced no major land use change for at least 50 years.’
Co-author Jeff Brawn, who has investigated birds at Parque Nacional Soberanía for more than 30 years, called the findings ‘concerning’.
‘This is one of the longest, if not the longest, study of its kind in the Neotropics,’ Brawn said.
‘Of course, it’s only one park. We can’t necessarily generalise to the whole region and say the sky is falling, but it’s quite concerning.’
The team say that the decline is most pronounced for ‘edge species’ – those that specialise in transition zones between open and closed-canopy forest.
Birds that migrate to high elevations require some degree of forest connectivity to be successful, but forest in Panama – like most places – became increasingly fragmented in the last several decades.
About 40 years ago, a paved access road cut through the site, which created the ideal habitat for edge species that like openings in the forest canopy.
But over time, the road stopped being maintained and has since turned into a small gravel road and the forest canopy filled in overhead.
Overall, edge species were hardest hit, most declining by 90 per cent or more.
It was back in 1977 that a University of Illinois faculty member initiated the twice-yearly bird sampling effort.
Since then, researchers have gone to park every year to set up mist nets in the rainy and dry seasons to capture birds.
Mist nets gently entangle birds, allowing the team to carefully pluck them out, identify, measure and band them, and then release them unharmed.
Over 44 years and more than 84,000 sampling hours, the researchers captured more than 15,000 unique birds representing nearly 150 species.
They gathered sufficient data to track 57 of those species.
After studying the 44 years of data, the researchers noted declines in 40 species (70 per cent), while 35 species lost at least half of their initial numbers.
Only two species – a hummingbird and a puffbird – increased.
Recently, even just capturing birds in the park has become more of a challenge, the team claim.
The white-flanked antwren (Myrmotherula axillaris), a species found throughout the entire Amazon Basin
The long-billed hermit (Phaethornis longirostris), which visits a variety of flowering plants for nectar
‘At the beginning of the study in 1977, we’d catch 10 or 15 of many species,’ said Pollock. ‘And then by 2020, for a lot of species, that would be down to five or six individuals.’
The researchers are reluctant to generalise their results beyond Parque Nacional Soberanía to the rest of the South American region.
‘Right now, this is really the only window we have into what’s going on in tropical bird populations,’ Pollock said.
‘Our results beg the question of whether this is happening across the region, but unfortunately we can’t answer that.
‘Instead, our study highlights the lack of data in the tropics and how important these long-term studies are.’
The plain xenops (Xenops minutus). This species is often difficult to see as it forages for insects, including the larvae of wood-boring beetles, on bark, rotting stumps or bare twigs
The spotted antbird (Hylophylax naevioides), found in Honduras, Nicaragua, Costa Rica and Panama
Loss of birds from any habitat can threaten the integrity of the entire ecosystem, according to the researchers.
In the South American region, these birds are key seed dispersers, pollinators and insect consumers.
Fewer birds could threaten tree reproduction and regeneration, impacting the entire structure of the forest, a pattern shown elsewhere after major bird declines, according to a 2017 study.
‘Almost half the world’s birds are in the Neotropics, but we really don’t have a good handle on the trajectories of their populations,’ said Brawn.
‘So, I think it’s very important more ecological studies be done where we can establish trends and mechanisms of decline in these populations. And we need to do it damn quick.’
Researchers haven’t looked at the impacts or the underlying causes of the declines yet, although this could be the focus of future studies.
The new paper has been published today in the journal Proceedings of the National Academy of Sciences.
MORE THAN 70% OF SMALL MAMMALS HAVE DECLINED IN THE UK SINCE 1970 – WITH WEASELS NOW CLASSED AS ‘VULNERABLE TO EXTINCTION’, EXPERTS WARN
Weasels are in sharp decline across the UK and need legal protection to save them from extinction, experts have warned.
Britain’s smallest native carnivore has halved in numbers over the past 50 years and has suffered the fastest population decline of 37 mammals studied by scientists.
The research, published in the journal Biological Conservation, also found that since 1970 more than 70 per cent of small mammals have been on the decline.
There are now fewer voles and shrews, while the harvest mouse has seen the biggest fall in numbers.
The stoat and weasel — classified as ‘mid-sized mammals’ in the study by the Mammal Society, Sussex University and Centre for Ecology & Hydrology — are also struggling because of a reduction in their prey, which includes mice and voles.
Weasels currently have no legal protection and are often killed by gamekeepers because they eat gamebird chicks.
The destruction by farming of hedgerows where they live has also hurt numbers so much that the species should be declared ‘vulnerable to extinction’, researchers said.
They studied the trends of two thirds of the UK’s land mammals from 1970 to 2016.
The experts analysed almost half a million records from surveys that involved dividing parts of the UK into 1km squares and recording whether the mammals studied were present in each one.
In 1971, weasels were found in 50 per cent of squares studied, but this dropped to 20 per cent in 2016.
Fiona Mathews, a professor at Sussex University and the study’s co-author, said: ‘Small mammals are critical, and usually abundant, parts of ecosystems.
‘They are tiny engineers that improve the water holding capacity of our landscapes, and are vital prey for many other species including barn owls, kestrels, stoats and weasels.
‘The disappearance of the long grass and overgrown areas they need has taken its toll.’
She added: ‘The whole of Europe continues to have a problem with any species that’s predatory.
‘As soon as we encounter something that isn’t quite aligned with our human interests, we as the ultimate predator decide that we better get rid of it.’
To reverse the decline in numbers, Professor Mathews suggested making it a requirement to obtain a licence before culling weasels.
To kill them, gamekeepers would then have to show an ‘overwhelming reason, like there’s another species of dire conservation concern that needs to be protected’.
Dr Stephanie Wray, chair of the Mammal Society, said the research was ‘the canary in the coal mine that tells us we need to act now to stop ecosystem collapse’.
Bank voles, common shrews, field voles, water shrews and stoats are all declining in population along with weasels and harvest mice, according to the study.
There has been no change in the numbers of red deer, fallow deer, grey squirrels, red foxes and several species of bat, while European badgers, sika deer and the yellow-necked mouse are all on the increase across the UK.
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