A protected area of rainforest has seen over 70% of its bird populations decline in the last 44 years. This, according to scientists, is an effect, in part, of climate change.
In recent years, scientists have sought to understand how climate change and environmental devastation directly affect plants and animals.
In addition to the effects on rising sea levels and temperature in the oceans, annual differences in more intense rainfall regimes and longer droughts have a direct effect on ecosystems, altering some relationships in ecological communities.
Over the past four decades, researchers have followed 57 species of birds found in Soberanía National Park in Las Cumbres, Panama. Of the total, 40 (70.2%) species had a decrease in their populations, 15 (26.3%) did not change and only two (3.5%) had an increase.
The decline was more than 50% in 35 of the 40 species with decline, and a group of at least nine species had a population reduction of more than 90%, including species more frequent in areas of young forests or in woodlands on mountain slopes.
The study was published on the 4th of this month in the specialized journal PNAS (Proceedings of the National Academy of Sciences), led by researchers Henry Pollock and Jeffrey Brawn, from the University of Illinois, in the United States.
To carry out the analysis, the researchers compared vocal and visual records and the animals found in capture nets (a technique for collecting birds) from June 1977 to September 2020 in an area of about 600 hectares of Soberanía National Park, whose total area is more than 22 thousand hectares.
With the monitoring, data were recorded on more than 15,000 birds included in 150 different species, of which 57 had population frequency data. The year-adjusted proportional change (ie, the total difference in populations divided by 43 years) indicated a decline in the frequency and abundance of different groups of birds whose feeding habits and behavior are fundamentally different.
“One of the reasons that led us to think that the data is really robust is that the difference [populacional] was observed in different species of birds, with different body sizes, that eat different things, so this can only be explained by a profound change in the ecosystem, it is not something individual”, explains Henry Pollock, first author of the study.
The largest annual differences observed were in nectivorous birds (such as hummingbirds), terrestrial frugivores, understory frugivores and aquatic birds (such as kingfishers), followed by insectivores and omnivores.
One of the hypotheses for population changes over four decades would be the direct impacts of drought (El Niño effect) and excessive rain (La Niña), climatic events that have happened more frequently in recent years thanks to global warming.
“Some bird species may reproduce less, or generate fewer chicks, in drier years, and this ends up affecting the demography in the medium and long term. With this happening more frequently, it is a possibility that this phenomenon was generalized to the different groups”, says Jeffrey Brawn, professor and chair of the Levenick department in Sustainability at the University of Illinois.
Despite the reduction in birds in the park, scientists say that there has not been a significant change in the forest area in recent years, precisely because it is a protected area. The only change that took place was an old highway that was paved and used by the US military during the years of occupation in Panama was left unattended and ended up being “dominated” again by the forest.
“In this environment bordering the highway, it was more common to see species that prefer open areas, and these species certainly had an impact because they are no longer seen. But in general, the species did not become extinct, they just disappeared from the place”, says Pollock.
The study, however, has some limitations, and should not be extrapolated to the entire diversity of birds that inhabit tropical forests on the planet. “Our research, despite having great relevance because long-term studies in tropical forests are rare, took place in a single area of about 22,000 hectares, and certainly larger sites, such as preserved areas in the Amazon, may not exhibit the same problem”, says the young researcher.
For Brawn, the effects observed in the long-term monitoring of the Panamanian park may reflect how public policies that affect biodiversity have a role today in ecosystems. “[O avanço do desmatamento] in the Brazilian Amazon keeps me awake at night. Certainly, if we think that tropical forests are the great repositories of biodiversity, we need to think about what we are doing now so that, a hundred years from now, we won’t be asked ‘what were they thinking?'”, he says.
