The bird population in a protected tropical forest in Panama is suffering great declines.

Scientists from the University of Illinois tracked bird species for 44 years in Soberania National Park to determine if populations had changed.

Every two years between 1977 and 2020, the authors of the research published in the Proceedings of the National Academy of Sciences deployed mist nets at multiple study sites, identifying and banding thousands of birds.

The scientists estimated changes in the abundance of 57 species. For example, the red-headed manakin, the most abundant frugivorous bird sampled and an important seed disperser. In 1977, 23 were detected, but in 2020, only nine were caught.

“The estimated abundances of 40 (∼70%) species decreased during the sampling period, while only 2 increased. Furthermore, the declines were severe: 35 of the 40 declining species exhibited large proportional losses in estimated abundance, amounting to ≥50% of their initial estimated abundances,” is part of the research summary published on Monday, April 4.

“Our findings provide strong evidence for tropical bird declines in intact forests and reinforce a large body of literature from temperate regions that suggests bird populations may be declining on a global scale. Identifying the ecological mechanisms underlying these declines should be an urgent conservation priority,” the scientists added.

The researchers said these severe and widespread declines are particularly “alarming” given that they occurred in a relatively large forested area.

The findings provide strong evidence for tropical bird declines in intact forests and reinforce a large body of literature from temperate regions that suggests bird populations may be declining on a global scale.

The researchers said that while tropical forests are often thought of as “biodiversity reservoirs,” this study suggests there is a worrying decline in species populations.

They concluded, based on data published in The Guardian , that further study is needed, writing: “The next logical step towards understanding and possibly preventing further decline is to identify the underlying ecological mechanisms. To achieve this, intensive long-term studies of individual species are likely to be needed to delve deeper into the factors.”