From 1977 to 2020, mist nets were set up twice a year in the rainy and dry seasons. Birds that become entangled in mist nets, a common tool used by ornithologists, are carefully removed. The researcher notes the species, size and other details before releasing the bird back into the forest. Using the number of unique birds captured in the nets, the team modeled the populations for a diverse range of 57 resident species.
Widespread declines
Over the study period, which consisted of more than 80,000 net hours of sampling time, the researchers captured over 14,000 unique birds. Irrespective of their body mass, foraging groups or initial local abundance, 40 out of 57 bird resident species (70%) declined in abundance over 44 years. Declines were severe for 35 species that lost more than 50% of their initial abundances.
Not only rare bird species, but even common species, such as the red-capped manakin (Ceratopipra mentalis), suffered steep declines. Birds perform valuable ecosystem services in forests; they disperse seeds, pollinate plants, and eat insects.
“The loss of common species, and especially in fairly large numbers, I think, is really concerning in terms of ecosystem integrity because when you don’t have these ecosystem services occurring, you’re going to have a degradation of the entire ecosystem altogether,” warned Pollock.
These findings add to a “small but growing body of evidence for significant long-term declines in biodiversity in undisturbed tropical forests—replicating previous findings from the Ecuadorian and Brazilian Amazon,” said Alexander Lees, senior lecturer at Manchester Metropolitan University in the United Kingdom, who was not connected to the research. According to a new report co-authored by Lees, entitled “State of the World’s Birds”, around 48% of bird species worldwide are known or suspected to be undergoing population declines.
Birds are often grouped into “foraging guilds” depending on the type of foods they forage on, such as insects or fruits. Previous studies from undisturbed forests found that understory insectivores (insect-eating birds) declined the most.
“We found that not only are understory insectivores declining, but also all the other guilds, except for maybe the hummingbirds that seemed to be doing a little bit better, but everything was declining,” Pollock said. “And that to us is really scary and suggests some sort of broader ecosystem-level process related to climate change,” he added.
Loss of forest connectivity and climate change
A couple of species that suffered 90% losses in populations may be explained by a loss of regional connectivity to forests outside of the reserve. Some species migrate seasonally to higher elevation forests to the east of the Isthmus of Panama while others are connected to wetter forests on the Caribbean side of the Isthmus. From 1950 to the 1980s, large swathes of forests around the Isthmus were cleared. As a result, regional connectivity between the study site and these forests was lost since the study began, explained Brawn. “So, the park as a whole has become more isolated.”
The mechanisms behind why so many species are declining are unknown, say the researchers. “For the majority of the species, we’re scratching our heads on why they’re decreasing,” says Brawn. To pinpoint the causes, the authors state that long-term studies are needed for each species.
The Black-throated Trogon (Trogon rufus), a common species that eats insects and plant material (an understory omnivore) found in the forests of Soberanía National Park. Image courtesy of Henry Pollock.
Since birds from a lot of foraging guilds declined, Pollock hypothesizes that “it could be some systemic change in food across the board.” Lees also says that changes in food resources as an indirect effect of climate change might be a contributor. “Warmer temperatures, often exacerbated by El Niño events, may extend dry season lengths leading to desiccation of normally humid forest microhabitats like the leaf litter, resulting in a drop in the abundance of key food resources such as insects,” he explains.
How to maintain bird populations?
One of the responses of populations to climate change is to move to another, more favorable area, explained Pollock. He suggests creating more corridors on a regional level to maintain forest connectivity. “Giving birds the ability to move—and birds are quite mobile—I think that would be one step in the right direction, at least for some species.”
The findings raise concerns that protected areas in the tropics may not be sufficient to preserve bird populations.
“We should always protect more habitat at the very least,” Brawn stressed. “That’s the first thing that needs to be done, but if other studies and other areas start to find what we found then we need to start looking at more of what might be going on at the ecosystem level within habitats that might be affecting the viability of these populations.”
Both Brawn and Lees underscore the importance of minimizing climate change. “Many tropical forest systems may be approaching their thermal limits and hence run the risk of breaching tipping points” that may “drive major loss of biodiversity and ecosystem services,” warned Lees. “It is imperative that we do everything possible to limit this change.”
Embera woman within the forest in Darien Province, Panama, on the shores of the Chuunaque, Sambu, Tuira Rivers and it’s water ways. Image courtesy of If Not Us, Then Who.
Could indigenously-managed protected areas be more effective in conserving bird populations than other protected areas? Pollock acknowledged that Indigenous people manage wildlife populations sustainably, but said that his team has not collected data on bird populations from such areas. “We don’t have anything to compare it with,” Brawn added.
“Indigenous reserves are often more resilient to external pressures on other types of protected areas,” noted Lees. “In this case, however, the threat from climate change is global in scope and the protected area type will likely make little difference—although Indigenous peoples themselves have been very vocal in protesting relative global inaction on the threat of climate change.”
Citation:
Lees, A. C., Haskell, L., Allinson, T., Bezeng, S. B., Burfield, I. J., Renjifo, L. M., … & Butchart, S. H. (2022). State of the World’s Birds. Annual Review of Environment and Resources, 47. doi:10.1146/annurev-environ-112420-014642
Pollock, H. S., Toms, J. D., Tarwater, C. E., Benson, T. J., Karr, J. R., & Brawn, J. D. (2022). Long-term monitoring reveals widespread and severe declines of understory birds in a protected Neotropical forest. Proceedings of the National Academy of Sciences, 119(16), e2108731119. doi:10.1073/pnas.2108731119
Banner image: The Ruddy-tailed Flycatcher (Terenotriccus erythrurus) is a common species that forages on insects in the forest understory (an understory insectivore). Image courtesy of Dr. John Whitelaw.
Related listening from Mongabay’s podcast: We speak with Sy Montgomery about his two most recent books about our avian comrades and Mongabay staff writer Abhaya Joshi about a new bird-counting app in Nepal. Listen here:
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Biodiversity, Birds, Conservation, Endangered Species, Forest Recovery, Protected Areas, Species, Wildlife, Wildlife Conservation
Central America, Latin America, Panama
Source link : https://news.mongabay.com/2022/05/drastic-declines-in-neotropical-birds-in-a-protected-panamanian-forest/
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Publish date : 2022-05-31 03:00:00
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