- Papua New Guinea is a global hotspot of avian biodiversity, home to spectacular and behaviorally complex bird species that occur nowhere else on the planet.
- A new study shows that forest fragmentation reduces unique forest-specialist birds, but boosts generalist species like pigeons, sunbirds and bulbuls.
- Birds suffered greater declines in habitats cut off from the surrounding landscape, compared to degraded habitats that remained connected to nearby intact forests.
- The shift in the bird community in degraded and isolated habitats undermines ecosystem stability and resilience, as birds that once performed vital pollination, seed dispersal and insect control services are lost.
From pollinating plants to dispersing seeds, birds play a variety of crucial roles that help to keep ecosystems in balance. But when we degrade and fragment their habitats, some species disappear much quicker than others — taking their specific ecosystem functions with them. New research from Papua New Guinea, one of the world’s last havens of intact tropical forest, suggests that forest-specialist insectivores and ground foragers are among the first to go.
Given these vulnerable groups of birds include various bird-of-paradise species along with bowerbirds and cassowaries, which are important emblems of PNG, the authors urge conservationists to focus on retaining forest-dependent birds as a strategy that would protect species of both ecological and cultural significance, as well as their forest home.
“PNG derives much of its cultural power from birds, as sources of Indigenous clothing, pride as national animals, [or the focus of] ecotourism,” study lead author Krystof Korejs, a zoologist at the University of South Bohemia in the Czech Republic, told Mongabay in an email.
Covering the eastern half of the island of New Guinea, PNG is a global epicenter of avian biodiversity. Some of the world’s most ornate and behaviorally complex species are found in its megadiverse old growth rainforests. However, mounting pressure from agricultural expansion and commercial logging are putting stress on these crucial ecosystems, sparking concerns among conservationists about how species will cope.
Specialists out, generalists in
To find out how PNG’s bird communities respond to forest degradation, Korejs and his colleagues from the Czech Republic and PNG’s New Guinea Binatang Research Center analyzed bird survey data from a range of sites, including areas recovering from traditional shifting cultivation, forests fragmented by roads and settlements, and forests within the Wanang Conservation Area, a 10,000-hectare (nearly 25,000-acre) Indigenous-managed forest reserve.
They identified a total of 113 bird species, which they grouped into four feeding guilds: insect eaters, fruit eaters, nectar eaters and omnivores. The team also classified the species by morphology, evolutionary history and dispersal ability, to model how these traits varied with disturbance.
Their findings, published in the Journal of Applied Ecology, show that forest fragmentation and degradation reduces populations of sensitive forest-dependent birds such as insectivores and ground-foraging species. These include species like blue jewel-babblers (Ptilorrhoa caerulescens), golden monarch flycatchers (Carterornis chrysomela), and the Arafura shrikethrush (Colluricincla megarhyncha) that control insect populations; and species that eat fallen fruit, disperse seeds and turn over leaf litter, such as northern cassowaries (Casuarius unappendiculatus), which have important mutualisms with several rainforest tree species.
In contrast, the researchers found that generalist species, such as nectar- and fruit-eating sunbirds, pigeons and bulbuls, increased in response to habitat fragmentation. The authors note that this made it seem like the overall “functional diversity,” or range of ecological roles, within the bird community was unaffected by fragmentation.
The authors suggest generalists might fare better in disturbed forests due to their wider tolerance of the open habitats created by the forest degradation. “Forest edges, clearings, openings in the canopy [and] woodland-scrub are all attractive habitats for more generalist birds that prefer low-density vegetation,” Korejs said. Fruit- and nectar-eating birds might also do well in disturbed landscapes close to settlements where people grow fruit and flowering trees in home gardens, he added.
Korejs said the findings underscore why solely relying on biodiversity metrics like functional diversity of an overall community of organisms can be misleading. “Interpreting these diversity metrics alone can be a fool’s errand,” he said, noting the influx of generalist species “masked” the loss of crucial forest specialists that had disappeared from the community. It’s vital to combine biodiversity metrics with a deeper analysis of species traits, as they did in this study, Korejs added.
Nature out of balance
Crucially, the loss of forest species that fulfill critical ecological roles like pollination, seed dispersal and insect control, can trigger what the authors refer to as “cascading extinctions,” when the loss of one species leads to the loss of other species that depend on it. The disappearance of species that control leaf-eating insect populations, for instance, could lead to swarms of pests that overgraze vegetation or spread disease. And a lack of forest-floor seed dispersers could reduce the capacity of forest fragments to regenerate after storms.
This loss of overall ecosystem integrity underscores “the critical need to conserve forest-dependent birds” since the highly specialized functions of forest-dependent species lost to fragmentation cannot be replaced by incoming generalists, the study says.
Ding Li Yong, head of Asia flyways and species conservation at BirdLife International, who wasn’t involved in the study, said the findings are consistent with many previous studies in other tropical forest fragments around the world. Structural changes in degraded forests alter the availability of microhabitats and niches, he said, so these patches can lose forest specialists as a result of dispersal or localized extirpations, while gaining more generalist species that are better adapted to the new niches.
“In Southeast Asia, for example, when forests get fragmented, the forest patches get invaded by species characterised as open country [birds], like some species of lapwing, sunbird, bulbuls,” Yong said. Since these types of birds are different from the species usually associated with dense forests, their sudden presence triggers an increase in functional diversity even as critical ecosystem functions are being lost.
Yong said he’s also noticed the sensitivity to fragmentation among insectivorous birds documented in the PNG study at other sites. Tree and ground babblers, for instance, are often heavily impacted by forest disturbance.
The new study backs up the body of knowledge that indicates insectivores are an excellent “sentinel” group of species for monitoring the impacts of forest degradation, Yong said. But they might need a little PR boost before they’re fully used as such in conservation strategies, he noted. Insectivores “tend to be overlooked or marginalised in conservation, because most [of them] are small, and not necessarily charismatic.”
While there’s no silver bullet that will solve the woes of PNG’s forest specialist birds, as a general practice, conservationists should be looking to preserve large areas of intact primary forest, while ensuring smaller forest patches remain connected via habitat corridors so that animals can move freely, Yong said.
Korejs agreed that the best way to protect birds is to maintain connectivity between isolated forest patches and large continuous tracts. Birds are more likely to decline in habitats cut off from the surrounding landscape, he noted, compared to degraded habitats that remained connected to nearby intact forests.
Maintaining well-connected forested landscapes across PNG in this way would not only benefit birds, but also countless other unique species of animals and plants that depend on PNG’s forests for survival.
The most promising way of achieving this level of habitat protection is through community-led initiatives, Korejs noted. “Our research shows that the most widespread taxonomic diversity impacts on birds are associated with large-scale forest fragmentation that mostly occurs as a result of commercial deforestation, rather than small-scale agriculture,” he said. “It is only when logging companies are involved, that bird populations plummet.”
To support grassroots efforts, Korejs and his colleagues recommend conservation programs encourage people to preserve forests on their land through incentives, and help Indigenous communities defend themselves against predatory logging firms through legal and technical support.
Meanwhile, the study notes conservation efforts in PNG could benefit from better baseline information on the status of bird populations across the country’s relatively unexplored landscapes beyond its forests. According to Korejs, plugging these knowledge gaps is an exciting opportunity for researchers, local bird experts and citizen scientists. “The fact that there are few ornithologists currently working in PNG makes it a good area to make new discoveries with global significance.”
Banner image: A northern cassowary in New Guinea. Image by Rhett A. Butler/Mongabay.
Carolyn Cowan is a staff writer for Mongabay.
Citations:
Korejs, K., Koane, B., Jeppy, S., Sam, L., Jorge, L. R., Novotny, V., & Sam, K. (2025). Comparing impacts of fragmentation on bird functional and phylogenetic diversity in primary and secondary rainforests. Journal of Applied Ecology, 62(7), 1674–1684. doi:10.1111/1365-2664.70083
Korejs, K., Koane, B., Jeppy, S., Sam, L., & Sam, K. (2025). Bird species richness, assemblage density, and feeding guild composition in human-modified lowland rainforests of Papua New Guinea. Journal of Field Ornithology, 96(1). doi:10.5751/jfo-00602-960105
Related audio from Mongabay’s podcast: Exploring New Guinea’s extraordinary natural and cultural richness, listen here:
See related story:
In New Guinea, megadiverse lowland forests are most at risk of deforestation
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