All over the world, forests are being increasingly reduced by human activities to smaller remnants scattered among the agricultural lands that have often replaced them. This has a marked negative impact on the ecosystems previously supported by forests, including a variety of bird populations, with the majority of bird species now struggling to survive in an increasingly human-dominated environment.
According to a recent study led by the University of Utah, for birds which used to inhabit the vast forests of Central America, the massive replacement of forested land with coffee plantations has significantly diminished the amount of their preferred foods, forcing them to change their diets and habitats in order to survive.
To examine changes in their diets, the researchers conducted isotope analyses of the feathers of four bird species (the orange-billed nightingale thrush, the silver-throated tanager, the white-throated thrush, and the ochre-bellied flycatcher) living in the land around the Las Cruces Biological Station in Costa Rica, whose previously luxurious forests have been largely replaced in recent years by coffee plantations.
Along with the radio tracking of their movements, the isotope analyses have revealed that birds eat fewer invertebrates in coffee plantations than in forests, suggesting that disruptions in their ecosystem significantly impacts their dietary options.
“Growing human ecological impact on the planet, especially via habitat loss and degradation and climate change, often impacts bird diets negatively as well,” said study lead author Çağan H. Şekercioğlu, a professor of Ecology and Ornithology at Utah. “These negative changes, including declines in key dietary resources like insects and other invertebrates can lead to reduced survival, especially of rapidly growing young, often leading to population declines and losses of these undernourished birds.”
To consume enough invertebrates – which offer them the necessary nutrients to survive – birds living in and around coffee plantations need to forage frequently in the small forest fragments and narrow forest corridors alongside rivers. While more mobile birds, such as the silver-throated tanager or the white-throated thrush move constantly to get their preferred, protein-rich food, less mobile species like the orange-billed nightingale thrush are forced to adapt to the poorer diets they can find in coffee plantations.
However, even for mobile birds, the situation is worse than it used to be. “These birds’ shifting their feeding to other places may result in new ecological interactions that can themselves have negative consequences,” Şekercioğlu explained. “For example, increased competition with birds in these new places or overpredation on a prey species that was formerly not consumed as much.”
To help protecting these bird populations, local governments in tropical regions should prioritize the conservation of intact forests, secondary growth forests, and strips of forest alongside rivers to increase the connectivity of forest remnants, while coffee-drinkers all around the world can choose to buy bird-friendly coffee that is grown in plantations with more tree cover and forest remnants, which are beneficial for native birds.
The study is published in the journal Frontiers in Ecology and the Environment.
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