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Forests are not only the lungs of the world, but also home to myriad living, breathing wonders alongside the vegetation.
Animals that live in the trees are called ‘arboreal’ and they have some amazing adaptations to make the most of their leafy surroundings at every level.
At the peak of the forest, trees reach their tallest and inhabitants must weather strong winds, heavy rain and sun exposure. Species need to be strong and agile to survive here, so birds of prey rule the roost. Found in rainforests from Mexico to Argentina, the harpy eagle is impressively huge and suitably named after the wind spirits of epic Greek mythology1. Rare throughout its range, it’s one of the largest eagle species in the world, one of most powerful predatory birds, and easily the rainforest’s biggest raptor. Females can weigh up to 9kg (20 pounds), but they have shorter wingspans than eagles of open habitats2, to allow greater manoeuvrability in the forest. As hunters, harpy eagles are described as sloth and primate specialists. They scan the canopy from a perch, looking and listening before swooping down to seize prey in their enormous talons – the hind claw of which can measure 7-10 cm (3-4 inches), the same size as the claw of a Grizzly Bear!3
The next highest layer in the forest is the canopy, where the crowns of many trees converge and provide shelter from the harshest of the weather. This is something of a Goldilocks Zone for arboreal animals, where thanks to protection from ground and sky predators a wide variety of species can be found. You might have seen the wonderfully constructed nests of orangutans4, or be aware of sloths’ cunning camouflage to protect themselves from eagle attacks5. But you may be less familiar with the talents of the kinkajou, a mammal found in the rainforests of Central America. More closely related to raccoons than any other canopy dwellers, kinkajous are nocturnal and feast on ripe fruit. Nimble fingers, flexible spines and ankle joints that turn 180 degrees allow them to easily navigate through the trees and feed at the end of branches. It’s not unusual to see them feeding upside down, suspended from a branch by their prehensile tail6.
Shaded by the canopy, it is darker and more humid in the understorey, providing an ideal niche for many amphibians that thrive where the air is moist. Central America’s red-eyed tree frogs are among the most striking inhabitants of this forest layer, with orange toes, stripey flanks and a rainbow of bright leg colours that vary across their range from electric blue, through orange, to purple-red blends7. When hunkered down their green backs perfectly blend in with the leaves, but when disturbed a flash of colour can dazzle predators or impress females seeking a mate. These frogs lay their eggs on vegetation overhanging forest pools and puddles; once they hatch, the tadpoles drop to the water to develop. Mature frogs will climb through the trees until they find a comfortable layer, sometimes ascending as far as the canopy in search of flying insects to eat. Researchers suggest tree frogs are protected from short-term climatic change as they can move around within the rainforest to find a sweet spot. But continued warming and consequent drying will drive them closer to the ground, with potentially fatal consequences.
You might not associate tree-dwelling with the forest floor. But that view overlooks countless species of insects that make the most of the decay down in the lowest reaches of the forest. If a tree falls in the forest, you can bet something is there to eat it – and maybe move in. Termites are one of the best clean-up crews in the rainforest. They can live underground, above ground in their iconic mounds, within dead wood, or in basketball-sized arboreal nests. These decomposers specialise in wood clearance, and as such have earned a bad reputation for destroying furniture and houses. Yet scientists have discovered that termites play an essential role in protecting rainforest trees. Studying a site in Borneo during a severe drought in 2015/16, researchers found that termites increased their activity, consequently boosting soil moisture and nutrients and allowing for greater survival of seedlings8.
Whichever layer of the forest you look at, there are creatures living fascinating lives among the leaves. Predatory talons, prehensile tails and stunning colour schemes are just some of the solutions species have evolved to aid their arboreal lifestyles and contend with the impact of adversities such as climate change.
Trees are amazing organisms and it's not only animals that network with the habitats they create, but also the trees themselves.