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Birds Feast on Bugs Living in Sloth Fur

1501 Birds Feast on Bugs Living in Sloth Fur

Zebras, rhinos, and capybaras often have their pesky ticks and other parasites pecked off by the hungry birdies perched on their backs. Now, for the first time, researchers have observed brown jays feasting on moths hiding in the fur of sloths. These unusual interactions are described in Frontiers in Ecology and the Environment this week. 

Back in May of last year, Kelsey Neam of Texas A&M University was studying the spatial ecology of three-toed sloths (Bradypus variegatus) in the cloud forests of Costa Rica. One afternoon in a tree plantation near the town of San Isidro de Peñas Blancas, Neam spotted a sloth feeding on leaves in a Cecropia tree while three brown jays (Psilorhinus morio) were perched on nearby branches. 


“As one brown jay audaciously inched closer, tilted its head, and drove its beak deep into the sloth's fur, I began to better understand the bird's behavior,” Neam writes. “While the sloth was busy feeding, the brown jay appeared to be searching for a meal of its own.” You can see the brown jay approaching the brown-throated three-toed sloth in this video and in the images below: 

Brown jays are opportunistic feeders who enjoy an assortment of prey ranging from fruit to spiders to lizards. But until now, a feeding association between brown jays and a mammal has never been documented—though their close magpie relatives have been known to nab insects off ungulates. 

The fur of three-toed sloths house lots of little inhabitants: algae, fungi, moths, and beetles, for example. Pyralid moths (genus Cryptoses) depend on sloths for phoresis—a type of commensalism, where one organisms benefits and the other appears to be neither helped nor harmed. In this case, the moths rely on the sloths for dispersal and reproduction: When the sloth comes down from the canopy to defecate (just once a week), gravid female moths leave to deposit eggs in the fresh dung on the forest floor. The poop provides sustenance for the newly hatched larvae, and when they mature, the moths fly up into the canopy to find mates and complete their life cycle in the fur of more sloths. 

It's not totally clear whether or not the sloths gain anything from their relationship with these sorts of arthropods. Although, some researchers have suggested that the moths help fuel the growth of algae, which may provide nutrients for the sloth, as well as camouflage against predators. If that’s the case, then the moth-eating brown jays might actually be some sort of parasite. 


On the other hand, it’s possible that these jays are also eating the ticks, biting flies, and mites feeding on the sloth’s blood. If so, then the jays are providing a beneficial service. Not to mention, having loud, raucous birds nearby could help alert the sloths to approaching predators. More field work will be needed to pinpoint their true ecological relationship. 

Images: (top), K.D. Neam, 2015 Frontiers in Ecology and the Environment (middle, bottom)


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