Fork-tailed Drongos: Marvelous Mimics

Fork-tailed Drongos: Marvelous Mimics

February 26, 2015 by  
Filed under Features

A recent study by evolutionary biologist Tom Flower of the University of Cape Town in South Africa has revealed that the African fork-tailed drongo mimics alarm calls of other species as part of its food gathering strategy. Wildlife observers in Africa have noted that the drongo is an accomplished thief, but it was thought that it was using its own alarm call to falsely alert other birds and meerkats that a predator was nearby, thereby causing them to drop their meal, which the drongo would swoop in and claim. It is estimated that the drongo steals more than twenty percent of its daily food. But the lengthy study carried out by Flower in the Kuruman River Reserve, located in the Kalahari Desert, yielded some astounding insight into the drongo’s ability to perfectly mimic a variety of bird and mammal species for its own advantage.

In the wild, birds and mammals often pay attention to other species in their environment when it comes to sounding the alarm. An extra pair of eyes and ears can be handy when it comes to safety. But as researchers have discovered, the drongo can’t be trusted. Perched high up in a tree a drongo watches with keen interest as meerkats forage, and when one of them catches something, an insect or lizard, the drongo sounds its own alarm call, anticipating that the meerkat will drop its prey and head for cover. However, the foraging meerkats are likely to ignore the drongo after it has used its own alarm call a few times. Undaunted, the drongo will switch to the alarm call of another bird species, often with successful results.

During the study, Flower and his colleagues tracked and recorded the calls of 42 drongos as they attempted to steal food from the same target. It was noted that of the 151 recorded incidents, the drongos switched to a different alarm call a total of 74 times. After giving its own alarm call without success, a drongo may give the alarm call of its target, which general proved successful.

Flower notes that he doubts the birds have ‘theory of mind’ – the ability to understand that another being has different beliefs and intentions – which is currently only attributable to humans. It’s more likely that they are responding to feedback, or have an ability to grasp cause and effect, and use this to their advantage. Nonetheless, this is another example of the keen intelligence of the feathered creatures that share our planet.

Snake Skin as Protection Against Predators

February 17, 2015 by  
Filed under Features

Birds use all sorts of materials to build and pad their nests with, and are very good in general at adapting whatever is at hand to suit their needs. Some birds even use the shed skins of snakes in their nest building, raising the question as to whether the snake skin is merely a handy and comfortable material to line a nest with, or whether it is actually intended to scare predators off. A study carried out by Arkansas State University ornithologists concluded that some bird species clearly use the snake skin to deter predators by incorporating it into their nests in some way, or by prominently displaying a snake skin near the nest, or both.

The Tufted Titmouse (Baeolophus bicolor) and Blue Grosbeak (Passerina caerulea) are among the bird species that include pieces of snake skin in their nests, while Great Crested Flycatchers (Myiarchus crinitus) are known to display a snake skin outside their nesting cavity, as well as using an entire coiled snake skin in the nest. These will remain there throughout the incubation and fledgling stage of breeding. The study noted that the main predators of the eggs of Great Crested Flycatchers are rat snakes and flying squirrels – the latter being fond of bird’s eggs and the former preying on both birds and their eggs, as well as on flying squirrels. It was also noted that flying squirrels and Great Crested Flycatchers have a very similar geographical spread, and as all three species favor cavities as habitats, it is likely they will encounter one another. As the flying squirrel does its best to avoid the rat snake, it has been suggested that the shed skin of the snake acts as a deterrent to the squirrel.

A test carried out by the researchers confirmed that to be so. Using 60 nest boxes in which quail eggs were placed, researchers added snake skins into 40 of the boxes, with 20 boxes having no snake skin in them. All of the 40 boxes with snake skins were left untouched, while up to 20 percent of the nests without snake skins were raided by flying squirrels – evidence that some birds use snake skins specifically to ward off predators, and it appears to work.

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