Birds in the Kalahari Desert have set up a mafia-style protection racket, according to a team of British and South African scientists, guarding other birds from predators in exchange for a hefty slice of the food they find.
Reported in the journal Evolution, the birds' behavior may represent a rare instance of two species evolving from a parasitic relationship to a symbiotic one, the researchers say. The racketeering birds, known as drongos, perch near pied babblers and make it clear they intend to steal their food, emitting periodic squawks every few seconds.
"Because drongos are parasitic birds who swoop in to steal food from other species, you'd expect them to keep a low profile while waiting," lead author Andrew Radford tells Science Daily. "Rather surprisingly, however, drongos perched above foraging babblers advertise their presence by issuing a call called a 'twank' every 4 or 5 seconds." And that "twank," Radford explains, has an interesting effect on the babblers. "When we played back these 'twank' calls to a babbler group, we found that they spread out over a larger area and lifted their heads less often, indicating that they were less fearful of predators when they thought a drongo was keeping watch. We think that drongos have evolved to alert babblers to their presence because helping the group forage more effectively leads to more frequent opportunities for theft."
And that's quite an adaptation, since drongos also have something else in common with gangsters — they lie, often making false alarms in an attempt to send babblers scrambling so they can steal their food.
But babblers aren't stupid, and have apparently learned to take drongo warnings with a grain of salt. "Like any good gangster, as well as lying and stealing, the drongos also provide protection by mobbing aerial predators and giving true alarm calls on some occasions," Radford says. "But, despite all of the useful services drongos provide, the foraging birds are still more responsive to calls from other babblers. It seems likely that the babblers simply don't trust the drongo mafia as much as their own flesh and blood."