Gangster birds running protection racket shed light on co-evolution

Friday, November 19, 2010

LONDON - A new research on Kalahari Desert drongos, which act like gangsters running a protection racket for other birds in order to steal a cut of their food catch, has provided important insights into co-evolution.

The study conducted by a team from the Universities of Bristol, Cambridge and Cape Town, may represent a rare example of two species evolving from a parasitic to a mutualistic relationship.

“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. Rather surprisingly, however, drongos perched above foraging babblers advertise their presence by issuing a call called a ‘twank’ every 4 or 5 seconds,” Nature quoted Dr Andrew Radford as saying.

“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,” he added.

Drongos cry wolf about the presence of predators to scare other animals into dropping their catch, which the birds then pounce on.

This research indicates that pied babblers have evolved to tolerate the drongos giving false warnings and stealing some of their hard-earned gains in exchange for the chance to forage in relative safety when a drongo is keeping watch.

Radford added, “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.”

The insight the research provides into complex co-evolution between species gives scientists a valuable way of understanding other important relationships, such as those between drugs and bacteria and between pathogens and hosts.

The research is published in Evolution and reported in Nature’s Research Highlights. (ANI)

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