How much a swan fears humans is partially genetically determined, new research has revealed. Moreover, birds whose genetics makes them less nervous in the face of our approach are more likely to make their homes in urban parks, demonstrating that nature and nurture interact to change responses to humans.
Like most wild birds, Australia's black swans (Cygnus atratus) take flight when humans get too close. Birds living in urban areas will let people get a lot closer before they decide to clear out – a necessity if they are not to be constantly on the wing. Dr. Wouter van Dongen of Victoria University, Melbourne, told IFLScience that this difference has usually been attributed to conditioning, with the city-dwelling swans slowly getting used to having people around.
However, van Dongen thought it worth investigating to see if there was any genetic component to the flight initiation distance (FID), or how close humans can get before a bird takes off. He measured the FID for swans at Albert Park Lake, which lies close to Melbourne's center and compared this with swans living near the outskirts of Melbourne.
The differences reported in BioMed Central were stark; the average FID of an urban swan was within 13 meters (43 feet), yet on the periphery it was 96 meters (315 feet). More interesting was the differences within the groups. The DRD4 gene has been associated with boldness behavior in other species and van Dongen found that birds with the most common version were willing to allow humans significantly closer in either environment than their fellows with rare versions.
It's not quite a black swan event, where something completely unprecedented occurs, but when van Dongen compared the two sets of swans' genomes he found an unexpected difference. Sixty percent of those living outside Melbourne carried the most common version of the DRD4, while among the Albert Park swans the figure rose to 89 percent.
In theory natural selection could be causing the more flighty versions of the gene to die out at the lake. As van Dongen said to IFLScience, living at the lake provides the swans with “access to food [even if much of it is bad for them], possible protection from predators, probably more breeding success.” However, van Dongen thinks that, given the large areas over which the swans travel, it is more likely the birds are sorting themselves, with those genetically predisposed to bravery more likely to settle at the lake.
Besides telling us something about the role of genetics in personality van Dongen said in a statement he hopes the finding will have practical applications, “Particularly for the introduction of animals bred in captivity, which could in future be screened for genotypes that are associated with wariness, allowing them to be released to a [suitable] location.”