Fearless swans tend to live in urban areas, while their wary counterparts play it safe in rural environments. It turns out these large birds are actually predisposed with a preference for either urban or non-urban habitats, according to a team of researchers from the scientific publisher BioMed Central. This could have important implications for releasing animals bred in captivity into the wild.

In a recent study, a team of researchers from Victoria University, Deakin University and The University of Melbourne, Australia, examined the wariness of two separate populations of black swans (Cygnus atratus), according to a news release

"Growing global urbanization means that wild animals are increasingly settling near to humans. Although we often assume that animals become less wary of humans by simply getting used to them, our results suggest that at least part of this response might be genetically determined," Wouter van Dongen, lead researcher of the study, explained in the release. 

The two populations of swans consisted of one group of 80 that were living in an urban parkland setting, where they frequently encountered humans, and a second group of 20 swans that live roughly 30 km away in a non-urban area, much less frequented by people. In order to assess the animals' level of wariness, researchers walked slowly towards them and measured their Flight Initiation Distance (FID): how close they could get before the birds flew away. DNA samples were also taken from the two populations so that researchers could look for variations in two sets of genes -- RD4 and SERT -- typically associated with behaviors related to anxiety and harm avoidance in animals. 

So what did they find? As expected, urban swans have a longer FID; the city-slicker swans possess an average FID of 13 meters, versus their rural counterparts with an average FID of 96 meters. Additionally, the genetic analysis revealed five different variants of DRD4, which are associated with different levels of wariness. 

While 88.8 percent of urban swans shared the most common genotype for DRD4, only 60 percent of the rural swans exhibited this genotype. When comparing FID averages to genotypes, researchers found that 83 percent of all swans with the most common variation of DRD4 had a shorter average FID. This suggests a bird's wariness is at least partly determined by their genes, researchers say. It follows then that these highly mobile birds arrange their migrations accordingly. 

"This has important implications for conservation, 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 location commensurate with their expected wariness," Dongen added

Their findings were recently published in the journal BMC Evolutionary Biology

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