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Swan in an urban lake


The mute swan (Cygnus olor) pictured above is a common sight at Lake Eola in downtown Orlando, FL. Mute swans are a Eurasian bird that were imported from Europe to the United States for decoration on parks and private properties. The bird gets its common name, mute swan, from the fact that its vocalization is quieter than other swans. The swan feeds mostly on aquatic vegetation that might be found at the bottom or edges of a lake like the one above, but also readily takes to feeding by humans, so the swan seems to thrive in urban lakes like this.

Upon first look, an observer might wonder about the swan's form: webbed feet, long neck. The bird's form relates to its lifestyle. The swan is equipped to swim with webbed feet, allowing access to those submerged aquatic plants. When the bird feeds on submerged vegetation, it sticks its tail-end and feet into the air then extends its long neck to feed in shallow water; this is called "dabbling." The swan will also feed at the surface of the water.

Even within the same species, we notice that wildlife in urban areas behave differently than in non-urban (rural areas). A study by Alicja Jozkowicz and Lucyna Gorska-Klek, "Activity patterns of the mute swans Cygnus olor wintering in rural and urban areas: A comparison" finds that urban swans spend their time doing different behaviors than rural swans. Mute swans in a rural area were spending almost 50% of their time feeding, but mute swans in urban areas were spending less than 15% of their time feeding and begging for food from humans. Rural birds were swimming and loafing (activities where the bird is generally not moving, like standing still) less than urban birds. The researchers note that the urban swans would swim for meters to acquire bread tossed by a person at a distance, often inciting the rest of the birds to flock to this location if they observed the human-induced feeding. Rural birds fed in the morning and evening but urban birds did not show this pattern. Additionally, the rural birds were less aggressive than city birds.

What does this mean? According to the authors of this study, the urban birds are likely adapting to the feeding by humans. This is an example of how humans directly and indirectly impact the wildlife in urban areas.

In this species of swan, we see populations changing (or adapting) their behavior to their environment. The urban birds have a different strategy for feeding than the rural birds, but it appears successful for them. If these differences in strategy and behavior have a genetic basis (inherited from generation to generation), and there is a change in the genetic basis over time, there is evolution at work. Evolution is defined by a change in allele frequencies (inherited traits) in a population over time. Although it's not clear whether these swan populations are evolving, humans have and continue to mediate the evolution of other organisms (antibiotic-resistant bacteria, for example).


References
Gorska-Klek, L., and A. Jozkowicz. "Activity patterns of the mute swans Cygnus olor wintering in rural and urban areas: a comparison." Acta ornitologica 31.1 (1996): 45-51.
http://www.glin.net/lists/beachnet/2006-08/msg00002.html
http://www.allaboutbirds.org/guide/Mute_Swan/lifehistory
https://web.stanford.edu/group/stanfordbirds/text/essays/Dabblers_vs._Divers.html
http://www.orlandomagazine.com/Orlando-Magazine/July-2013/Life-on-Swan-Lake/
http://www.audubon.org/field-guide/bird/mute-swan
http://www.dec.ny.gov/animals/7076.html
http://myfwc.com/wildlifehabitats/nonnatives/birds/mute-swan/

Written by: Tiffani Manteuffel

Tiffani is a biologist with a particular interest in ecosystem ecology and plant interactions with microorganisms and their environment. She coordinated a summer camp for high school students while working on her Master’s degree. When not investigating the living world around us, she paints nature-inspired oil and watercolors, dabbles in photography, gardens and plays the trombone (which sits out in the open to remind her to practice) that she’s had since middle school. Learn more about Tiffani’s research interests at her website: tiffanimay.weebly.com.