For many species, the slow process of evolution makes it very difficult to adapt to a dynamic society. However, some birds have evolved certain characteristics to assist in ensuring the survival of the species in the face of an ever-changing world. Others have learned behaviors that can assist in their survival.
With the advance of climate change, seasonal weather and climatic patterns have been altered. These changes have resulted in adaptations in response to changing conditions. For example, the European Great Tit (Parus major) has begun to breed earlier so that their offspring hatch when caterpillars are at their peak abundance (University of Berkeley 2008). Great Tits have also evolved higher-pitched songs in order to be heard over the cacophony of an urban environment.
The Great Tit has been observed evolving in response to global warming and other human behavior. Photo by Stian Waaler, a member of Project Noah.
In Australia, a similar behavior has been observed in Silvereye (Zosterops lateralis) populations, with urban birds “singing 195 hertz higher and calling 90 hertz higher,” according to Wendy Zukerman of New Scientist (2011). “It’s a bit of a shock. The city is pushing these birds to evolve, ” says Dominique Potvin, a researcher at University of Melbourne.
The Silvereye is yet another species of bird which has been observed evolving in response to humans. Photo by Christiane Geissler, a member of Project Noah.
A study of Dark-eyed Juncos in both wildland and urban settings show the urban juncos tend to be less timid around humans, which is likely an adaptive or evolutionary response to the cramped conditions of a city (Atwell et. al 2014).
Both males and females showed significantly bolder exploratory behavior in the urban study site in San Diego compared to birds in a nearby wildland montane habitat (Atwell et. al 2014).
A species’ inability to adapt could result in a detrimental population decline. However, another European bird, the Blackcap (Sylvia atricapilla) has evolved a new overwintering sub-population in the United Kingdom, thought to be a result of warmer temperatures resulting from climate change. The overwintering Blackcaps in the United Kingdom have an advantage in interspecific competition as they reach breeding grounds prior to the southern migrants (University of Berkeley 2008). The early bird not only gets the worm, but a crucial evolutionary edge!
The Blackcap is a European warbler responding to the warming Earth by overwintering in warmer areas closer to breeding grounds. Photo by Malcolm Wilton Jones, a member of Project Noah.
With an estimated 80 million birds killed by cars every year, John Dankosky of NPR explains that such a “death toll is high enough…that it’s turning out to be a powerful force of natural selection.” Charles Brown is a behavioral ecologist at the University of Tulsa in Oklahoma. While studying the social lives of Cliff Swallows (Petrochelidon pyrrhonota), Brown began to find Cliff Swallows who had been killed by collisions with vehicles. Brown compared the wingspans of the birds killed by traffic with birds who had inadvertently died in mist nets. Surprisingly, the birds killed by cars had wings noticeably longer than those who had died in mist nets.
“During a 30-year study on social behavior and coloniality of cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, we found that the frequency of road-killed swallows declined sharply over the 30 years following the birds’ occupancy of roadside nesting sites and that birds killed on roads had longer wings than the population at large.” (Brown and Bomberger 2013).
In an interview with National Public Radio, Charles Brown stated “it’s quite likely that road mortality is one of the factors [in Cliff Swallow wingspan decline],” but other possible contributors include changes in diet and weather.
The Cliff Swallow has recently been thought to evolve shorter wings in order to dodge traffic. Photo by Jacob Gorneau.
A study conducted in France found that birds anticipate the speed of vehicles based on the average speed of cars on that road. If the speed limit was higher (meaning, the cars, on average, drove faster), birds would fly away from cars sooner, even if the car was driving slower. The study assessed flight initiation distance, which is the distance between a moving object and a bird before the bird to take flight. Birds that lived near faster roads had a greater flight initiation distance than those on slower roads. This suggests birds can sense an average speed on roads and calculate a safe time to leave the road. Birds left at relatively the same time, regardless of speed. Although this is likely a learned behavior rather than instinctive, it is amazing to see adaptations to humans on such an individual level.
“Human development can affect animal population persistence. Species differentially respond to these changes; some avoid anthropogenic habitats while others benefit from exploiting them….some species are known to change their behaviour in adaptive ways in response to human-induced habitat changes.” (Legagneux and Ducatez 2013).
A little over a century after the invention of the first car, birds have begun to adapt to not only motorized vehicles, but the bustle of cities, and the advance of climate change. But although birds have evidently proved themselves adapt to an ever-changing world, we must avoid testing their evolutionary capabilities to avoid Rachel Carson’s A Silent Spring at all costs.
References
- Brown, Charles R., and Brown, Mary Bomberger. “Where has all the road kill gone?” Current Biology: Volume 23, Number 6. Pages R233 and R234.
- Dankosky, John (host). “Birds evolve shorter wings to escape traffic crush.” NPR. 22 March 2013. Retrieved 6 Jan 2014.
- Slabbekoorn, Hans and Peet, Margriet. “Ecology: Birds sing at a higher pitch in urban noise.” Nature. 17 July 2003. Retrieved 11 Jan 2014.
- Berkeley: Understanding Evolution. “Warming to evolution.” July 2006; updated July 2008. Retrieved 1 Jan 2014.
- Zukerman, Wendy. “Hipster bird species evolving to tune out urban sounds.” New Scientist. 7 January 2011. Retrieved 17 Jan 2014.
- Legagneux, Pierre and Ducatez, Simon. “European birds adjust their flight initiation distance to road speed limits.” Biology Letters. 21 August 2013. Retrieved 3 March 2014.
- Atwell, Johnathan W., Cardoso, Gonçalo C., Whittaker, Danielle J., Campbell-Nelson, Samuel, Robinson, Kyle W., and Ketterson, Ellen D. “Boldness behavior and stress physiology in a novel urban environment suggest rapid correlated evolutionary adaptation.” Behavioral Ecology. 4 May 2012. Retrieved 21 March 2014.