Don’t Get Too Excited, but Syrian Woodpeckers Like Pollution
(Originally published January 25th, 2014 on http://scienceofbirds.blogspot.com)
The myriad ways that we affect our environment are pretty dumbfounding, aren’t they? Just by releasing chemicals like CO2 and Methane into the atmosphere, we increase the acidity of the ocean, create a runaway greenhouse effect that elevates global temperatures, and deteriorate polar and alpine ecosystems that depend on the existence of ice. We know all this. And there are people that are doing something about it. That’s all good. We’ll talk about that some other time.
Another effect merely of our pollution of the atmosphere, however, that is of interest to me, is how air pollution affects trees. And all plants, for that matter. When plants, especially trees, are exposed to air pollution, and worse yet forced to grow and develop in it, things go amiss. Trees grown in air polluted areas often grow into weaker forms, with lower quality wood and disrupted processes within the tree. It would be like us trying to grow up with a constant supply of toxic gases at levels that are slightly too high to be healthy in our bloodstream. We would grow up weak and malnourished, regardless of how much food we get.
Now apply this back to trees. In cities, many trees receive plenty of good soil, fertilizers, access to sunlight, and watering from caring gardeners. But with the addition of air pollution, however, something will always be slightly off for the tree. And often, this “slightly-off-ness” manifests itself in a reduction of natural defenses from parasites and insects living within the tree, to the tree’s detriment. In its slightly weaker form, polluted trees are worse off at defending themselves from, for our purposes, insects.
If you were wondering when birds come in (because they have to here, right?), we’re there. Woodpeckers, specifically Syrian Woodpeckers (Dendrocopos syriacus), were studied around Krakow, Poland, to see how their numbers relate to thirteen urbanized habitats and the amount of pollution in those areas. Because of the air pollution in the study area, trees had reduced defenses and thus harbored more insect life. And all pollution aside, that means food for the Woodpeckers. The study found that:
The number of trees, coverage of woody vegetation, total vegetation cover and level of pollutant emissions were significantly higher in Syrian Woodpecker breeding territories than in the random points.
So, counterintuitively, it was found that habitats often thought of as negatively correlated to bird numbers hold a hidden twist…a bit of an incongruity. The pollution of urbanized habitats indirectly holds benefits for insectivorous wood-clinging birds; weaker trees equal higher susceptibility to insect infestation, and that equals a buffet for woodpeckers.
But this is not a case where we should leap up in victorious arms and yell, “Yes! City’s aren’t that bad for wildlife!” The effects of atmospheric pollutants still take place on the birds, and more significantly, affect their breeding cycles. We can’t negate all the research throughout the years that have exposed the negative effects of urban environments on their avian inhabitants.
In this case, we have what is called an Ecological Trap. Animals, when selecting habitats to live in take in a variety of environmental cues. Quantity of food, cover/shelter, and density of other animals of that same species are some of these cues. In an ecological trap, one or more of these cues appear to be higher in quality to the selector, while others are coincidentally far worse. A good analogy would be selecting a home in a dirty, overcrowded, crime-ridden neighborhood just because it’s near a world-renowned yet inexpensive restaurant. Woodpecker foodies are selecting dirty and overcrowded urban environments because they’re full of easy-to-access food in decrepit trees. They have been ecologically “trapped”.
While we have, in our various human doings, provided a reliable and predictable food source for woodpeckers, we have also created in them a habit of sacrificing the quality of their home for this food source. Now exposed directly to the pollutants of the city, Syrian Woodpeckers and their young are subject to the many detrimental effects thereof.
So what may seem at first to be a hidden positive of existing in the city actually reveals itself to be our confusing of the natural tendencies of the Syrian Woodpecker.
Fascinating, if not a little bit worrying.
Ciach, Michał, and Arkadiusz Fröhlich. “Habitat Preferences of the Syrian Woodpecker Dendrocopos syriacus in Urban Environments: An Ambiguous Effect of Pollution.”Taylor and Francis. Bird Study, 24 Oct. 2013. Web. 25 Jan. 2014. <http://www.tandfonline.com/doi/abs/10.1080/00063657.2013.847899#.Um4yvxZy_8s>.
