Nature has an undeniable power over the arts, for after all, in a way, everything goes back to nature. All the way from cave paintings up to the most representative art movements of the twentieth and twenty-first centuries, Nature has been a constant trope. Literature is not exempt from Nature’s grasp since when it’s not acting as a setting, Nature is the source of rich metaphors and symbolism. William Shakespeare, the sixteenth Century poet and play writer, is normally considered the highest exponent of English language literature, although some people even argue his authorship or even his mere existence. In his work, Nature is also frequently called into action as a setting (A Midsummer’s Night Dream) or even as a story driving force (The Tempest). His mentions of nature as metaphors are even greater, as he constantly mentions among other things, birds. In his wilder dreams, the bard might have imagined how renowned and respected his work will turn out to be, but I’m sure he never thought, less of it, intended, to be indirect to blame for profound environmental disasters.
The whole point about Invaded Planet is to let a general audience learn more about invasive species. On this space, I will try to dig a little bit into the theoretical aspects of Invasive Ecology as a whole, but more constantly, I will be doing this through real life examples (and believe me, there are many), all through the backup of scientific paper research. I should first highlight that I’m in no way an expert on the topic, nor have I read all the existing bibliography on a given topic before attempting to do this. Therefore, constructive comments and corrections are more than welcomed.
Shakespeare’s unwanted role in the invasion
Getting back to Shakespeare, or better said, his enthusiasts, we should return to the end of the 19th Century, and to a group called The American Acclimatization Society, based in New York, whose explicit goal was to “introduce foreign varieties of the animal and vegetable kingdom as may be useful or interesting”. In other words, these guys were unwarily dedicated to wreaking havoc on the continent’s ecosystems. That being said, New York is not the most welcoming of habitats, having winters that can indeed be really cold, which helped limit the number of successful attempts at foreign species introduction. However, the American Acclimatization Society is to blame for one of the most infamous cases of foreign species introduction, that brought by a drug maker called Eugene Schieffelin, then acting as the Society’s President, who gave himself the task of introducing all the birds mentioned in Shakespeare’s work. These included chaffinches, sparrows, skylarks, and nightingales, but the most “successful” introduction was that of a bird mentioned barely once on the bard’s bodywork, the European starling, which makes an appearance on Henry IV Part 1: “I’ll have a starling shall be taught to speak nothing but “Mortimer,” and give it him, to keep his anger still in motion.” The line was spoken by the character Hotspur, after being upset about King Henry’s refusal to pay ransom for Mortimer, his brother-in-law.
The European starling conquers America
The European starling (Sturnus vulgaris) is a 20 cm long bird, with a dark plumage, which is often complemented by white specks. His feathers give iridescent green and purple colors under certain light conditions. They are well known for forming massive flocks, also known as murmurations of up to 1.5 million individuals, which fly in unison with no apparent leader. This is considered to be a technique that helps them avoid bird predators. They are also known for mimicking the calls of other birds, which is the origin of the before mentioned Shakespearean quote.
Schieffelin took to releasing around 100 starlings on Central Park during the years of 1890-1891. The birds were able to withstand rigorous winters, were quick to settle, and once their numbers increased, they set themselves to conquer new territories. By 1930 they were already in the Midwest, and by 1942 had been reported around California. Today, their distribution extends South all the way to Mexico, and its number for the North American invaded region is estimated to be around 200 million individuals. And that’s without taking into account that European starling (through human help) has also invaded other regions, like South Africa, South America, and Australia.
A constant we’ll commonly find on successful invasive species is their effective reproductive rate. A high number of offspring capacity, which combined with the lack of predators and disease, allow these populations to thrive even more than they normally would on their native ranges. Starlings are no different since they are able to produce 2 chick broods per year, with each containing an average clutch of five eggs. They will not only compete with native species for nest cavities, but will also affect other birds food, and even humans, since they’re known to attack croplands, as well as eating food pellets from livestock, which might, in turn, contribute to the spread of disease among them. They’re strong and resistant; they’re noisy and dirty, with their feces being able to intoxicate full fields of crops or trees.
Over the 20th Century, starling dispersal was taken as a chance to try to sort out how the now-native birds might have colonized the continent millions of years ago. Their distribution patterns certainly made sense, since these were influenced by geographical features, with mountains acting as barriers, and rivers acting as highways. More recent studies have also taken the European starling invasion as a chance to further develop the theory that invasive species become less susceptible to parasites and diseases once they invade a new range. A research evaluation allowed verifying that indeed, starling parasites had more similarities to those European starlings on their native English range, than to those natives on the Russian side. However, the study actually found a wider variety of parasites on their invaded range, since the birds now didn’t have only to deal with whatever they carried to America, but also with American parasites, ready to jump to a new host, and possibly, parasites carried by other invasive birds, whether starlings or different species.
Scientists are smart and always try to take the best advantage even from the direst situations. However, it’s also part of the scientist’s responsibility to assess the possible impact caused by invasive species and if it is indeed a problem, try to offer the best possible solutions. You can imagine that the introduction of millions of new birds will surely have an impact on native species populations. As we said before, European starlings brought further pressure for birds sharing ecological similarities, like nesting sites and food.
Since starlings are tree cavities nesters, it can be assumed that they’ll get into some conflict with woodpeckers. A study carried out during the 90s, compared the effect of invasive starlings on three different native woodpecker species, the red-headed woodpecker (Melanerpes carolinus), the red-bellied woodpecker (Melanerpes erythrocephalus) and the northern flicker (Colaptes auratus). These native birds share an environment, but their reproduction and breeding stages are carried out during different parts of the year, from April to May, with some minor overlapping. However, the European starling starts breeding at pretty much the same time as the red-bellied woodpecker, who is not every aggressive (compared with other more hot-tempered woodpeckers), was calculated to have lost 39% of its freshly excavated nests to European starlings (the other two species were just ousted of 15% of their cavities). The starling has brought even more competition to a bird that already had to deal with flying squirrels, house sparrows and other woodpeckers to a total usurpation of up to 50% of their nests on said study. Most red-bellied woodpeckers were found to have bred successfully during the season, though their clutches were limited to one, since their breeding time was chronologically delayed in what’s called a “niche displacement”.
How to control such a pest?
It shouldn’t come as a surprise that controlling starling populations has been a long concern for farmers in the US. Not only can they devastate an entire crop yield, but they can also take advantage of their livestock’s food, even being capable of selecting for nutritionally enhanced pellets and transmitting diseases among livestock populations. Crops like grapes and cherries can be covered with netting, but more severe measures have also been taken. In the US, where 45% of the world European starling population is believed to reside, the species is unprotected, and techniques ranging from bird-proof livestock feed, propane explosions (and other frighteners which include light and water sprinkling), to lethal measures like Avitriol or the specially developed starlicide.
Today, the bird is considered by the IUCN to be of “less concern”, since although native populations are declining, the bird has proven to be one of the most successful world invaders and a reminder of how much a “good-willed” out-of-ignorance action can bring changes that deeply affect the ecology and evolution of ecosystems. And as I will try to illustrate on this blog, these kinds of actions are not limited to Shakespearean or Nineteenth Century times, they keep occurring as we speak.
References
Brinkman G. Let’s Blame it on Shakespeare! Rough and tough birds. 1986. AFA Watchbird
Colautti RI, Muirhead JR, Biswas RN, MacIsaac HJ. 2005. Realized vs apparent reduction in enemies of the European starlings. Biological Invasions 7: 723-732
Ingold DJ. 1994. Influence of nest-site competition between European starlings and woodpeckers. Wilson Bull. 106(2): 227-241
Johnson JR, Glahn JF. 1998. Starling Management in Agriculture. Nebraska Cooperative Extension NCR 451
Kessel B. 1953. Distribution and migration of the European starling in North America. The Condor 55(2): 49-67
Mirsky S. 2008. Call of the Reviled. Scientific American
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