For evolutionary biologists, it is an interesting object of study. For those who grew up in Poland, it is a beloved character of 1980s cartoons and storybooks. The sparrow is a bird which has accompanied humans for some ten thousand years.
Small, gray, inconspicuous: the sparrow. In comparison to other birds, those more colorful and magnificent, it might appear rather unattractive. However, what sets it apart from many other species is an unusual feature—its extraordinary ability to adapt to life in new environments. It thrives in rural areas, as well as in large cities, where it picks at leftovers, like those left behind on coffeeshop patios. It even does well north of the Arctic Circle, on the Scandinavian Peninsula, in the deserts of California, or in the tropics of Panama. There’s just one condition that has to be met—humans must live next door. It has been observed that when settlers moved out of an area, shortly after, so did the sparrows. This unusual attachment to humans is also reflected in the bird’s Latin and English name—house sparrow. In 1758, the father of the classification system of organisms, Carl Linnaeus, gave the sparrow the species identifier domesticus, derived from the Latin word domus, meaning “house.”
Although it may be hard to believe, until recently we knew very little about the origin of sparrows and the influence humans had on their evolution. The classic 1958 work of Polish ornithology, Ptaki ziem polskich. Tom 1 (Birds of the Polish Lands: Volume 1) by Jan Sokolowski, reads, “In prehistoric times, when Central Europe was covered with forests, the sparrow most certainly was not present in our area. It came from the south, most likely from southern Asia. Its southern origin is given away by many details. For example, the first frosts distress the animal, so it ruffles its feathers and looks rather saddened, whereas other birds still hold up smoothly and seem cheerful.” It has taken more than half a century since the publication of this book for us to finally figure out how the sparrows likely reached Europe.
From the Middle East
To better understand the origin of this species in Europe and its strong relationship with humans, one must go back some eleven thousand years and travel to the Middle East, to the Fertile Crescent region. This is where the Neolithic Revolution began. People started to change their lifestyles from hunter-gatherer to more sedentary roles. They took to growing crops (mainly wheat) and raising animals.
Interestingly, an ancestor of today’s house sparrow, that is, of the Passer domesticus domesticus subspecies, was present in the area at the time. That former subspecies of sparrow, which for the purposes of this article we can call “primitive,” resembled the contemporary subspecies Passer domesticus bactrianus in appearance and behavior. Although, at first glance, they are quite similar to the house sparrow, on closer inspection one can observe significant differences. This is because the contemporary house sparrow has a thicker skull and altered facial structure. The beak is larger, more powerful, and extra pointed, and the muscles responsible for its movement are better developed. Scientists studying adaptive traits pay special attention to beaks—the tools with which birds collect and adjust food to make it suitable for consumption—as their size and shape are related to natural selection. A textbook example of such adaptation—displaying the effect of the availability of a particular type of food on the shape of beaks—are Darwin’s finches. Long-term field studies of this group of birds, inhabiting the Galapagos Islands, have provided strong evidence that beak morphology evolves rapidly in response to changing environmental conditions, including the type and availability of food, as well as interspecies competition.
It is very likely that until the Neolithic Revolution, primitive sparrows fed on the seeds of grasses and other commonplace vegetation, just as P. d. bactrianus does today. They nested in bushes, trees, near rivers, over time also near budding grasslands and pastures. In the fall, they would migrate in large flocks, traveling south: from breeding grounds in Central Asia, to wintering grounds in what is now southeastern Iran and western parts of the Indian subcontinent.
With the availability of a new type of food, one that was more common, but also more difficult to consume due to its greater hardness, came the need to develop a more efficient tool—a tougher beak and a stronger skull. However, scientists suspect that before this change took place, primitive sparrows abandoned migration—a larger beak meant more body weight, which in turn generated higher energy costs of travel. Yet another evolutionary trade-off.
And what were the best places to settle? Naturally, those close to a fixed food source, namely . . . in the vicinity of humans, near their fields and granaries. Some six thousand years ago, when agriculture started spreading across Europe, sparrows, which have now evolved into the house sparrow, followed humans from settlement to settlement. And so they finally reached the territories of Poland today. And despite their constant presence, we still know relatively little about them. The small volume of house sparrow remains in archeological excavation material is also astonishing. In Poland, they have only been found in two places—near Jakuszowice and Ostrów Lednicki, and they most likely come from the early medieval period. That’s fairly recent, given when sparrows started following humans across Europe. Still, almost a thousand years of coexistence have caused them to settle here for good, becoming an important element not only of the Polish landscape, but also of our culture.
Among People and Storks
Readers who grew up in Poland may remember the children’s television series A Few Adventures of Sparrow Tweet. The title character lives in a stork’s nest and forms friendships with various representatives of the Polish avifauna. Though it is a work of fiction, it still has some relationship with reality. Fact: sparrows actually do like to be near the white stork (which, for its part, also values human neighborliness), and are very happy to settle in its nest, in the spaces between the sticks and branches. In addition, storks extend a protective umbrella over them, which makes sparrows feel safer, allowing them to hide from predators. A marten or a sparrowhawk is unlikely to approach a nest inhabited by storks, as it is too risky for them to subject themselves to a blow from the stork’s mighty beak.
If, for some reason, a stork permanently abandons its nesting site, after a while—as in the case of settlements abandoned by humans—the sparrows will eventually follow. They do not, however, abandon the nest during the period when storks migrate to Africa, but wait patiently for their larger avian roommates to return. Furthermore, they prefer to be surrounded by farmland, especially if it’s covered by grain crops. Therefore, it is ideal for them to settle near a farm which has a resident stork, on account of the humans providing food and the storks providing protection. The ideal accompaniment.
Because of Us
The current state of affairs for sparrows is not looking rosy. Over the past forty years, Europe has lost close to 250 million sparrows. This is the largest population decline of any bird species. There is no single simple explanation as to why this is happening. A number of factors must be taken into account when looking for an answer. Sadly, humans are behind most of them. Historically, human activity has contributed to the increase in the bird’s numbers, but nowadays it is leading to the species’ decline.
One of the gravest threats is the elimination of suitable nesting sites. In cities, sparrows mostly nest in the cavities of various objects. True, they can construct nests in the form of balls made of grass blades and rhizomes, which they place in hedges or even on television antennas, but they do so rarely and reluctantly. An ongoing, large-scale, building insulation program, which has been underway for many years across Poland, has led to a dramatic decline in the number of places where sparrows can nest.
The other major factor behind the declining number of sparrows in highly urbanized areas is air pollution caused by nitrogen oxide coming from exhaust pipes. In such conditions, the proper development of chicks is impaired; among other things, their body weight decreases and their chance of survival is lowered. The third reason is cat predation. Sparrows are among their most common prey. The fourth factor is linked to fear. In fear of sparrowhawks— their greatest natural enemy—our heroes will eat less food during the day to be more agile and better avoid predatory attacks. However, during the cold winter nights, these meager rations often contribute to significant hypothermia and death. The fifth threat are the increasingly common avian malaria infections, which are even reported as far as northern Europe—for example, as many as 70 percent of sparrows have been affected in London. In the era of global climate change, diseases have spread to places where they did not exist before, and birds can no longer feel safe among these new threats.
Lastly, it is worth pointing out the negative consequences of tree and shrub removal, over-mowing of lawns (which prevents plants from producing seeds), the removal of unused land plots, increased construction, and the widespread chemicalization and mechanization of agriculture. Also of equal importance is the reduction of the food base, whether related to the tighter packing of waste that would be suitable for consumption by birds, or caused by the disappearance of free-ranging poultry and horses that used to be fed in backyards or corrals, which the sparrows also enjoyed.
So why should we not ignore all this? Sparrows have been our companions for thousands of years, and no one likes to lose good friends. What will the world look like without their scuffles outside our windows, their family quarrels at the bird feeder, the flutter of their wings as they flee in panic from unknown danger into the depths of a nearby spruce tree? Without sparrows, the “silent spring” predicted in the early 1960s by Rachel Carson, a biologist and author of nature books, is unfortunately more and more likely.
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