It is no secret that progress and urbanization have brought about consequences, many of them negative, on the environment, but some also show the capacity to which species have to adapt, even in adverse conditions. You are the birds Urban birds, such as thrushes (to which thrush belongs), hummingbirds and others, do indeed show remarkable differences in behavior, even physical differences, when compared to populations that live far from civilization.
Image copyright Becky MatsubaraFlickr🇧🇷
This finding is not recent, it has been observed over many years, but only in 2020, in a survey published in International Journal of Ornithology 🇧🇷Ibis), by a team of ornithologists from the University of Costa Rica, pointed out signs of what could lead, in the long term, to a process of speciation, when, after generations and genetic changes, separate populations can no longer reproduce with each other.
The study focused on research that had been conducted for more than 15 years, which had already indicated changes in urban populations of blackbirds, tits, and taco-ticoes, which live respectively in Europe, Asia, and the Americas; Samples that live in cities, competing with all kinds of urban noise, sing louder than those that live in the country.
Luis Andrés Sandoval Vargas, one of the ornithologists involved in the 2020 study, recalls that in most bird species, especially those that live in the tropics, singing has functions of demarcation, attracting mates for males, and defending their territory for females.
According to Vargas, birds that live in cities need to compete with urban noise, from machinery under construction to chaotic traffic, music, screams, etc., and one way to do this, to be heard by their peers, is through breeding. from the corner. But will this be valid for all species?
The study focused on analyzing the known species, the wren (Troglodytes aedon), distributed practically throughout the entire American continent. From Costa Rica to Brazil, where the species lives all year round, they tend to coexist well alongside humans, feeding on insects and lizards, and making nests in any hole, under roof tiles, or in abandoned jon-john homes. .
Vargas explains that male wrens sing practically year-round, for long periods of the day, and make vocalizations to discern their intentions, so the species would be ideal for a long-term study, which takes two years. The results were interesting, to say the least.
As expected, the urban wren sang in higher pitches than those living in the countryside, but that wasn’t the only discovery. Vargas’ team found that the song repertoire of urban-dwelling samples was much smaller, directly related to the population’s exposure to human-made noise.
Scientists have also realized that reduced vocalizations are present on both a collective and individual level, and the bird tends to sing more variedly on days with less urban noise.
Having a rich repertoire of bird songs is important, Vargas recalls, as younger individuals listen to adults to learn how to sing. If they suffer from competition from the noise of cities, and sing less, succeeding generations will end up with a smaller group to use, and they will pass on the little they have learned to their offspring.
In the long run, populations living in town and country will not be able to recognize themselves as one community, because of differences in repertoire, and even if scientists try to introduce birds from one group to another, “strangers in the nest”, so they will not be able to reproduce.
According to Vargas, this poses no danger to the sparrows themselves, nor will the urban population disappear; But over time, isolating this group from those living in the countryside, or in areas inhabited by humans with less noise, would cause behavioral and genetic differentiations, leading to homospecification, a phenomenon noted by Charles Darwin in the Galapagos Islands. , with birdsong.
In this case, the populations of country and urban wrens would become separate species, which, though they might have genetic similarity, would not be recognized as parts of a whole, and so would not be able to reproduce with each other.
Of course, not all species deal with a noise problem in the same way, and that can actually create complications. decoy or European milheirinha (Sirenus Sirenus), which is common almost throughout Europe, offsets longer singing, which according to researcher Mario Diaz Esteban, of the National Museum of Natural Sciences in Spain, is detrimental to other activities such as searching for food and mates, and protecting oneself from predators.
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Song is just one of the phenotypes (observable characteristics) that change in birds as they survive large cities. blue tit (cyanistes caeruleus), another European species that usually feeds on insects Drink milk from open bottles🇧🇷 Australian white ibis (Moloka Threscurness) began feeding on human excrement as well.
Of course, there are those who say that progress is an aggression against nature, and it is in many aspects, but it is necessary to consider that man is not an animal in isolation from him, and everything he does will have consequences for the environment that will always be bad. In some cases, they are elements that eventually lead to changes in species, similar to the consequences of a volcanic eruption, or continental break-up.
Moreover, regardless of the difficulties and challenges, life always finds a way.
the reviewer
JUÁREZ, R., ARAYA-AJOY, Y.G., BARRANTES, G., SANDOVAL, L. House Wrens Troglodytes aedon Reducing repertoire size and changing song element frequencies in response to human noise. Ibis (International Journal of Ornithology)Volume 163, Issue 1, 13 pages, June 9, 2020. Available over here🇧🇷
source: Well-known magazine (in Spanish)
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