Birds that live in urban environments are more aggressive when it comes to defending their territory than their rural counterparts, according to a study on the melodic sparrow (Melospiza melodia) carried out in the United States, where it is a widespread species.
The greater aggressiveness of city birds is due to the fact that they have better food and shelter but also more competition for these resources, according to researchers from the Polytechnic Institute and Virginia State University (United States).
"The study comes to endorse what other investigations have already pointed out: cities can be hostile environments for birds," the coordinator of the SEO / BirdLife Monitoring Area, Juan Carlos del Moral, explained in a statement.
The North American scientists, whose study has been published in the journal Biology Letters, measured the level of aggressiveness of the melodic sparrow by reproducing a recording of the song of one of these birds and observing the reactions of the inhabitants of the area to the intrusion.
While in urban areas sparrows moved closer to the loudspeaker, flapping their wings "furiously" and joining the loud chant of the loudspeaker to then initiate a duller trill - which researchers associate with an imminent attack - in field sparrows the reaction was not as strong.
Indicators of the health of a habitat
Urban birds, "indicators of the health of a habitat" according to SEO / BirdLife, have lost 18% of their population in the last twenty years, so "it is necessary to guarantee that cities and suburbs are friendly spaces" for biodiversity .
The impact of urban pollution on birds also affects their physical conditions, as indicated by a previous research carried out by the Complutense University of Madrid that explained that the health of the birds resident in the city was much worse than that of their congeners. from the periphery or rural areas.
"The sparrows in the center of Madrid, for example, have anemia and their defense systems seem altered", added del Moral, who indicates that they breathe the same air pollution and are subjected to the same noise level as human beings who work and they reside in the capital ”.