The bar terrace diet is harmful to sparrows and may be one of the reasons for the decline in their population, warns a study by several Spanish universities.
“Eating leftover chips, bread or other foods of that type, as urban sparrows do, is not the same as eating insects or grain from crops, the typical sustenance of rural specimens,” says Edgar Bernat-Ponce, biologist and one of the authors of the research.
On Wednesday, World Sparrow Day, the ornithology NGO SEO/BirdLife recalled that the population of this small and popular bird has suffered a drop of almost 20% of the population since 1998, when they began collecting data.
The decline is more pronounced in urban areas than in rural areas and has been stabilizing in the last decade.
It is difficult for a sparrow not to succumb to the many
delicacies
that they easily find on bar terraces.
“Even we offer them these leftovers because we don't think it is a problem,” warns Bernat-Ponce.
To experimentally find out the effects of this type of diet on the species, the scientists captured 75 specimens (44 males and 31 females) from rural areas, which were not exposed to air pollution or any urban stress factor. , as occurs with city residents, a fact that could have masked the results.
Their diet was healthy as they were fed in chicken coops and crops and had no contact with urban environments or diets.
“Our objective was to find out how changing to a junk food menu would affect them and to do so we prepared two different diets, which simulated those frequently eaten by their peers in the metropolis,” explains the researcher.
One was made up of leftover bread, cheese and croissants, processed foods that sparrows can find on the floor of any bar terrace and which is nutritionally poor (low in protein, but high in carbohydrates and fats).
The second was a dry menu, typical of cats' sustenance, of ground beef and chicken.
It was selected because sparrows visit the cat feeders at the University of Alicante and pet food is a regular part of their diet.
This menu is very rich in proteins and fats, but poorer in refined carbohydrates than the one in the bars.
The first option – leftovers from bars – caused the sparrows to show signs of anemia and malnutrition, and the females tended to lose their body condition by losing weight, for example, the study indicates.
“Something very worrying because it could affect the reproduction of the species,” says Bernat-Ponce.
Cat food also did not have a very beneficial effect: it increased oxidative stress (accumulation of molecules called free radicals when an organism lacks enough antioxidants to eliminate them).
The study was carried out by the University of Valencia, the University of Alicante and the European University of Valencia and the samples were collected between November 2018 and February 2019.
“It is not easy to capture a sparrow because they are very smart and if they fall the first time they do not do it a second time, we use mist nets [made with mesh and one of the usual ways to catch birds or bats] in an area surrounded by crops in Alcoy (Alicante)”, remembers Bernat-Ponce.
Before introducing the specimens into the cages, which were located in a small town isolated from urban areas, they were ringed, measured and took blood samples to check their levels of cholesterol, uric acid, glucose... and the oxidative state of the blood.
“It was as if we were performing an analysis on a human being, but with certain adjustments,” the scientist clarifies.
The research offers physiological data on the species, but it is not decisive when it comes to specifying the role that nutrition plays in the reproduction and population decline of the species.
“Our study covered 20 days, more analysis is needed,” warns Bernat-Ponce.
Cities without healthy food
It is difficult for birds to find healthy food such as seeds or invertebrates in cities because green areas are progressively disappearing.
The most readily available is junk food, the leftovers that we humans throw away, which we find around the terraces of bars and in garbage containers, the researchers point out.
This food “can even increase winter survival and maintain larger populations, but it has hidden effects,” he warns.
The diet is poor and does not contain the necessary amounts of amino acids and vitamins (antioxidants) for urban birds.
On the contrary, they add, they are usually characterized by having an excess of fats, carbohydrates or even proteins, which can alter uric acid, glucose levels, total proteins and cholesterol, which in birds can cause kidney disease, anorexia, starvation and heart disease, respectively, pose.
The factors that have caused the decline in the sparrow population have not yet been identified.
"The only thing that seems evident is that it is related to excessive urban developments, atmospheric pollution, excess noise, lack of nesting places, scarcity of insects, especially necessary in their diet during the breeding season, or management of green areas that It does not take biodiversity into account,” highlights Beatriz Sánchez, from the SEO/BirdLife Urban Biodiversity program.
The organization considers it essential to undertake a naturalization of the cities.
It proposes, for example, reducing the frequency of mowing in grass meadows, that the tree pits have vegetation or allowing the so-called "weeds" to grow in ditches and open fields.
Thus, sparrows and other wild species will benefit and will be able to eat seeds and insects.
SEO/BirdLife develops this type of measures in cities such as Santander, Girona, Valencia or Pinto, in Madrid.
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