The kind of food eaten by birds in the city – largely discarded junk food – is harmful for the gut bacteria of the birds, according to research carried out by scientists from the universities of Antwerp, Ghent and Toulouse in France.
The researchers set up two aviaries, one containing city birds and one containing birds from the countryside. Some of the birds were fed foods commonly found in the city, such as fries, potato chips, cake and bread – foods that are low in fibre.
The other birds were fed worms, seeds and grains such as birds would find in the rural habitat, rich in fibre.
The researchers found significant changes in the gut bacteria of both sets of birds when they were fed the opposite diet to their normal one.
The rural birds saw a diminution of the health of their intestinal flora or microbiota when they were fed a city diet.
The city birds, on the other hand, while there was some improvement, it was not substantial, suggesting that a poor diet leads to a situation where the bird is no longer able to benefit from an improved diet, because of the low quality of microbiota starting out.
“From the research it appears that diet plays an important role in the differences noted between the city and the countryside,” said biologist Erik Matthysen of the university of Antwerp.
“City sparrows have a less fibre-rich diet, which means the diversity and composition of the intestinal microbiota – the sum total of the micro-organisms in the gut – diminishes. And due to the low diversity of gut bacteria, the city sparrows are not even able to benefit from a fibre-rich rural diet.”