Crows may not be as 'bad' as previously believed

A new study has helped demystify the bad reputation of crows, suggesting that their notoriety is not entirely merited.

Corvids, the bird group that includes crows, ravens and magpies, are the subject of several population control schemes, in both game and conservation environments. These controls are based on the belief that destroying them is good for other birds. They are also considered to be effective predators capable of reducing the populations of their prey.

Researchers at the University of Castilla-La Mancha analysed the impact of six species of corvid on a total of 67 species of bird susceptible to being their prey, among which are game birds and passerine birds.

Author Beatriz Arroyo said that in 81percent of cases studied, corvids did not present a discernible impact on their potential prey and furthermore, in 6percent of cases, some apparently beneficial relationships were even observed.

According to the study, when crows were removed from the environment, in 46 percent of cases their prey had greater reproductive success, while their abundance fell in less than 10percent of cases.

Additionally, these experimental studies carried out in nine different countries (Canada, France, Norway, Poland, Slovakia, Spain, Sweden, the UK and the USA) revealed that, if corvids are eliminated but other predators are not, the impact on the productivity of their prey would be positive in only 16 percent of cases; whilst without corvids and other predators, including carnivores, the productivity of other birds improves in 60percent of cases.

This suggests that crows, ravens and magpies, amongst others, have a lower impact on prey than other threats. Compensatory predation can also occur, the researcher explains.

The study is published in the journal Ibis.