The number of birds that feed on insects has declined significantly in Europe over the course of 25 years, a study has found.

There was a 13 per cent average decrease in the number of insect-eating birds in Europe between 1990 and 2015, according to a scientific paper published in journal Conservation Biology.

While the decline reflects a trend in the fall of the insect population, the study's authors also attributed it to the loss of grasslands and the conversion of land for agricultural uses.

"It is probably a mixture of many things: loss of insects and thus lack of food, loss of hedges and thus breeding grounds, the sealing-off of land," said Katrin Boehning-Gaese, one of the study's authors.

Around half of all bird species in Europe feed on insects. Omnivorous birds have not seen a similar population decline.

The study found that the insectivores do not fare equally badly everywhere. Many of the species had stable populations, especially ones that were adaptable to a range of different habits and conditions.

The researchers are associated with the Senckenberg Biodiversity and Climate Research Center and the German Centre for Integrative Biodiversity Research.