For several years, the size of migratory birds has been decreasing. Researchers from the University of Michigan (USA) have revealed that from 1978 to 2016, more than 70,000 migrating birds from North America have, on average, declined by 2.5%. Their wings are getting bigger and bigger. According to the scientific community, the decrease in the size of birds is directly correlated to the temperature of breeding areas. Under the same effect, the wings of birds have lengthened to perform longer migrations with smaller bodies. Photo credit: Jan Niclas Arberle