An Audubon Society will release a study of the birds’ migration on Tuesday, in order to explain the big number of birds which leave the United States because of the global warming effects. As the temperature in the U.S. goes warmer, more and more species of birds decide to move their nests 400 miles farther north that they had used to.

The study conducted by the Audubon Society has found out that half of the 305 species of birds from North America , including robins, owls, gulls and chickadees have moved their nests for the winter almost 35 miles farther north than they had done nearly 40 years ago.

For example, the purple finch has been the most important mover toward the north, but it can now be found along the latitude of Milwaukee than of Springfield. There can be many reasons for which birds decide to migrate and change their locations. Factors such as deforestation and the urban sprawl may make some species fly away from their normal location.

Yet, the researchers are stuck to the fact that the explanation for so many birds flying away over such a wide area during the winter is the global warming. The study also provides the information about the growing temperature over the last 40 years. According to specific data, the average temperature in January has climbed by about 5 degrees Fahrenheit in the United States.

The warming was recorded especially in the northern states, which have already recorded a big invasion of the southern species of birds. Greg Butcher, the lead scientist on the study and the director of bird conservation at the Audubon Society, stated that this wide variety of birds is the one which tells that the problem is connected to the global warming and not with ecology.