Buy AumSum Merchandise: http://bit.ly/3srNDiG Website: https://www.aumsum.com A research conducted over 40 years by collecting more than 70,000 samples of 52 North American migratory birds clearly shows that birds are definitely decreasing in size. The lower leg of the bird is commonly used as a measure of its body size. It was found that its length reduced by more than 2% during this period. Researchers believe that this decrease in body size is related to increase in global temperature. Why? Because a smaller body size allows the birds to cool off more quickly i.e. lose body heat faster. It was also observed that during the same period, wingspans of birds increased by more than 1%. Researchers believe that migratory birds compensate for smaller body sizes by increasing their wingspans. This makes them better equipped to survive their long migratory journeys. References: https://www.bbc.com/news/science-envi...