In the spring, the western tanagers(唐纳雀)prepared to migrate(迁徙)thousands of miles to the forests of the Mountain West, flying through grasslands, deserts, and occasionally, suburban yards.
To fuel them on their lengthy journey, western tanagers feed on insects and berries. They must take advantage of the early-season boom in insects that started with springtime plant growth to produce healthy young. But as global climate change caused spring to start earlier, birds such as western tanagers were arriving at their destination after what was known as "green-up", when flowers began blooming and insects popped up. With the shift of the time when plants put out new leaves, western tanagers became more likely to reach their destinations when food is in shortage or after insect numbers have begun to drop.
Scott Loss, a professor at Oklahoma State University and his colleagues used satellite imagery to calculate the average start of spring green-up along the typical migration routes of 150 North American bird species, and then compared that timing with the current green-up. They found that spring was indeed beginning earlier along birds' migration routes. The trend continued this year.
The paper continued to build this picture of the inability of birds to track the changing seasons caused by climate change. Timing mismatches between birds and their food could affect whether birds survived the migration and how many chicks they had.
Morgan Tingley, an researcher at UCLA said that the migration research could indicate conservation efforts in the future. "Part of it suggested which species were vulnerable(易受伤害的)to various threats," Tingley said. "This added to the knowledge about vulnerability of a wide range of bird species." And he hoped that the information would serve to highlight the urgent need to lower greenhouse-gas emissions as fast as possible: "It was really important, if we couldn't address climate change immediately, to try to stop habitat loss as much as we can."
