A new study, published in Science, finds that the number of birds in North America has declined by 29 percent since 1970.
Researchers have been tracking changes in bird populations at Hubbard Brook for 50-plus years. While the recent Science paper is continental in scope, the story looks somewhat different from our zoomed-in perspective within the White Mountain National Forest.
At Hubbard Brook, bird abundance is down from its peak in the early 1970s but the drop occurred largely due to changes in bird species composition associated with forest aging. Since the low point in the mid 1990s, some species have decreased and others have increased or stayed the same, with the overall number of birds actually rising slightly in recent years.
Taken together, the data from Hubbard Brook and those presented in Science suggest that bird populations may look healthy on a local scale even if they are declining on a larger scale. Major drivers of change at larger scales include habitat loss, pesticides, building collisions, and nonnative predators, while at the local scale—such as at Hubbard Brook—food abundance and vegetation structure are more important.
The dramatic declines described in the Science study echo issues that Hubbard Brook scientists have highlighted in the past—that events happening during the breeding season, migration, and in the winter grounds can all have a significant impact on bird abundance.
The Hubbard Brook team is actively in the process of analyzing a half century of data, and is eager to share new information and hypotheses as they emerge.