Why are migratory bird populations declining? OSU researchers seek answers 

STILLWATER, Okla. – Migratory bird populations are declining due to the variety of threats they face across their annual migration routes.

Summary:

• Migratory bird populations are declining: More than 50% of the world’s migratory bird species are in decline, with declines exceeding 60% in North America.
• Birds face threats throughout their annual migration: Habitat loss, pesticides, building collisions and other threats can affect birds at different points along their migration routes, making population declines difficult to understand.
• OSU researchers and their collaborators say that reversing population declines requires better monitoring, habitat protection, reduced threats, international cooperation and interdisciplinary research. People across the world can take practical steps to help.
• OSU research found dotted-pattern window markers reduced collisions by 70%.

Why are migratory birds important?  

Migratory birds provide valuable ecosystem functions like seed dispersal, pollination and pest control.

“They also provide services to humans,” said Scott Loss, professor in the Oklahoma State University Department of Natural Resource Ecology and Management. “Having birds around and hearing birdsong have been shown to benefit people’s mental health and reduce stress. The U.S. Fish and Wildlife Service estimates there are roughly 100 million bird watchers in the United States alone.”

With the assistance of researchers and bird enthusiasts across the world, researchers from the Smithsonian Conservation Biology Institute, Oklahoma State University, Georgetown University in Washington, D.C, and bird conservation organizations have joined forces to answer an important question.

Why are migratory bird populations declining?

More than 50% of the world’s migratory bird species are in decline, and the number is even higher in North America, where there has been more than a 60% decline.

“The fact that we’re losing so many birds is a troubling warning sign. What does that mean about the status of the Earth’s systems that support us?” Loss said. “We have been trying to determine how we need to better monitor these migratory birds to understand their populations and what’s affecting them.”

Things like habitat loss, pesticides, collisions with buildings and a long list of other threats have contributed to bird mortality and reduced reproduction, but knowing what the exact causes of population decline for a specific species and when that cause is affecting them is a challenge with migratory birds.

Why are migratory bird threats difficult to identify?

Loss and the partner agencies have documented declines in migratory bird populations and identified some of the threats affecting them. But discovering the full spectrum of their decline is not easy, because migratory birds are exposed to a variety of landscapes throughout the year.

“Migratory birds travel vast distances in a year and are exposed to varying landscapes, both habitat landscapes and political landscapes in regard to the regulations protecting them, so knowing what’s going on with their populations is complicated,” Loss said. “If you’re not aware of their entire life cycle, all the threats along the way, and at which point bird populations are being affected by things like mortality or reduced reproduction, then you don’t have a complete picture.”

The Oklahoma state bird, the scissor-tailed flycatcher, spends the summers in the southern Great Plains and winters in the tropics from Mexico to Panama.

“I could study scissor-tailed flycatchers in Oklahoma and find that an issue like pesticides is a big problem, but someone in Costa Rica might study them and find it’s the loss of their grassland habitat,” Loss said. “There’s a laundry list of threats affecting birds, and it’s difficult to identify the exact threats responsible for a bird species’ decline, because tracking birds over the course of their entire year is a challenge.”

How can people help migratory birds?

In “Status, threats and conservation of Earth’s migratory birds,” published in Nature Portfolio in July, Loss and his colleagues outline a species-centered approach to conservation, saying that reversing population declines will require integrating a focus on individual species with improved habitat protection and reduced threats. The research article also outlines the need for stronger international cooperation and financing, improved communication of conservation needs and interdisciplinary research that includes diverse perspectives.

“A species-centered approach starts with understanding precisely what factors are preventing the species from thriving, and then, through coordinated effort, targeting those factors with conservation action,” said Nathan W. Cooper, research ecologist with the Smithsonian’s National Zoo and Conservation Biology Institute. “Legislation like the Endangered Species Act shows us that this approach works. Now, we just need to extend this approach to species before they become threatened and endangered.”

There are also ways that everyday people can help. Road to Recovery is an international initiative that brings together scientists, governments, conservation organizations, landowners and local communities to form species working groups. These groups help identify the harms bird populations face and make tracking them more precise. Individuals can visit the Road to Recovery website to find out how to get involved.

“Road to Recovery was established to marshal and integrate the best available biological and social sciences – both of which are rapidly advancing – to pinpoint the causes of decline and put effective, lasting solutions into action,” said Peter Marra, dean of Earth Commons at Georgetown University’s Institute for Environment and Sustainability. “By working together throughout the process of identifying the factors affecting bird species, designing strategies to address the causes of decline and implementing conservation actions, the Road to Recovery community will turn research into results.”

Dotted-pattern window markers reduced bird-window collisions by 70% 

Progress has already been made in other areas of research to address key threats to migratory birds. In previous research, Loss and collaborators estimated that building windows are the largest source of bird collision mortality in North America, killing up to 1 billion birds annually in the U.S. alone.

In response to the research, Loss and colleague Tim O’Connell, associate professor in the OSU Department of Natural Resource Ecology and Management, spearheaded an initiative to install dotted-pattern window markers with 2×2-inch spacing on two OSU buildings with large windows that were causing many migratory bird collisions. They studied the effectiveness of this preventive measure and found that the window markers decreased bird-window collisions by 70%.

“Our research results showing that these window markers are highly effective provide further motivation to implement simple fixes on a broader scale, from neighborhoods to campuses to office buildings and more,” Loss said. “We hope these and similar solutions are applied widely as one way to help declining migratory bird populations.”

 

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