By Frank La Sorte and Kyle Horton
Millions of birds travel between their breeding and wintering grounds during spring and autumn migration, creating one of the greatest spectacles of the natural world. These journeys often span incredible distances. For example, the Blackpoll warbler, which weighs less than half an ounce, may travel up to 1,500 miles between its nesting grounds in Canada and its wintering grounds in the Caribbean and South America.
Blackpoll warbler. PJTurgeon / Wikipedia<p>We used this information to determine how the number of migratory bird species varies based on each city's level of <a href="https://www.britannica.com/science/light-pollution" target="_blank" rel="noopener noreferrer">light pollution</a> – brightening of the night sky caused by artificial light sources, such as buildings and streetlights. We also explored how species numbers vary based on the quantity of tree canopy cover and impervious surface, such as concrete and asphalt, within each city. Our findings show that cities can help migrating birds by planting more trees and reducing light pollution, especially during spring and autumn migration.</p>
Declining Bird Populations<p>Urban areas contain numerous dangers for migratory birds. The biggest threat is the risk of <a href="https://doi.org/10.1650/CONDOR-13-090.1" target="_blank">colliding with buildings or communication towers</a>. Many migratory bird populations have <a href="http://dx.doi.org/10.1126/science.aaw1313" target="_blank">declined over the past 50 years</a>, and it is possible that light pollution from cities is contributing to these losses.</p><p>Scientists widely agree that light pollution can <a href="https://doi.org/10.1073/pnas.1708574114" target="_blank">severely disorient migratory birds</a> and make it hard for them to navigate. Studies have shown that birds will cluster around brightly lit structures, much like insects flying around a porch light at night. Cities are the <a href="https://doi.org/10.1002/fee.2029" target="_blank" rel="noopener noreferrer">primary source of light pollution for migratory birds</a>, and these species tend to be more abundant within cities <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13792" target="_blank" rel="noopener noreferrer">during migration</a>, especially in <a href="https://doi.org/10.1016/j.landurbplan.2020.103892" target="_blank" rel="noopener noreferrer">city parks</a>.</p>
Composite image of the continental U.S. at night from satellite photos. NASA Earth Observatory images by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NASA's Goddard Space Flight Center
The Power of Citizen Science<p>It's not easy to observe and document bird migration, especially for species that migrate at night. The main challenge is that many of these species are very small, which limits scientists' ability to use electronic tracking devices.</p><p>With the growth of the internet and other information technologies, new data resources are becoming available that are making it possible to overcome some of these challenges. <a href="https://doi.org/10.1038/d41586-018-07106-5" target="_blank">Citizen science initiatives</a> in which volunteers use online portals to enter their observations of the natural world have become an important resource for researchers.</p><p>One such initiative, <a href="https://ebird.org/home" target="_blank" rel="noopener noreferrer">eBird</a>, allows bird-watchers around the globe to share their observations from any location and time. This has produced one of the <a href="https://doi.org/10.1111/ecog.04632" target="_blank" rel="noopener noreferrer">largest ecological citizen-science databases in the world</a>. To date, eBird contains over 922 million bird observations compiled by over 617,000 participants.</p>
Light Pollution Both Attracts and Repels Migratory Birds<p>Migratory bird species have evolved to use certain migration routes and types of habitat, such as forests, grasslands or marshes. While humans may enjoy seeing migratory birds appear in urban areas, it's generally not good for bird populations. In addition to the many hazards that exist in urban areas, cities typically lack the food resources and cover that birds need during migration or when raising their young. As scientists, we're concerned when we see evidence that migratory birds are being drawn away from their traditional migration routes and natural habitats.</p><p>Through our analysis of eBird data, we found that cities contained the greatest numbers of migratory bird species during spring and autumn migration. Higher levels of light pollution were associated with more species during migration – evidence that light pollution attracts migratory birds to cities across the U.S. This is cause for concern, as it shows that the influence of light pollution on migratory behavior is strong enough to increase the number of species that would normally be found in urban areas.</p><p>In contrast, we found that higher levels of light pollution were associated with fewer migratory bird species during the summer and winter. This is likely due to the scarcity of suitable habitat in cities, such as large forest patches, in combination with the adverse affects of light pollution on bird behavior and health. In addition, during these seasons, migratory birds are active only during the day and their populations are largely stationary, creating few opportunities for light pollution to attract them to urban areas.</p>
Trees and Pavement<p>We found that tree canopy cover was associated with more migratory bird species during spring migration and the summer. Trees provide important habitat for migratory birds during migration and the breeding season, so the presence of trees can have a strong effect on the number of migratory bird species that occur in cities.</p><p>Finally, we found that higher levels of impervious surface were associated with more migratory bird species during the winter. This result is somewhat surprising. It could be a product of the <a href="https://www.epa.gov/heatislands" target="_blank">urban heat island effect</a> – the fact that structures and paved surfaces in cities absorb and reemit more of the sun's heat than natural surfaces. Replacing vegetation with buildings, roads and parking lots can therefore make cities significantly warmer than surrounding lands. This effect could reduce cold stress on birds and increase food resources, such as insect populations, during the winter.</p><p>Our research adds to our understanding of how conditions in cities can both help and hurt migratory bird populations. We hope that our findings will inform urban planning initiatives and strategies to reduce the harmful effects of cities on migratory birds through such measures as <a href="https://www.arborday.org/programs/treecityusa/index.cfm" target="_blank" rel="noopener noreferrer">planting more trees</a> and initiating <a href="https://aeroecolab.com/uslights" target="_blank" rel="noopener noreferrer">lights-out programs</a>. Efforts to make it easier for migratory birds to complete their incredible journeys will help maintain their populations into the future.</p><p><em><span style="background-color: initial;"><a href="https://theconversation.com/profiles/frank-la-sorte-1191494" target="_blank">Frank La Sorte</a> is a r</span>esearch associate at the </em><em>Cornell Lab of Ornithology, Cornell University. <a href="https://theconversation.com/profiles/kyle-horton-1191498" target="_blank">Kyle Horton</a> is an assistant professor of Fish, Wildlife, and Conservation Biology at the Colorado State University.</em></p><p><em></em><em>Disclosure statement: Frank La Sorte receives funding from The Wolf Creek Charitable Foundation and the National Science Foundation (DBI-1939187). K</em><em>yle Horton does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</em></p><p><em>Reposted with permission from <a href="https://theconversation.com/cities-can-help-migrating-birds-on-their-way-by-planting-more-trees-and-turning-lights-off-at-night-152573" target="_blank">The Conversation</a>. </em></p>
EcoWatch Daily Newsletter
By Brett Wilkins
Despite acknowledging that the move would lead to an increase in the 500 million to one billion birds that die each year in the United States due to human activity, the Trump administration on Friday published a proposed industry-friendly relaxation of a century-old treaty that protects more than 1,000 avian species.
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Like many other plant-based foods and products, CBD oil is one dietary supplement where "organic" labels are very important to consumers. However, there are little to no regulations within the hemp industry when it comes to deeming a product as organic, which makes it increasingly difficult for shoppers to find the best CBD oil products available on the market.
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By Jane Kirchner
Right now, more than a 150 species of birds are on their way northward from tropical wintering grounds to take advantage of emerging insects, budding plants and an abundance of nesting locations. While larger birds tend to travel during daylight hours, songbirds and smaller species fly at night and will stop off and stick around for a day to eat and build up fat stores before continuing their journey. The best time to see and hear them in your yard is the first two hours after the sun rises!
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A legal memo by the U.S. Interior Department reverses a longstanding agency practice and last-minute ruling released by the Obama administration in January 2017. The Obama-era policy meant that oil, gas, wind and solar operators could face prosecution for accidentally killing birds.
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For some people, spring means tax time; for others it brings thoughts of Easter or Passover. For me, the best thing about spring is that it is time for the spring bird migration, the best time of the year to see certain species. It’s also a time to reflect on what a tremendous accomplishment migration is, and how fraught with peril it is for far too many birds.
The average songbird may only weigh about half an ounce, and burns a tremendous amount of energy during migration. Photo courtesy of Shutterstock
While some species of birds remain in the same area year-round, most of our songbird species are “neotropical migrants”—meaning that they breed in the U.S. or Canada, but winter in the warmer climes of the Gulf Coast, or even farther into Central and South America. The month of May, when many of the birds return north, is a particularly good time to be a birdwatcher, for a couple of reasons: first, it is an opportunity to see birds that aren’t present most of the year.
Certain warbler species, for instance, breed only in New England and Canada, so many Americans only have a fleeting chance at a glimpse of these species. Also, migration routes tend to be concentrated into “flyways,” with certain spots being “hotspots” where birds reliably congregate to eat and rest up for the next leg of the journey. A good outing during migration can thus turn up a lot more birds than during the breeding season, when species and individuals tend to be more dispersed.
Birds that undertake migration face triple-whammy of threats: Not only do they need quality habitats in both their wintering and breeding ranges, but they also need to survive the trip, which can be thousands of miles in length and full of dangers along the way. Collisions with buildings kill several hundred million birds each year, and other structures, like communication towers and wind turbines, can also be deadly. Feral and free-ranging cats may kill even more songbirds than collisions do. And the evidence is mounting that climate change is playing an increasingly important role in bird declines. Sea level rise is damaging coasts and wetlands that are important feeding grounds. Increased droughts and fires are damaging forest and shrubland habitats.
And more subtle, but perhaps even more important changes are happening as well, having to do with the timing of important food sources, particularly the emergence of insects. The average songbird may only weigh about half an ounce, and burns a tremendous amount of energy during migration and breeding, making it especially critical that their arrival at stopovers and breeding sites be timed to match food availability.
As climate change throws seasons out of whack, some of these critical timings are getting thrown off—a phenomena known as “phenologic mismatch.” Researchers in Europe have found that phenologic mismatches are an increasingly important cause of bird declines. And in the U.S., birds are actually altering their migration timing to match changing weather conditions—a good strategy, but one that puts them at risk of missing out on major insect emergences.
Get out there this spring and see some birds. While you’re at it, help them survive their migration by keeping your cat indoors, limiting the use of pesticides and other chemicals in your yard, making windows and glass doors more bird-friendly, and providing backyard habitat like sources of water, cover and food.
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