How Climate Change Is Affecting Migrating Birds

How Climate Change Is Affecting Migrating Birds

Bird Migration Climate Change. Courtesy of Maksim Shutov, Unsplash

Just under half of all known bird species are migratory: every year, billions follow the same route back and forth between their breeding and wintering grounds, a journey that has taken place for millennia. But now, evidence is mounting that suggests those historical routes are changing as global warming gains pace, and some scientists have seen that migration appears to be ceasing entirely for some species.

Taking the long way home

Thousands of bird species across the world live a nomad’s life to ensure that they stand the best chances of survival wherever they are. Triggered by the subtle change in temperatures and daylight hours as the seasons progress, towards the end of summer in their breeding grounds, and winter in their non-breeding grounds, migratory birds start to feed as often and as heartily as they can to store up fat reserves which they hope will sustain them on their lengthy flight.

Main international flyways of bird migration. Courtesy of Pinpin, Wikimedia Commons

These ancestral routes are known as flyways. To conserve energy, most species aim for the shortest possible route they can find, but some species need to fly thousands of miles, which means this endeavor is often not covered in one go. At various strategic points along the way, birds will stop to rest and refuel at places called stopover sites.

These are often exactly the same place each year, where the habitat has been suitable enough to support huge numbers of birds needing food and sleep. Over the past few decades, centuries in some cases, tracking and recorded data has allowed experts to determine that there are eight major flyways that crisscross the world.

courtesy of Barth Bailey, Unsplash

A warming world

If we look at a scaled down model version of our planet, on a desktop globe or in the image above, you can see equidistant lines that run from west to east all around the sphere. These are latitude lines, and they run parallel to the equator, separated in 10˚ increments. The equator divides our world into the northern and southern hemispheres, and with the equator symbolizing zero degrees latitude, eight consequent latitude lines each lie between the north and south poles, (which themselves are assigned the value of 90˚). Each degree of latitude covers around 111 kilometers of physical surface area in width.

Waterfowl flyways in the United States. Courtesy of Wikimedia Commons

Viewing the world in this way helps us understand where those regions are that experience strikingly different temperature ranges and therefore geological and habitable conditions, and these regions, or zones, are named accordingly. In the middle latitudes, the Temperate zone describes parts of the world that experience relatively mild climates with cold but not terrible winters and hot but not scorching summers.

The Tropics lie 23.5˚ either side of the equator and these zones do not experience conventional seasons as many know them, but only a wet or dry season. Lastly, the Polar regions, namely the Arctic and Antarctic Circles, those at the top and bottom of the world, experience a summer where the sun never sets and a winter where it never rises. Despite summer sun, temperatures only average around 10˚C / 50˚F, and it remains a very cold environment which is mostly uninhabitable except for the hardiest of species.

Migration routes of birds. Courtesy of L. Shyamal, Wikimedia Commons

At least, that’s how the world used to be, until relatively recently.

The zones’ delineations are now blurring, with temperatures creeping up across all latitudes – global warming. The year 2022 saw several new and concerning readings in various fields of research: large parts of North America and Europe had their hottest summer since records began, with prolonged and intense heat waves affecting western and northern Europe; low rainfall in combination with high temperatures led to widespread drought conditions, and France, Spain, Germany, and Slovenia all had their highest level of wildfire outbreaks.

Aerial view of floods in Pakistan. Courtesy of Department of Foreign Affairs and Trade, Wikimedia Commons

Across the Atlantic, 33,000 fires were detected in the Brazilian Amazon basin in August, a new record. Elsewhere, prolonged heat wave conditions affected Pakistan which saw a third of the country covered by widespread flooding as a result of extreme rainfall that displaced 33 million people; New Zealand had its warmest winter to date; Antarctic Sea ice reached its lowest minimum extent in its 44-year satellite record.

Courtesy of Georg_Wietschorke, Pixabay

Rest stop is closed

Migratory birds respond to environmental changes differently depending on the species; short and middle-distance migrating birds usually adapt to climate change more easily, but long-distance migrants will suffer greatly, as their migration instinct and route is more fixed.

Species that are usually associated with lower and middle latitudes are being seen more and more in higher latitudes, such as cardinals and wood thrush up into the Maritimes of Canada, but what concerns some people more is how long-distance migrant populations are declining in line with these drastic fluctuations in temperatures and consequent weather events.

Drier and hotter conditions bring on desertification of what was normally healthy wetland – those all-important stopover sites that harbor lakes, ponds and marshes dry up, but the birds will still go to them as this is their pattern. Upon finding there is no water and therefore food to be had, they will have to move on, still exhausted, thirsty and hungry.

Global Desertification Vulnerability Map. Courtesy of USDA, Wikimedia Commons

This is already being seen in California and Turkey where huge populations of birds are now simply bypassing their historical stopovers because they are now practically dust bowls. The crossing of the Sahara is one of the most challenging journeys for birds, but the Sahara expansion will make it nearly impossible for African-Eurasian migrants to cross this deadly barrier.

Similarly, coastal areas have in the past provided refuge before or after the long and perilous flight across open water; rising tides are now destroying those habitats, and the food that lives there that is so highly sought is now gone.

Siberian tundra. Courtesy of Ninaras, Wikimedia Commons

Breeding habitats are also being affected, such as the Siberian tundra and other historically frozen areas. Warming is thawing out the permafrost, which is enabling vegetation to prosper there; this may sound like a good thing, but not if you use that dry and barren land as your nesting ground, like arctic geese do. This green carpet enables forest to expand, not only making it unsuitable habitat for nesting but also brings predators. Experts estimate that anywhere between 10 and 93% of the arctic geese species’ breeding territory will be lost in the next few years if this expansion continues.

Courtesy of Frates Jim, PIXNIO

No way but the flyway? 

A lot of migratory birds have changed or shortened their routes to try and counteract these drastic effects, but some species have also been seen to cancel their journey completely as a result of changing temperatures. More and more species of passerines are no longer wintering in Spain, France or in the north of Africa, preferring to stay in the UK and breed there, similarly with cranes and other species who breed in Europe who would then normally travel to the ends of Africa before the colder winters set in.

Tufted Titmouse from Bird Buddy

Spring has also been occurring earlier for some time now, as well as the rising occurrence of false springs, where temperatures in December and January are unusually high, promoting plants to bud early and birds to be triggered into movement. However, just a few weeks or even days later, temperatures can plummet again – crops can die and the promising possibility of newly hatched insects vanishes – there is no food and everywhere is cold, the ground frozen again.

Not only does this increase pressure on food resources and territory for resident birds who would normally expand their range once the migrants had gone, but the migrating species are not physically equipped to deal with those kinds of winters; most won’t survive a cold snap.

Of course, the earth’s climate has been changing since time began as a natural process, and many bird species were able to adapt to these changes, whilst others became extinct. However, human-induced global warming is happening at an accelerated rate and it is becoming increasingly difficult for many bird species to keep up.

Courtesy of Diane Constable, Wikimedia Commons

Whilst scientists accept that a balance will inevitably come into play, this will undoubtedly be too late for many, especially those long-distance migrants. Thus, it is in everyone’s interests that we all play our part in not only mitigating the effects of climate change by reevaluating how we use energy and fossil fuels, but also by replacing what has been lost where we can, by planting native trees and flowers and other crops, installing water features into your yard, and holding back on “tidying up” leaf litter and dead trees and branches that can at least provide food to any wayward or exhausted migrants, just trying to find somewhere to rest and refuel. It may not seem like much, but until the world acts as one to slow the pace, any small step goes a long way.

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