FLYING IS NO ESCAPE: MIGRATORY BIRDS AND CLIMATE CHANGE

By Luisanna Carrillo-Rubio

Figure 1: Winged Migration

According to Hans Verolme, Director of World Wildlife Fund (WWF) Global Climate Change Program, “birds have long been used as indicators of environmental change,” and a recent global status report entitled Bird Species and Climate Change (2006) indicated that birds are “the quintessential ‘canaries in the coal mine’ when it comes to climate change.” So it is of particular concern that, at present, the prognosis for bird species—whether they are migratory, mountain, island, wetland, Arctic, Antarctic or seabirds—is most dreadful. The report clearly assembles scientific evidence which demonstrates a “trend towards a major bird extinction from global warming.”

The May, 2008, International Union for the Conservation of Nature (IUCN) assessment concluded that “climate change—and even some attempts to tackle it—are pushing one in eight species of birds towards extinction.” In the past year alone, 26 of the 1,226 species on their “Red List” of threatened bird species became more endangered, while only 2 species improved in status.

The Bird Species and Climate Change (2006) report warns that extinction rates “could be as high as 38 per cent in Europe, and 72 per cent in northeastern Australia, if global warming exceeds 2ºC above pre-industrial levels (currently it is 0.8ºC above).” Unfortunately, the current approach to bird conservation which focuses on protecting specific and limited areas containing high bird diversity will inevitably fail, simply because climate change will force birds to shift into unprotected zones as they desperately try to cope with an ever-warming planet and the shifts this brings to their habitats. In the United States bird populations have also shrunk, and nearly a third of the bird species living in the eastern Midwest and Great Lakes areas could be lost. In other parts of the world, the situation is just as precarious, if not worse.

In the Australian north-eastern wet tropics, almost three-quarters of rainforest birds are at risk of disappearing. Elsewhere on that continent, increased severe droughts accompanied by forest fires have decimated the populations of Australian Mallee Emuwren (Stipiturus mallee). Their numbers have now plummeted, and “the largest population now numbers just 100 and is constrained to a 100 square kilometre plot of land. The IUCN warns that a single forest fire could have dramatic consequences, and has listed the species as ‘endangered.” The plight of the Australian Mallee Emuwren is not unique. In fact, many regions on which birds depend may soon become unsuitable due to climate change; “Island and mountain birds may simply have nowhere to go,” and changes may make it impossible for annual migrations to take place.

Figure 2: Arctic terns, whose total yearly migration can equal up to 30,000 miles—the longest among all animal species. Source

A 2007 article by Alister Doyle, “Migratory Birds and Whales Confused by Warming,” revealed that “a warmer climate disrupts the biological clocks of migratory species including bats, dolphins, antelopes or turtles.” These animals are now “the most visible warning signs [or] indicators signaling the dramatic changes to our ecosystems caused in part by climate change,” scientists warn. In North America, “Spring migration is occurring earlier and fall migration later in many species. For example, 25 migratory bird species are arriving in Manitoba, Canada, earlier than they did 63 years ago." As changes between seasons continue to become less clear, many birds are mistiming their migratory pattern. These shifts make them quite vulnerable to heat waves, droughts or cold snaps.

Of particular concern is the fact that some bird populations are abandoning their migrations altogether. For instance, cranes are starting to spend the winter in Germany rather than fly south to Spain or Portugal.” Birds exhibiting this behavior risk remaining in regions that can potentially be too cold for them to survive. In such cases, a single severe winter event could decimate entire populations.

Furthermore, migratory birds “are particularly vulnerable as they depend heavily upon separate breeding, wintering and stop-over sites. Changes to any one of the habitats can put them at risk.” The report Bird Species and Climate Change points out that “climate change is pushing birds out of synchrony with key elements of their ecosystems.” The fact that migratory birds are characteristically very prompt and sensitive responders to any fluctuations in climate leaves them particularly vulnerable. Species of birds that rely on limited areas for their breeding, to which they may travel very long distances, may be pushed out of existence in a large scale much sooner than previously anticipated, while some bird populations are already facing drastic reductions in their numbers. In fact, “Scientists have found declines of up to 90 per cent in some bird populations, as well as total and unprecedented reproductive failure in others.”

With the increase in temperature in the Arctic region, for example, “forests could take over from tundra, complicating life for many birds that nest on the ground and have to fly from Africa to find sites with few predators. [While] Warmer weather could bring predators north.” As climate changes, migratory birds or other endemic species may soon find themselves outnumbered by invasive ones.

Changes in seasonal temperatures and increases in global temperatures also affect the availability and proliferation of insects, which in turn are essential parts of the diets of many bird species. For instance, “Birds are sometimes hatching early in a warmer climate, but sometimes insect food can flourish even earlier. Pied Flycatcher birds in Europe, for instance, have suffered from a lack of caterpillars for their chicks.”

Figure 3: A Whooping Crane—the tallest of all North American flying birds, Source

Hear Cranes Call in Unison

Hear an Adult Crane Give a Warning Call

Take, for instance, the critically endangered Siberian Crane, a wetland migratory bird whose numbers worldwide are down to 3,000 individuals. The cranes breed in the Arctic confines of Russia and Siberia, and spend their winters in the mid or lower ranges of the Yangtze River.

Figure 4 Siberian Crane Migratory Route, from: http://www.npwrc.usgs.gov/resource/birds/cranes/grusleuc.htm

Unfortunately, “this bird’s Arctic tundra habitat is forecast to decline by 70 percent.” The tundra where they breed is not the only climate region on which the cranes rely on that is now in jeopardy, as “decreased precipitation, coupled with more intense rainfall events, also negatively affects the crane in its habitat in China.” Siberian Cranes have not been exempt to other climatic changes, since “Increasing drought due to higher temperatures is thought to be one factor that caused a subpopulation of Siberian Cranes, which once wintered in India’s Keoladeo National Park, to shift out of the park and become locally extinct.”

The Pied Flycatcher serves as another example of a bird species facing similar challenges. These long-distance migratory birds are changing the timing of their migrations in an effort to adapt to climate change. The problem with this measure to keep up with climate change and its impacts is that “the plants and animals they interact with do not shift at the same rate.” In Europe, it has been observed that an earlier spring climax in insect numbers means that Pied Flycatchers “no longer arrive from Africa in time to match food peaks with peak demands of their nestlings.” The species has seen as a result a 90 per cent decline in some of its European populations within the last two decades.

Other bird species have also seen their existence increasingly threatened. In Australia, for instance, desertification and temperature increase are contributing to eliminate the habitat of many different species. For example, “the habitat of the Golden Lowerbird is predicted to shrink by 97.5 per cent with a future warming of 3°C and a 10 percent decline in rainfall,” and an increase beyond 3˚C would cause the bird to disappear entirely. Because the Golden Lowerbird occupies the cooler areas in Australia’s more humid tropics in mountains enclosed by warmer regions, as temperatures rise, the habitat will continue to shrink.

In the United Kingdom, the North Sea saw an apian breeding collapse in the year 2004. The direct cause for this crash was a shortage of sandeels, a small fish essential to the diet of many birds, including the Hercules of all apian migrators: the Arctic Tern. This shortage of food was related to global warming, and according to the World Wildlife Fund Global Climate Change Program, “Warming ocean waters and major shifts in species that underpin the ocean food web are thought to be behind the major sandeel decline.”

The Arctic Terns (see figure 2) demonstrate perfectly how susceptible migratory birds are to climate disruptions, especially since this is a bird whose annual journey round-trip totals between 22,000 and 30,000 miles. Since Arctic terns live up to 30 years, a single one of these 14-17 inches long, two-pound birds may travel during its lifetime more than 650,000 miles. Interestingly enough, Arctic terns see more daylight than any other creature on the planet, “since they are in both the Arctic and Antarctic during the periods of longest days.”

Arctic Terns rely on the North Sea (see the map on figure 7) as a source of food in their long journeys. In the year 2004, the terns saw their habitual feeding stop unable to supply them with enough food. In fact, “no Arctic tern chicks were reared in the south of Shetland [archipelago in Northern Scotland] in 2004. And although hundreds of Arctic Terns arrived at the RSPB’s [a wildlife reserve owned by BirdLife International, UK] Mousa reserve this spring, no young were fledged. All the large Arctic Tern colonies in Orkney [Northern Scotland] failed, and for the first time in living memory, none nested at the RSPB reserve on Papa Westray [also in Scotland].” The Terns were not alone in their plight: “The nearly 7,000 pairs of Great Skuas in the Shetlands [another species dependent on the North Sea for food] produced only a handful of chicks and starving adult birds ate their own young.”

Figure5: An Arctic Tern, and its migration route, from the National Wildlife Federation website.

The collapse of fish productivity in the North Sea in the year 2004 has been called by scientists “a regime shift” because “rising sea temperatures have fundamentally changed the plankton mix to the detriment of sandeels,” the fishes that are essential as part of the diet of the many birds that stop in the North Sea to feed, as reported by BirdLife International in a press release entitled “Seabirds in the North Sea: victims of climate change?” Sandeels also are essential to other links of the marine food chain, which means that other fish and bird species have started to see their numbers drop as well, such as mackerels, cod, or kittiwakes (a seabird). The 2004 collapse “was so severe that fishermen voluntarily shut down the fishery in the worst affected area” of the United Kingdom’s North Sea. The Marine Policy Head of BirdLife International concluded that “We could be witnessing the single biggest change in the North Sea since it was formed 10,000 years ago.”

Figure 6: The North Sea

So what?

We know that bird species are great indicators of climate change—the canary in the coal mine—and as such, they are extremely vulnerable to all the impacts of global warming, particularly the species that depend on food sources in their specific stops along the way during their yearly migrations. We also know that a very significant percentage of these—one in eight bird species, to be precise—are at risk due to a warmer climate. But, why are bird species important in order to keep the ecosystems worldwide healthy?

If we can picture a world in which there’s no seed dispersal, pollination or pest control naturally done, then we’d be picturing a world devoid of bird species which do the planet an essential ecological service. In fact, studies done as to the cost of such services provided by nature to humanity (by insects, birds, plants) were estimated in a 1997 study to be 30 trillion dollars, according to Harvard University Professor Emeritus, E. O. Wilson (from the BBC Planet Earth series, “Saving Species” fragment).

In the case of migratory birds, if we consider their stopping to feed and breed in particular regions in perfect timing with the massive hatching of worms, or any other insect, we have a natural pest and parasite control in these winged pilgrims. And, at the same time, these birds may be essential to nourish other creatures in the same ecosystem, essential predators at a higher level of the food chain. The arrival of these birds to their breeding grounds, the eggs they produce and eventually their nestlings, are an essential source of food for small predators to feed on and to nourish their young. A disturbance in the population and arrival timing of migratory birds would entail problems for all predators that await this annual food bonanza.

The problems faced by bird populations worldwide, and especially by migratory birds that may be traveling up to tens of thousands of miles, mean that drastic changes in any single world region could push a wide variety of bird species out of existence. Human activity responsible for greenhouse emissions is eliminating at unprecedented rates all that too many species need to survive and to keep the ecosystems alive and healthy. Birds such as the Floreana Mockingbird (Nesomimus trifasciatus) of the Galápagos Islands of Ecuador—now a critically endangered bird—is yet another casualty, among countless others. These birds live on two small islands, Champion and Gardner-by-Floreana, and its total population is now fewer than 60 individuals.

Unfortunately for all animal species the very few measures taken to counter global warming can actually be more damaging and make matters worse. The IUCN showed that “In Papua New Guinea, increased cultivation of the palm oil – a source of biofuel – has accelerated deforestation. This, in turn, poses a new threat to bird species including the New Britain Goshawk.” In the words of Stuart Butchart, of BirdLife International, “Species are being hit by the double whammy of habitat loss and climate change […] [and as] populations become fragmented the effect of climate change can have an even greater impact, leading to an increased risk of local extinctions.” Sadly, within decades, the spectacular winged migrations; the singing of so many bird species, and the many ecological services apian species provide for the world and its various ecosystems may all cease to exist.

Figure 7: Cranes. Source

RESOURCES

Additional Resources

*Dr. Terry L. Root and Stephen H. Schneider, who is also a Board Member of the Climate Institute, have published extensively on climate change and its impacts on wildlife and ecosystems.

Some of her published work along with her husband's on ecosystems and climate change impacts appears on her biographical page, at: http://cesp.stanford.edu/people/terrylroot/

*Article entitled "Do changes in climate patterns in wintering areas affect the timing of the spring arrival of trans-Saharan migrant birds?" by Dr. Terry L. Root is available at (abstract):
http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2486.2004.00875.x

*Climate Change: Overview and Implications for Wildlife, by Dr. Terry L. Root and Dr. Stephen H. Schneider is available at: http://stephenschneider.stanford.edu/Publications/PDF_Papers/Overview(1-56).pdf

FLYING IS NO ESCAPE: MIGRATORY BIRDS AND CLIMATE CHANGE

RESOURCES

Organizations:

Articles

Resources on Birds, World Wildlife Fund

Additional Resources