A spate of new research studies has confirmed a disturbing pattern: climate disruption is confusing migratory birds, causing trees to relocate and allowing tropical diseases to spread northward. “Human society has yet to appreciate the implications of unprecedented species redistribution for life on Earth, including for human lives,” states a study, “Divergence of Species Responses to Climate Change,” published May 17, 2017, in Science Advances.
Imagine if you had to travel thousands of miles and arrive at a specific time each year, but you had no way of knowing the precise time you needed to get there. That’s what it’s like for many songbirds that migrate from Central and South America each spring to breeding grounds in the US and Canada. If they were to arrive too early, they wouldn’t find food and could freeze to death. If they arrive late, the best nesting sites may be taken and there will be fewer opportunities to find a mate.
For countless generations, these birds have been able to rely on seasonal signals such as the length of daylight. That hasn’t changed of course, but now, due to a rapidly changing climate, the conditions at their summer homes may not be what they’ve come to expect, according to another study published May 15 in Scientific Reports.
“We’re seeing spring-like conditions well before birds arrive,” said lead author Stephen Mayor, a postdoctoral researcher with the Florida Museum of Natural History at the University of Florida, in a press release. “The growing mismatch means fewer birds are likely to survive, reproduce and return the following year.”
This groundbreaking study combined 12 years of NASA satellite imagery tracking the arrival of spring greenery, with citizen-collected science data extracted from eBird, which records more than 60 million observations a year. An online tool used by amateur and professional bird watchers, eBird is a joint project of the Cornell Lab of Ornithology and the National Audubon Society.
“It’s powerful. Whether they know it or not, birders are helping scientists do their work, and they could end up helping birds in the process,” stated study co-author Rob Guralnick, Associate Curator of Bioinformatics at the Florida Museum.
The researchers looked at 48 species of songbirds and found that the average gap between the onset of spring and the arrival of these birds has lengthened by half a day per year, or five days per decade. Nine of these species fell further behind, losing a full day or more per year. Those struggling most were great crested flycatchers (Myiarchus crinitus), indigo buntings (Passerina cyanea), scarlet tanagers (Piranga olivacea), rose-breasted grosbeaks (Pheucticus ludovicianus), eastern wood pewees (Contopus virens), yellow-billed cuckoos (Coccyzus americanus), northern parulas (Setophaga americana), blue-winged warblers (Vermivora cyanoptera) and Townsend’s warblers (Setophaga townsendi).
“If anything could adapt to climate change, you’d think that birds that migrate thousands of miles could,” Mayor said. And that may happen, but it will take many generations, as evolution selects for earlier-arriving birds. Adding to the complexity, these scientists also found that greening is beginning earlier in eastern forests and later in western forests in the US.
All this is happening while forest trees themselves are moving in response to a disrupted climate. Yet another corroborating study, led by Purdue University and published May 17, 2017, in Science Advances, looked at 86 species of trees in the US over three decades. Researchers found that 73 percent shifted westward and 62 percent shifted northward, including some species that moved simultaneously in both directions. Of course, the trees themselves don’t move, but over time, the highest concentration for each species has been notably shifting.
The movement has thus far been greater in the westerly direction, equaling 50 feet per decade. Northward movement was measured at 36 feet per decade. The shifts are attributed to changes in precipitation and temperature — both outcomes of climate destabilization.
Another study on vegetation migration was carried out by scientists at the University of Tennessee at Knoxville (UT), published May 8, 2017, in Science Daily. That research, like Purdue’s analysis, found trees in the Rocky Mountains moving northward. “One general expectation is that tree ranges will gradually move toward higher elevations as mountain habitats get hotter,” said Michael Van Nuland, the project’s lead researcher and a doctoral student in UT’s Department of Ecology and Evolutionary Biology. “It is easy to see the evidence with photographs that compare current and historical tree lines on mountainsides around the world. Most document that tree lines have ascended in the past century.”
In Europe, 34 percent of timber forests will be suitable only for Mediterranean vegetation by 2100, according to the Purdue University study. Looking at the redistribution of species under climate disruption, the authors found many other changes coming. “For marine, freshwater, and terrestrial species alike, the first response to changing climate is often a shift in location, to stay within preferred environmental conditions,” they wrote.
Of more than 4,000 species studied around the world, half are relocating, says National Geographic. In the Arctic, brown bears (Ursus arctos) are expanding their range northward, in some cases competing with and even mating with polar bears (Ursus maritimus). Beavers (Castor canadensis) have been found as far north as the coast of the Beaufort Sea. The list includes mammals, amphibians, fish and insects.
“Movement of mosquitoes in response to global warming is a threat to health in many countries through predicted increases in the number of known and potentially new diseases,” states an additional report titled “Biodiversity Redistribution Under Climate Change: Impacts on Ecosystems and Human Well-Being,” from an international team of 41 scientists, published March 31, 2017, in Science. The World Health Organization (WHO) counted 212 million new cases of malaria in 2015, primarily in Africa, Southeast Asia and the eastern Mediterranean. But climate change will allow the disease to spread to new areas, according to the University Corporation for Atmospheric Research (UCAR) Center for Science Education.
That will be a problem for health officials. “Climate-related transmission of malaria can result in epidemics due to lack of immunity among local residents and will challenge health systems at national and international scales, diverting public and private-sector resources from other uses,” state the authors of the UCAR report.
Other insect-borne diseases are on the rise due to climate change as well. Of the approximately 3,500 species of mosquito around the world, according to the Centers for Disease Control (CDC), only a hand-full carry and transmit the dreaded West Nile virus, dengue fever and the lesser-known Chikungunya. West Nile claimed 146 lives in the US in 2015 while an island-wide epidemic in Puerto Rico in 2007 tallied 10,000 cases. Black-legged ticks (Ixodes scapularis), which carry Lyme disease as well as other deadly pathogens, have spread to 41 states as the blood-sucking bugs enjoy warmer, shorter winters.
“The natural world is very complex,” said the University of Florida’s Stephen Mayor. “When you kick it with a big change by altering the climate, different parts of that natural world respond in different ways. We’re just beginning to understand the consequences of this grand unnatural experiment.”
Atop Maine’s Bradbury Mountain, for the past 11 years, a lone volunteer spends his or her days from March 15 to May 15, scanning the skies for birds. It is often cold and windy into late April, sometimes requiring snowshoes to ascend the summit. From the rounded granite top of the mountain, the view extends outward to the ocean. It’s the site of the northernmost hawk watch in the Eastern Flyway — one of the major north-south routes for migratory birds in North America. Ospreys (Pandion haliaetus), bald eagles (Haliaeetus leucocephalus) and broad-winged hawks (Buteo platypterus) can be seen and counted, soaring above the tall white pines and iconic sugar maple trees.
“It has not escaped our attention that they are recording increasing numbers of raptors while the more southern hawk watches are showing an opposite trend,” stated the 2016 spring Eastern Flyway Report, published by the Hawk Migration Association of North America (HMANA). “This coupled with the dramatic decrease in more northern migrants such as the northern goshawk (Accipiter gentilis), which are at 32 percent of historical values for the Eastern Flyway this year, leads us to consider if climate change is a potential factor.”
On a positive note, citizen science is increasingly coupling with academics, scientists and government researchers from around the world to document the disruption to wildlife wrought by human-caused destabilization of the climate. These volunteers help to create a more scientifically complete picture of what is happening in the natural world. “It’s like ‘Silent Spring,’ but with a more elusive culprit,” added Mayor. “These are birds people are used to seeing and hearing in their backyards. They’re part of the American landscape, part of our psyche. To imagine a future where they’re much less common would be a real loss.”