Humpback whales may risk collision with vessels in the Magellan Strait

MAY 14, 2020

by Smithsonian Tropical Research Institute

Every summer (November-April), the Magellan Strait in the southwestern part of Chile becomes a popular feeding area for migrating humpback whales (Megaptera novaeangliae). The narrow strait is also a heavily used shipping route. A new study by scientists at the Smithsonian Tropical Research Institute (STRI) and collaborating institutions tracked and modelled the movement of individual whales in order to evaluate the potential of vessel collisions and provide policy recommendations for the protection of whale species.

Humpback whales have the longest migratory journeys of any mammal on Earth. The Southern Hemisphere population spends its summer months feeding in the Antarctic and Chile and their winters in the warmer tropical Pacific waters of northern South America and Central America, as far as Nicaragua. Their movements often overlap with boat traffic and may put them at risk of collision, leading to injury or death. Years ago, STRI researcher Héctor M. Guzmán led a study that resulted in international regulations to separate vessel traffic from whale routes near the Panama Canal and in southern Costa Rica, which drastically reduced collision rates in the breeding areas.

"Designing and implementing traffic-separation schemes for Panama and Costa Rica was difficult, because any measures had to be adopted by the International Maritime Organization," said Guzmán, also lead author of the new study in Chile. "It was achieved by having the scientific information explain the whale movements and thanks to the unconditional support of both governments."

The new study, published in Marine Policy, took place in southern Chile, where about 100 humpback whales feed each summer: a population small enough for occasional ship strikes to have important consequences. By tagging and tracking 25 individuals over different years and comparing their movements with available records of vessels traversing the Strait, the team found that, on average, each whale was near a ship about seven times per season. Due to the detailed tracking records of multiple whales, the researchers were able to show that individual animals differed enormously in how often they encountered ships: from less than one to as many as 18 encounters per season.

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Caribou migration linked to climate cycles and insect pests

DECEMBER 12, 2019

by University of Maryland

Caribou weakened by harassing insects in the summer take longer to migrate to calving grounds the following spring. This means calves have less time to fatten up before winter. As Arctic summers continue to grow warmer and favor more insects, caribou populations could suffer. Credit: NPS/Kyle Joly

Caribou, the North American cousin of reindeer, migrate farther than any terrestrial animal. They can cover thousands of miles as they move between winter feeding grounds and summer calving grounds. But many caribou herds are in decline as the warming climate changes much of the landscape they depend on. Inedible shrubs are rapidly encroaching on the tundra, and more frequent forest fires and disease are destroying the trees that provide caribou with lichen for food. The role of climate on their migration patterns has never been well understood, but knowing what drives caribou movements is crucial to predicting the future for the iconic species that plays a key roll the ecological and economic stability of the Arctic region.

A new study led by a University of Maryland biologist discovered two unexpected drivers for migration timing that dispute long-held assumptions and provide insight into potential future effects of climate change on caribou. First, the study found that caribou herds all across North America are triggered to start spring migration at roughly the same time by large-scale, ocean-driven climate cycles. Second, despite a synchronized start, arrival at their respective calving grounds depends on the previous summer's weather conditions. Warm, windless summers that favored insect pests lead to poorer maternal health and delayed arrivals at the calving grounds the following spring.

The study, which accounted for approximately 80% of all North American migratory caribou, is the largest caribou migration study to date. It was published in the December 12, 2019 issue of the journal Ecosphere.

"This was completely unexpected," said Eliezer Gurarie, an associate research scientist in UMD's Department of Biology and lead author of the study. "There was no reason to think that herds that calve near the Hudson Bay in the East would begin migration at the same time as the herds along coastal Western Alaska, or that summer conditions would play an important role in the following spring migration. Prior to this, it had been assumed that migration timing depends on some combination of snowmelt and availability of useful vegetation at the endpoint of the migration. Neither of those held up."

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Migrating mule deer don't need directions, study finds

Date: August 23, 2019

Source: University of Wyoming

How do big-game animals know where to migrate across hundreds of miles of vast Wyoming landscapes year after year?

Among scientists, there are two camps of thought. First is that animals use local cues within their vicinity to determine where to migrate. Animals might move up to areas with greener forage -- often termed green-wave surfing -- or move down from mountains with deeper snow. The second idea is that animals develop memory of the landscape where they live and then use that information to guide their movements.

Recent research from the University of Wyoming has found that memory explains much of deer behavior during migration: Mule deer navigate in spring and fall mostly by using their knowledge of past migration routes and seasonal ranges.

The study found that the location of past years' migratory route and summer range had 2-28 times more influence on a deer's choice of a migration path than environmental factors such as tracking spring green-up, autumn snow depth or topography.

"These animals appear to have a cognitive map of their migration routes and seasonal ranges, which helps them navigate tens to hundreds of miles between seasonal ranges," says the lead author of the paper, Jerod Merkle, assistant professor and Knobloch Professor in Migration Ecology and Conservation in the Department of Zoology and Physiology at UW.

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Monarch butterflies bred in captivity may lose the ability to migrate, study finds

JUNE 24, 2019

by University of Chicago

Monarch butterflies purchased from a commercial breeder did not fly in a southward direction, even in offspring raised outdoors, in a new study conducted by scientists at the University of Chicago. Wild-caught monarchs bred indoors under simulated outdoor conditions also did not orient south, suggesting that captive breeding disrupts the monarch's famous annual migratory behavior.

The National Wildlife Federation estimates that the North American monarch population has declined 90% over the last two decades. As the number of butterflies that reaches their winter habitats in California and Mexico dwindles, monarch enthusiasts have turned to a variety of conservation efforts, including captive breeding and release of the butterflies throughout the summer and autumn. However, the new study, published this week in the Proceedings of the National Academy of Sciences, shows that these well-intentioned practices may not have the desired effect.

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Migrating blue whales rely on memory more than environmental cues to find prey

Date:  February 26, 2019

Source:  Oregon State University

Blue whales reach their massive size by relying on their exceptional memories to find historically productive feeding sites rather than responding in real time to emerging prey patches, a new study concludes.

Researchers examining records of both whale migration and oceanic conditions in the California Current Ecosystem found that blue whales almost perfectly match the timing of their migration to the historical average timing of krill production, rather than matching the waves of krill availability in any given year.

The findings suggest that blue whales locate prey by relying on memory to return to stable, high-quality foraging sites, which historically have served them well but could make it difficult for the whales to adapt if novel ecosystem changes emerge as a result of climate change.

Results of the study are being published next week in Proceedings of the National Academy of Sciences.

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How a Painted Turtle Finds Its Way – via Herp Digest

Unlike many species, this common reptile migrates from memory

By Timothy Roth, Aaron R. Krochmal from Blogs Scientific American January 30, 2019

Animal migration is one of the most charismatic, awe-inspiring phenomena of the natural world. Faced with unfavorable, often seasonal, changes in climate or habitat quality, animals, from birds to butterflies and wildebeests to sea turtles, migrate vast distances—often thousands of miles—in search of more favorable conditions. They return the following year, in many cases to the exact location where their journey began.

We know that some species use the Earth’s magnetic field to navigate with GPS-like precision and others gaze skyward and guide their migration by the stars. We are just now learning that for some animals, the key to a successful migration is all in their heads—complex thought and memory are also necessary for a successful migration.

For nearly a decade, we have studied the roles of cognition, learning and memory in the migration of a fairly atypical species—the painted turtle, common to neighborhood ponds and roadside ditches. Yep, that turtle—the one you see in virtually every small body of water in the Eastern U.S., as well as occasionally crawling through your backyard or crossing the road by the grocery.  

They’re not as charismatic as sea turtles, and they sure don’t travel as far (several kilometers for a painted turtle versus several thousand kilometers for a sea turtle), but what they lack in outward charisma they make up in tenacity. When these turtles take to land each summer, migrating to new habitats when their home ponds dry up, they face seemingly insurmountable odds: scorching heat, dehydration, and the crushing tug of gravity (you can’t just float around anymore). And that’s not to mention the new predatory threats from both land and air, and the ever-present threat of vehicles when crossing a road. For a painted turtle, there’s a lot going on during migration.

Painted turtles at our research site, which is on conservation land within a patchwork of old growth woodlands and agricultural fields, follow long, intricate routes with amazing precision—specific to within a few meters—to far-off, permanent water sources year after year, returning home again when the seasons next change. Is this behavior instinctual or learned?

To see just where this incredible migratory behavior came from, we introduced into our site animals without any experience migrating there and monitored their ability to respond to seasonal changes in their habitats. Would they be able to migrate successfully?

For some, yes. Naive juveniles under four years old learned to navigate the complex paths just as precisely as experienced local turtles and were able to locate far-off water sources. Naive adults could not. These results suggest a narrow age window, or critical learning period, in which animals must learn to navigate. This phenomenon is not unlike the process of language learning in humans.

But how can they do this? How can a turtle possibly think its way through migration?

They do it the same way that we do: they form and remember memories of space and place using the neurotransmitter acetylcholine, just like humans. 

Acetylcholine has long been known to play a role in spatial memory in mammals. To test whether the turtle brain also works this way, we gave freely migrating turtles (both experienced adults and naive juveniles) mind-altering drugs that temporarily block acetylcholine in their brains.

While the drugs were active and the turtles were without access to spatial memory, the adults with previous experience in the system wandered aimlessly and were unable to follow their traditional migration routes. As soon as the drugs wore off, they got right back on track and were able to successfully migrate to their winter home. 

And what about naive juvenile turtles? They were unaffected by the drug; they followed the paths perfectly whether on the drug or not. Why? They had no memory to disrupt! This demonstrates that adults use spatial memory to navigate during migration, and that they form these memories as juveniles prior to the age of four. This type of higher-order cognitive processing during migration has been previously attributed only to birds and mammals.

For some, yes. Naive juveniles under four years old learned to navigate the complex paths just as precisely as experienced local turtles and were able to locate far-off water sources. Naive adults could not. These results suggest a narrow age window, or critical learning period, in which animals must learn to navigate. This phenomenon is not unlike the process of language learning in humans.

They do it the same way that we do: they form and remember memories of space and place using the neurotransmitter acetylcholine, just like humans. 

Acetylcholine has long been known to play a role in spatial memory in mammals. To test whether the turtle brain also works this way, we gave freely migrating turtles (both experienced adults and naive juveniles) mind-altering drugs that temporarily block acetylcholine in their brains.

While the drugs were active and the turtles were without access to spatial memory, the adults with previous experience in the system wandered aimlessly and were unable to follow their traditional migration routes. As soon as the drugs wore off, they got right back on track and were able to successfully migrate to their winter home.

 And what about naive juvenile turtles? They were unaffected by the drug; they followed the paths perfectly whether on the drug or not. Why? They had no memory to disrupt! This demonstrates that adults use spatial memory to navigate during migration, and that they form these memories as juveniles prior to the age of four. This type of higher-order cognitive processing during migration has been previously attributed only to birds and mammals.

So, it turns out that if you’re a turtle, migration is more than just showing up and muddling through on instinct; you actually have to pay attention and think. And for the turtles, that’s a good thing.

Challenging environments—those with the most extreme, highly variable conditions—tend to produce animals with advanced cognitive abilities, including flexibility in learning and memory.

As climate change continues to disrupt environments, animals will have to rely on cognition to learn new things, including altering the timing, direction and destination of their migrations.

So even though the odds are stacked against them, maybe, just maybe, turtles can outsmart the impacts of climate change.

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https://blogs.scientificamerican.com/observations/how-a-painted-turtle-finds-its-way/#googDisableSync

For authors background-background-see bottom of page

The views expressed here are not necessarily those of Scientific American

Outdoors: Monarch butterfly’s decline should be a sign

By Glenn Ayers / Times-News correspondent

Posted Oct 27, 2018 at 9:06 PM

As per annum, the monarch butterflies are on their migratory move to Mexico.

Accompanying them this year is their champion, Lincoln Brower, with a flight of angels singing him to his rest. He passed away in July at age 86.

Brower, the leading authority on this species, is world-renowned for his work in the field. A biology professor at Sweet Briar College, he wrote his PhD dissertation on butterflies, and has worked steadily to understand and resist the monarch’s decline in numbers.

He well understood the mysterious migration of the monarchs, never discovered until 1976, when the mountain peaks were located that held millions on millions of the fliers wintering in fir trees. They are parents and grandparents (no single one does the full odyssey) of the monarchs that began their fall journey from as far away as the Canadian Atlantic provinces and proceeded to Mexico — 3,000 miles away.

In spring, they will head back north.

How? Brower could only answer, “If you’ve ever looked inside of the brain of this butterfly, it’s about the size of a pinhead, and yet the mini-computer inside that pinhead has all the necessary information to get them to Mexico without having been there before.”

The key to the miracle is food for the journey. Though they feed on goldenrod, lilacs and thistle, their survival depends on milkweed which is the only food for their caterpillars. This plant’s destruction from herbicides, pesticides and maybe climate change, has caused a 90 percent decline in monarch populations during the last 20 years.

Brower spent much of his life dedicated to the preservation of this species, from fighting chemical killers and agricultural clean-field measures, to protecting Mexican fir trees. Why?

He saw the monarch’s free fall as a warning sign of something larger.

“The monarch is whispering to us that things aren’t quite right,” he said. “Bio-diversity has to have a chance. Otherwise, we will eliminate ourselves in the process. That’s a pretty strong statement, but I believe it’s true.”

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International Turtles, National Laws- Migrating marine species experience inconsistent protections as they travel the world. - via Herp Digest

by Erin Van Rheenen, Hakai Magazine, 10/11/18

Leatherback turtles—nearly two meters long and weighing up to 500 kilograms—are built to move. They are the only sea turtle to have tough, ridged, rubbery skin instead of a hard shell, and their streamlined shape and powerful front flippers enable them to swim thousands of kilometers through the open ocean during their migrations.

In their multi-year journeys, leatherback turtles face a variety of lethal threats, from ingesting plastic debris to being caught as by-catch by commercial fishers. Yet the protections leatherback turtles get during various stages of their journeys can vary wildly. According to a new study, leatherback turtles will frequently cross through the waters of as many as 30 different countries, each with its own set of laws and enforcement capabilities.

Leatherback turtles are not the only species to face such shifting protections. In the new paper, Autumn-Lynn Harrison, an ecologist at the Smithsonian Conservation Biology Institute, and her colleagues used tracking data to analyze the movements of 1,648 individual animals from 14 species—from white sharks to sooty shearwaters to leatherbacks. They found that, cumulatively, these animals visit 86 percent of Pacific Ocean countries during their migrations.

The study used data from the Tagging of Pelagic Predators (TOPP) program, which began tracking the movements of predators throughout the Pacific Ocean in 2000. To date, more than 200 scientific studies have been based on this data set.

Bryan Wallace, a marine conservationist at Conservation Science Partners and an expert in global leatherback population dynamics who was not a part of this recent study, lauds the fact that extensive, hard-won data sets like TOPP continue to be put to use to try to answer “tangible questions.” He says Harrison’s study “provides a strong scientific foundation for the more challenging geopolitical and resource management discussions.”

The international travel of leatherbacks and other marine species makes conservation efforts challenging, Harrison says. Coastal nations pass laws to exploit or protect marine life, but these regulations only extend up to 370 kilometers from each country’s shoreline in what is called its exclusive economic zone (EEZ). Outside of EEZs lie the high seas, a global commons that is one of the least protected areas on Earth—and one in which the studied species spend the majority of their time.

Wallace points out that in the high seas, technologies designed to reduce by-catch, such as circle hooks, are not required, though some fleets and boats do use them. In contrast, other areas have stringent regulations—such as near the leatherback turtle nesting beaches in Las Baulas National Marine Park, on the northwest coast of Costa Rica, where fishing of any sort is prohibited.

Harrison presented her research at the recent United Nations meeting in New York, where diplomats were negotiating the world’s first legally binding treaty for the high seas. She says she left the meeting feeling optimistic. 

“There wasn’t complete consensus on whether there needs to be global oversight, but I did feel a pretty overwhelming sense that, globally, nations know that something needs to change in the high seas.”

Harrison hopes her research will provide critical information for designing international agreements to protect at-risk species as they travel through multiple jurisdictions and across the open ocean.

Big game animals must learn to migrate and pass knowledge across generations

Date:  September 6, 2018

Source:  University of Wyoming

A team of scientists at the University of Wyoming has provided the first empirical evidence that ungulates (hooved mammals) must learn where and when to migrate, and that they maintain their seasonal migrations by passing cultural knowledge across generations.

The results were reported today in Science.

Biologists have long suspected that, unlike many bird, fish and insect migrations that are driven by genetics, ungulates learn to migrate from their mothers or other animals in the herd. Previous research had hinted that migration was socially learned in ungulates, but a clear test had eluded researchers until now.

The authors of the study made use of a grand experiment that has been occurring across the American West over the last 60 years. After hunting and disease triggered the loss of bighorn sheep across much of their range, a cadre of dedicated wildlife managers, hunters and conservationists pioneered translocation programs to re-establish lost herds. Bighorn sheep from the few populations that persisted continued to migrate; some of these animals were captured and released into landscapes where bighorn sheep occurred previously. The conservation effort has been successful in establishing many new "translocated" herds.

"The pattern was striking," says lead author Brett Jesmer, a doctoral student at UW. "Detailed GPS data revealed that fewer than 9 percent of translocated animals migrated, but 65 to 100 percent of animals migrated in herds that had never been lost."

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For the first time, biologists track cownose rays to Florida and back

August 23, 2018, Smithsonian

Every summer, cownose rays stream into Chesapeake Bay to mate and give birth to their pups. When autumn comes, they disappear—presumably to migrate south, but no one knew for certain where they spent the winter. Now, after a three-year tagging study published Aug. 23 and led by the Smithsonian Environmental Research Center (SERC), scientists have solved the mystery. Cownose rays all along the Atlantic winter near Cape Canaveral, Florida, and it is likely they return to the same spots each summer.

Cownose rays are large stingrays native to the Chesapeake, with dark brown or olive-gray backs and white bellies. They reproduce slowly. Most mothers give birth to only one pup a year, and they do not mature until age 7 or 8, making them vulnerable to intense fishing or sudden population declines. And yet cownose rays have been dogged by controversy. In the early 2000s, they were saddled with partial blame for oyster declines because their diet includes shellfish. (Later studies cleared their names. Oysters had been declining years before cownose rays became more abundant.) Later, in 2015, bowfishing tournaments for cownose rays began raising alarm among some Marylanders. In response, the Maryland government voted to become the first state to create a fishery-management plan to conserve the cownose ray.

"Because of the slow birth rate, we know that if we don't manage them, and instead harvest them in a way that heavily impacts the population and causes a population decline, it'll take a long time for them to recover," said Matt Ogburn, SERC marine biologist and lead author of the study. "If we lose something important, we could lose it for decades."

The new study, published in Marine Ecology Progress Series, marks the first time scientists have tracked cownose ray migrations along the Atlantic coast for a full year or more. Knowing where they go every year will help fill in some longstanding knowledge gaps about the rays, as Maryland officials decide how to manage them. It is part of the Smithsonian's new Movement of Life Initiative. Scientists from the Virginia Institute of Marine Science (VIMS) and Savannah State University also joined the effort.

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Monarchs ride west coast winds: Proof of butterfly migration gathered

June 25, 2018, Washington State University

After five years and nearly 15,000 tagged butterflies, scientists now have proof that Monarch butterflies migrate from the Pacific Northwest to California in late summer and fall, a journey averaging nearly 500 miles.

Most of the tagging was done by citizen scientists and inmates from the Washington State Penitentiary in Walla Walla. The prisoners are carefully trained in raising, tagging, and releasing Monarchs.

The findings were recently published in the Journal of the Lepidopterists' Society. WSU entomology professor David James spearheaded the project, which took a massive amount of time and coordination to put together, ultimately involving hundreds of volunteers. The research was unfunded, making the volunteers indispensable.

Long distance travelers

"On average, these butterflies averaged almost 40 miles of travel each day," James said. "That's pretty remarkable for such a small creature."

Though scientists don't know exactly how the butterflies travel that far, they suspect the Monarchs may ride warm air currents called thermals a few thousand feet up in the air, then use the strong upper-air currents to navigate, James said.

The paper covered the initial five years of the project, from 2012 to 2016. Participants tagged and released 13,778 Monarchs that were raised in captivity and tagged 875 wild Monarchs. More than one-third of the raised Monarchs were reared by inmates at Walla Walla, James said.

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Moths fly 1000 kilometres with Earth’s magnetic field as a guide

21 June 2018

Eric Warrant

By Michael Marshall and Andy Coghlan

An Australian moth uses the Earth’s magnetic field to help find its way across the continent. While other insects have been shown to navigate using Earth’s magnetic field, the moth is the first to do so over long distances and at night.

Bogong moths (Agrotis infusa), like the famous monarch butterflies in the Americas, make an epic migration. In spring, about 2 billion of them leave their breeding grounds on the dry, flat plains of south-east Australia, and fly over 1000 kilometres to …

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Could we predict the next Ebola outbreak by tracking the migratory patterns of bats?

Lehigh University researchers' framework tracks the ecological drivers of bat migration patterns to predict the next Ebola outbreak

Date: May 22, 2018

Source: Lehigh University

Javier Buceta, associate professor of bioengineering, Paolo Bocchini, associate professor of civil and environmental engineering, and postdoctoral student Graziano Fiorillo of Lehigh University have created a modeling framework that takes a zoonotic perspective on Ebola.

The team's approach works by tracking the migratory patterns of bats, which are believed to be a main carrier of the Ebola virus. Bats, in this instance, are the reservoirs of Ebola. This means that they are carriers and transmitters of the virus, though it does not cause them harm.

"In our model, the appearance of outbreaks is tightly linked to fluctuations in environmental conditions which have an impact on both bat migration patterns and infection rates," says Buceta.

Buceta, Bocchini and Fiorillo worked with satellite information and parameter sampling techniques to create their framework, which integrates data and modeling to predict the conditions linking bats' behavior with the outbreak of Ebola. They have detailed their work in a paper titled "A Predictive Spatial Distribution Framework for Filovirus-Infected Bats" published online today in Scientific Reports.

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Longest recorded whale shark migration eclipses 20,000 kilometers

by Mongabay.com on 14 May 2018

Scientists followed the movements of a whale shark for nearly two and a half years as she swam more than 20,000 kilometers (over 12,000 miles) from the coast of Central America to the Marianas Trench near Asia.

Whale sharks, whose numbers have dropped by more than half in the past 75 years according to the IUCN, are taken by fishing boats for their fins, cartilage, meat and teeth, and studies have shown that boats bringing tourists to swim with the largest fish in the ocean change the species’ behavior.

Given these threats, scientists hope studies such as this one will help guide conservation policy aimed at protecting these animals throughout their migrations.

A team of scientists has tracked a whale shark (Rhincodon typus) across more than 20,000 kilometers (over 12,000 miles) of ocean, the longest migration ever recorded for the species.

In 2011, the researchers attached a transmitting tag to a shark they named “Anne” in the Pacific Ocean near Panama’s Coiba Island. Over the next 841 days, Anne’s transmitter would ping the ARGOS satellite whenever she swam near the surface. Those data points allowed the team to follow her movements south to the Galapagos Islands and clear across the Pacific to the Marianas Trench south of Japan and east of the Philippines — a distance of 20,142 kilometers (12,516 miles).

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Vulnerability and extinction risk of migratory species from different regions and ecosystems worldwide

Date:  March 26, 2018

Source:  University of California - Santa Barbara

Summary:

Forty million miles of major roads crisscross the Earth's continents -- enough to circle the planet 1,600 times. For humans, these thoroughfares are a boon, enabling them to move with ease from place to place. But for migrating animals who are also hemmed in by dams, rivers, shipping lanes, urban development and agriculture, they create another barrier.

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Ocean winds influence seal pup migration

Date:  February 13, 2018

Source:  American Geophysical Union

Summary:

Scientists have confirmed what native Alaskans have observed for centuries -- maritime winds influence the travel patterns of northern fur seal pups. New research shows strong winds can potentially displace seal pups by hundreds of kilometers during their first winter migration.

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To breed or not to breed? Migratory female butterflies face a monsoonal dilemma

Date: October 3, 2017

Source: National Centre for Biological Sciences

What do CPUs, stockbrokers, and butterflies have in common? They are good at investing their resources in the right place at the right time so as to maximize their returns! Trade-offs are a way of life for butterflies and other small insects that must budget their energy between numerous morphological features and activities during their short lifespans. Time, food, and space are always at a premium, and optimizing resource use is particularly important for migratory butterflies that must prepare for arduous journeys in uncertain environments. A new study by researchers at the National Centre for Biological Sciences (NCBS-TIFR, Bangalore) reports on butterfly migrations in peninsular India and explores the effect of migration on resource investment strategies of migratory butterflies. It reveals that migration affects the morphology and physiological states of female butterflies much more prominently compared to that of males.

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‘Devil weeds’ threaten wildebeest migrations in Serengeti

13 June 2017

By Andy Coghlan

With names like “devil weed” and “famine weed”, perhaps it’s little wonder that these invasive plant species threaten to disrupt one of the great wonders of the world: the annual migration of 2 million animals across the savannahs of eastern Africa.

Initially planted for decoration at tourist lodges in Kenya’s Masai-Mara National Reserve, the invasive species are now spreading into and displacing natural vegetation out on the savannah. The large animals that cross these grasslands each year depend on them for food.

That’s the grim message from a new survey of the spread of invasive exotic plants in the Serengeti-Mara ecosystem, focusing on six species that pose the most serious threat to the migrating animals.

“Rampant invasions in the Serengeti-Mara ecosystem will certainly reduce forage production, leading to drastic declines in the populations of wildebeest, zebras and other large grazing mammals,” says Arne Witt of CABI Africa in Nairobi, Kenya. “These invasive plants are toxic or unpalatable, meaning there’s less forage available for wildlife to feed on.”

One invader, called famine weed (Parthenium hysterophorus), has already been shown to displace 90 per cent of food in fields for livestock, and the effects would be the same for wildlife, says Witt.

Already, the animals’ food sources have been hit by drought and depletion of the Mara river, so their plight could be exacerbated if the plants continue to spread. The survey shows that the species are already infiltrating areas of grassland, creating impassable thickets of inedible vegetation where once there was only grass.

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