Dragonflies Make Epic Migrations, But Climate Change Could Foil Their Itineraries
By Jason Bittel
It's that time of year again: Right now, monarch butterflies are taking wing in the mountains of northwestern Mexico and starting to flap their way across the United States.
The great monarch migration always makes headlines, in part because climate change, along with our pesticides and agricultural monocultures, threatens to erase the natural spectacle, but also because this natural phenomenon is simply amazing. The trip of nearly 5,000 miles is an unlikely one for an insect, but these butterflies don't have a monopoly on the massive, multigenerational migration game.
It's time to give some love to the epic feats of dragonflies.
According to a study published by the Royal Society last fall, common green darners, which are found from Cuba to Canada, make a long, complex journey that takes three generations and spans a distance of more than 1,500 miles. Scientists are still trying to figure out exactly how they do it, but temperature seems to play a key role in telling the animals when to move. Unfortunately, this means climate change could well wreck the whole event even before we fully understand it. Worse, it would leave much of eastern North America without an important member of its food web.
The news that dragonflies migrate probably won't shock people who study insects, says the study's senior author, Colin Studds, a wildlife ecologist at the University of Maryland. "We've had an inkling of how many insects migrate," he said. "There are moths, there are beetles, and there are probably about 20 species of dragonflies that we have expected of migration. But we don't know much about it other than that it's a phenomenon."
One of the reasons why insect migration remains so much of a mystery is that bugs are tough to track. They're tiny, they die all the time, and they're quick as heck — especially dragonflies. "Unlike monarchs, common green darners are fast fliers," said MaLisa Spring, state coordinator for the Ohio Dragonfly Survey at the Museum of Biological Diversity just north of Columbus. "This makes them hard to catch and potentially add identification tags or stickers, and even harder to photograph. Most photo observations are a blur of blue and green, so a tiny sticker doesn't work so well."
This is why Studds and his coauthors decided to study where the dragonflies had been, rather than where the critters were heading. To do this, they took tissue samples from the wings of more than 850 green darners, some collected from the wild and others from museum specimens going back 140 years. A molecular analysis of the wings allowed the scientists to identify hydrogen isotopes that revealed the latitudes at which the dragonflies were born. (These isotopes vary at reliable rates as one moves north or south, so determining which ones are present and in what quantities can drop a pin of origin within about 100 to 200 miles.)
The team also made use of 21 years' worth of citizen science data to understand when and under what conditions dragonflies appear across their vast range. With all of these pieces put together, common green darner migration patterns are no longer so much of a blue-green blur.
Tina Vance / Flickr
In February the dragonflies appear only in warm latitudes, which is reflected in data showing dragonfly emergences at this time in Florida, Louisiana and Texas, as well as Puerto Rico, Cuba and southern Mexico. But come March, this first generation has already winged it up to the American Northeast, the Great Lakes region and southern Canada. And then those well-traveled dragonflies mate, lay eggs and die.
In May and June, the second generation hatches onto the scene. Some live their whole lives locally, but others — driven by what, we do not know — point their beautiful compound eyes south. Between September and November, these snowbirds don floral shirts and sunglasses and can be found flitting around the southern U.S. and Caribbean. Like the first generation, these dragonflies mate, lay eggs and die.
This leaves us with the third generation in the cycle, which are the population's homebodies. Because winter hits the south soon after they hatch, and they definitely don't want to head north to even colder climes, these lucky darners live out their life span locally. And then they ... mate, lay eggs and die like the rest. Their offspring then hatch around February, transform from larvae to adults, and head up north, starting the cycle anew.
The great dragonfly migration has likely been taking place for many millennia. Each generation has a job to do and an itinerary to follow, and every step is tied to a specific temperature range.
"So one of the things that we figured out from the citizen science data of over 20 years across the whole eastern United States is that the dragonflies don't begin migrating until it gets to about 9.5 degrees Celsius, or just shy of 50 degrees Fahrenheit," said Studds. "They kind of wait for it to go up to that point and they follow that temperature north."
Enter climate change. Temperature patterns are shifting all over the U.S. (indeed, the whole planet), and research on monarchs is already showing that such fluctuations may affect how the butterflies inoculate themselves against parasites. Could there be similar consequences for other migratory insects?
"If we are moving into a period where winter temperatures are warming and spring temperatures are getting warmer through time, then that will probably affect the entire timing and pace of dragonfly migration," said Studds. "It will affect how far north they go and how quickly they develop."
In some areas, warmer temperatures year-round may mean dragonflies won't even need to migrate at all. This isn't necessarily bad for the darners, mind you. But because dragonflies are important predators of mosquitoes, aphids, and other insects, as well as nutritious food for ducks, toads, newts, fish and even carnivorous plants like sundew, losing a seasonal influx of these creatures could ripple out through North America's ecosystems. (Plus, dragonflies are beautiful, and people up north will miss them.)
The truth is, scientists still know very little about how these seasonal shake-ups will affect wildlife, and common green darners and monarch butterflies are just two species among many that are facing big changes. But given that insects are experiencing dramatic declines worldwide, we need to unpack as many of these little mysteries as we can now — instead of trying to piece the puzzle back together after it's too late.
Reposted with permission from our media associate onEarth.
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Natural gas is a versatile fossil fuel that accounts for about a third of U.S. energy use. Although it produces fewer greenhouse gas emissions and other pollutants than coal or oil, natural gas is a major contributor to climate change, an urgent global problem. Reducing emissions from the natural gas system is especially challenging because natural gas is used roughly equally for electricity, heating, and industrial applications.
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="6bd9fda1316965a9ba24dd60fd9cc34d"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/3KaMnkmf0tc?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span>
What RNG Is and Why it Matters<p>Most equipment that uses energy can only use a single kind of fuel, but the fuel might come from different resources. For example, you can't charge your computer with gasoline, but it can run on electricity generated from coal, natural gas or solar power.</p><p>Natural gas is almost pure methane, <a href="https://www.eia.gov/energyexplained/natural-gas/" target="_blank">currently sourced</a> from raw, fossil natural gas produced from <a href="https://www.eia.gov/energyexplained/natural-gas/where-our-natural-gas-comes-from.php" target="_blank">deposits deep underground</a>. But methane could come from renewable resources, too.</p><p><span></span>Two main methane sources could be used to make RNG. First is <a href="https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks" target="_blank">biogenic methane</a>, produced by bacteria that digest organic materials in manure, landfills and wastewater. Wastewater treatment plants, landfills and dairy farms have captured and used biogenic methane as an energy resource for <a href="http://emilygrubert.org/wp-content/uploads/2019/02/eia_860_2017_map.html" target="_blank">decades</a>, in a form usually called <a href="https://www.eia.gov/energyexplained/biomass/landfill-gas-and-biogas.php" target="_blank">biogas</a>.</p><p>Some biogenic methane is generated naturally when organic materials break down without oxygen. Burning it for energy can be beneficial for the climate if doing so prevents methane from escaping to the atmosphere.</p>
Renewable Isn’t Always Sustainable<p>If RNG could be a renewable replacement for fossil natural gas, why not move ahead? Consumers have shown that they are <a href="https://www.nrel.gov/analysis/green-power.html" target="_blank">willing to buy renewable electricity</a>, so we might expect similar enthusiasm for RNG.</p><p>The key issue is that methane isn't just a fuel – it's also a <a href="https://www.eia.gov/environment/emissions/ghg_report/ghg_overview.php" target="_blank">potent greenhouse gas</a> that contributes to climate change. Any methane that is manufactured intentionally, whether from biogenic or other sources, will contribute to climate change if it enters the atmosphere.</p><p>And <a href="http://doi.org/10.1126/science.aar7204" target="_blank">releases</a> <a href="https://doi.org/10.1016/j.wasman.2019.07.029" target="_blank">will happen</a>, from newly built production systems and <a href="https://theconversation.com/why-methane-emissions-matter-to-climate-change-5-questions-answered-122684" target="_blank">existing, leaky transportation and user infrastructure</a>. For example, the moment you smell gas before the pilot light on a stove lights the ring? That's methane leakage, and it contributes to climate change.</p><p>To be clear, RNG is almost certainly better for the climate than fossil natural gas because byproducts of burning RNG won't contribute to climate change. But doing somewhat better than existing systems is no longer enough to respond to the <a href="https://doi.org/10.1038/nclimate2923" target="_blank">urgency</a> of climate change. The world's <a href="https://www.ipcc.ch/sr15/chapter/spm/" target="_blank">primary international body on climate change</a> suggests we need to decarbonize by 2030 to mitigate the worst effects of climate change.</p>
Scant Climate Benefits<p><a href="https://iopscience.iop.org/article/10.1088/1748-9326/ab9335/meta" target="_blank">My recent research</a> suggests that for a system large enough to displace a lot of fossil natural gas, RNG is probably not as good for the climate as <a href="https://investor.southerncompany.com/information-for-investors/latest-news/latest-news-releases/press-release-details/2020/Southern-Company-Gas-grows-leadership-team-to-focus-on-climate-action-innovation-and-renewable-natural-gas-strategy/default.aspx" target="_blank">is publicly claimed</a>. Although RNG has lower climate impact than its fossil counterpart, likely high demand and methane leakage mean that it probably will contribute to climate change. In contrast, renewable sources such as wind and solar energy do not <a href="https://www.eia.gov/environment/emissions/carbon/" target="_blank">emit climate pollution directly</a>.</p><p>What's more, creating a large RNG system would require building mostly new production infrastructure, since RNG comes from different sources than fossil natural gas. Such investments are both long-term commitments and opportunity costs. They would devote money, political will and infrastructure investments to RNG instead of alternatives that could achieve a zero greenhouse gas emission goal.</p><p>When climate change first <a href="https://www.nytimes.com/1988/06/24/us/global-warming-has-begun-expert-tells-senate.html" target="_blank">broke into the political conversation</a> in the late 1980s, investing in long-lived systems with low but non-zero greenhouse gas emissions was still compatible with aggressive climate goals. Now, zero greenhouse gas emissions is the target, and my research suggests that large deployments of RNG likely won't meet that goal.</p>
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By Charli Shield
When an elephant dies in the wild, it's not uncommon to later find its bones scattered throughout the surrounding landscape.
Elephant Burial Grounds<p>Highly social creatures that form deep familial bonds, elephants have long been observed gathering at the site where a peer or family member has died — often spending hours, even days, quietly investigating the bodies or the bones of other dead elephants.</p><p>Although the popular idea that dying elephants are instinctively drawn to special communal graves — so-called "elephant graveyards" — is a myth, their tendency to go out of their way to visit the bones and tusks of the deceased isn't unlike human rituals at graveyards, says animal psychologist Karen McComb.</p><p>"They spend a lot of time touching and smelling skulls and ivory, placing the soles of their feet gently on top of them, and also lifting them up with their trunks," McComb, who's been studying African elephants for 25 years in Kenya's Amboseli National Park, told DW.</p><p>The most striking part of watching an elephant experience loss, Poole recalls, is the quietude. She still remembers one of the first elephant deaths she witnessed; a mother who birthed a stillborn calf. That elephant stayed with its baby for two days, trying to lift it and defending it from vultures and hyenas.</p><p>"I was so struck by the expression on her face and her body. She looked so dejected. It was really like, 'Oh God, these animals grieve…'. It was just so different," Poole told DW. </p>
Witnessing Emotions in Animals<p>Not all scientists are comfortable concluding that elephants grieve. Among the more than 30 reports of elephant reactions to death that Wittemyer co-reviewed in <a href="https://link.springer.com/article/10.1007/s10329-019-00766-5" target="_blank">a study published in November 2019</a> were accounts of "enormous variation and nuance" he says. "It can be incredibly involved and intricate for extended periods or can be relatively cursory checks."</p><p>In Wittemyer's own experience, it can be difficult not to attribute some kind of emotional experience to the more involved interactions between elephants and their dead.</p><p>He shares the story of an "extraordinary event" involving the death of a 55 year-old matriarch in Kenya in a protected area that happened to be near his place of work. She was visited by multiple unrelated families while she was dying, including another matriarch that exerted such enormous effort attempting to lift her to her feet that she broke her tusk, which Wittemyer says, is "like breaking a tooth." </p><p><span></span>"It was a remarkable example of this heightened emotional state, it was very clearly a very stressful interaction," he says.</p>
A Different Sensory World<p>One factor that limits our ability to fully grasp the way elephants process and respond to loss is our markedly different sensory experiences of the world.</p><p>An elephant's world is fundamentally olfactory — based on smell. Ours is visual. Previous <a href="https://pubmed.ncbi.nlm.nih.gov/25053675/" target="_blank">research</a> has shown elephants possess the most scent receptors of any mammal, and can <a href="https://pubmed.ncbi.nlm.nih.gov/17949977/" target="_blank">use smell</a> to discern the difference between different human tribes from the same local area.</p><p>That could explain why elephants exhibit such interest in sniffing the bones and tusks of others, as a <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1617198/" target="_blank">2005 study</a> from McCombs highlighted. When presented with the skulls and ivory of long-dead elephants and those from other large herbivores, including rhino and buffalo, McCombs and her team found elephants approached and were specifically attracted to the remains of their own species. </p><p>Without access to the smells an elephant picks up on, Wittemyer says "an enormous amount of stuff" could be missed by humans when studying these behaviors.</p>
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