Dutch gulls eat their young on Sundays

By John Upton

The durations of days and years are calibrated by celestial turntables: The spinning of the Earth and its arcing around the sun. Humans and wildlife alike live out rituals according to daily and annual schedules.

But the seven-day week is a human construct. It’s an arbitrary chunk of time that cocoons timetables of work and rest, of television programming and soccer practice. Whenever you see wildlife falling into a weekly routine, you can be confident it’s the result of a human influence.

A weekly schedule plays out among European herring gulls and lesser black-backed gulls nesting in the dunes of the Dutch island of Texel. And it’s a macabre one.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

A chick being reared in these dunes may dread Sunday more than a young atheist dreads their mandatory church outings. It’s on Sundays that adult gulls are most likely to cannibalize the young. Saturdays are also popular chick-eating days among the Texel gulls, though not to the same extent as is the case on Sundays.

Sometimes the gulls eat their own chicks — or their own eggs. But more often they steal the unattended young of other birds, in some instances to be shared with their own hungry broods.

That’s not the only weekly pattern that marine ornithologist Kees Camphuysen has discovered during his studies on the island. Chicks tend to grow in spurts during the week, then their growth slows down over the weekends.

The Royal Netherlands Institute for Sea Research scientist thinks he knows what’s going on. He contends that it’s the weekly patterns of the region’s beamtrawlers and shrimpers that are driving the hebdomadal trends.

“[A] very strong weekly pattern in fleet size occurred, with high numbers of boats at sea Monday through Thursday, a much reduced number (mostly homeward bound) on Friday, and near to nothing on Saturdays and Sundays,” he wrote in his Ph.D. thesis.

The Texel Dunes gulls feast on the by-caught scraps of the fishing fleet, trailing the boats to scavenge protein for themselves and for their growing chicks. But when this supply of human surplus dries up over the weekends, the chicks’ growth rates slow, and hunger can drive the birds to cannibalism.

“Only commercial fisheries have a periodicity that can explain the strong, cyclic synchronisation in chick growth,” Camphuysen wrote. “Chick cannibalism rates were a mirror image of the rhythmic cycle in growth increments.”

The following series of photographs was published in Camphuysen’s Ph.D. thesis, showing an attack on an unattended chick by a bird from a nearby nest. The attacking gull can be seen sharing the kill with its own chick. If you would prefer to not see an adorable lesser black-backed gull chick being pecked to death and gutted by its own kind, then stop scrolling now.

cannibal-gull-in-action

How birds avoid cuckoos

By John Upton

One of nature’s more ridiculous sights is that of a pair of adult birds rearing an oversized cuckoo chick.

Cuckoos are members of a large family of birds, some of which have done away with chick rearing, instead depositing their eggs in the nests of other species. This is called brood parasitism.

The parasitized birds rear the cuckoo chick as if it were their own, even as it grows to dwarf them in size — and as it pushes any other chicks from the nest to certain death.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

(Ever noticed a dead chick beneath a tree and wondered how it fell out? Next time look up for a nest, and wonder whether a cuckoo is being raised therein.)

It seems that the the parental compulsion to raise young is so strong that the parasitized birds remain blind to the possibility that the brood contains none of their own DNA.

While many bird species remain oblivious to what would seem to be obvious signs that they are raising an unrelated chick, selection pressure has of course led to the evolution of some defenses against brood parasites.

Scientists compared defensive strategies developed by barn swallows living in China with those in Europe and found that they developed different defenses.

In Europe, martins and barn swallows, which seem to be better than some similar species at avoiding cuckoos, prefer to build their nests indoors. That’s where cuckoos are less likely to strike; they prefer open areas and avoid human habitation.

“Suitable cuckoo hosts breeding close to human habitation enjoy a selective advantage from breeding indoors,” the researchers wrote in a paper published in the journal Behavioral Ecology and Sociobiology. “These findings suggest that birds benefit from association with humans in terms of reduce risk of parasitism.”

The scientists say it’s harder for the barn swallows to build nests indoors in China. There, they have developed an alternative trick that’s largely lacking among their European counterparts: A Chinese barn swallow will often recognize a cuckoo egg. So when a cuckoo egg shows up in its nest, it will toss it over the side.

“These findings suggest that barn swallows in China have gained egg rejection behavior because they cannot avoid parasitism when breeding outdoors.”

Watch a Reed warbler feed a much larger cuckoo chick:

Mosquitoes hunt us by our smell, then zero in on our heat

By John Upton

The Zzzz–zzZZZzzz–zzZZ sound that a mosquito makes while you’re trying to sleep isn’t the random modulation of a directionless insect. It’s the sound of a predator carefully circling its prey, smelling body odors and reading body heat, planning its strike.

Blood-hungry mosquitoes are females, on the desperate hunt for protein with which they can manufacture eggs. They repeat their hunt several times, making them dangerous vectors of disease. Their eggs will be laid in standing water before the female buzzes the last buzz of a short life as an airborne adult. Between the egg and adult stage comes the larvae, commonly known as mosquito wrigglers.

To find their prey, the female mosquito hones in on our smell. As they close in on their prey, they scan our body heat to help direct their strike.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

That’s the conclusion of Dutch researchers, who set up a small wind tunnel with 3D tracking equipment and conducted experiments with hungry week-old female specimens of Anopheles gambiae, an African mosquito that hunts human blood and can transmit malaria. For some of the tests, the researchers placed a used sock at one end of the wind tunnel to gauge how they responded to human smell. In others, they placed a heat element at the end, set to 34°c to mimic the temperature of a human. Other tests involved using neither the sock nor the heat; and others used both. The researchers studied how the mosquitoes zeroed in on a specific point at the end of the wind tunnel under the different conditions.

The result?

Check out the following figures. Each row shows three views of the same wind tunnel experiments. The blue circles show the location of the plume of smell blown through the wind tunnel from the sock. The green lines track the mosquitoes approaching the end of the wind tunnel through the smell plume; red lines track the other mosquitoes. The target is at the center of the end of the tunnel.

mozzietracks“With heat alone, flights were … short and direct,” the scientists wrote in their paper, published in the online journal PLoS ONE. “The presence of human odor, in contrast, caused prolonged and highly convoluted flight patterns. The combination of odor+heat resulted in longer flights with more landings on the source than to either cue alone.”

So next time a mosquito is keeping you awake at night, don’t think of it as an idiot that’s buzzing mindlessly around your head. It’s just getting a good read on its prey before launching its strike.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

A hungry red tide is a dangerous red tide

By John Upton

When fertilizer or sewage runs into a waterway, or when phosphorous and nitrogen rise up from the ocean depths, algae can converge and feast and mushroom on the buffet of growth-inducing nutrients.

But scientists have discovered that starving a poisonous red tide of its nutrient supply can trigger a very dangerous and counterintuitive response.

Red tides are freaky types of algae blooms. They often occur in the ocean or in salty bays, and they frequently produce poisons. Scientists prefer the term “harmful algal bloom,” since a red tide isn’t always red and it is most certainly not a tide.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

The most common type of algae in Gulf of Mexico red tides is a dinoflagellate called Karenia brevis. The neurotoxin produced by these single-celled creatures help protect them from predation: Would-be hunters can die if they take a mouthful. But as the red tides break down, the poison escapes from the plankton cells and it can drift through the marine environment, poisoning it. The toxin can even spray into the air, aerosolized by crashing waves, where it can get into lungs and trigger serious ailments in people and other animals. The Floridian West Coast is often the worst affected.

Concentrations of the poison in each of the algae cells varies widely — from a mild 1 picogram per cell to a treacherous 68 picograms per cell. Needless to say, figuring out what causes a bloom to be especially poisonous would be valuable for public health officials.

Since Karenia brevis uses nutrients to grow, one may assume that starving them of phosphorous and nitrogen, such as by preventing fertilizer or sewage runoff into the Gulf, would protect the environment from their poisons.

But that’s only true up to a point. If you can keep nutrients out of the water, a bloom will not materialize, so there will be no danger of the waterway being poisoned by it. But if the nutrient supplies suddenly dry up, an existing bloom will switch into a defensive mode, stop growing and become very toxic.

The ecological theory to describe this response comes to us from botany. It is called the carbon:nutrient balance hypothesis.

North Carolina scientists grew samples of the dinoflagellate in water taken from the Gulf in a laboratory. Some samples were fed plenty of phosphorous, but others received very little. The scientists found that K. brevis strains living with limited phosphorous supplies produced 2.3 to 7.3 times more poison than did those that had plenty of phosphorous available.

“Because PbTxs [K. brevis brevetoxins] are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth,” the scientists wrote in their paper, published last month in PLoS ONE.

The algae samples living without much phosphorous put their carbon to a defensive use, since it couldn’t be used as effectively for growth. The proportion of carbon that each cell used to produce poison as much as doubled when phosphorous was limited.

This is consistent with the carbon:nutrient balance hypothesis. When vegetation has lots of carbon and lots of nutrients available, it invests those building blocks of life into fast growth. But when nutrients, be they phosphorous or nitrogen, are in short supply, the carbon is put to a different use: Defense against predators.

It also helps explain some of the late season bursts in toxicity noticed in the red tides: They become poisonous after they have greedily slurped down the last of the available nutrients.

This research was limited to phosphorous. But previous research uncovered a similar red tide response when nitrogen was limited.

The discovery could help public health managers predict the potency of red tides in the Gulf of Mexico. By measuring the amount of phosphorous in the ecosystem, it could become possible to determine how dangerous the red tides will become.

Forests pump carbon into soil

By John Upton

Photosynthesis is easy enough to understand: Plants use the power of the sun to combine carbon dioxide and water into sugar. What’s perhaps less easy to understand is what happens to all of the carbon-rich sugar that it produces. New research shows that vast amounts of it are pumped down to fungi deep in the ground, keeping the carbon out of the atmosphere and keeping the climate cool.

Some of the energy-rich sugar is shipped around the plant to power cells, and then is often eaten by herbivorous animals or flutters to the ground with fallen leaves to be gobbled up by microscopic organisms. But some of the sugar is pumped down to the roots and traded with mycorrhizal fungi in exchange for nutrients.

The mycorrhizal fungi take the sugar from the plants, and in return they feed nutrients to the plants. Fungi send stretching tentacles, called mycelia, through the ground to forage for nitrogen, phosphorous and other nutrients that are valued by the plants. They use those nutrients as currency with which they buy sugar.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The sugar that’s passed from the plant to the fungi contains lots of carbon, which the plant originally sucked out of the air as carbon dioxide. Scientists have discovered that most of the carbon that’s stored in some forest floors is sequestered in the bodies of the dirt-dwelling fungi — not, as had been presumed, in the decomposing leaf litter.

Karina Clemmensen, a researcher at the Swedish University of Agricultural Scientists, led research that investigated where carbon was being stored in two forested Swedish islands. The researchers discovered that 50 to 70 percent of stored carbon in the forests was locked up in the root layer, where the mycorrhizal fungi thrive.

The research took place in boreal forests, but Clemmensen said other ecosystems might also push much of their carbon down into the soil.

“In agricultural fields, arbuscular mycorrhizal fungi are normally the dominant mycorrhizal type,” Clemmensen said in an email. “Our result though – as stands here – is valid for the boreal forest only.”

Cicada wings rip bacteria apart

Illustrated by Perry Shirley

By John Upton

Forget sanitary hand wipes. Scientists have discovered that cicada wings have evolved to kill bacteria without using any chemicals.

The wing are coated with tiny blunt bumps that are so small and plentiful that when a bacterium lands on them, it becomes skewered through multiple parts of its tiny writhing cell wall.

The bacterium doesn’t pop — it is torn open, shredded to pieces by the bumpy wing.

The Australian and Spanish scientists, who published their findings in Biophysical Journal, say the discovery could lead to antibacterial materials “incorporating cicada wing nanopatterns.”

Watch a simulation of a bacterium that was unlucky enough to land on a cicada wing:

Study: ‘safe’ nitrogen levels unsafe for wildflowers

By John Upton

When we think about air pollution, it’s easy to imagine airborne chemicals that kill or stunt wildlife by infiltrating tissues and disrupting cellular processes. But that is not the case with nitrogen pollution.

Nitrogen pollution is released from vehicle exhausts and power plant smoke stacks, which liberate the long-dormant compounds from tainted fossil fuels. Nitrogen is a fertilizer — plants lap it up — and farmers and gardeners have a habit of using too much of the stuff, causing it to spill into waterways and over nearby habitats.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

When airborne nitrogen pollution fertilizes nutrient poor ecosystems, such as the rocky, serpentine soils of inland California, the native plant species that long ago adapted to the difficult growing conditions can be quickly edged out by weeds. It’s a typical case of environmental havoc helping generalist species displace specialists.

Governments are aware of the hazards of nitrogen pollution and they set limits that are considered safe. But scientists who studied wildflower populations growing within so-called safe limits of nitrogen pollution discovered major impacts on the native flowers.

“We studied many grasslands along the natural gradient of pollution across Europe,” Manchester Metropolitan University Professor Nancy Dise, one of the authors of the study, which was published in December in the Proceedings of the National Academy of Sciences, told The Ecologist. “We found that at even relatively clean sites, low levels of pollution had an effect on the abundance of some plant species.”

The scientists say their findings highlight the need for governments to review pollution rules and to vigorously protect areas that have not yet been tainted.

“Our results highlight the importance of protecting currently unpolluted areas from new pollution sources,” they wrote in their paper. “We cannot rule out ecological impacts from even relatively small increases in reactive N deposition.”

How do plants cope with shade?

By John Upton

Plants can tell when they have germinated in the shade of their competitors. Neighboring leaves absorb most of the red and blue wavelengths from the sun but reflect the far-red wavelengths. A preponderance of waves of light at the far-red end of the spectrum, compared with the intensity of light that’s more readily visible to humans, warns a plant that it’s going to need to fight to survive.

Plants growing in the shade can fight to survive by adopting one of two strategies: They can try to avoid the shade, or they can adapt to it.

Shade avoidance is the more common strategy, especially in grasslands and in other habitats where most of the plants grow to roughly the same height. To escape the shade, a plant using this strategy will prioritize the growth of its stem over its roots and over its leaves, most of which will be grown high along the stem, in a bid to stretch itself into the sun’s nourishing rays.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

That’s according to Dutch researchers, writing in the February issue of Trends in Plant Science. But the scientists point out that precious little is known about how plants pursue the alternative strategy of shade adaptation. They argue that specific additional research is needed to help explain how some plants, such as shrubs that grow in forests, have adapted to shady environments. There are indications that these specialized plants tolerate shade by regulating levels of certain proteins and hormones, and by suppressing the plant kingdom’s normal instinct to spend lots of energy to grow out of the shade.

“Analysis on pairs of shade and non-shade species could provide information,” the scientists, led by Charlotte Gommers and Ronald Pierik of Utrecht University, wrote in their paper. “To investigate shade tolerance fully, we will need to venture outside our genetic models.”

Better understanding shade tolerance wouldn’t just fuel cocktail party chatter among ecophysiologists — it could help to increase the amount of food available around the world. If scientists could train crops to develop shade adaptation strategies, then those crops would be expected to invest more energy into growing harvestable yields, such as juicy cobs of corn, instead of unnecessarily wiry stalks.

“This might lead towards crop varieties which, when grown in high density, do not invest in undesirable shoot elongation, but do adapt their shaded, lower strata of the vegetation for more efficient photosynthesis.”

Yosemite National Park
Shade avoidance is common in meadows, grasslands and in other habitats where most plants grow to the same height; Shrubs growing in forests often adopt shade tolerance strategies / John Upton

California’s water hightails east

Illustration by Perry Shirley

By John Upton

California’s Central Valley is one of the world’s most productive crop-growing regions. But growing crops in the vast rich soils requires a lot of water. Some of that water comes from melting Sierra mountain range snow, with a pinch of rainfall mixed into the rivers that are tapped for irrigation. But farmers also pump a lot of their water out of the ground.

Since the early 1960s, about 60 million acre-feet more water has been pumped out of the valley’s aquifers than has seeped back into them. That’s enough water to supply every resident of California for eight years.

Where has that water gone?

A lot of water that is pumped out of the ground evaporates. In some places, that contributes to rising seas, with water being shifted from the land into the oceans.

But in California, scientists have discovered that evaporating Central Valley water turns into clouds that deposit their consignments east of the Sierra, fueling the monsoons of the Southwestern United States and increasing flows in the Colorado River by more than one quarter. The findings were published online Tuesday in Geophysical Research Letters.

California ends up getting some of the water back. Some Colorado River water is diverted and sent west through what the study’s lead researcher, Jay Famiglietti of the University of California at Irvine, dubs an “anthropogenic loop.”

Famiglietti told me that the study illustrates that large-scale water management practices, such as irrigation, can have “profound regional, and even global” impacts.

“We need to understand, much better, what those impacts are,” Famiglietti said.

Valley Grapes
Grape vines growing in California’s Central Valley / Flickr: AquaMaven

 

New island, same old ecological succession theory

Norderoogsand / Illustration by Perry Shirley

By John Upton

It’s easy to think of the earth’s lands as static. But shorelines are constantly shifting as sea levels and land masses rise and fall. New islands can appear, and old ones can be engulfed by the tides.

Sandbanks appear frequently in the  Wadden Sea National Park, off the coast of Germany, as tides and waves push particles of sand around. These are normally ephemeral features that wax and wane like an erratic moon.

But during the past decade, scientists have watched with interest as one particular sandbank has weathered the storms and grown into a full blown island.

Norderoogsand, as it is named, is sheltered by nearby islands and has benefited from rare occurrences of high storm surges during its short life. As reported by The Telegraph, some of the dunes on  the 34 acre island have reached four meters.

Norderoogsand is already home to grasses and seabirds. These are among the wildlife that typically first occupy a new island. According to ecological succession theory, pioneer species such as these are the first to colonize a new or recently scorched land mass. Pioneer species travel easily and they are generally hardy.

Once pioneer species have been established, the environment becomes more accommodating for other species, such as mammals and slow-growing trees.

“Birds are usually first to arrive naturally, and they can often bring in plant seeds or other species in their feathers or droppings,” Dan Grout, a scientist at the nonprofit Island Conservation, told me. “The rate of colonization will depend on the few usual factors such as distances to other land masses, likely migration routes and, not insignificantly, whether human visitation will assist in any directed or inadvertent release of organisms.”

Scientists are looking forward to watching as ecological succession plays itself out on the young island, where gulls, geese, plovers, terns and peregrine falcons have been spotted. “It is to be hoped that the rare sandwich tern will also discover these dunes as a breeding place,” a conservationist told Die Welt newspaper.

But the ecological extravaganza could be fleeting, the experts warn. The entire island could yet be wiped out by a strong tide surge.

Illustrated ecology news.