Living World | Subject area | New Zealand Geographic

Insectpocalypse now

The first global review of studies about the decline of insects predicts the planet will lose its insects within a century if the current rates of extinction continue. Notable insect population crashes have been documented in Puerto Rico, where one study found a 98 per cent decrease in ground insects over 35 years, and the United Kingdom, where butterfly species dropped by 58 per cent in a decade on agricultural land. In Oklahoma, only half of bee species recorded in 1949 were found in 2013, while in Germany, the abundance of flying insects in national parks declined by 75 per cent over 25 years. Insects are the most abundant animals on Earth—they outweigh humans by 17 times—but their mass has been declining by 2.5 per cent a year for the past three decades. The insect rate of extinction is eight times higher than that of birds, mammals and reptiles. According to the analysis, which will be published in Biological Conservation in April, the decline in insect numbers is primarily due to intensive agriculture, heavy pesticide use, loss of habitat through urbanisation and climate change. “Unless we change our ways of producing food, insects as a whole will go down the path of extinction in a few decades,” write the authors of the review. “The repercussions this will have for the planet’s ecosystems are catastrophic, to say the least.”

Geo News

Moth magnet

On spring nights, bogong moths migrate to the Australian Alps, travelling distances of more than 1000 kilometres to reach the cool mountain caves where they spend their summers aestivating. But how does the moth navigate from its winter breeding grounds to the alps? Tests in a flight simulator found moths found their way by the stars and moon, but became disoriented when researchers deliberately misaligned the sky and the Earth’s magnetic field. That magnetic field is crucial to the moths’ ability to find their way, making bogong moths the first nocturnal insect known to use magnetic sensitivity as a tool in long-distance migration. (Birds have long been known to navigate using the Earth’s magnetic field.) Do other insects have an internal compass tuned to the Earth’s magnetic field? Study co-author Eric Warrant, a sensory physiologist from Lund University in Sweden, says monarch butterflies, which migrate by day across the United States to overwinter in Mexico, may also have some magnetic sensitivity, but their primary compass is the sun: “Bogong moths must rely on the Earth’s magnetic field because the moon is a very variable and unreliable cue compared to the sun—which is a very constant cue day after day.”

Geo News

Safety in flamboyance

Birds with colourful plumage are better at attracting mates, but also more likely to attract predators—right? Well, no. When a team of New Zealand and Australian biologists investigated whether dull-coloured birds had better survival rates than brightly coloured ones, they found both were equally likely to be attacked. The fairy-wren, an Australian songbird, varies wildly in colour—some have brilliant plumage, while others are nondescript. The researchers placed 3D-printed models of the birds at eight fairy-wren sites in Australia, then settled in to watch. They found that 13.1 per cent of brightly coloured female birds were attacked, compared to 13.6 per cent of dull-coloured females. But there was a wide discrepancy in the rate of attacks between sites, suggesting that survival had more to do with vegetation and location than the flashiness of the birds’ feathers. “While being brightly coloured can be important, for example in competing for a mate, the assumption has been that it is costly for birds because it appears to scream ‘Here I am, come eat me’,” says lead researcher Kristal Cain of the University of Auckland. “It suggests the relationship between predation and colour is not as simple as we might have thought. “Instead, it appears that because males and females behave differently—females often take more risks—bright feathers may be more dangerous for females than for males.”

Geo News

On the spectrum

Birds fly at high speed through dense forests without crashing into trees or leaves—and this navigational prowess may be due to their ability to see ultraviolet light. Two researchers photographed forest habitats with a multispectral camera, allowing them to look at the scenes through the birds’ eyes. In a paper published in Nature Communications in January, they determined that contrast between leaf surfaces was greater with UV vision, and speculated that UV vision also helps birds search for particular leaf surfaces, leading them to prey or safe refuge.

Geo News

Why don’t birds have teeth?

Birds may have lost their teeth to speed up hatching time, according to a new theory published in May in Biology Letters. The toothless beak is a relatively recent invention. Dinosaur birds had teeth, and incubated their eggs for a lengthy three to six months. Research on fossil embryos shows tooth formation took 60 per cent of this time. But eggs in open nests are vulnerable to predation, compared with mammal embryos that are protected inside the womb, or eggs that are buried. Losing teeth would allow for a shorter incubation time—and thus a higher survival rate for chicks. Other theories postulate that birds lost their teeth in order to become light enough to fly, and that the toothless beak is better adapted to certain foods.

Geo News

Taking calls

A happy hihi, or stitchbird, has a call that sounds like two marbles clacking together. Using sound-recording devices, researchers listened to hihi calls in Rotokare Scenic Reserve in Taranaki to determine whether the reintroduction of the birds to the area was successful. “By recording and listening to the hihi calls, we were able to figure out how the birds were using the area they’d been reintroduced to,” says PhD candidate Oliver Metcalf, from a Zoological Society of London research team. “Using the calls, we found the birds moved from an initial exploration phase around the habitat, to a settlement phase—meaning the birds had established their own territories.” It’s hoped that auditory monitoring may replace more-invasive radio tracking for some species. Since 2004, six new populations of hihi have been established across their former range.

Features

Road to recovery

Takahē numbers are rising by 10 per cent a year. The problem now is where to put them.

Geo News

Building blocks

The wombat is the only species in the world capable of organically producing cubes. Thanks to the varying elasticity of its intestinal walls, wombats poop cubes, which they then stack up to mark their territory and attract the attention of other wombats. How they produce droppings in this shape has long been a biological mystery, solved only when Patricia Yang, a postdoctoral fellow in mechanical engineering at Georgia Institute of Technology, studied the digestive tracts of roadkill wombats from Tasmania. Cubes are rare in the natural world. “We currently have only two methods to manufacture cubes: We mold it, or we cut it. Now we have this third method,” said Yang in a presentation of her research. “It would be a cool method to apply to the manufacturing process—how to make a cube with soft tissue instead of just molding it.”

Geo News

Noise ages birds faster

Zebra finches exposed to the sound of traffic appear to age faster than those in quieter environments. In a study published in Frontiers in Zoology, birds were found to have shortened telomeres, which indicates accelerated ageing, if they were played recordings of street traffic once they had left the nest. The birds heard the noise from the age of 18 days until 120 days. But if birds were exposed to noises only while in the nest, their telomeres were of normal length. The authors suggest the birds are more sensitive to noise between 18 and 120 days of life—the time when they are learning song.

Geo News

The gannet diet

The Australasian gannet forages by plucking fish from the sea, then regurgitates food for its young—and sometimes its meals are interrupted by researchers studying gannet nutrition. A team of Australian and New Zealand scientists took a close look at what the gannets were providing their chicks. They found that the fish and squid they were eating had a lower ratio of healthy fats to protein when the sea was warmer than the 10-year average. In addition, GPS trackers showed the birds worked harder to get enough nutrition, increasing their foraging area by more than 200 square kilometres and their time spent feeding from more than 13 hours in duration to more than 21 hours. Study author Gabriel Machovsky-Capuska says the right proportion of healthy fats to proteins is crucial to gannets for good body function and healthy chicks.

Features

Tending the flock

New Zealand has only one endemic gull, the tarāpuka, and it’s more endangered than the takahē, the hoiho and all five species of kiwi. Its survival depends on the preservation of the South Island’s unique braided-river ecosystems.

Geo News

The long life of tortoises

Lonesome George was the last of his species, a Galápagos giant tortoise from the island of Pinta. Though he died in 2012, he continues to inform scientific research—his genome was sequenced and more than 3000 genes thought to be involved in ageing and cancer were analysed by an international team of researchers. Galápagos giant tortoises are among the longest-lived species, reaching up to 200 years, and it’s thought they have evolved mechanisms for preventing cancer. The researchers identified variants in several genes previously unassociated with ageing, opening up avenues for further research.

Geo News

Dolphin fingerprints

Ninety-five per cent of common dolphins have a unique ‘fingerprint’ of pigmentation on their dorsal fin that lasts a lifetime. Scientists hope machine learning could use the dolphin photographs taken by people all around New Zealand to track where the dolphins travel. Common dolphins occur around the globe, and it was thought they were too numerous and similar to tell individuals apart—there are thousands that swim in the Hauraki Gulf alone. Currently, dolphins are told apart by the nicks and notches on their dorsal fins—scars received socially or from boats or fishing lines. These accumulate over a dolphin’s lifetime. Bottlenose dolphins are very social and may acquire many scars, but 50 per cent of common dolphins have no scars at all. Scientists from Massey University and NIWA used 240,000 photos of nicks and notches to manually identify 2083 individuals in the Hauraki Gulf. Then they demonstrated that over ten years, the pigmentation on common dolphins’ dorsal fins doesn’t change, making it a reliable mark of identity. Lead researcher Krista Hupman is now developing an algorithm that will identify dolphins, and hopes that photos of individuals taken by recreational boaties and tourism operators could be used to get a better understanding of how many dolphins there are, where they go, and how they behave.

Virtual Reality / 360 Video - NZ 360

Snapper - Goat Island

Snapper congregate in the shallows of Cape Rodney-Okakari Point Marine Reserve at an abundance and maturity that may closely reflect the original snapper populations of the Hauraki Gulf. There are three to four times the number of snapper inside the reserve as outside and up to ten times the number of crayfish.

Virtual Reality / 360 Video - NZ 360

Kina barren -Three Kings

Fishing effort, day after day, century after century, has changed the shape of this place. It’s still heaving with reef fish, but the predators are gone. It’s still resplendent with sargassum weed, but kina that were once devoured by snapper and other reef predators are tearing holes through the fabric of the ecosystem.

Virtual Reality / 360 Video - NZ 360

Stingray - Northern Arch

Northern Arch is a 40-metre-deep cut in a sheer rock wall at the northern end of the Poor Knights. Like a busy city alley it attracts hoards of life—thousands of fish,

Virtual Reality / 360 Video - New Zealand Journeys

Tie Dye Arch - The Pinnacles

South of the Poor Knights stand a crop of rocky spires called The Pinnacles. Under the largest is a cathedral-like cavern called Tie Dye Arch, named for the kaleidoscope of colours that clad every surface like graffiti.

Geo News

The biggest bird brain

Birds that evolved on islands, such as the North and South Island, tend to have bigger brains than those that evolved on large continents, even if the species are close cousins. A study published in Nature Communications in July compared brain size relative to body size in more than 1900 bird species, spanning 91 per cent of bird families. The researchers then analysed several bird lineages that had relatives on both islands and continents. Having a large volume in some areas of the brain enables adaptability—the pallial regions, for instance, help with pattern-finding and planning. Because island environments are unpredictable, say the authors, adaptive capability is a significant advantage. “For instance, the Galápagos finch uses tools, instead of the more frequent gleaning technique, when there are droughts and insects are only found in wood crevices,” says lead author Ferran Sayol. The New Zealand tomtit, Petroica macrocephala, has a much larger brain than its closest mainland relative, and the kea has an unusually large brain for a parrot.

Geo News

Aerial roots

If a root is above ground, how can it take in water? The Lord Howe pandan has evolved a solution: it has developed grooves that function like aqueducts, according to Victoria University researcher Matt Biddick. Pandans are found on tropical and subtropical coasts around the Pacific. They have weak trunks, but grow tall by sending roots down from the canopy that form stilts when they reach the ground. Most pandans grow to less than five metres high, but a Lord Howe Island species, Pandanus forsteri, grows to more than 15 metres, so it takes years for the aerial roots to reach the ground. Without being able to draw moisture from the earth, the roots gather it by other means. The leaves of P. forsteri are shaped like gutters, and funnel water toward the trunk. Then, grooves on the top surface of the roots channel the water to the roots’ tips, where spongy absorptive tissue carries the collected rainwater to the rest of the plant.

Geo News

Fatal memory fail

It took just 13 generations for quolls to forget about their major predator, the dingo, according to Australian research published in Biology Letters in June. After noticing that northern quolls were eating toxic cane toads, with lethal results, researchers moved a group of quolls to a toad-free, dingo-free island in 2003. The quolls were trained to avoid cane toads and reintroduced to their native territory in 2016, where they were promptly eaten by dingoes. They had forgotten how to identify and avoid the dingoes’ scent.

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