 is extinct on the North Island of New Zealand, spelling trouble for the flowering plants it pollinates. Saving the stitchbird and its fellow threatened bird species might, in turn, help preserve the plants.)
A STITCH IN TIME: The stitchbird (or hihi) is extinct on the North Island of New Zealand, spelling trouble for the flowering plants it pollinates. Saving the stitchbird and its fellow threatened bird species might, in turn, help preserve the plants.
Image: © Dave Kelly / University of Canterbury
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Earth's last passenger pigeon—Martha—died in 1914 at the Cincinnati Zoo, the final remnant of flocks that once darkened the sky. What's unknown, even nearly a century after this extinction, is how many of the plants in the eastern woodlands of the U.S. might have suffered as a result—or even gone extinct themselves. Now, new findings from halfway around the world suggest plants may indeed suffer in the absence of the animals they have relied on for pollination or dispersing seeds.
The work was done by a team of biologists, fresh from showing that New Zealand's mistletoe species are struggling due to a lack of pollinating birds, who set out to determine if other plants shared this problem. After all, the country has lost nearly half of its native land bird species since 1839.
They homed in on one native shrub—Rhabdothamnus solandri, or New Zealand gloxinia, renowned for its brilliant orange flowers—which relies on several species of birds for pollination, and is found nowhere else in the world. The tui (Prosthemadera novaeseelandiae), bellbird (Anothornis melanura) and stitchbird (Notiomystis cincta) all have beaks and long tongues perfectly suited for the shrub's 10-millimeter-long orange flowers. But bellbirds and stitchbirds are gone on the New Zealand's North Island thanks to bird-eating animals brought along by European colonizers, such as house cats (Felis catus), ship rats (Rattus rattus), stoats (Mustela erminea) and brushtail possums (Trichosurus vulpecula).
Fortunately, those bird species survive on some small islands off the coast—Little Barrier, Tiritiri Matangi and Lady Alice—too small to have had much contact with humans or the invaders they often bring along. And in many cases mammal pests, such as the feral cats that roamed Little Barrier Island until 1980, have been eradicated.
So the biologists painstakingly catalogued the instances of the flowering shrub in plots on both the bird-friendly islands and the mainland. As a result of the missing birds, the flowering shrubs on the mainland produce smaller fruit and only 37 seeds per flower, compared with 232 seeds per flower for shrubs on the bird-friendly islands. Nearly 80 percent of flowers on the small islands showed evidence that birds had visited, whereas only 25 percent of mainland flowers did so. And although fully grown shrubs persist on the mainland in roughly similar numbers, there are less than half as many young plants sprouting up to replace them.
This pollination failure has likely been going on for a long time. "Pollination probably failed about 1870, which is when bellbirds and stitchbird densities on the North Island plummeted," says biologist Dave Kelly of the University of Canterbury in Christchurch, one of the scientists involved in the research.
Other possible pollinators, such as insects, apparently are not up to the task in the case of R. solandri, unlike the case for endemic New Zealand mistletoes or trees that have also lost bird pollinators, according to Kelly. Flowers encased in chicken wire mesh cages on the mainland and the offshore islands to keep out birds also failed to produce many seeds, "showing that birds are essential for pollination," the biologists wrote in the paper detailing their findings, published online in Science on February 3. Kelly adds: "Usually when a bird-adapted flower is not well pollinated by insects it's because the flower is too big for insects to touch the right parts [for pollination] as they visit it."
Of course, humans could take over for the missing birds, pollinating by hand and sowing the seeds. When the biologists did so, R. solandri immediately boosted its numbers. As for why the decline of the brilliantly colored flowering shrub had gone unnoticed, Kelly offers the idea of "shifting baselines"—people (and scientists) tend to ignore reports of abundance that existed before their own lifetimes—and wrote in the Science paper, "This decline could very easily have escaped notice, because it is so gradual…. It may be that similar slow plant declines as a result of failing ecological interactions have begun elsewhere."
After all, many regions of the world host plants that rely on specialized birds for pollination, from the tropics of Central and South America to South Africa and Southeast Asia. "I would bet that there are other plants declining in other parts of the world for this same reason, but it's not been measured yet," Kelly says. "In New Zealand we want to check other bird-pollinated plants to see if they too are declining. We know that a majority of them have [a] reduced seed set."
At the same time, R. solandri is still not considered in danger of extinction for two reasons: First, it still manages to produce some seed even without effective pollinators. Second, the shrub can apparently live for years. "We don't know exactly how long-lived the plant is as it does not seem to have growth rings," Kelly admits.
As for 19th-century North America, the passenger pigeon was a big consumer of the nuts of hickories, beeches and chestnuts in the vast eastern deciduous forest of North America. That forest has largely disappeared—and chestnuts were almost entirely wiped out by disease—but it is possible that the trees are also missing their one-time avian agent of dispersal. That could very easily be a problem for plants the world over, given that at least 190 species of birds have gone extinct since 1500 and more than a thousand are currently at risk of disappearing.
"The interactions among species are important for keeping ecosystems functioning properly," Kelly notes. "If we can get the birds right, the plant conservation will come as a secondary benefit."
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14 Comments
Add CommentA very simple minded solar powered flying robot directed by wifi can now be built and delivered by the millions that sleep at night and then does the pollinating during the day,and then be collected when the job is done.Then taken to the the next job when done.The technology is currently available.Why isn't it being done?If somebody does this now I would like a finder's fee please.It can be built out of biodegradable materials so they are green as well.
Reply | Report Abuse | Link to thisYou left out some very relevant pieces of information. The passenger pigeon was hunted to extinction by humans. And there is an additional reasons why there are so few hickories, beeches and chestnuts left. Logging removed the large trees. Now an overpopulation of deer caused by the removal of all large carnivores, keep the forest floor cleared of brush and tree sprouts.
Reply | Report Abuse | Link to thisBellbirds are not extinct in the north island and hihi have been released to ZEALANDIA, Maungatautiri and Ark in the park sanctuaries.
Reply | Report Abuse | Link to thisAs for jack's robot fantasy, In New Zealand we are better off preverving and enhancing our forests with large scale tried and tested methods of multi-species pest control (albeit new zealand is somewhat unique with our natural absense of terrestrial mammals, save a few bats). This is the best way to preserve biodiversity.
Perhaps humans will have to evolve to replace the functions of these missing species. Isn't that what usually happens when one species eradicates another?
Reply | Report Abuse | Link to thisJack could apply for the job of hand pollinator.
not to demean the article(very important info)...but how can a pigeon have an affect on a chestnut...it would either have to participate in the pollination or contribute to the spread of the seeds.....I don't see it doing either....
Reply | Report Abuse | Link to thisAs I recall, there is a tree that only the dodo bird, now extinct, was the spreader of it's seed. When the current generation of this tree grows old and dies, that tree will also become extinct. In a sense it already has.
Reply | Report Abuse | Link to thisMy idea was as a supplement not a replacement of nature.Hopefully we can head off the tragedy of huge crop losses caused by the the loss of some of our current pollinator's and the starvation that would follow.One example is bee colony collapse.Almost all major crops require pollination of some kind,I just thought we could head off a catastrophe.In the end the real fantasy is thinking that doing nothing is the path we should follow.
Reply | Report Abuse | Link to thisBees are cheaper.
Reply | Report Abuse | Link to thisDidn't read your second post before my post. Bee colony collapse isn't universal and some areas are already recovering. Robots have to be programmed to identify each specific type of plant and generally have limited functional range. Biological life is much more efficiently packaged and would take up far less space than robotic analogies.
Reply | Report Abuse | Link to thisAgro robots are in use in some areas but the price tag to make it viable is very high at the moment.
The date palm lost it's pollinator. Now the flowers have to be pollinated by hand. The pollinator was was chased away but still lives, it was the giraffe. These little tufted horns on it's head did the pollinating. Later the giraffe wold eat the dates in competition with people who like the fruit too.
Reply | Report Abuse | Link to thisIt would be nice if some zoo would plant a few date palms in the place where they keep a giraffe. The giraffes will like it.
They are now using big tom turkeys, that are force-fed the seeds with modewrate results. Most furniture made of this wood is in Holland.
Reply | Report Abuse | Link to thisThe date palm is wind-pollinated. Perhaps ennui might like to think about the huge difference between the habitats of Giraffes, the African grasslands, and the habitats of date palms, primarily desert oases.
Reply | Report Abuse | Link to thisI agree. I'm not sure what they are getting at there. Unlike some seeds, chestnuts, beechnuts, hickory nuts, and acorns have to be whole to germinate. They cannot be eaten then excreted and still grow. They are primarily spread by mammals that cache nuts (and forget a few of the caches).
Reply | Report Abuse | Link to thisI'm not sure how a passenger pigeon could even crack a hickory nut's tough casing to reach the meat.
In our biology classes we learned that they were hand pollinated.
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