Pisonia: The Tree That Kills Birds

An awesome majority of vegetation rely upon birds and bugs for seed dispersal. Vegetation appeal to pollinators by releasing fragrant compounds into the air, or by producing candy nectar that birds and bugs feed upon. Species of the Pisonia plant aren’t any totally different. They entice small birds to construct nests on its branches, and when the birds brush towards these seed-laden branches, the Pisonia’s sticky seeds get caught to the birds’ feathers. After a while the seeds fall off, ideally when the birds had travelled to a different island. However someplace alongside the Pisonia’s evolutionary historical past, one thing went horribly fallacious. As an alternative of utilizing the birds as vectors of pollination, the Pisonia finally ends up killing numerous birds by ladening them with a lot seeds that the poor birds are unable to fly away. They fall to the bottom and starve to dying, or get eaten by predators.

Black noddies nest on Pisonia timber in Heron Island, Queensland. Photograph: Christopheb / Dreamstime.com

Pisonia timber, additionally nicknamed “bird-catchers”, are present in tropical habitats, primarily islands within the Caribbean and Indo-Pacific. The timber produce lengthy seeds, coated with a thick mucous and tiny hooks that follow nearly something that brushes towards them. The seeds develop in giant tangled bunches, and every bunch can bear something from a dozen to over 200 seeds.

The Pisonia tree flowers twice a yr, and the timing of those occasions coincide—naturally via years of evolution—with peak seabird site visitors to the islands. These seabirds use the Pisonia for nesting, and when the younger ones hatch and fledge, the result’s usually tragic. The younger birds get entangled and entrapped within the sticky bunches. Even a handful of seeds can weigh a chicken down, making them unable to fly. They fall down and ultimately die of hunger, or turn out to be meals for scavengers. At different occasions, the birds die within the timber; their mummified corpses hanging from the branches “like macabre Christmas tree ornaments.”

Seeds of Pisonia trees

Seeds of Pisonia timber. Photograph: Christopheb / Dreamstime.com

Seeds of the Pisonia tree are covered by a sticky resinSeeds of the Pisonia tree are covered by a sticky resin

Seeds of the Pisonia tree are coated by a sticky resin. Photograph: Scott Zona/Flickr

The Pisonia tree’s grisly conduct has a devastating impact on the chicken inhabitants. A research performed on seabird inhabitants on Cousin Island in Seychelles revealed that the Pisonia tree killed 1 / 4 of White Terns and practically a tenth of Tropical Shearwaters through deadly seed entanglement.

Scientists have questioned if there may be any evolutionary profit derived by the Pisonia tree by killing birds. One speculation said that the timber get elevated vitamins from the decomposition of chicken corpses that fall on the foot of the timber. However when Alan Burger, an ecologist on the College of Victoria, analyzed seedlings sprouting close to chicken carcasses on Cousin Island, he didn’t discover any proof that appeared to point that the seeds have been sprouting any higher. As well as, the tree obtained much more fertilizer from the chicken’s droppings and fallen eggs, indicating they have been price much more to the tree alive than useless.

A wedge-tailed shearwater covered in sticky Pisonia grandis seeds in Tiam'Bouene islet, New-Caledonia

A wedge-tailed shearwater coated in sticky Pisonia grandis seeds in Tiam’Bouene islet, New-Caledonia. Photograph: Tristan Berr/Twitter

A white capped noddy tangled in Pisonia seeds at Heron Island, Queensland, Australia.

A white capped noddy tangled in Pisonia seeds at Heron Island, Queensland, Australia. Photograph: Christopheb / Dreamstime.com

Subsequent Burger tried immersing Pisonia seeds in seawater to check one other speculation that the carcasses of useless birds may wash ashore on one other islands, serving to seed dispersal. To check the idea, Burger dunked the seeds in salt water and located that they died after simply 5 days, ruling out the chance that the Pisonia could be utilizing useless birds as rafst to disperse seeds to faraway island.

“The outcomes from my experiments confirmed fairly convincingly that the Pisonia derived no apparent profit from fatally entangling birds,” Burger concluded in a paper than appeared on the Journal of Tropical Ecology in 2005.

“The entanglement and mortality of among the potential vectors will be seen as a unfavorable side-effect of choice for seeds with ample adhesion to slick to a chicken’s plumage for a number of weeks and resist the efforts of preening birds to take away the seeds,” Burger wrote.

A fledgling brown noddy entangled with seeds across its chest and tail

A fledgling brown noddy entangled with seeds throughout its chest and tail. Photograph: BBC

pisonia birdcatcher

Photograph: BBC

In different phrases, the seeds completely have to be sticky in order that they don’t fall off the birds. And since the resin steadily loses its adhesion, particularly when immersed in sea water, the seeds have to start out out extraordinarily sticky. Inadvertently, this ends in the dying of a whole bunch of hundreds of seabirds yearly.

Conservationist on Cousin Island at the moment are working to switch Pisonia timber with different native tree species to assist the ocean chicken inhabitants to get well. In addition they actively search out entangled birds and thoroughly clear them, earlier than placing them again in a tree.

Surprisingly, many seabirds appears to like Pisonia timber. “It’s uncommon to see a Pisonia tree that doesn’t have seabirds in it,” says Beth Flint, a wildlife biologist for the U.S. Fish and Wildlife Service.

Flint and her colleagues really work to encourage Pisonia groves, as a result of they’re prime nesting habitats for red-footed boobies, frigatebirds and black noddies.

References:
# Alan E. Burger, Dispersal and Germination of Seeds of Pisonia grandis, an Indo-Pacific Tropical Tree Related to Insular Seabird Colonies, Journal of Tropical Ecology
# Pisonia grandis…A grand drawback?, Seychelles Seabird Group
# Jason Bittel, This tree lures birds with a free lunch after which kills them, Washington Post
# The island paradise with a darkish coronary heart, BBC

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