Most living species attack -- for food, for survival -- but they usually do so out of instinct. There's one tree in the world that doesn't seem to play by the usual rules: Pisonia grandis. This genus of tree kills birds regularly with no clear reason whatsoever.
According to a report from the Washington Post, Pisonia trees -- also known as "birdcatcher trees" -- are found in Hawaii and New Zealand as well as in India. It's not quite as in-your-face deadly as other killer plants, but the growing pile of dead birds at its feet speaks volumes about its lethality.
The Pisonia produce sticky seeds that can trap insects. When birds land on the branches of the tree while hunting for insects, these seeds can land on them. Too much of the seedpods and the creatures are too weighed down to fly.
Not only are they stuck on the ground or the branches -- virtually sitting ducks for predators -- but even left untouched by other animals, they starve to death. Other predators like owls and various birds who come close to feed on the dead birds have also been known to get stuck and killed after getting pelted with the seedpods as well.
The strange thing about this is that there's no good reason for this regular massacre. Back in 1999, University of Victoria ecologist Alan Burger tried to find out the benefit the trees gain from killing the birds with their seeds, but came up quite empty.
"The results from my experiments showed quite convincingly that the Pisonia derived no obvious benefit from fatally entangling birds," Burger explained of his travels to Seychelles in the Indian Ocean. Seeds didn't grow any faster or better with proximity to dead birds, and nutrients from the dead birds are minimal compared to the ones the trees get from all the living birds.
One potential reason for the Pisonia tree's behavior is that the birds are meant to act as carriers for the seeds to reach other islands. Dead birds making their way to bodies of water to get to other islands don't work as the seeds die within five days of being submerged in the water. However, Burger discovered that the seeds survive when they are dunked occasionally over four weeks.
"Having the birds alive seems to be the key to dispersal, but an unfortunate consequence of having extremely sticky seeds, and producing many seeds in a cluster, is that some birds get fatally entangled," Burger said, suggesting that the deaths of the birds are merely an unfortunate side effect rather than the point of Pisonia's actions.
Burger's research on the trees was published on Journal of Tropical Energy.