This Tree Appears to Kill Birds Just For The Heck of It
It's not unusual for plants to stick, prick, or entangle their seeds into some hapless animal that steps too close in search of a meal or a place to rest.
But one genus of tree found in the tropical waters of the Indian and Pacific oceans has taken this method of distributing its seeds a little too far, killing many of the birds that land in its branches by weighing them down and preventing them from flying away.
The thing is, there doesn't seem to be a clear reason for this wanton slaughter, leading one ecologist to suggest that it's just one of those macabre quirks of evolution.
Alan Burger from the University of Victoria in Canada had heard of the Pisonia tree and its killer reputation back in the 1990s, so travelled to Cousin Island in the Seychelles to take a closer look at a population of Pisonia grandis and its seabird colonies.
Many of the tree's species produce long seeds coated with a thick mucus and small hooks, which stick to almost anything that brushes against them, including insects and many of the seabirds – such as noddies – that land or nest in the tree.
What sets the Pisonia apart from other trees that use glue or prickles to hitch a ride is that these seeds can pile up rather quickly – especially if a bird falls or lands among the pods on the ground – weighing down smaller individuals and making it impossible for them to fly.
If they're not picked off by a passing scavenger or predator, most birds die and decompose at the foot of the tree. Some poor victims can sometimes be seen still stuck high in the branches, as Jason Bittel at The Washington Post so colourfully puts it, "like macabre Christmas tree ornaments".
This isn't some occasional mishap either; it's so common, the Pisonia has been nicknamed 'the bird-catcher tree'.
