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The ibis and the kiwi are stubborn diggers, probing in the sand and soil for worms and other buried prey. Sandpipers can also be seen along the shore digging up small creatures with their beaks. It has long been thought that these birds used trial and error to find their prey.
But then the scientists discovered something much stranger: their beaks are threaded with cells that can detect vibrations traveling through the ground. Some birds can directly feel the movements of their distant prey, while others pick up waves bouncing off buried shells – echolocating like a dolphin or bat, essentially, across the land.
There is another strange detail in this story of the unusual senses of birds: Ostriches and emus, birds that definitely don’t hunt in this way, have beaks with a similar internal structure. They are honeycomb with pits for these cells, even though the cells themselves are missing. Now, scientists in a study published Wednesday in Proceedings of the Royal Society B report that the ancestors of prehistoric birds dating back almost to dinosaurs were most likely able to sense vibrations with their beaks.
Birds that use this remote sensing today are not closely related to each other, said Carla du Toit, a graduate student at the University of Cape Town in South Africa and author of the article. This made her and her co-authors curious to know when exactly this ability evolved and whether ostriches, which are close relatives of kiwis, had an ancestor that used this sensory ability.
“We took a look to see if we could find fossils of early birds from that group,” said Ms du Toit. “And we are very lucky.” There are very well-preserved bird fossils called lithorniths that date back soon after the event that led to the extinction of non-aerial dinosaurs.
First they had to collect data on the beaks of over 50 bird species so they could tell how similar or different the fossil birds were to modern birds. The team recorded the number of pits in the beak bone and the size of the beak and head – important details because birds that dig for their food have a distinctive shape.
Then they took a look at the litornites. And indeed, the ancient beaks and head structure were extremely similar to the beaks of kiwis, ibis and sandpipers, much closer than any other bird in the study.
“They appear to have this organ and have been able to use their remote sense of touch to probe and locate prey as well, which is really interesting, because it just shows this is really old,” said Ms du Toit.
This means that the ancestors of ostriches and emus lost the ability sometime after the litornites lived, leaving only traces in their bone structure of this lost talent. They also lack the enlarged brain regions that kiwifruit, ibis, and shorebirds devote to processing sensory information flowing from their beak.
Ms. du Toit and her colleagues are now studying the hadeda ibis, a South African bird that uses remote sensing, to see how far it can sense hidden objects, perhaps buried up to eight inches below the surface.
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