Monday, December 15, 2014

An Avian Sensory Organ

Male Northern Cardinal

I have suspected for a long time that birds must have some kind of organ that allows them to determine when a major weather system is approaching. There is a very obvious parallel between the number of birds at the feeder and severe weather. Turns out, there is a connection. Not only that, it was discovered one hundred years ago! That didn't take too long to enter into the stream of modern knowledge.

Female Northern Cardinal

The person who discovered this organ around 1912 or so was named Giovanni Vitali, an Italian anatomist. He was nominated for the Nobel in 1934 for the discovery of what is called the paratympanic organ (PTO) found in the middle ear of most birds. Yes, birds have ears. Vitali postulated that the sense organ functioned as a detector of minute changes in barometric pressure.

Tufted Titmouse

It is this receptor that puts birds in a frenzy to feed and find shelter before a storm arrives.  The PTO is like a built-in barometer which signals that air pressure is falling. It causes birds to change their behavior towards other birds. The sensory organ also causes them to change when they are active as well as their foraging habits.

Male House Finch

By surgically removing the PTO in pigeons, Vitali found that the organ was indispensable to flight. I am speculating here, but I would be willing to bet that eventually, scientists discover that the same organ plays a role in coordinating large murmurations (see my blog from November 27th) of birds, those large flocks of birds that seem to move and change direction as one organism.

Carolina Chickdadee

In the one hundred years since Vitali's discovery, there has been amazingly little research performed in the area. Birds are so sensitive to barometric pressure that the PTO essentially functions as an altimeter, helping to inform them of where they are in the air column. Not surprisingly, there is an equivalent sense organ in fish called the spiracular sense organ which has a similar function. When you think about how fish need to know where they are in the water column and how schools of fish can act very similar to large flocks of birds, it is not surprising that they would have a similar sense

Female Red-winged Blackbird

Navigation, migration, flight. There are modern mysteries in each of these areas that have yet to be understood. I wonder if the paratympanic organ isn't key in all of them. The difficulty of reaching and operating on this organ is to a large degree what has hindered research on it.

Male Common Grackle

Apparently, not all birds have a PTO. Then again, some birds that you might not expect to have the organ - flightless penguins, for example - do have the organ. When you consider that emperor penguins, for one, are known to coordinate their swimming (water column) in groups, perhaps it is not to be unexpected. Plus, penguins navigate over long distances of open ocean foraging for food before returning to feed their young. It is possible the organ plays a function here also.

Dark-eyed Junco

It will be interesting to see what scientists discover about this fascinating organ in the future.

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