http://bukaymedia.com I first noticed this upside-down crashing into water while reviewing footage one frame at a time. During their high-speed dives, a fraction of a second before hitting the water, the 15 diving Brown Pelicans in this 10 second clip all twisted their bodies left to assume an upside-down position while maintaining their heads right-side up! The actual real time 10 second clip is shown at the end of the video. Another video at https://youtu.be/IRB9IVDM7Ns shows shows additional footage of the pelicans diving to catch fish at 40% actual speed.
Why would pelicans crash at high speed into the water back-first instead of belly-first? Why would they keep their heads right-side up, while flipping their bodies 180° on their backs before impact? Interestingly, all these birds rotated left when flipping over! Why didn't they ever rotate right? After hours of web research, I don't have all the answers. Here are my findings and some additional ideas. Perhaps you can help figure this out!
WHY CRASH INTO THE WATER UPSIDE DOWN?
Pelicans are sometimes described as crashing ungracefully into the water while diving for fish. Perhaps the "ungraceful" high speed crash is purposeful! Researcher Sandy Scott states that "They utilize a fascinating fishing technique of diving into the water at high speeds, crashing into the water upside down hence stunning the fish near the surface, and then scooping them up in their pouch." http://bit.ly/1OfCFR8.
If this is the case, why not crash belly first...unless perhaps the bony backside is more protected against the high speed impact. A person who autopsied a dead bird stated that "Brown pelicans, however, have a very nifty piece of flesh that helps them compensate for all that rough impact; as you can see, just underneath the skin, this bird looks like it’s wrapped in bubble-wrap or Saran wrap, and that’s exactly how it functions- it contains pockets of insulating air so crashing becomes a less jarring experience." http://bit.ly/1EHAa9B.
Maybe hitting backside first results in less physical damage than would result from impact on the softer underbelly. Consider how a chicken is built with a bony back and a fleshy softer underside. If the structurally strong bony back of the pelicans is cushioned by a "bubble wrap" layer of air to cushion the blow, perhaps this helps explain why this evolutionary back flip has become standard operating procedure for the Brown Pelican.
It also makes sense to me that the bird would be more stable in the water after a dive if it had more bubble wrap on it's back than its belly. Otherwise a high buoyancy belly might make the bird tend to float belly-up when it wants to be belly-down in the water. Perhaps a bird anatomist out there in Internet-land, who happens to read this, will provide us with some insight on this "bubble wrap" theory.
My step-daughter, Jessica, thinks that landing on its back this somehow provides an advantage in scooping up the fish. Wouldn't it be interesting to have underwater footage of this event?
WHY ROTATE LEFT AND NOT RIGHT?
Sandy Scott believes it is because this maneuver protects the vital tracchea and esophagus organs which are located on the right side of the neck at http://bit.ly/1OfCFR8.
I have searched for anatomy pictures related to Brown Pelicans and couldn't find any additional information to support this theory. If there is a wildlife veterinarian or bird pathologist out there who could confirm that the trachea and esophagus is actually located on the right side of the Brown Pelican's neck, please let me know or post a comment.
WHY ROTATE THE BODY BUT NOT THE HEAD?
The body rotation event happens so fast, once I started to see it in slowed down footage, I assumed that the head would also do a 180°. Only by looking frame by frame did it become obvious that the head didn't flip along with the body. The orange-colored throat pouches made it easy to see that the heads remained in their original orientation throughout the dive.
Perhaps nature is following the adage that "if it's not broken, don't fix it." As long as the head works topside up, why flip it upside down? That's the best I can do on this mystery.
If you would like to see some still images of the upside down behavior, check out the following links:
Yep, that really is surprising! Birds are very good at holding their head still while moving their body about. It facilitates a fixed gaze at their target while moving in. I suspect the head doesn't rotate so as to be sure to keep their eyes locked on their prey.
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