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Hollow bones and air pressure

By Ranger Steve Mueller

Many people have heard birds sense weather change before clouds, wind, or other obvious indicators. Some have heard birds perceive air pressure drop causing altered behavior. 

One indication reported is that bird feeders empty more rapidly before a storm. A family or school activity might document this by observing the length of time required between feeder filling when weather is stable or lowering. Experiment to determine if it is different when air pressure shifts. 

I described a personal experience a decade ago and it is time to revisit the topic. Repetition helps and many readers likely did not read my original account. Weather forecasters reported a new United States record low air pressure on Thursday, 28 October, 2010 and it impacted me physically. In retrospect I hypothesized what happened and now I empathize better with avian neighbors in my yard. 

The day before, I moved lightweight lawn chairs to the shed because hurricane force wind gusts were on the way due to rapid air pressure lowering. We were advised loose items could become projectiles. It only required lightweight lifting and it seemed within my capabilities. I had seven fractured vertebrae that occurred spontaneously from the cancer. I needed to be careful and cautious because of my porous deteriorating bones.

Thursday morning, I was experiencing severe low back pain in my sacrum. I wondered if I had fractured another bone moving chairs. Family members thought I should see the doctor because pain was obvious from my stooped posture and frequent face grimaces. 

The winds howled for two days and by Friday night I was feeling fine. I think high air pressure in my abnormally porous bones was forcing its way out to equalize air pressure associated with the big drop in air pressure outside my bones. The force exerted great pressure outward in the bone causing pain. Perhaps the pressure could even crack fragile bones. Pay attention to your bones during big air pressure changes.

Birds have hollow air-filled lightweight bones that permit easier lift for flight. The hard outer layer of bones, called the periosteum, does not easily permit quick air movement. I suspect when air pressure changes slightly or greatly, bird bones are more sensitive than mammal bones because of greater air space in bird bones. Air pressure equalizes and will be most noticeable when pressure is high inside bones and low outside. 

Compare this with pressure in your ears when going up or down mountain elevations. A pressure problem is not noticed when walking up or down 3000 feet because pressure equalizes slowly. Driving is different. We experience ear pain with rapid elevation and air pressure changes. It is worse when sinuses are congested and makes pressure equalization more difficult.  

Birds probably do not normally feel bone pain with small weather changes. When there is a rapid air pressure drop, it may likely be perceived with moderate ache sensation. I wonder if birds learn to associate bone ache with the coming of a storm and deliberately begin feeding or storing food more heavily. I have previously written about American Robins and Black-headed Grosbeaks having a rain song minutes before a strong weather front even though we perceive no apparent pressure difference. 

I am currently reading about bird brains and associated learned behaviors. No mention is made about air pressure changes in bones or how it might impact bird nature niche behavior. Normally air pressure changes gradually and should not create discomfort. I hypothesize it might bring about subtle anatomical sensations that might alter bird behavior consciously or subconsciously. 

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at the odybrook@chartermi.net  Ody Brook, 13010 Northland Dr, Cedar Springs, MI 49319-8433, 616-696-1753.

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