Sunday, July 25, 2010

Great Blue Heron Gular Fluttering

By opening their bills, and vibrating their upper throat muscles and bones, herons (and a few other bird families) are able to increase the passage of air across the mucus membranes of their throats.  This behavior, called gular fluttering, increases heat loss on hot days.  Because of its permanent down coat and lack of sweat glands, the ability to lose excess heat is important to a bird.
On Friday I happened upon this Great Blue Heron gular fluttering. Temperatures, high for Minnesota, reached the mid-80s F.  In the photo below, you can see that the upper throat is expanded in this process, thus expanding surface area.  Blood flow in the throat is also increased and vessels are dilated to facilitate heat loss.
I am surprised that the bird, in order to cool off, did not wade into the water.  I suspect, however, that relatively little heat is lost through a heron's feet.  Heron feet contain counter-current exchanges between their arteries and veins, which have evolved to maintain heat during cold winter days.  I suspect that these exchanges can not be turned off and on.
While I watched, the heron occasionally peered into the water below its perch and speared small minnows. The heron successfully caught a small fish in each of the three attempts I witnessed. After consuming the minnows, the heron returned to gular fluttering.

Wikipedia incorrectly writes, "birds also avoid overheating by gular fluttering, flapping the wings near the gular (throat} skin."  Good Heavens!  You CAN'T believe everything you read on the Internet?

6 comments:

  1. Dan:

    Thank you for this particular post. I reside in the Tampa Bay area of FL where the mid 90's plus is common currently. Also as a beginning level birder w/ only a few years under my belt learning little bits of bird behavior as this are very helpful. I have noticed many times Great Blues w/ their beaks open, but did not give it any thought.

    Would this be also true for most Egrets? What about Ospreys?

    On a personal note I want to thank you for your course. As being retired I've been looking for a program to help me increase my basic knowledge before I purchase a more in depth ornithological-type textbook and try to delve into the subject more. I've been enjoying your course.

    Thank you.

    ric//

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  2. According to the Handbook of Bird Biology, birds that gular flutter include Pelicans, cormorants, herons, owls and nighthawks.

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  3. Thanks for this information. Last weekend on Mt. Ranier in Washington I took a video of a White-tailed Ptarmigan "panting". You can look at the video among other photos on my flickr site.
    http://www.flickr.com/photos/42693729@N04/
    I didn't know it was called gular fluttering. This is good information.
    Bill Bradford
    billbradford1@gmail.com

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  4. Very fine ptarmigan video, Bill! I have only seen ptarmigan once, and that was in Colorado. I will look for them on Mt. Ranier next time I am there--soon I hope! Your ptarmigan may well be panting. My heron had a lot more movement on the sides of its throat. Heat-stressed Domestic Chickens may pant 300 times per minute (Welty and Baptista, The Life of Birds, 1988!

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  5. Great info thanx, just saw my pigeon doing this didn't know it was panting till now

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  6. Please, daily, I get a blue heron hanging out by my yard, in front of a Lake our home faces. In some cases, like today, the temperature is about 55 degrees F and windy. As expected, our friend showed up and I noticed he/she was fluttering. You say they do it when it's hot...any reason for this fluttering when is actually chilly outside? We live in the Tampa area of Florida. Thank you for all your valuable information!! Best Regards..Val

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