Serendipitous discovery landed me on the page Spiritual Meaning of Birds, Fowl, where I was surprised to read that at least Biblically "birds signify things rational and intellectual"; OK, owls I can accept - from at least the literary point of view - but the average garden-variety chicken?
Which then made me wonder where/how the acceptance of "bird-brained" (as in silly, of limited attention span, etc) came about, as opposed to the intellectual quality of your basic fowl. Of course, like all good cliff-hangers, I'm not going to reveal the specifics of which particular "bird-brainism" was engaging me at the time.
Nevertheless, for my own protection, I must point out the reference to "AC" on the above-mentioned hyperlink is not me. I did not put the reference there. I do now know who did. I have not gained any monetary or other benefit from the "AC" link on the Bible Meanings page.
Curses!!! I didn't mean to wreck the cliff-hanging experience for my reader. Sorry about that ...
Anyways, as an aside - it being the holidays 'n' all - this is an image of Keuleman's Laughing Owl, courtesy of Wikipedia. It is reproduced here under Creative Commons licence.
"This image is in the public domain because its copyright has expired. This applies to the United States, Australia, the European Union and those countries with a copyright term of life of the author plus 70 years."
So if you're resident in another country that possibly does not apply the Rule of The Shorter Term, I guess the answer is to not look at the image?
However, a really fascinating fact about the Laughing Owl is that it hasn't been seen since 1914. Which I guess is about the last time anyone heard someone whistling a tune for no apparent reason. Now that's going to be a really hard one to research! Good luck with that.