I looked in on a chickadee incubating eggs in a nestbox once and it puffed up and to me, it sounded like it exhaled all the air in it's tiny body. I don't remember that it was a "popping" noise, but it certainly surprised me and I closed the box and left it alone. Kathleen __________________________________________________ ########################################################### * Audubon Society of Missouri's * * Wild Bird Discussion Forum * *---------------------------------------------------------* * To subscribe or unsubscribe, click here: * * https://po.missouri.edu/cgi-bin/wa?SUBED1=mobirds-l&A=1 * *---------------------------------------------------------* * To access the list archives, click here: * * http://po.missouri.edu/archives/mobirds-l.html * * * * To access the Audubon Society of Missouri Web * * Site: http://mobirds.org * ###########################################################