Hanging out in our back yard on a hot afternoon are two of our local murder. They were hot and in poor feather. It is that time of year after the babies have been kicked out of the nest and weaned, when molting begins.
On the Audubon.org web site they give us this little blurb about birds and how they use this open mouth behavior to cool off.
When it’s hot, some species will also resort to gular fluttering. The bird will open its mouth and “flutter” its neck muscles, promoting heat loss (think of it as the avian version of panting).
If you want to know more about molting check out a post I did earlier around this topic. I like to think of molting like getting new school clothes each fall. Birds are not the only thing that molt but they are the ones we notice the most.