Birds have no sweat glands, but need to regulate their body temperature like you and I on a hot day. The other day I saw a great blue heron in a wooded area by a pond’s edge, yet could not get a photo so I walked the trail and looped back 50 minutes later to see if the bird emerged. It did!
The great blue heron had its wings open to catch a breeze. I could understand the need to cool off in the almost 100 degree air temperature, but I actually had never seen a bird doing this behavior. The bird held his wings open for 8 minutes.
Then the heron closed its wings and opened its mouth as shown in this photo:
Birds open their wings to circulate air to their hot skin and lower body temperature. Passerines or perching birds will pant to lose heat through their respiratory system, but a great blue heron is not a passerine. It will lose heat through a rapid vibration of their upper throat and thin floor of their mouth. I was across the pond from the bird; however, I could see the bird’s throat vibrating. Eleven minutes later the bird had its wings and mouth open.
This bird was working hard to cool off. It had been a half hour observing this bird, so this was the last photo I took … I needed to cool down my own body too. Fun fact I learned while researching birds cooling themselves: turkey vultures urinate on their legs to capitalize on evaporative cooling … what? really?, wow! Isn’t it fun to learn something new everyday?