Heat can be deadly for our pets. Pet birds, for example do not do well when they become overheated. They can easily go into a distressful situation that needs immediate medical attention. Overheating can be deadly. The bird will stay on the bottom of the cage and become very listless, due to lack of energy -- not moving.
You can mist your pet bird with water if that won't scare it. A fan directed near the cage can cool your bird down. Do not place the fan so it is blowing directly on your bird. Air conditioning can help a lot.
Be sure to keep the cage out of direct sunlight near a window during the summer months. Glass heats up very fast.
You can place gel freezer packs inside the bottom of the cage to provide more cool air.
Lastly, always remember to change drinking water and bath water often. Food should be taken away if it's not eaten, because bacteria can quickly contaminate the food.