In many parts of the country, one thing you can count on for opening day of the bird season is warm weather.
What's your dog's best defense against heat? Aside from not hunting at all, it's critical that he be well conditioned. Like people, overweight and poorly conditioned dogs are at a much greater risk for heat stroke and other heat-related problems. A few days of running him prior to the opener isn't enough. You should start conditioning your dog with every-other-day runs at least a couple months prior to the season.
Assuming your gun dog is in good shape, you've taken care of one of several controllable variables. Consider hunting right after daybreak when it's still
cool and quitting by mid-morning, before temperatures rise to dangerously high levels.
What temperatures are dangerous? For a hard-charging pointing dog, it might be a mercury reading as low as the mid 60s. On the other hand, a retriever sitting in a blind near a pond or stream can cool off at will and should be able to handle temperatures considerably higher than that. Remember, though, that all hunting dogs handle the cold much better than they do the heat.
Dogs that are actively engaged in running and hunting in warm weather need to be monitored closely. Always carry extra water--a gallon isn't too much for a half-day hunt--and water your dog whenever he asks for it. If he doesn't ask, water him every 15 or 20 minutes anyway, and make sure he drinks at least a little.
A dog's normal temperature is between 99.5 and 102 degrees; when his temperature reaches 103 or above, he may be in trouble. Watch carefully for signs of distress: glassy eyes, a staggering walk, drooling or panicky, uncontrolled panting. If any of those signs are present, stop the hunt immediately, water your dog and immerse him in cool water if there's a pond or stream nearby. Lacking that, splash some water on his belly.
If there's no cool (not ice-cold) water available, immediately find shade and keep your gun dog there. When he regains his composure, take him straight back to the truck, turn the air conditioner on and retire him for the day. He's done hunting until he's completely rested. A follow-up trip to the vet isn't a bad idea, either.
Always pay attention to the heat. Remember, a dog works close to the ground, where green vegetation slows the breeze and raises the temperature. Air that seems cool to you may be too hot for your pup. Rest your dog often, water him and watch for signs of distress. A good dog will hunt until he collapses. It's up to you not to let him do that.