In my practice it has shown that around half of game in the bag can be contributed to the dog. A lab will assist with flushing and retrieving ducks and upland birds. He will flush ducks that otherwise would never leave the water. Then, ducks that have been knocked into the weeds can be recovered. It's part of ethical hunting to pursue and recover any game that may be injured. A good labrador will recover any injured game. The same applies to hunting upland game. Pheasants, especially the once that are hunted and educated by falcons or hawks will not flush by stumping to the grass. A lab will get any of them going.
A good nose goes a long way. The lab should mark live or wounded birds at 20 yards or more. Only testing in the field will show the quality of the labrador's scenting abilities.
The lab needs to have good drive and bird sense. This doen't mean he needs to have a title studded field trial pedigree. Most labradors have good retrieving drive. However, full field trial dogs are too hyper to be calm around the falcon. Full show dogs don't have enough stamina to work all day. The best bird dogs are service dog type labs. They should have around 50/50 genetics.
Not all labs are created equal this way. The labrador needs to work independently. The lab needs to mark any bird that is knocked down and work it independently, without a lot of directions from the handler. I'm busy to recover the falcon after the flight.
Make sure the parents of your labrador are health tested. Too many times, I have seen hunting labs with genetic disorders. I have seen a lab collapse from exercise induced collapse at a pheasant preserve, people hunting with half blind Labradors or lead their lab up a ramp because of bad hips. None of these needs to happen in this day and age. Genetic testing is available