Absolutely. About 90 percent of the adult bird population will perish whether they are hunted or not. For efficiency at bird slaying, you, your student, or the both of you together, come no where near that of a skunk, fox, or crow that happens upon a nest, pre-hatch. If avian predators in your neighborhood are doing what they are doing in mine, it won't be long before bird numbers are depressed even further. There is very little you can do about the avians, either.
If you were going to take two birds anyway, and you just happened to get them off the same point, just unload the gun and continue the walk.
Shooting birds at 15 yards with number 9 shot doesn't actually sound that appealing to the gourmet in me. And he is a pretty lame gourmet, at that.
There were birds on that property before you were born. Birds will fly there after you are dead. The notion that you will effect that outcome by taking two instead of one seems a bit far fetched to me. I understand you are both old farts, but, the weight of an extra bird in the bag is it's own pleasure, and shouldn't tax either of you too much. Simply enjoy the day for what it is.
For a good book on the same subject, might I suggest "For a Handful of Feathers", by Guy De La Valdene?
An enjoyable read.
Best,
Ted