I do it all the time , and yes it is ethical IMO. The state of Ohio dose it a few times a year in several different places to allow hunters in areas that don't have many wild birds hunt them .
I am a member of a hunt club , 6-8 times a season we release quail, chucker and pheasants (both hens and cocks)and we hunt them either a few hours later or the next morning.
We have hold over birds nesting and raising young.
In my area there is also pay to hunt places that are liscensed by the state ,they place birds in the feilds for you to hunt .
Here in ohio many bird hunters and their dogs only see these birds unless they go out of state.
YES the birds are not as smart but they eat just as good.