I've been looking at pumps, CO2s, springers, and now PCPs for weeks.  I need to eliminate some avian pests.  Secondarily I would like to get mice and ground squirrels as needed.  Third, it would be cool to shoot tiny tiny dots in my backyard, 20-25y.  Maybe farther in the desert surrounding my home.

Noise is not a HUGE issue, however it is a consideration.  More of a consideration is neighborhood use.  I have a large field behind my home, however there are houses several hundred yards away, and folks walk and ATV in the wash between my house and the distant houses.  I had considered the Marauder .25cal deal posted in this forum (thanks to OP) but I'm afraid misses and/or pass-throughs would encroach on others' yards and folks in the area.  

I'm thinking either airsoft (?) or .177 in the 500fps +/- range?  Growing up, my little Daisy 10 pump was plenty accurate for an 8-year-old, and my CO2 pistols were fun but loud.  

I'm now a hunter and big centerfire rifle shooter, precision long range at times, and the idea of an "accurate enough of an 8-year-old" $59 wal-mart gun does not appeal to me at all.  However, the $600 +/- investment for a good PCP + pump + accessories, all the while likely being way too powerful for suburban use, is of concern.

Rifle, pistol, or hybrid, what is the happy medium between wal-mart box gun and entry-level PCP?  .177 I suppose, reasonably quiet, relatively accurate, not strong enough to send a stray pellet 500y.

Thanks.

https://www.ar15.com/forums/t_1_5/2722163_Starling-eradication----birds--Need-a-good-pellet-rifle-recommendation-.html

The .177 pellets of just about any design will not go any further than about 450 yards (no matter the initial velocity), and are adequate for any of the critters you have described.  In addition, the pellets are less expensive than the .22 or .25 per shot as the tins are more based on price per weight than per round.  For PCPs, the Benjamin Marauder has been the benchmark for entry level guns, and you cannot go too much wrong with them.  There are others by different companies which compare favorably at similar price points.  

If you are fortunate enough to have an airgun store near you, I'd advise going to it and get a feel for how the particular models handle.  Some you may find awkward and clunky, while others just seem to fit well.