Some of those birds are very powerful, like American Redstart. It only costs 2 food, is worth 4 pts, and allows you to get an extra food from the feeder of any type. That ability is huge.
Others that are very strong are the Red-Breasted Merganser. It's Ruddy Duck and Pied-Billed Grebe, but is worth 3 pts instead of 0. The Brant can be powerful if the birds in the tray are good. Canvasback is good because it connects to a lot of bonuses and is a star nest. Scaled Quail is a cheap bird you can drop immediately in the grassland if you get it in the beginning.
These cards are meant to make learning the game a lot easier for beginners and gives them good cards so they don't get pummeled by a bad starting hand. The problem is that if a player gets a few of these in their opening hand, then it becomes very difficult to overcome them, especially with Painted Whitestart (Or any bird that gives a food on activation) and American Redstart. They'll be able to get whatever food they want and basically can drop whatever food they want.
There are also players who got the game when it originally didn't have those cards and prefer to play the vanilla version.
