Okay, so I DEFINITELY agree with the eagle and the platypus and the animals reproducing. I also think it would be cool to add more temperate animals to the show, since although there are lots of polar and tropical critters, the temperate area seems kind of neglected.
Deer. This docile animal would be an easy source of meat, and would also give up leather. They could also add an occasional stag to the field that tries to defend the deer like bulls do cows.
Rabbit. Yes, another easy source of meat, and it would reproduce like CRAZY. Lots of defenseless rabbits for easy agriculture.
Grouse/pheasant/turkey. I see a lot of people requesting chickens, but no offense this is SURVIVAL craft. Chickens have been domesticated for thousands of years, and wild chickens really don't exist anymore (yes there are feral birds, and yes there are Junglefowl, but no they don't exist as you would find them on a farm). We DO however have these turkeys, grouse, and pheasants in the wild, and they are all known to be fairly common eggs layers. A defenseless brown bird that can but rarely flies and lays a lot of eggs would be EXTREMELY helpful. Ducks fly too much in this game, keeping them penned in is worthless really.
Goats: milk, meat, and even hair. Easy, semi-docile animal, can be a nice replacement for sheep. Goats are far more common in the wild than sheep. They should come when you ring a bell.
Bullfrogs. Yes it probably sounds stupid, but listen. In Challenging and cruel mode, it is WAY too hard to find food. A cheap, two punch-kill bullfrog would give frog legs and keep you alive for an extra day. They could possibly give poison too if they add it.
Swans. Someone mentioned swans earlier. Yes I think they are ugly, horribly aggressive creatures, but in the game they could be an aggressive creature that swims quickly and is not afraid to mail you if you get too close. Plus you could get bird meat and feathers. I come in contact with geese and swans on a regular basis, and while everybody thinks the other way around, swans are much more likely to kill you than a goose.
Pike: piranhas for the tropics, sharks and barracudas for the oceans, we need an aggressive fish for the cold regions. Pike would work perfect for this.
Otter. I love otters. They could eat fish and just be loveable and docile.
Also: it might be nice to add guinnea fowl and ivory. You dont have to add all of these, but at least a few would be nice.
Thanks for reading.