Chicken à la King

Whenever a 6 is rolled on a six-sided die, put a +1/+1 counter on each Bird. (You may roll dice only when instructed to.)
Tap an untapped Bird you control: Roll a six-sided die. (Like now.)

Dovescape

({W/U} can be paid with either {W} or {U}.)
Whenever a player casts a noncreature spell, counter that spell. That player creates X 1/1 white and blue Bird creature tokens with flying, where X is the spell's mana value.

Free-Range Chicken

{1}{G}: Roll two six-sided dice. If both results are the same, Free-Range Chicken gets +X/+X until end of turn, where X is that result. If the total of those results is equal to any other total you have rolled this turn for this ability, sacrifice it. (For example, if you roll two 3s, it gets +3/+3. If you roll a 4 and a 2 for this ability later that turn, sacrifice it.)

Poultrygeist

Flying
Whenever a creature dies, you may roll a six-sided die. If you roll a 1, sacrifice Poultrygeist. Otherwise, put a +1/+1 counter on Poultrygeist.

Attempted Murder

Choose target creature. Roll X six-sided dice. For each even result, put two -1/-1 counters on that creature. For each odd result, create a 1/2 blue Bird creature token with flying named Storm Crow.

Mesa Chicken

Stand up, Flap your arms, Cluck like a chicken: Mesa Chicken gains flying until end of turn.

Chicken Egg

At the beginning of your upkeep, roll a six-sided die. If you roll a 6, sacrifice Chicken Egg and create a 4/4 red Giant Bird creature token.

Neverwinter Hydra

As Neverwinter Hydra enters, roll X d6. It enters with a number of +1/+1 counters on it equal to the total of those results.
Trample
Ward {4} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {4}.)

Ancient Ziggurat

{T}: Add one mana of any color. Spend this mana only to cast a creature spell.

Elvish Impersonators

As Elvish Impersonators enters, roll a six-sided die twice. Its base power becomes the first result and its base toughness becomes the second result.

Animal Sanctuary

{T}: Add {C}.
{2}, {T}: Put a +1/+1 counter on target Bird, Cat, Dog, Goat, Ox, or Snake.

Goblin Bookie

{R}, {T}: Reflip any coin or reroll any die. (Activate only any time it makes sense.)