Bird

The Bird Egg is the Uncommon-rarity egg of the Forest, and the pet inside it is Bird. Forest is the starting zone, so there is no speed gate — the Chicken guardian is the only thing between you and the nest.

Base income is $8/s. Among the 8 pets tagged Forest on the wiki that puts Bird at number 6 — Brr Brr Patapim tops the Forest at $1.8K/s. Remember the game multiplies this base by the size roll and by the mutation, so two Birds can earn very different amounts.

With a colour mutation and no size bonus, the same Bird would earn roughly: Silver ×1.2 ≈ $9/s, Golden ×2.5 ≈ $20/s, Rainbow ×3.5 ≈ $28/s (multipliers from the wiki's Mutations page; arithmetic is ours). Add a Giant (×3) or Huge (×5) size roll on top and the numbers multiply again.

Hatching it pays a one-off reward of +500 Speed, $800, and the egg takes 25s to grow in the pen. That reward is the reason low-income eggs are still worth stealing early: the speed bonus is what gets you into the next zone.

Uncommons are cheap speed: hatch them for the reward, then move on.