It is important that you clean your birdhouse regularly and consistently.
When you leave your birdhouse to get hot and unhealthy often, your birds stop laying eggs until you clean your birdhouse again. When your birds aren't laying, that costs you as you no longer get eggs you would normally be getting.
Players who are consistent and diligent with their birds often end up with at least the correct number of eggs by their birds, and sometimes, even a little extra.
Your cozy friends rely on you for their care. Look after them, and reap the rewards.