I purchased a cockatiel from a pet store 2 weeks ago. He mostly just sits silently on his perch all day. He doesn’t chirp or play. He will move to eat or drink. He generally looks healthy. I called the pet store and they told me to give him time but seems odd the bird is so silent. He generally seems pretty nervous. He will eat seeds out of our hand but will hiss or bite if we try to pick him up. Is this normal bird behavior? Does he just need more time to warm up?