Entities Cease to Exist

I had 2 parrots sitting and walked maybe 50 blocks away. Came back and both parrots were gone. Not on my shoulders, no chirping to be heard, no "Parrot was killed by X" message. In addition to this, I later logged out while in a boat, only to log back in with the boat nowhere to be found. Not in my inventory, not lagging behind, nothing.