Similarly to real life, these greedy douchebags will try to steal your sandwiches, however if you are drunk enough, you can stay up into the late hours of the evening and have deep insightful conversations with these feathered friends as they simply stare at you in confusion and bark in bird language. In return they will bring you magical fish as a reward.
I was attacked by one while mining flint and it stole my pick. Then it got my pike when I went to fight. That's when I noticed noticed that it didn't actually "steal" what was in my hand, but just disarmed me and dropped it in the ground. Check the ground and see if your stuff is there after they attack you. My pick was laying there near the spot of the initial attack.
When set to "Hunt & Retrieve" it will bring you dodos or fish and the dodos will give raw prime or a few of it. And fish will give raw prime fish meat. You'll know cause the corpse will glow yellow as the icthyornis is bringing it to you!