What you need to tame the pelagornis :

1 bow with around 12 tranq arrows/club

1 bola

Around 6 fish

Step 1 : Find a pelagornis they are usely around beaches

Step 2 : bola it

Step 3 : Club it or use tranq arrows but be careful clubbing wil not work if its to high level

Step 4 : put the fish in the invetory and then you have yourelf a decent flyer for the earlygame