So no ones gonna mention that you can use a fishing rod on its back (apparently).

This bird restore stamina very fast when in water up to let the others see this

The Pelagornis can get a lot of Organic Polymer from penguins.

Since patch 2.25 released April 8th they now reduce the weight of polymer by 80% when in the Pelagornis and they harvest it 30% more now

Only eats fish, don't forget that

Hate that you fall off of your pteranodon if you hit water? Not only do you stay on your pelagornis, but it lands on top of the water! Better yet it will swim!

One Pelagornis can get you SO much organic polymer if and only if you kill the non-adult Kairukus. On my rates (2× harvest and 2× resource hp) I got roughly 230 organic polymer from just one juvenile Kairuku. The fact it also has insane weight reduction for the poly makes it optimal, and while you might say "The dangers of the ice biome are on your tail," then remember that a Pelagornis can just sit on water, which is where most ice biome creatures fail due to their immensely slow swimming speed, so you always have a save zone.

Single player uses:

1. Early game travel mount: Pelagornis is slightly slower than pteranodon and has equally bad weight and stamina, but since it can swim you won't immediately get dismounted if it force lands you into the water.

2. Free organic polymer: Pelagornis has the best gathering rate for organic polymer of any dino, set one to aggressive in a cage with mating penguins and air conditioners.

Pelagornis' can land on both land and water, so they are very ideal for scouting as they can go anywhere, but they have a low movement speed and weight so not an all around good flier