How to farm golden hesperornis eggs efficiently:

1. Get a tamed female hesperornis and set it to neutral

2. Put it on your shoulder

3. Go to a river or a place with a lot of fish

4. Go to either a coelacanth or sabertooth salmon nd kill it (piranhas don't work)

5. Release the hesperornis and let it harvest the corpse

6. Put the hesperornis back onto your shoulder

7. Do steps 4-6 four more times, essentially letting it harvest 5 fish corpses.

8. Release the hesperornis on land

9. Wait for it to lay a normal egg, if it's not ready to lay an egg, it will say "enable wandering or mating to mate", if it is ready, it will say "ready to mate" (basically wandering will be automatically turned on if it is ready to lay an egg)

10. Pick up the normal egg

11. Repeat steps 3-7 three more times

12. Release the hesperornis on land

13. Wait for it to lay a golden egg, if it's not ready to lay an egg, it will say "enable wandering or mating to mate", if it is ready, it will say "ready to mate" (basically wandering will be automatically turned on if it is ready to lay an egg)

14. Pick up the golden egg

15. Repeat the entire process to farm golden eggs. You can also put the golden egg in somewhere that preserves food or cook it into extraordinary kibble right away, they have a noticably short spoil time but it's not that bad.

Summary:

Basically you have to have the hesperornis harvest 20 coelacanth or sabertooth salmon corpses, which can be divided into 3 intervals of 5 for it to lay a normal egg, and finally another 5 for the golden egg.

Explanations:

Turning the hesperornis to neutral will have it be able to harvest coel and salmon corpses, while preventing your other tames (if you have them nearby) to also target whatever your hesperornis is targeting if it is set to aggressive.

It will also save time if you don't want to wait for the hesperornis to do the dive attack again after it kills a fish.

Having the hesperornis harvest the coel/salmon corpse is enough for it to be stacked to the hesperornis to be able to lay eggs, you don't have to have the hesperornis kill the coel/salmon.

After it harvests 5 coel or salmon corpses, wandering will automatically be turned on to prevent it from doing any other action, (and probably for it to wander to land) this can be indicated if it says "ready to mate", in the creature window.

It will always have to harvest 5 fish corpses every time you want it to lay an egg, no more, no less, that's a fact.

It will always lay 3 regular eggs before it wants to lay a golden egg, that's a fact.

And finally:

No, piranhas don't work for hesperornises if you want them to lay eggs. That's a fact, and probably the source of some of y'all's error.

For going against the norm, i'll gladly accept your downvotes, but please consider everything in this tip as 100% accurate.