To tame a Hesperornis, first kill a fish and then drag its body to the bird for it to eat. The fish's size is significant in determining the number of fish needed; for instance, a fish of size 1.0x seems to be twice as effective as one of 0.5x. The fish's level doesn't influence the taming process. Among all fish, the Sabertooth Salmon is the most efficient, equaling around four Coels of the same size. Meanwhile, a Piranha is roughly equivalent to 2.4 Coels.