My theory is that there is more to the name bird mom. In "Giant Woman" as soon as Pearl begins to Squawk the Big Bird Appears. I said that I think Pearl is made of shards. The Big Bird is as well. When it poofs (disappears) it can make sparkles that become little birds that can move on there own and attack. Pearl has a similar ability. When her spear disappears many little sparkles appear. In Sardonyx she can make living dragonflies when her curtains disappear. Opal can make her arrow split into many tiny arrows. Pearl has a spear that can pierce through things. The big bird has a beak and talons that can pierce through things. The only difference is that the Big Bird loves to eat and Pearl doesn't. You can become corrupted when you think that you are a monster like in "reformed" with Amethyst being close to corruption. Also in "so many Birthdays" with Steven becoming old because he thought he was. So when you corrupt you become like the opposite of what you really are.
Amethyst isn't really a monster and Steven isn't old. So Pearl that wouldn't eat, would want to eat when it corrupts.