For birds, siblinghood can be a matter of life or death

https://www.npr.org/2024/05/01/ [login to see] /bird-siblings-siblingcide-boobies-woodpeckers-life-death
Human sibling relationships can get pretty complicated, but in the world of birds, siblings can be so impactful that their existence can mean the difference between life and death.

That's because avian nest-mates sometimes forge close, collaborative relationships that last their entire lives.

Other times, after an egg hatches, a baby bird might immediately get killed by its older brother or sister.