Boo-Birds (also known as Doom Hens) are rare and sinister little birds that have the power to wilt anything they despise thanks to their antenna which can transform their hate into a beam of hateful energy which can cause objects to wilt and people to lose all strength and ambition for as long as the Boo-Bird directs its hate at them. The Boo-Bird is named as such because every time it uses its power it yells out "BOO!" as though it were heckling its target.
In issue 29 of the Popeye comic book, it is revealed that the Sea Hag had been raising a Boo-Bird for 20 years, teaching it to despise Popeye by showing it a picture of the sailor every time she deprived it of food. She then tricks Wimpy into giving Popeye the Boo-Bird as a present on his birthday, who then turns Popeye into a helpless weakling the minute it yells out its "BOO!". The Sea Hag soon arrives with her minion and has him pummel Popeye. Olive Oyl then tries to give Popeye his spinach in hopes that it will restore his vitality but is unable to due to being thrown around by the big palooka. Olive then uses a shotgun to shoot the spinach into Popeye's mouth, which quickly gives him back his will and vitality and he proceeds to wallop The Sea Hag's minion to a pulp before sending him flying through the roof. The Sea Hag then flees with her Boo-Bird, and the little bird of doom was luckily never seen again.
- The Boo-Birds can be seen as the opposite of the Whiffle Birds, as Boo-Birds discourage others and drain their energy while Whiffle Hens can encourage others and bring them good luck.