The other situation is if mom has O type blood. The same thing can happen as with the (-) and (+) blood type difference, but it is not as severe. If mom has O+ or O- blood type, and the baby has A+, A-, B+, B-, AB-, or AB- blood type, an ABO incompatibility can develop.
Why do howler monkeys howl? Howler monkeys live in family groups in the rain forests of South America. They howl so that other monkey groups do not stray into their territories. The sound also helps group members stay in contact with each other. Monkeys are communal animals that live in exclusive groups.
(see video below). Growls may be in the ear of the beholder. If a person is expecting a growl, anything a bear says might be interpreted as a growl. And some sounds do sometimes have a throaty quality. One of the sounds people might call a growl is the moan of fear. Bears that escape up trees at campsites sometimes moan plaintively in a deep voice.