Orca moms fiercely protect their sons from bullying and fights — but not their daughters, study suggests

• Older orca mothers may protect their sons from bullying well into adulthood.
• Orca males carry fewer bite marks if their moms are alive in their old age, a study found. 
• The research may explain why orcas are one of only six species to have menopause. 

Killer whale mothers may be protecting their adult sons from bullying and fights — but leave their daughters to fend for themselves, a new study suggests.

The research found that adult male orcas were much less likely to carry the marks of "social injury" — orcas attacking other orcas — if their mothers were still around past their reproductive age.