All parents make sacrifices for their offspring, though some parents – and some species – make greater sacrifices than others. Children are lifelong commitments, after all. While this is typically the norm in the human world, it may surprise you to learn that the same sacrificial nature can be observed in the animal world, as well. Researchers studying killer whales have discovered that female orcas with adult sons are less likely to reproduce again. Interestingly, this effect is not observed in female orcas with adult daughters. According to Dr. Michael N. Weiss, research director of the Center for Whale Research, raising a son “cuts a female's chances of having a new calf in a given year by more than 50%.”
While researchers are unsure why orcas are less likely to reproduce after having a son, some believe that sharing food may be the answer. The mother shares food with her male offspring even into adulthood. Sharing precious food resources forces her to make do with less of what she needs, which can ultimately compromise her health and fertility. Adult female offspring, meanwhile, hunt independently and thus do not depend nearly so much on their mothers.
One theory for the differential treatment of male and female offspring could relate to reproduction issues. Mothers know that their female offspring will reproduce in the same group, which can cause reproductive conflict. A son’s offspring, on the other hand, are more likely to be born in another group, thus making it less likely for those offspring to compete with her.
A mother orca's love?
- Female orcas can live up to 80 years. Males, on the other hand, are very lucky if they reach 40.
- The Center for Whale Research has been instrumental in enabling biologists to carry out multi-generational studies of orcas. Since 1976, it has produced a complete census of the Southern Resident population of orcas.
- Male orcas are very dependent on their mothers for survival. According to Dr. Weiss, "Our previous research has shown that sons have a higher chance of survival if their mother is around.”