Female orcas, like their human counterparts, live decades beyond their reproductive years.

Earlier research has suggested that postmenopausal orcas are thought to boost the life chances of their offspring and grandchildren — known as the grandmother effect. The head of a killer whale pod shares her knowledge of the best hunting spots and more than half the fish she catches with her family members.

Now, according to a new study published last week in the journal Current Biology, these orca matriarchs, which can live up to 90 years, also like to spend their later years indulging in some helicopter parenting of their sons. Female orcas help their sons navigate the complexities of orca social life and protect them from fights with other killer whales.

In a group of orcas, known as the Southern Resident population, that lives off the Pacific Northwest coast of North America, scientists studied “tooth rake marks” — the scarring left when one whale scrapes their teeth across the skin of another.

The research team found males had 35% fewer marks if their mother was present and had stopped breeding, according to the study’s analysis of data and images gathered by the Center for Whale Research in Friday Harbor, Washington.

Orcas have no natural predators — except humans — and the tooth marks on their skin can only be inflicted by other killer whales, either within social groups or when two pods meet.

“Tooth rake marks are indicators of physical social interactions in killer whales and are typically obtained through fighting or rough play,” said lead study author Charli Grimes, an animal behavior scientist at the U.K.’s University of Exeter.

“We think that older females use their enhanced knowledge of other social groups that obviously comes with time (and) experience … to help their sons navigate the interaction — whether that is signaling to them vocally or behaviorally,” she said. “That’s one hypothesis of how they might be protecting them. Another one is that they involve themselves in a conflict if a fight looks risky.”

The researchers found no evidence that postmenopausal orcas — which can expect to live some 22 years on average after they stop reproducing — reduce the bite marks on their daughters.

Why not protect orca daughters? Grimes said that it makes more evolutionary sense for the orca matriarchs to focus on their sons because they have more potential to pass on their mother’s genes — and in a way that doesn’t put any additional burden on the group.

“Males have the opportunity to mate with multiple females, and they do this outside of their own social group. When a male’s calf is born … the cost of that calf lies with the other group,” she said.

Words to Learn

相关词汇

【直升机父母】

zhíshēngjī fùmǔ

helicopter parent

parents who are overprotective and obsessed with every aspect of their children’s lives

【造成】

zàochéng

inflict

cause to be suffered by

雌性虎鲸和人类一样，绝经后还能活几十年。

早先的研究表明，绝经后的虎鲸能提高其后代和孙辈的生存机会 —— 这就是所谓的祖母效应。虎鲸群的首领会将自己了解的最佳狩猎地点以及捕获鱼类的一半以上与家庭成员分享。

根据上周发表在《当代生物学》杂志上的一项新研究，这些可以活到 90 岁的虎鲸女族长也喜欢在晚年充当儿子的“直升机家长”。雌性虎鲸帮助儿子适应复杂的社会生活，并在它们和其他虎鲸打架时提供保护。

科学家研究了生活在北美西北太平洋沿岸的一群虎鲸（被称为南方居留种群）的“齿耙痕”（打斗后留在皮肤上的疤痕）。

研究小组对华盛顿州星期五港鲸鱼研究中心收集的数据和图像进行分析后发现，如果有绝经后的母鲸陪伴，雄鲸身上的齿痕会减少 35%。

除了人类之外，虎鲸没有天敌。因此它们皮肤上的齿痕或者是本社群的其他虎鲸造成的，或者是在两个虎鲸群遭遇时留下的。该研究的主要作者、英国埃克塞特大学动物行为科学家查莉•格莱姆斯说：“齿耙印是虎鲸身体接触的印记，通常是打斗或粗暴嬉戏时留下的。”

她说：“我们认为，年长的雌性会利用它们对其他社群的了解，这种了解会随着时间和经验的增加而增加 ...... 来帮助儿子在社群中胜出；她们通过声音或者动作指导儿子。”

“这是一种假设。另一种假设是，如果打架看起来有风险，虎鲸奶奶就会亲自下场。”

没有证据表明，绝经后的虎鲸会减少女儿身上的咬痕。虎鲸在生育期结束后平均能活22年左右。

虎鲸为什么不保护女儿？格莱姆斯说，从进化论的角度来看，虎鲸的母系首领更应该关注儿子，因为儿子更有可能将母亲的基因遗传下去，而且不会给虎鲸群体带来任何额外的负担。

她说：“雄性虎鲸有机会与多个雌性交配，而且它们是在自己的社群之外交配的。雄性幼崽出生后 ...... 照顾它的成本由其他群体承担。”

(SD-Agencies)