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← The amazing grandmothers of the killer whale pod - Darren Croft

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Showing Revision 4 created 12/13/2018 by Kayla Wolf.

  1. Off the rugged coast
    of the pacific northwest,
  2. pods of killer whales
    inhabit the frigid waters.
  3. Each family is able to survive here
  4. thanks mainly to one member,
  5. its most knowledgeable hunter:
  6. the grandmother.
  7. These matriarchs can live eighty years
    or more,

  8. while most males die off
    in their thirties.
  9. Though killer whales inhabit
    every major ocean,
  10. until recently we knew
    very little about them.
  11. The details of their lives
    eluded scientists
  12. until an organization called
    the Center for Whale Research
  13. began studying a single population
  14. near Washington State and
    British Columbia in 1976.
  15. Thanks to their ongoing work,
  16. we’ve learned a great deal
    about these whales,
  17. known as the Southern Residents.
  18. And the more we learn,
  19. the more this population’s elders’
    vital role comes into focus.
  20. Each grandmother starts her life as a calf

  21. born into her mother’s family group,
    or matriline.
  22. The family does everything together,
  23. hunting and playing, even communicating
    through their own unique set of calls.
  24. Both sons and daughters spend their entire
    lives with their mothers’ families.
  25. That doesn’t mean a young whale
    only interacts with her relatives.

  26. Besides their own special calls,
  27. her matriline shares a dialect
    with nearby families,
  28. and they socialize regularly.
  29. Once a female reaches age fifteen or so,
  30. these meetings become opportunities
    to mate with males from other groups.
  31. The relationships don’t go much
    beyond mating—
  32. she and her calves stay with her family,
  33. while the male returns to his own mother.
  34. Until approximately age forty,

  35. she gives birth every 6 years on average.
  36. Then, she goes through menopause—
  37. which is almost unheard of
    in the animal kingdom.
  38. In fact, humans, killer whales and
    a few other whales
  39. are the only species whose females
    continue to live for years
  40. after they stop reproducing.
  41. After menopause,

  42. grandmothers take the lead
    hunting for salmon,
  43. the Southern Residents’ main food source.
  44. Most of the winter they forage offshore,
  45. supplementing salmon with other fish.
  46. But when the salmon head
    towards shore in droves to spawn,
  47. the killer whales follow.
  48. The matriarch shows the younger whales
  49. where to find the most fertile
    fishing grounds.
  50. She also shares up to 90% of
    the salmon she catches.
  51. With each passing year,
  52. her contributions become more vital:
  53. overfishing and habitat destruction have
    decimated salmon populations,
  54. putting the whales at near-constant
    risk of starvation.
  55. These grandmothers’ expertise

  56. can mean the difference between
    life and death for their families–
  57. but why do they stop having calves?
  58. It’s almost always advantageous for a
    female to continue reproducing,
  59. even if she also cares for her existing
    children and grandchildren.
  60. A couple unique circumstances
    change this equation for killer whales.
  61. The fact that neither sons or daughters

  62. leave their families of origin
    is extremely rare—
  63. in almost all animal species,
  64. one or both sexes disperse.
  65. This means that as a female
    killer whale ages,
  66. a greater percentage of her family
  67. consists of her children
    and grandchildren,
  68. while more distant relatives die off.
  69. Because older females are more closely
    related to the group than younger females,
  70. they do best to invest in the family
    as a whole,
  71. whereas younger females should
    invest in reproducing.
  72. In the killer whale’s environment,

  73. every new calf is another mouth to feed
  74. on limited, shared resources.
  75. An older female can further her genes
    without burdening her family
  76. by supporting her adult sons,
  77. who sire calves other families will raise.
  78. This might be why the females have evolved
  79. to stop reproducing entirely
    in middle age.
  80. Even with the grandmothers’ contributions,

  81. the Southern Resident killer whales
    are critically endangered,
  82. largely due to a decline in salmon.
  83. We urgently need to invest in restoring
    salmon populations
  84. to save them from extinction.
  85. In the long term, we’ll need more studies
    like the Center for Whale Research’s.
  86. What we’ve learned about
    the Southern Residents
  87. may not hold true for other groups.
  88. By studying other populations closely,
  89. we might uncover more
    startling adaptations,
  90. and anticipate their vulnerabilities
    to human interference
  91. before their survival is at risk.