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Dozer is back

December 12, 2017

The loveable, 3,450-pound Pacific walrus who wowed Point Defiance Zoo & Aquarium visitors last fall and spring with his 17-inch tusks and humongous bulk, then delighted them with his whistling ways, recently arrived in Tacoma from SeaWorld San Diego.

Though he is sure to inspire zoogoers with a large love for walruses, that isn’t Dozer’s main mission. He is in town to woo the ladies.

As he was earlier this year, the 24-year-old Dozer is at Point Defiance Zoo & Aquarium on a breeding loan.

“The population of walruses in accredited U.S. zoos  and aquariums numbers only 15,” said Lisa Triggs, senior staff biologist in the zoo’s Rocky Shores area.

Only five accredited zoos and aquariums have the animals on exhibit in this country.

“Dozer is here for the breeding season, and we are hopeful that he will mate with our three female Pacific walruses, Joan, Basilla and Kulusiq.”

That was the purpose of his last visit, zoo General Curator Dr. Karen Goodrowe Beck said.

“We know from tests that Dozer and the females are capable of reproduction and that copulation took place with all three,” Goodrowe Beck said. “But, sadly, none of the females is pregnant.”

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A successful walrus pregnancy would both increase the numbers of walruses in the U.S. and help scientists understand more about walrus reproduction, Triggs said.

She wrote a thesis on walrus reproduction while earning a Master of Science degree at the University of Washington.

Joan is 22, Basilla is 33 and Kulusiq (pronounced koo-LOO-sic.) is 23. Dozer is 24. Kulusiq is in Tacoma on a breeding loan from New York Aquarium while their walrus habitat is being rebuilt.

There are no guarantees that Dozer will breed with the three, but members of the Walrus Conservation Consortium believe the odds are greatest when a male has a bevy of females, Triggs said. Dozer’s frequent whistling – one of the sounds male walruses use to attract females – was often heard all the way across the zoo grounds last winter and spring.

The consortium is a group of zoos and aquariums that either have walruses in their care or are active in the quest to conserve the iconic marine mammal.

Dozer likely will show signs of rut in late December. They eat large quantities of food and gain a huge amount of weight in preparation for the breeding season, which runs from December through March.

Females have brief annual estrus periods that last between one and several days, Triggs said. Hormone levels show that Joan, Basilla and Kulusiq reliably come into estrus each year. Triggs and other zoo staff members track the animals’ hormones with blood samples obtained voluntarily from the walruses.

Female walruses generally are sexually mature between 8 and 10 years old. Males come into breeding age at around 10 years old and remain fertile well into their 30s, Triggs said.

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Point Defiance Zoo & Aquarium is a leader in the study of walrus reproduction. Triggs has worked with and studied the species for more than 25 years. She’s researched walrus reproduction for more than a decade and spoke in China last year at a scientific forum on walruses.

Goodrowe Beck holds a Ph.D. in reproductive biology and has a worldwide reputation among zoos as an expert in her field.

Zoo staff and visitors hoping for a walrus calf must be patient. Hormone-level testing eventually will allow staff biologists to know if one of the females is pregnant.

The process of producing a baby walrus takes time. Once a walrus egg is fertilized, it’s not implanted in the uterus for four to five months. The gestation period is about 15 months.

Pacific walruses are covered by the U.S. Marine Mammal Protection Act and are considered a “vulnerable” species by the International Union for Conservation of Nature (IUCN), meaning they are on the cusp of becoming endangered. Shrinking sea ice due to climate change poses a grave threat to the animals, which use the ice as “hauling out” platforms for resting, giving birth and nursing their calves.

Zoo staff believe Dozer’s presence, along with Joan, Basilla and Kulusiq, will inspire more guests to take action to help curb climate change. Making a difference can be as simple as not idling a car while waiting for a passenger. Or putting on a sweater and turning a thermostat down a couple of degrees in winter to use less electricity.

In addition to the conservation leadership the zoo provides at home, it aids the advancement of scientific knowledge about walruses in the wild.

The Zoo Society’s Dr. Holly Reed Wildlife Conservation Fund provides grants to support operations and research at a walrus refuge on Round Island, Alaska. A grant also was awarded this year to help support a study of food sources available to walruses in Bristol Bay, Alaska.

In recent years, Point Defiance Zoo & Aquarium staff members also have engaged in studies and aided other researchers to:

  • Investigate the physical characteristics and mechanisms that allow walruses to produce a variety of unique sounds
  • Assess variations in food consumption and body conditions of walruses
  • Identify a reliable blubber measurement to assess body condition in marine mammals, using Pacific walruses as the model
  • Study the development of diving physiology and capacity in walruses

Point Defiance Zoo & Aquarium Logo“Each of these studies helps marine mammal experts and other researchers better understand these magnificent mammals,” Triggs said. “The more we learn about them, the more we can help wild walruses as they adapt to changing climates and altered landscapes.”