Tilly, a North American River Otter at the Oregon Zoo, gave birth to a pup on November 8 —her second this year. The new arrival weighed just shy of 5 ounces (28.3 g) at birth and has nearly tripled that thanks to mom’s naturally high-fat milk.
“We’re pretty sure this pup’s a male,” said Julie Christie, the zoo’s senior North America keeper. “But Tilly is very protective, so we can’t be positive until our vets conduct a more thorough exam.”
Tilly and her pup are currently in a private maternity den, and it will be another month or two before visitors can see them in their Cascade Stream and Pond habitat. Young River Otters usually open their eyes after three to six weeks, and begin walking at about five weeks.
“Young River Otters are very dependent on their moms, and Tilly has been very nurturing,” said Christie. “She did a great job with her first pup, Mo, earlier this year. She raised him up from this tiny, helpless creature into the sleek, agile, full-grown otter he is today. We’re confident Tilly will be a great mom to her new pup as well.”
Surprisingly, swimming does not come naturally to River Otters; pups must be taught to swim by their moms. Earlier this year, this video of Tilly teaching Mo to swim drew more than half a million views on the zoo’s YouTube channel.
Take a peek behind the scenes as the newborn pup is weighed:
Keepers have yet to decide on a name for the new pup, though it is likely he will be named after a local river or waterway. (Mo is short for Molalla, after the Molalla River.)
North American River Otters typically give birth from late winter to spring, but Tilly seems to be on her own schedule, keepers say. The breeding season for River Otters is December through April, and actual gestation only lasts a couple of months. Unlike their European cousins however, North American River Otters usually delay implantation so that the time between conception and birth can stretch to as much as a year. That hasn’t been the case with Tilly.
Christie said it is also unusual — though not unheard of — for an otter to give birth to a single pup, as Tilly has now done twice. Litters usually consist of two or three pups, though the range is anywhere from one to six. Family groups typically consist of an adult female otter and her pups, with males moving away once they reach adulthood.
Since both Tilly and the pup’s father, B.C., were born in the wild, they and their offspring are considered genetically important for the breeding otter population in North American zoos. Both parents are rescued animals who had a rough start to life.
Tilly, named after the Tillamook River, was found orphaned near Johnson Creek in 2009. She was about four months old, had been wounded by an animal attack and was seriously malnourished. Once her health had stabilized, Tilly came to the Oregon Zoo in a transfer facilitated by the Oregon Department of Fish and Wildlife, which oversees the species’ protection.
The pup’s father, B.C. (short for Buttercup), was found orphaned near Star City, Ark., also in 2009. He was initially taken in by the Little Rock Zoo, but transferred to Oregon the following year as a companion for Tilly. The two otters hit it off quickly and have been playful visitor favorites ever since.
Now that the threat from fur trappers has declined, North American River Otters are once again relatively abundant in healthy river systems of the Pacific Northwest and the lakes and tributaries that feed them. Good populations exist in suitable habitat in northeast and southeast Oregon, but they are scarce in heavily settled areas, especially if waterways are compromised. Because of habitat destruction and water pollution, River Otters are considered rare outside the Pacific Northwest.
Metro, the regional government that manages the Oregon Zoo, has preserved and restored more than 90 miles of river and stream banks in the region through its voter-supported natural area programs. By protecting water quality and habitat, these programs are helping to provide the healthy ecosystems needed for otters, fish and other wildlife to thrive. River Otters are frequently observed in Metro region waterways.