Berry-gorging bears disperse seeds through scat and feed small mammals

July 05, 2018

CORVALLIS, Ore. -- New research shows that mice and voles scurry to bear scats to forage for seeds, finding nutritional value in the seeds and in some cases further dispersing them.

The study is published in the journal Ecosphere by researchers at Oregon State University and the Alaska Department of Fish and Game. The research builds on an OSU study that determined that bears are the primary seed dispersers of berry-producing shrubs in Alaska.

In southeastern Alaska, brown and black bears are plentiful because of salmon. Bears frequently supplement their salmon-based diet with fruit as they build their fat stores for winter hibernation. As a result, their seed-filled scats are found throughout the landscape.

"Salmon can have a far greater impact on the ecosystem than we thought," said study lead author Yasaman Shakeri, an Oregon State University graduate now with the Alaska Department of Fish and Game. "Our study shows how small mammals can benefit indirectly from salmon through high bear densities that salmon support and the resulting seed-filled scats on the landscape. Not only are small mammals spending months feeding and fighting for the seeds in scats, they're also scattering the seeds on the landscape, which allows some of the seeds to become future fruiting plants."

The researchers placed motion-triggered cameras near bear scats in the upper Chilkat Valley, 30 miles north of Haines, from June to October in 2014 and 2015. They recorded visits to the scat made by small mammals and birds.

Northwestern deer mice made 4,295 total visits to the scats - an average of 8.5 a day. Northern red-backed voles visited 1,099 times at an average of 2.2 times a day. In addition to the cameras, the researchers also live-trapped and tagged small mammals to estimate their abundance and population densities.

The team collected bear scats on roads and trails within the study area from July-September in 2014 and 2015 and analyzed the nutritional characteristics found in the 12 species of fruit found in the scats, including gross energy, total dietary fiber, crude protein and crude fat. From those samples, they estimated digestible energy per seed.

The energy within the seeds in bear scats can be a significant portion of the energy budget of rodents. For example, a single bear scat contained 73,230 devil's club seeds, which was capable of meeting the daily energy requirements of 91 deer mice. In coastal Alaska riparian areas, bears are potentially capable of indirectly subsidizing the energy needs of 45-65 percent of local deer mouse populations, Shakeri said.

In addition to consuming the seeds at the site, the mice appear to scatter-hoard the seeds in much the same way that gray squirrels scatter-hoard acorns, said Taal Levi, an ecologist in OSU's College of Agricultural Sciences and co-author on the study. Scatter-hoarding is creating a large number of small hoards, as opposed to a large hoard found in a single place.

"This process is called secondary seed dispersal and forgotten seeds can have much higher survival than unburied seeds," Levi said.

The study was also co-authored by Kevin White, a wildlife biologist with the Alaska Department of Fish and Game. The M.J. Murdock Charitable Trust and OSU's Department of Fisheries and Wildlife provided funding for the study.

Shakeri has posted videos on YouTube of deer mice and a vole foraging for berries in bear scat.
-end-


Oregon State University

Related Salmon Articles from Brightsurf:

Alaska's salmon are getting smaller, affecting people and ecosystems
The size of salmon returning to rivers in Alaska has declined dramatically over the past 60 years because they are spending fewer years at sea, scientists report.

Chinook salmon declines related to changes in freshwater conditions
A new University of Alaska-led study provides the first evidence that declines in many of Alaska's chinook salmon populations can be attributed in part to climate-driven changes in their freshwater habitats.

Size matters in the sex life of salmon
For Atlantic salmon, size matters when it comes to love.

What does drought mean for endangered California salmon?
Droughts threatens California's endangered salmon population -- but pools that serve as drought refuges could make the difference between life and death for these vulnerable fish.

Salmon provide nutrients to Alaskan streambanks
Nutrient cycling of stream ecosystems dependent on portion of salmons' lifecycle.

Melting glaciers will challenge some salmon populations and benefit others
A new Simon Fraser University-led study looking at the effects that glacier retreat will have on western North American Pacific salmon predicts that while some salmon populations may struggle, others may benefit.

Bigger doesn't mean better for hatchery-released salmon
A recent study in the Ecological Society of America's journal Ecosphere examines hatchery practices in regards to how Chinook salmon hatcheries in the PNW are affecting wild populations over the past decades.

Salmon get a major athletic boost via a single enzyme
A single enzyme anchored to the walls of salmons' blood vessels helps reduce how hard their hearts have to work during exercise by up to 27%.

Salmon are shrinking and it shows in their genes
Male salmon are maturing earlier and becoming smaller, and it shows in their genes.

Young salmon may leap to 'oust the louse'
A study by Simon Fraser University aquatic ecologists Emma Atkinson and John Reynolds reveals that young salmon may jump out of water to remove sea lice.

Read More: Salmon News and Salmon Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.