Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Yosemite bears and human food: Study reveals changing diets over past century

03.03.2014

Management strategies implemented since 1999 have successfully limited the availability of human food to black bears in Yosemite, but problems remain

Black bears in Yosemite National Park and elsewhere are notorious for seeking out human food, even breaking into cars and cabins for it. A new study reveals just how much human food has contributed to the diets of Yosemite bears over the past century.


Researcher Jack Hopkins used barbed-wire snares to collect hair samples from bears in Yosemite National Park. Analysis of isotope ratios in hair samples showed how much of the bears' diets came from human food.

Credit: Photo courtesy of Jack Hopkins

Researchers at the University of California, Santa Cruz, were able to estimate the proportion of human-derived food in bears' diets by analyzing chemical isotopes in hair and bone samples. The results, published in the March issue of Frontiers in Ecology and the Environment, show how bears' diets have changed over the years as the National Park Service took different approaches to managing bears and people in Yosemite.

"Yosemite has a rich history of bear management practices as a result of shifting goals over the years," said Jack Hopkins, lead author of the paper and a research fellow at UC Santa Cruz. "What we found was that the diets of bears changed dramatically after 1999, when the park got funding to implement a proactive management strategy to keep human food off the landscape."

That funding has been used primarily to buy bear-resistant food-storage containers and increase enforcement of their use, hire more staff to manage problem bears, and establish a "bear team" to increase visitor compliance with rules for storing food in areas such as campgrounds and hotels. The study, which focused on bears that had learned to eat human food or food waste, found that the proportion of human foods in their diets decreased by about 63 percent after the new strategies were implemented. Unfortunately, according to Hopkins, once a bear gets used to eating human food it will continue looking for it, and even when visitor compliance is high, there will always be a few people who make the mistake of leaving their food where bears can get it.

Hopkins, who worked as a biologist in Yosemite National Park for several years, conducted the study as a graduate student at Montana State University. He teamed up with coauthor Paul Koch, a professor of Earth sciences and dean of physical and biological sciences at UC Santa Cruz, to do the isotope analysis of hair and bone samples. Contemporary hair samples were collected during bear management actions and from barbed-wire hair snares deployed throughout Yosemite. Historical samples were obtained from museum collections.

"This study shows the power of using museum specimens and archived historical material to reconstruct the ecology of a species and to answer pressing management questions," Koch said. "The remarkable thing is that the bears that eat human food are now back to the same level of dumpster diving as in 1915, despite the fact that there are now millions of visitors in Yosemite every year and presumably a lot more garbage."

Yosemite National Park was established in 1890, and Hopkins obtained samples from bears killed between 1915 and 1919 to represent the earliest time period. In those early years, bears were attracted to garbage dumps in the park and were often killed when they became a nuisance. Visitors liked to see bears, however, and in 1923 the park began intentionally feeding bears where visitors could watch them. The last artificial feeding area closed in 1971. There was also a fish hatchery in Yosemite Valley, from 1927 to 1956, where bears once helped themselves to fresh trout from the holding tanks. But closing the hatchery and the feeding areas didn't stop bears from eating human food.

"The bears just went back to the campgrounds and hotels and continued to find human food," Hopkins said.

The average figures for the proportion of human food in bear diets during the four time periods in the study were 13 percent for the period from 1915 to 1919; 27 percent for 1928 to 1939; 35 percent for 1975 to 1985; and 13 percent again for 2001 to 2007.

These results are based on a kind of chemical forensics in which Koch's lab specializes. Isotopic analysis of an animal's tissues can yield clues to its diet because of natural variability in the abundance of rare isotopes of elements such as carbon and nitrogen. Isotope ratios (the ratio of carbon-13 to carbon-12, for example) are different in human foods than in the wild plants and animals that black bears naturally eat in Yosemite, partly due to the large amounts of meat and corn-based foods in our diets.

In order to analyze the data from Yosemite bears that ate a mixture of human and natural foods, Hopkins had to get samples from bears that did not eat any human food, and he had to track down samples of the non-native trout that had been raised in the hatchery. He also needed data representing a 100 percent human food diet, for which he turned to the Smithsonian Institution for samples of human hair from different periods over the past century.

"He searched far and wide to get the collection of samples we analyzed, and that collection made the study powerful enough to answer the question of how management practices affect bear diets," Koch said.

According to Hopkins, the key to managing bear problems is to prevent bears from becoming conditioned to eat human food in the first place. He has done other studies using genetic analysis to show that the offspring of bears that eat human food end up having the same foraging behaviors as their mothers. And when problem bears are relocated away from human food sources, they eventually return and continue seeking human food until they are killed, often by management staff.

"People like to see bears, and they don't like to hear about bears being killed. But the bears they often see in visitor-use areas like Yosemite Valley are the ones that are conditioned to eat human food, and those are the ones that become problems and have to be killed," Hopkins said.

In addition to his current affiliation with UC Santa Cruz, Hopkins has postdoctoral fellowships with Peking University in Beijing, China, and the University of Alberta in Edmonton, Canada. The coauthors of the paper include Jake Ferguson at the University of Florida and Steven Kalinowski at Montana State University. This research was funded by the Yosemite National Park Bear Council.

Tim Stephens | EurekAlert!

Further reports about: Hopkins Yosemite Yosemite National Park bears chemical isotopes isotopes

More articles from Studies and Analyses:

nachricht Brands are Perceived in the Same Way as Faces
28.08.2015 | Leuphana Universität Lüneburg

nachricht “Bank & Zukunft 2015” trend survey highlights the need for banks to reform business models
21.08.2015 | Fraunhofer-Institut für Arbeitswirtschaft und Organisation IAO

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: An engineered surface unsticks sticky water droplets

The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. As slippery as these surfaces are, however, tiny water droplets still stick to them. Now, Penn State researchers have developed nano/micro-textured, highly slippery surfaces able to outperform these naturally inspired coatings, particularly when the water is a vapor or tiny droplets.

Enhancing the mobility of liquid droplets on rough surfaces could improve condensation heat transfer for power-plant heat exchangers, create more efficient...

Im Focus: Increasingly severe disturbances weaken world's temperate forests

Longer, more severe, and hotter droughts and a myriad of other threats, including diseases and more extensive and severe wildfires, are threatening to transform some of the world's temperate forests, a new study published in Science has found. Without informed management, some forests could convert to shrublands or grasslands within the coming decades.

"While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease...

Im Focus: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

Im Focus: What would a tsunami in the Mediterranean look like?

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).

Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...

Im Focus: Self-healing landscape: landslides after earthquake

In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.

These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

Large agribusiness management strategies

19.08.2015 | Event News

 
Latest News

Siemens sells 18 industrial gas turbines to Thailand

01.09.2015 | Press release

An engineered surface unsticks sticky water droplets

01.09.2015 | Materials Sciences

New material science research may advance tech tools

01.09.2015 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>