Bears are omnivores, and on Kodiak, they eat a large buffet of food items, including elderberries and salmon, two of their favorite foods. What happens, though, if a bear has a choice between elderberries or salmon? Which will he choose, or will he choose both? More importantly, why does it matter?
I’m sure you have controversies in your neighborhood. It may be a fight over a bill to fund a new school, a fight over a tougher crime initiative, or something as simple as whether or not to put a stop sign at the end of your street. In my neighborhood here in the wilderness, the recent research I’ll discuss in this post is what we call controversy. I’ve avoided writing about this scientific article until now because I know I will irritate several people, some of them friends. I finally decided, though, I couldn’t continue to avoid voicing my opinion on something this significant. I have invited some of the biologists involved in this study, other biologists, and local guides to read my blog, and I hope they will weigh in on the issue by leaving comments. I am sorry this post is long, but I didn’t want to break it into two parts.
The study I will discuss is titled, “Phenological synchronization disrupts trophic interactions between Kodiak brown bears and salmon.” It was published in the July 18th edition of the Proceedings of the National Academy of Sciences. I think it is an excellent study, and more importantly, other biologists must think it is an excellent study. The Proceedings of the National Academy of Sciences is a prestigious scientific journal, and to be accepted by this journal, a research paper must be peer-reviewed at the highest level. I do not disagree with the methods or the results of the study. What I do have a problem with are the broad, far-reaching conclusions drawn from what is, in my opinion, a preliminary field study.
Let me do my best to explain the focus and significance of this study. A large body of research concerns what happens due to global warming when coevolved species shift out of synch with each other. For example, consider a plant that is only pollinated by one bee species, and these two species co-evolved so the plant flowers at the exact same time the bee is ready to gather its nectar and pollinate it. What happens, if the bees hatch earlier each year due to a warming environment, but the flowers bloom at the same time because their cue for blooming is based on the amount of daylight, not temperature. The two species will slowly grow out of synch with each other, and the plant species may go extinct when the bees are no longer available to spread its pollen.
In this study, though, lead researcher William Deacy and his colleagues set out to investigate the opposite situation: what happens when warming temperatures cause climate-induced synchronization? In this case, when elderberries fruit several weeks earlier than usual on Kodiak Island during the middle of the sockeye salmon run, will bears choose to eat salmon or berries?
The Karluk River on Kodiak Island, where this research was done, supports a large sockeye salmon run lasting from June to early August. On a normal year, bears on the Karluk River feast on sockeye and other salmon until late August, when they begin eating elderberries and salmonberries which are just then ripening. Once the berries are gone, bears return to the river and side streams to eat other species of salmon.
When William Deacy worked on another research project in the Karluk area in 2013, he noted typical bear behavior. Throughout July, bears ate their fill of salmon and left the scraps for birds and other animals to scavenge. In 2014, after a warm spring, elderberries ripened two weeks earlier than usual, and plants produced ripe berries longer than normal. Deacy noted that bears in late July were eating berries instead of fish. Why, he wondered, would bears opt for elderberries over sockeye salmon? The winter and spring of 2015 were also warm, and Deacy again observed bears ignoring sockeye salmon while they ate berries.
Deacy and Kodiak National Wildlife Refuge biologist Bill Leacock gathered a team of scientists from several universities and organizations, including Oregon State University, the University of Montana, Washing State University, and the National Park Service, to examine this surprising bear behavior.
From meteorological records, the biologists determined the temperature on Kodiak is slowly getting warmer, and 2014 was the warmest year on record. When the winter and the spring are relatively warm, elderberries ripen earlier than normal, and when elderberries ripen earlier, bears seem to eat berries instead of salmon. What, they wondered, will happen when temperatures continue to warm? If the berries are ripe all summer, will bears only eat berries and ignore salmon? If this happens, what will the birds and small animals eat? They depend on bears to leave them scraps of salmon on the banks of streams. Not only do animals depend on bears for leftover salmon, but salmon carcasses provide fertilization for riparian vegetation. Another point of concern is if bears only eat berries and avoid salmon, will bears get enough nutrition?
Deacy and his colleagues headed for the lab to determine if elderberries are nutritious enough to sustain bears, and why bears like berries better than salmon. Fortunately, elderberries are protein-rich compared to other berries. They don’t have as much protein as a salmon, but a bear would do fine if he ate elderberries instead of salmon. I won’t discuss the part of the study suggesting why bears prefer elderberries over salmon because I believe this conclusion is based on a very shaky assumption.
Do bears prefer elderberries over salmon, and if provided with both, would they choose the berries? I don’t know the answer to this question, and neither does William Deacy or any other biologist. As I said earlier, I think this is a well-done, interesting, thought-provoking study, but let ’s not get carried away. This is a preliminary study consisting of three years of data taken over a fairly small geographical area. It is unprofessional for any biologist to draw sweeping conclusions from a limited, preliminary study.
I would like to believe the media is responsible for jumping to wild conclusions regarding this research. I corresponded with Dr. Deacy after the research was published and asked him if he was trying to say bears are now eating berries instead of salmon. I may have misunderstood him, but I thought he said he was only suggesting what might happen as our climate warms. Then I found articles titled, “Alaskan grizzly bears choose berries over salmon—thanks to climate change,” “Kodiak bears found to switch to eating elderberries instead of salmon,” “Grizzly bears go vegetarian due to climate change, “Climate change is luring Kodiak bears away from their iconic salmon streams,” and “As a warming climate changes Kodiak bears’ diets, impacts could ripple through ecosystems.” Deacy, himself, wrote this last article. In it, he claims, “climate change dramatically altered bear behavior.”
The researchers state the ecosystem on Kodiak Island has been disrupted. I have lived in the Kodiak wilderness and have helped my husband guide bear viewers for 35 years. My husband has lived in the Kodiak wilderness all his life. Warm springs and big berry crops are not unusual, and when the berries, especially salmon berries and elderberries, ripen, we know we will see fewer bears on the rivers feeding on salmon where we can show them to our eager bear viewers. The bears will instead be in the bushes eating berries. I seriously doubt bears prefer berries to salmon, though! Berries are an easier food source than salmon because all the bear has to do is sit on his rear end and eat them. He is required to expend energy to chase down a salmon.
I believe either from instinct or learned behavior, bears know that when berries ripen, they are usually only available for a short period. Salmon, though, can be eaten from June into November. One fact I feel these researchers did not stress enough is that five species of Pacific salmon return to spawn each year in the streams and rivers on Kodiak Island. Pink salmon, not sockeye salmon, are by far the most prevalent of these species, and I have thousands of photos to prove how much bears love to eat pink salmon. Pinks are in the rivers until late September, and Coho salmon remain in the rivers until November.
Yes, the spring and summer of both 2014 and 2015 were warmer than usual, and the berries were plentiful. Once the berries began to decline, though, bears were back on the rivers eating their fill of salmon and leaving scraps for the birds and other animals. I suspect when these warm springs and summers become the norm, bears will learn they have a longer period to eat berries and will split their time between berries and salmon. I may be wrong, and bears may choose berries, but I know it should take more than a two-year study before biologists begin telling reporters that Kodiak bears have abandoned salmon for berries.
The spring and summer of 2017 were cool. The berry crop was poor, and the salmon run on Kodiak was better than it has been in several years. Bears packed the salmon streams, and we wondered whether they would eat enough berries to gain the necessary calories they need to carry them through hibernation. A biologist arriving at Karluk Lake last summer observing abundant salmon and few berries might have designed a very different research study from the one I’ve been discussing in this post.
What worries me, is that as the planet warms, salmon populations will drastically decline because salmon are sensitive to even a small increase in water temperature. As this research suggests, though, when salmon are no longer available, perhaps bears will maintain a healthy diet by eating berries.
I would like to make one more comment before I get off my soapbox. Why must biologists live in a bubble? Why didn’t the researchers in this project talk to guides who have been watching bears for decades? I realize they can’t use anecdotal evidence in their study, but perhaps we could have offered possibilities in addition to the conclusions Dr. Deacy made.
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Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.
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I don’t understand why the authors didn’t specify the type of salmon in the title(s) mentioned. That seems to be a gross misrepresentation.
This seems to be academia at its best: short study time, global warming, questionable conclusions = more grant money!
Hello Robin,
Thank you for posting about this paper. It is great to have a forum for discussing bear research. I am excited to respond to your critiques, but first, I want to talk about an important issue: the challenge of communicating science in today’s media environment. I think scientists have a responsibility to spread the word about research that may affect the animals that people care about, but the message often gets muddled by journalists and media outlets. Scientists can prevent misinterpretation by not giving out press releases or interviews, but the result would be many fewer people would hear about research (some of which is funded by tax dollars). As challenging as it is, we must attempt to engage with the media to try and accurately communicate science.
I was very disappointed in how poorly the media translated our very careful study into “click-bait” internet articles. They are more motivated by ad revenue than scientific accuracy, so they create deliberately misleading titles to attract readers. One journalist that I complained to informed me that most journalists don’t control the titles of their articles. They make a suggestion, but editors ultimately decide what the title should be. Each step (scientist – press release – the journalist – editor) adds opportunities for inaccuracy. This is why the careful, measured statements in our paper resulted in internet articles with the terrible titles you mentioned in your post.
Many of the people who were critical of me and my coauthors seem to have a fundamental misunderstanding about how the media works. This is summed up nicely by Tony’s comment above where he says “I don’t understand why the authors didn’t specify the type of salmon in the title(s) mentioned.” As scientists, we have zero control over what the media outlets publish. We are not consulted about the content, titles, or any other part of the articles Tony mentions. The most scrupulous authors will sometimes check some details for accuracy, but generally this is rare. One reason for this is journalistic independence, but I think the main reason is time. The journalists are trying to crank out a lot of articles and it takes too long to do a fact check with scientists. Most of the articles that came out did not contact us at all—they just read other inaccurate articles, change a few sentences and try to one-up the title of the last article. I think that is why we saw the article titles get worse with time, finishing with the horrible “Grizzly bears go vegetarian due to climate change”. I can’t express how much it personally pained me to see these terrible titles go out into the world!
One final note about science and media: After most of the poor press coverage had ended, I was invited to write an article for The Conversation, a not-for-profit publication that helps scientists present their work to the public. I think this is a great publication that avoids some of the media issues I mentioned above. The goal is to be accurate and understandable, but I think there is an inevitable tradeoff (especially when trying to be brief), between being precise and being engaging and understandable to the public (Robin seems to have a knack for striking a good balance). Moving forward, this is a skill I hope to hone, because I still think it is my professional duty to attempt to communicate complex science to the public, but feel burned by the normal process of communicating through media outlets that are more interested in clicks than accuracy.
To end my comments on science and media on a positive note, I think people are better at filtering through click-bait than we give them credit for. Anyone who regularly uses the internet is accustomed to seeing countless “articles” that are designed to attract our attention. Even though most of us do not blindly believe what the articles say, we do need to get better at tracking down the source of articles and making judgements for ourselves. All of the wildlife scientists I know are willing to respond to reasonable questions and comments and their contact info is always listed on publications. Finally, if a science journal is trying to charge you money to see a journal article, email the corresponding author—they will almost always send you a copy directly.
Now I’ll try to address the science issues/ critiques. Overall, I think it is important to remember that no science exists in a vacuum and that science is a process rather than a single product. The things we got right will receive more support in the future, and things we got wrong will be refuted by new evidence.
One of the ideas you mention is about berry timing shifts. You pose the question of what will happen “if the berries are ripe all summer.” The evidence we have so far suggests that in warm years elderberries ripen earlier, but also die earlier as well. This would mean that the ripe elderberry period doesn’t get longer in warm years, just earlier. Because of this, one outcome is that warming could increase bear use of pinks as the ripe berry period gets earlier and stops overlapping the pink salmon spawning period. Does this match your observations on Uyak streams/rivers? Did you see many bears in 2014/2015? This is an area of uncertainty, along with how climate affects the number of berries produced. Bill Pyle has been conducting a study on berries and may have data that could address this.
I want to talk about this quote from your blog post: “It is unprofessional for any biologist to draw sweeping conclusions from a limited, preliminary study.”
First, about the sweeping conclusions: as should be clear from the media section above, please do not judge us on what the popular articles said. We definitely did not conclude that bears are forever ditching salmon for berries, that the whole Kodiak ecosystem is disrupted, or that bears are likely to be harmed by the behavioral change that we documented with our observations. We were very careful about our conclusions and only discussed the empirical evidence that we directly collected. Here are the most direct statements from the paper:
“Bears switched from eating salmon to elderberries, disrupting an ecological link that typically fertilizes terrestrial ecosystems and generates high mortality rates for salmon.”
“By triggering food switching, shifts in elderberry fruiting phenology disrupted a normally strong predator–prey interaction between brown bears and salmon.”
“…coastal brown bear populations will continue to depend on healthy salmon runs to meet much of their energy needs.”
“Phenological shifts in elderberry likely triggered prey switching away from salmon, attenuating a trophic linkage with disproportionate ecological significance.”
These statements are backed up by the evidence that we presented, which was collected in SW Kodiak, mostly on rivers and streams. They do not mean that bears will no longer eat salmon (as you point out, there are other salmon species, and sockeye populations that spawn at other times), or that this phenomenon is necessarily widespread (more on this below), but it is certainly reasonable to conclude that when bears stop fishing at streams where they normally kill 70% of sockeye, an ecological link is disrupted and bear behavior has changed. Is there another conclusion where you think we over stepped the evidence (I know disagree with the preference of berries issue: I’ll address that below)?
As for the “limited, preliminary study” part of the statement:
This study presents the most comprehensive dataset available for bear foraging in a bear-salmon-berry system. We had four independent sources of data, including unprecedented salmon counts on several streams, which has never been collected in conjunction with bear use data. I am not stating this to give myself a pat on the back, but merely to counter the idea that this study was “limited, preliminary”. It was limited in the sense that we did not cover every bear or every area of the island, but I can confidently say that it is the best, most comprehensive dataset on bear-salmon-berry foraging ever collected. Would we prefer more data- of course, but we are limited by time and resources. I agree that the study should be preliminary in that it should spark more research to pin down some critical remaining questions: 1) how widespread is this behavior? 2) Will elderberry productivity change in the future? Etc. But, I do think we had strong independent data sources that all supported the notion that bears switched to berries. Along these lines, in the part of your post where you are questioning the bears’ preference of berries, you say “…it should take more than a two-year study before biologists begin telling reporters that Kodiak bears have abandoned salmon for berries.” This unnecessarily minimizes the amount of data we presented: 3 years of salmon abundance data, 3 years of GPS collar data, 1 scat survey, a 66 year temperature record, and 31 years of aerial surveys (317 individual surveys). It is a lot of data which, most importantly, all supported the hypothesis that bears switch to elderberry when it overlaps in time with salmon.
I am surprised that you don’t think that the bears prefer berries even though you see bears leave Uyak streams/rivers during big berry years. I agree with your point that bears take feeding effort into account when they are choosing their foods (I’m sure they would like to eat more deer, but they are probably hard to catch), but I don’t think that eating elderberries and catching stream-spawning salmon are very different effort-wise. In the small streams around Karluk lake, the bears do not have a hard time catching salmon. It is common to see yearlings (and even COY) catch salmon in these streams because it is often as simple as picking them up.
I think the ultimate test of food preference would be seeing what a bear would choose when presented with two piles of two different foods (in other words, removing the issue of catching salmon/ picking berries). When they have done this in captivity, bears choose foods that have much less protein than salmon. It seems counter-intuitive, but if a person wanted to gain weight rapidly, would they eat mostly sugary foods, or lean chicken and protein shakes? This gets at a key idea, which is that some foods are used more efficiently for weight gain than others (a larger portion of the calories are retained instead of burned off or lost). For bears, we know that foods high or low in protein are inefficient, and foods ~20% protein are most efficient for weight gain. Q: If this is true, then why do bears eat so much salmon? A: Bears in most places and for most of the year do not have access to foods in the perfect protein range, so they instead just eat a lot of calories. They can gain weight by eating a lot of calories that they digest inefficiently. I think about it like this: you can get your house warm with a modern stove or an open fireplace, you just need burn a lot more wood with an open fireplace. For bears, eating salmon is like using an open fireplace. This concept is called the macronutrient optimization hypothesis, and it has been used to successfully explain bear diet choices all over the world. Although we don’t know for sure, I would put money on bears all over Kodiak and the rest of Alaska choosing abundant elderberries over salmon when they are both available.
Well, I’ve officially taken up too much space on your blog 🙂 To wrap up I want to talk about your “bubble” comment. Certainly, biologists could be better at reaching out to hear the perspectives of people who live around bears and see different things. As you mentioned, biologists are often limited to using hard data as evidence, but hearing from guides and others is particularly useful for making hypotheses about what is happening; from working with Bill Leacock and being on the ground myself, I know there is a lot to learn just by seeing bears every day and paying close attention. I think some of the frustration with this paper is that we documented something different in SW Kodiak than people saw in other places. A more island-wide effort would help us overcome our place-specific biases and help us understand all the bears on Kodiak better. In the end, we published the conclusions that were supported by the data we had, and I feel good about everything that is in the paper we published.
I want to thank you for sincerely digging into this issue and being such a well-informed local bear naturalist and bear enthusiast. I’m know I didn’t respond to everything in your blog post, but I’m happy to keep the conversation going if you and/or others have more comments or questions.
I am so excited to have found this blog, this article and the response from Deacy! We need more exchanges like this in the world.
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