Naturalist Selections is an interview series produced by the American Society of Naturalists Graduate Council. We showcase graduate student and postdoc authored work in The American Naturalist, a premier peer-reviewed journal for ecology, evolution, and animal behavior research. Catch up on exciting new papers you may have missed from the journal, and meet some truly brilliant early career naturalists!

In this episode, Anna Rouvière talks with us about her new paper Rouvière et al. 2022: ‘The Effects of Local Enhancement on Mean Food Uptake Rate.’ We chat about how you spot locally enhancing behavior in vultures and other creatures, when local enhancement might be a beneficial strategy vs when it might not, how understanding local enhancement behavior can impact species conservation, and more. You can read Anna’s full paper here: https://www.journals.uchicago.edu/doi/10.1086/717207.

Still foraging for answers? Email Anna at anna.rouviere@outlook.com.

<figure class="aligncenter size-large is-resized"><figcaption>Anna Rouvière, St. Andrews University graduate, 2021</figcaption></figure>

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Credits

Featured Guest: Anna Rouvière, formerly St. Andrews University, Scotland

Host, Editor, Producer: Sarah McPeek, University of Virginia

Original Music: Daniel Nondorf, University of Virginia

Transcript:

Welcome to Naturalist Selections, an interview series featuring student and postdoc-authored work in The American Naturalist, produced by the American Society of Naturalists Graduate Council. Today we hear from undergraduate student first-author Anna Rouviere about her new paper ‘The Effects of Local Enhancement on Mean Food Uptake Rate.’ Anna conducted her undergraduate research with Graeme Ruxton at the University of St. Andrews in Scotland. She studied local enhancement, a behavioral strategy where foraging individuals cue on groups of other foragers to locate distant food patches. But is this strategy any good? Graeme’s previous theory work from the 90s suggested that animals using local enhancement actually consumed less food than they would if they had searched the environment on their own. Anna’s revised model confirms Graeme’s findings and clarifies a few cases when we might expect local enhancement to still be beneficial for foragers. I spoke to Anna to enhance my understanding.

Sarah:

So the first thing I want to ask you is if you can describe for us what local enhancement is, and how would you determine whether the species that you work on does local enhancing behavior.

Anna:

Okay. So local enhancement is a foraging strategy that’s used in the search for food. And it’s when a searching individual sees a group of animals in the distance and it assumes that there’s going to be food there, even though it’s too far away to see the food at that point. So it joins the group hoping to find food. And in that way, it can locate food more quickly since big groups are often easier to spot from a distance than just an unoccupied food patch. But it is actually really difficult to spot in nature. It’s really difficult to spot because it involves decision making, first of all, which is a difficult thing to study because you’re never in the head of the animal that you’re studying. So you don’t know why they make the choices they make. And it’s also a behavior that occurs over very long distances. So there have been many empirical studies that have said that a certain taxon uses local enhancement. And the way that they showed that it’s local enhancement is that they showed that individuals of that taxon purposefully join a feeding group. So, for example, a bird lands out of feeding group more often than would be expected just by chance, if that makes sense. But the thing is, there are many reasons to join a feeding group other than wanting to find food more quickly. I mean, you could join a group for safety because there’s safety in numbers. You could join a group because it facilitates your access to food, like cattle egrets following cattle around because they dig up insects for them. You could also join a group to find a mate. So then how can you tell if it’s actually local enhancement? And it’s really difficult, but I do think that’s kind of where studies like ours come in and are useful because instead of empirically trying to figure out which animals use local enhancement, we can try to theoretically predict which animals would benefit from it, and then that would give us an indication on which animals probably do use it.

Sarah

Is there one animal system where you think there is really convincing evidence of local enhancement behavior? I know in your paper you talk a lot about vultures.

Anna

Yes. Vultures are kind of the poster child for local enhancement. I feel like because, as obligate scavengers, they have a food source that’s very rare, and it’s very scarcely distributed in the environment. And as the paper we wrote kind of outlines, a rare food source is one of the reasons why you would want to use local enhancement. And yeah. So there’s been tons of studies on them, and it’s been shown that they do kind of join carcasses that are already occupied maybe more often than they would join other carcasses. The reason why I find that kind of more convincing than other studies like that is that they’ve also looked at the detection distances of vultures. So there was this kind of old paper where they were flying next to vultures in a glider and trying to figure out at which point the vulture sees this whole plume of vultures circling over a carcass. And it was often from tens of kilometers away. And you wouldn’t expect a vulture to be able to see just a single carcass on the ground from that distance. Right.

Sarah

Huh. Well, that makes me wonder if part of the reason why the vultures circle over their food before they land is to maybe facilitate local enhancing? Do you think that’s possible?

Anna

Maybe. I don’t know if that would be the kind of behavior that you would want to facilitate for others?

Sarah

Yeah.

Anna

I don’t know.

Sarah

I don’t know how you would test that, but it’s such a conspicuous display that they do. If I was a Vulture, I would certainly follow that.

Anna

Yeah. But yeah, there could really be reasons to believe that it has something to do with local enhancement and making that food more visible. We’d have to find a way to test that. Could be exciting!

Sarah

So getting a little bit into the theory of your paper and why you wanted to undertake this study, the paper that you wrote for American Naturalist revisits a previous paper in American Naturalist from 1995 that your advisor Graham Roxton wrote. You talk a little bit in the paper about why that older paper was so controversial when it first came out. So why was it controversial and why did you want to go back to it and dig into it again?

Anna

Yeah. So that paper, when it came out, it was quite the bombshell in the whole local enhancement foraging behavior research area because it basically said that local enhancement decreases feeding efficiency. And that was controversial because when you think about local enhancement as behavior and what it does, it actually reduces an individual’s search time, time spent searching for food. So you’d think if I spend less time searching for food, then surely I’m going to be able to eat more in a given time unit over a certain amount of time.

Sarah

Yeah.

Anna

But what that study said was that it was actually the opposite. That reduction in search time led to less efficient feeding, and that’s quite counter intuitive. And it didn’t really explain why that would be so it caused a lot of puzzlement in that field. So 25 years later, we kind of wanted to dig back into it for several reasons. First of all, because it was such a controversial and surprising finding. And also that study used a model of local enhancement. And when we looked back into that mo