Different Bird Species May Team Up For Migration

KATHLEEN DAVIS: This season, billions of birds will take to the skies as they flock to their wintering grounds. And with so many different species on the move, they’re bound to run into each other. A new study suggests that this mixing and mingling might not be coincidental. In fact, different bird species could have their own social networks that might boost each other’s survival.

Joining me to talk about this is my guest, Dr. Joely DeSimone, migration ecologist at the University of Maryland Center for Environmental Science in Frostburg, Maryland. Welcome to Science Friday.

JOELY DESIMONE: Thanks, Kathleen. Happy to be here.

KATHLEEN DAVIS: Thanks for joining us. So walk me through what you found in this study.

JOELY DESIMONE: Yeah, so we analyzed banding records from bird observatories across Eastern North America, totaling hundreds of thousands of individually banded birds. And we analyze that data set to test for, as you said, these non-random associations among these various migrating songbirds.

So we know they all are co-occurring in high numbers at stopover sites where they stop along their migratory journeys. But we were testing whether it’s not just a coincidence who appears next to who. And so we conducted these social network analyses of these big data sets and found that is the case. It’s not a coincidence. There are persistent relationships that are consistent across the various stopover sites we looked at in between spring and fall migration.

KATHLEEN DAVIS: Was this a surprising finding to you?

JOELY DESIMONE: Yes and no. So I think we were expecting that because these migrants are all migrating at the same time. They must be interacting with each other in some way, even though there isn’t a lot of literature on the topic. But I think the persistence of these relationships was really striking to me. And really the key point of evidence supporting this idea that these are communities migrating across landscapes together, not just random assemblages of species migrating across landscapes together.

KATHLEEN DAVIS: And so what do those interactions between bird species actually look like?

JOELY DESIMONE: Yeah, so from our data set, we actually can’t tell and are excited to conduct future research to tease apart what these interactions are. What we suspect are two main species interactions. The first is competition. These birds migrate 12, 20 hours nonstop, land in these unfamiliar habitats, and have to feed and refuel quickly and continue on their journey. And so likely they could be competing with each other for limited food resources at these stopover sites.

And then on the flip side is they might be benefiting from each other. So in these unfamiliar habitats, songbird species don’t typically stop at the same stop year after year, so they usually are landing in a place they’ve never been before. The presence of these other familiar species whose diets might be similar to theirs, whose predators might be similar to theirs, could provide valuable information to help these birds locate good habitat, locate good food, avoid predators along the way.

KATHLEEN DAVIS: So one bird species could see, oh, there’s this other bird species that I run into all the time, this must be a spot where I can hopefully survive for the next stop.

JOELY DESIMONE: Yes, exactly. I think of it a little bit like Yelp, providing, yeah, information about a place you’ve never visited before.

KATHLEEN DAVIS: OK. Is it also possible that these birds are sharing maybe distress calls or warning calls with each other?

JOELY DESIMONE: Yeah, I think that is very likely. A lot of birds have warning calls when there’s a predator nearby. And if they have similar predators, that could be valuable information to you.

KATHLEEN DAVIS: Yeah, I would imagine, even if you don’t speak the same bird language, the call out for runaway is probably pretty similar across species. So what are a couple examples of species that might be tag teaming migration?

JOELY DESIMONE: Yeah, so we found a lot of strong relationships, particularly among a variety of warbler species. One of the strongest and most persistent was between American Redstarts and Magnolia Warblers.

KATHLEEN DAVIS: So now that there seems to be this evidence for cross-species relationships, is it possible that this could impact our understanding of conservation?

JOELY DESIMONE: Yeah, I think so. So this really encourages a– I think, a more holistic approach to these animal migrations by highlighting how interconnected they all are. Many migratory birds around the globe are experiencing steep population declines. And I think this paper shows that the population declines of one particular species isn’t a problem just for that species. It means that now there’s a whole node missing from these migratory social networks and whatever competitive interactions that species was engaged in are now gone or whatever valuable social information that species was providing to its other co-migrants is now gone.

KATHLEEN DAVIS: Well, that is about all the time that we have for right now. Joely, thanks so much for joining me.

JOELY DESIMONE: Thanks for having me.

KATHLEEN DAVIS: Dr. Joely DeSimone, a migration ecologist at the University of Maryland Center for Environmental Science in Frostburg, Maryland.

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