October 9, 2017
Everyone knows that doves are peaceful and jays are feisty… right? If you have ever watched birds interacting at your feeders you know that some species are likely to kick others off the feeding trays, and some species are likely to be kicked off. But are doves really peaceful and jays really feisty, or are we letting our imaginations influence what we see? The only way to find out is by collecting data. FeederWatchers rose to the challenge of collecting a totally new type of data—behavioral data—and opened the door to measuring species’ “personalities” on a continental scale.
FeederWatch participants have been gathering data on bird interactions. Blue Jay displaces Mourning Dove… check. Downy Woodpecker displaces Tufted Titmouse…. check. Chickadee displaces Hairy Woodpecker… no way! These conclusions may seem obvious, but it took over a thousand participants watching their feeders for tens of thousands of hours to collect enough data to verify these displacement patterns. Collecting the data is one thing, but making sense of it all is another. Thankfully, Postdoctoral Research Associate Eliot Miller at the Cornell Lab of Ornithology had the skills to do it. After sifting through 7,685 observations, Eliot had some answers. How do feeder birds relate to one another on a hierarchy of dominance? To put it simply, bigger is better.
Some surprises hidden in the data
Eliot organized observations between 136 species at over 1500 FeederWatch sites. He ranked each species based on how often it would displace other species and how often it would get displaced. Then he arranged all those species in their order of dominance, with the most dominant species at the top of the list, and the least dominant at the bottom (see diagram at right). What do you think was the highest ranking species? Believe it or not, the Wild Turkey came out on top. This may seem like a surprise—turkeys seem peaceful enough—but if you think about how often other birds displace turkeys, it starts to make sense; never! Turkeys are so large that there aren’t any other feeder-visiting species that can displace them; so not surprisingly, they don’t.
Who was at the bottom of the list? Another surprise: the Eurasian Tree Sparrow. This species is similar but not identical to its congener the House Sparrow, and apparently it is a lot more peaceful than you might expect. Eurasian Tree Sparrows were introduced into the St. Louis, Missouri, area in 1870 and have become establish in Illinois and parts of Iowa and Missouri, but they have not expanded their range very far. Perhaps their relatively peaceful personality contributes to this lack of expansion compared to more aggressive House Sparrows.
Placement on the dominance hierarchy is one thing, but which species are more or less aggressive than you would expect based on their body size alone? Eliot figured that out too. He mapped the dominance rank of each species on a phylogeny of all the species that interacted (see diagram at left) and statistically controlled for the mass of the birds. It turns out that doves, buntings, and grosbeaks are less dominant than we would expect based on their body size, whereas crows, jays, woodpeckers, and blackbirds are more dominant than we would expect based on their size. These findings mean our intuitions weren’t so far off: doves really are peaceful, and jays really are feisty.
Where do we go from here?
You might think that there are no more questions to answer, but this is just the beginning. One of the next questions that Eliot will tackle involves digging into some of the specific, subtle relationships between certain species. For instance, based on the data received to date, some trios of species appear to co-exist in a rock-paper-scissors arrangement. For example, European Starlings are dominant to Red-headed Woodpeckers, Red-headed Woodpeckers are dominant to Red-bellied Woodpeckers, and Red-bellied Woodpeckers are dominant to European Starlings (see diagram at right). This rare non-linear hierarchy may help balance continental patterns of abundance. Each species competes with another for nest cavities, but no species is always the winner. Since Red-headed Woodpeckers are infrequently observed at feeders, we don’t have many observations for the species, so we need to collect more data on its interactions this coming season to verify these patterns.
Stay tuned for more updates as we continue to explore these fascinating behavioral data, and keep those data coming! Do you want to add your feeder observations to the project? Join Project FeederWatch and you can contribute too.
Research reported in: Fighting over food unites the birds of North America in a continental dominance hierarchy. 2017. E. T. Miller, D. N. Bonter, C. Eldermire, B. G. Freeman, E. I. Greig, L. J. Harmon, C. Lisle, W. M. Hochachka. Behavioral Ecology. doi:10.1093/beheco/arx108. Abstract.
Cutout bird photo credits: Blue Jay by Joe Martin, Eurasian Tree Sparrow by Marge Fonner, Common Grackle by Cheryl Fagner, Mourning Dove by Susan Szeszol, Red-bellied Woodpecker by Barbara Houlihan, European Starling by Ed Hass, Red-headed Woodpecker, Wild Turkey, and Rose-breasted Grosbeak by Joan Wiitanen.