Since I’ve been birding editor here on Bellaonline, I’ve noticed two articles have had the most hits. In the winter it is “Where do Canada Geese Migrate” and in the warmer months, it is “How do Robins find Worms?” Neither of these were written by me, but by previous birding editors, although you will see my picture next to both of these articles. I haven’t written anything nearly as popular yet, although I am thinking of writing about how Canada geese find worms. Except, of course, they mostly eat grass, so probably wouldn’t be all that interested in them. But anyway.
While nobody is too upset over the goose story, the robin story has stirred a bit of controversy with certain readers. They do not believe that robins use the sense of sound to locate worms, but rely entirely on sight.
Realistically, this should not be a major source of concern. Robins are fine and possibly the most numerous bird in the country, at least to some reports. They are not starving, not like the poor birds in the gulf that wish to eat shrimp. But for some, it is very, very important that the correct information is out there. So I will dedicate this column to How Robins Find Worms: The Sequel.
As any good graduate student knows, you must look in scholarly journals to find the correct answer to anything. Unfortunately, scholarly articles are not always free on the Internet, and since I am a volunteer here, I have decided not to purchase these writings, as wonderful as they may be. They have been summarized on free sites, however, although it is not certain how accurately. Where I can, however, I will use the official abstract of the publication.
The first important study on how robins find worms was by Frank Heppner in 1965. It is summarized on a web site which I will link below, called “American Robin.” According to this study, Heppner determined that robins use only their sense of sight to find worms. He put dead worms in a wormhole, worms that could not be making a sound or giving off a vibration (because they were dead, duh!) The robins were able to see the glistening flesh of the deceased annelids through the tiny holes and ate away!
The second famous scholarly article about robins and worms was published in 1997, by Robert Montgomerie and Patrick Weatherhead. It is this article that the original author of the original “How Robins Find Worms” referred to.
In this study, robins were able to locate buried meal worms using their sense of sound alone. In fact, Weatherhead and Montgomerie found that if they played some “white noise” the robins had trouble finding their worms. They concluded that robins use the sense of hearing to locate their prey. It doesn’t say that they never use their sense of vision. Certainly, if a robin sees a silent worm on the on top of dirt, it will eat it. But somehow, robins were able to locate worms underground that they could not see, and Weatherhead and Montgomerie found that the sense of hearing was used to do that.
Now, here is something interesting that was not brought up: meal worms and earthworms are completely different animals! Meal worms are not worms, but long, skinny insects. They are actually the larva of a beetle. They have a hard covering called an exoskeleton and six legs. An earthworm is soft, with no legs. They crawl on tiny, bristle-like setae
It is quite possible, that it is noisier when a hard, legged “worm” walks than when a soft, mushy worm does. In general, the harder something is, the noisier it is. Perhaps the robins could hear the meal worms but could not hear an earthworm. I don’t know. But in two peer-reviewed journals, one scientist proved the hypothesis that robins use their eyes, another team proved their hypothesis that they use their ear holes (which are buried under their feathers.) For a hypothesis to become a theory, studies must be duplicated by other scientists, and this didn’t seem to happen. It’s obvious the second study is quite different from the first, as different prey is involved.
So how do robins find worms? It’s safe to say they use both their senses of sight and hearing, to some extent. It is also clear, that this question is not exactly setting the ornithological world on fire. Thirty-two years went by between the first and second major robin/worm studies, and it’s been thirteen years since the second. Maybe someone out there will get a Ph.D. in ornithology and finally answer this question once and for all.