Going off the rails: Soras increase alarm calling when they hear owls, but not ducks

Featured Scientist: Daniel Lorenz Goldberg (he/him/his), PhD (Anticipated December 2021), Illinois State University, Biological Sciences.

Daniel looking at the camera and pointing to a sign that reads “Illinois State University RAIL COUNT”
Daniel in his office in Illinois State University Science Laboratory Building with his official research vehicle plaque.

Birthplace: Riverside, California

My Research: I study vocal behavior and how it evolved in a group of birds called rails. Rails vocalize frequently at night and in dense vegetation to communicate with each other.

Research Goals: I am interested in pursuing research in bird conservation after I graduate. I hope to learn more about birds to protect them and their habitats. My dream is to increase public understanding about birds by sparking interest through birdwatching.

Career Goals: I aim to do a combination of research and teaching as a university professor.

Hobbies: I enjoy birdwatching, hiking, swing dancing, and tabletop games with my friends.

Favorite Thing About Science: I love the vast amount of primary literature that we have at our fingertips as scientists. There have been so many discoveries that have been documented, and we can  access it by reading about it in books or online. If you have an interesting research question, chances are good that there is some background information out there to get you started!

My Team: This project was a group effort, though I am the first author on the published article. My advisor Dr. Angelo Capparella helped me develop the project, while Dr. Mike Ward provided field equipment. Both professors provided advice on writing the article. My hardworking undergraduate, Toby Bassingthwaite, assisted with fieldwork and transporting our equipment, and she also knew where to hunt down some delicious food in the Chicagoland area!

Organism of Study: I study the Sora (Porzana carolina), a common rail in Illinois.

A photo of a Sora (Porzana carolina). It is a brown bird with a bright yellow beak, and it is standing with its feet in the water.
A photo of a Sora (Porzana carolina). Photo credit: Tim Lindenbaum, The Nature Conservancy

Field of Study: Behavioral Ecology

What is Behavioral Ecology? Animal behavior is shaped by an animal’s habitat and its interactions with other organisms. Behavioral ecology is the study of how an animal’s behavior affects its life and survival. Behaviors that help animals to survive become more common. Behaviors that do not help animals survive become less common.

Check Out My Original Paper: “Calling owl: Rails adjust vocal activity rates in response to changes in predation risk”

A QR code that links to the original publication.
QR code to the original publication

Citation: Goldberg, D.L., Bassingthwaite, T.A., Ward, M.P. and Capparella, A.P., 2020. Calling owl: Rails adjust vocal activity rates in response to changes in predation risk. The Wilson Journal of Ornithology. 132(4):1038–1043.

Research At A Glance: Animals use sound-based communication to signal to each other to defend territories, attract mates, or maintain group contact. However, this communication can be risky because predators can eavesdrop on these sounds. Predators can then home in on the calling animal, and more easily capture and eat it than if the animal had remained silent. Animals can recognize the calls of their predators and often react by reducing the number and rate of their own sounds. For example, birds that are preyed on by raptors fall silent upon hearing raptor calls. One group of birds that has shown little evidence of varying their calling behavior in response to predator sounds are rails. In previous studies, rails have been found to flick their white tails as a visual signal to predators, indicating that the rail is aware that it is being watched. We tested the hypothesis that rails will recognize raptor calls as a predator threat. We predicted that rails would reduce their calling rates when they hear the calls of a raptor, but not when they hear the calls of a different and harmless bird.

The Lake Calumet wetlands near Chicago are a restored habitat that is home to large numbers of rails, including the Sora. We used Autonomous Recording Units (ARUs) to record the calls of rails in 10 locations at the water’s edge of three marshes in the region during the spring breeding season of rails in April 2019. At half of these recording locations, we broadcast the hoots of a raptor, the Great Horned Owl. At the other half of these recording locations, we broadcast quacks of a harmless bird, the Blue-winged Teal duck. We made these broadcasts in the evening, night, and early morning, when rails tend to call the most. At the end of the month, we retrieved the ARUs and counted the number of Sora calls recorded at each of the 10 locations. We then compared the number of calls the rails made per hour at each location. We found that Soras increased their calling rates after broadcasts of the Great Horned Owls but decreased their calling rates after broadcasts of the Blue-winged Teals. This result is the opposite of our hypothesis because birds usually decrease their calling rates when they hear predator calls.

Highlights: Our results indicate that Soras do not recognize Great Horned Owls as a major threat, as the rails were not threatened into silence after the owl broadcasts. This finding made sense because Soras are not the primary prey of this raptor, even though the owl does eat Soras on rare occasions. We found that Soras called at higher levels after the owl broadcast than beforehand. They also maintained high levels of alarm calling for an entire week after the owl broadcast (Figure 1). Other research has found that Soras tend to stay hidden in thick emergent vegetation in their wetland habitats. The plants in this habitat should give rails cover from Great Horned Owls, which use their superb vision to hunt down their prey. If the owls cannot see the Soras, then they are more safely able to make an alarm call because they are not revealing their location.

A line graph shows the frequency of Soras calls per hour from April 13th – 29th. The owl and teal broadcast were done on April 21. The graph depicts an increase in the rate of Soras calls after the owl broadcast.
Figure 1. During the study period of April 13th – 29th, 2019, we recorded Sora calling rate as the number of calls made per hour (y-axis) for several days (x-axis) after owl broadcasts. The dashed line shows the broadcast date when we played either an owl call or a teal call to the soras. The black line shows calling rates of soras that were exposed to owl calls, the grey line shows the calling rate of soras exposed to teal calls.  Figure adapted from Goldberg et al. 2020.

What My Science Looks Like: Rails are shy birds that tend to live in dense emergent vegetation in wetlands, grasslands, or forests. They are difficult to see but are quite loud and produce a variety of sounds that can be heard easily. This allows us to study them using ARUs. ARUs allow us to listen to all the sounds in an area and make recordings when the birds are calling. We can then identify rail calls by their appearance in spectrograms using a computer in the laboratory. This approach cuts down on the amount of time that we need to spend on fieldwork, because instead of going out at dawn, dusk, and night to listen for rail calls, we can simply place an ARU out in the rail habitat to detect calls.

An image of a marsh. There are plants growing in the water, with taller vegetation lining the sides of the marsh.
The view from the north side of Big Marsh Park, looking south past the deployment spot of an ARU, during the spring of 2019. Image adapted from Goldberg and Bassingthwaite 2020.
An image of an ARU. It is a green box mounted on a green pole, with a microphone sticking out the side.
A close-up view of an ARU placed in the field to detect rail calls throughout the day. Image adapted from Goldberg and Bassingthwaite 2019.

The Big Picture: Many rails are endangered, as they have lost habitat due to humans converting wetlands, grasslands, and forests to farm fields and cities. Some rails, like the Sora, are also hunted by humans for food and sport. Because rails produce many calls that are easily recognized, predators can use their calling behavior to identify rail species in the wild. We can use their calls to learn more about how they respond to predators and how they may return to habitats that have been restored. This research is important because it may be used to help rails to increase in number. Conservation of wetland species will benefit other birds and animals that live in those habitats. Wetlands provide many benefits, such as reducing the impact of flooding, improving water quality, and maintaining water levels during droughts. These habitats cannot persist without the presence of a variety of organisms, including rails.

Decoding the Language:

Autonomous Recording Unit (ARU): Autonomous Recording Units (ARU) are battery-powered recording devices. They can be left outside because they have protective covers that shield them from the weather. When they are turned on, they will record all sounds made around them until they are turned off or the batteries run out of power.

Emergent vegetation: Plants that grow in wetlands and stick up partially out of the water. They provide an ideal habitat for rails, which can hide among the plants to avoid detection by predators.

Endangered: Animal species that is at risk of extinction.

Fieldwork: Fieldwork is a type of scientific research that takes place outside of the lab. For my research, fieldwork includes deploying and analyzing sound recordings to listen for rails at the Lake Calumet wetlands near Chicago.

Primary literature: Primary literature is a collection of historical and scientific documents such as books, recordings, or journal articles. Essentially, it is the write-up of information that was collected in a study.    

Rail: Diverse group of birds which includes about 127 different species, including Soras. Most rails are small to medium, and while typically found near marshes they can be found throughout the world.

Raptor: Raptors are meat-eating birds such as hawks, eagles, vultures, falcon, and owls.      

Signal: A signal is a type of communication, such as a sound produced by an animal.    

Sora: Small waterbirds found throughout North America typically in marshes. Usually 19-30 cm in length, they have a grey face and belly while the rest of the body is brown with black & white patches.

Spectrogram: A spectrogram is a type of graph that shows a visual representation of sound, with the frequency of the sound on the y-axis, and the timing of the sound on the x-axis.

Learn More:

For more information on bird call research using ARUs, check out Dr. Mike Ward’s laboratory webpage.

The Macaulay Library of the Cornell Lab of Ornithology, a website devoted to collecting recorded calls of birds and other animals in a database for scientific and general use, was the source of the Great Horned Owl and Blue-winged Teal calls that I broadcast in my study.

There are many articles written about prey animals’ responses to predator sounds. These papers summarize what is known about changes in calling behavior:

Hettena AM, Munoz N, Blumstein DT. 2014. Prey responses to predator’s sounds: a review and empirical study. Ethology. 120:427–452.

Hughes NK, Kelley JL, Banks PB. 2012. Dangerous liaisons: the predation risks of receiving social signals. Ecology Letters. 15:1326–1339.

Zuk M, Kolluru GR. 1998. Exploitation of sexual signals by predators and parasitoids. Quarterly Review of Biology. 73:415–438.

The papers that initially piqued my curiosity about this avenue of rail research:

Randler C. 2006. Disturbances by dog barking increase vigilance in Coots Fulica atra. European Journal of Wildlife Research. 52:265–270.

Randler C. 2007. Observational and experimental evidence for the function of tail flicking in Eurasian Moorhen Gallinula chloropus. Ethology. 113:629–639.

Synopsis edited by Ian Rines, BS 2018, Wofford College, and Emily Kerns, PhD student, University of Wisconsin-Madison, Integrative Biology.

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