Safety In Numbers: Bean Geese And Ship Noise

Environmental noise influences animal activity in a myriad of ways. Both trains and highway noise are loud enough to cause observable effects on animal behavior, including birds. In wetland environments, ship sounds have been shown to disturb waterfowl. Prior research has shown that container ships, oil tankers, ferries, and bulk carriers create the most noise. High-traffic fishing and patrol ships also contribute significantly to noise pollution on rivers and lakes, causing increasing ecological damage. 

Earlier research on avian response to noise has been done with captive birds. This study examines the effect of ship noise on the behavior of wild wintering waterfowl. Researchers selected the bean goose, a common bird wintering in the middle and lower Yangtze floodplain, for this project. They studied a farmland area of the Lianhe village in the Shengiin Lake Nature Reserve as the fieldwork site. To obtain recordings of ship noise for the research, they captured the sound near the exhaust cylinder from 1,000 ships on the Nanfei River in the city of Hefei. 

For the experiment, researchers simulated ship noise at playback volumes of less than 50, 60, 70, 80, 90, and 100 decibels(dB). The recordings were played at distances of less than 100 meters (short), 100-200 meters (medium), and 200-300 meters (long). They also varied the duration of the playback from 0-1 minutes (short), 2-3 minutes (medium), and 4-5 minutes (long). As they ran the different noise scenarios, they used binoculars and monoculars to identify changes in goose foraging (e.g., head lowering, pecking at ground food), vigilance (e.g., neck elongation, scanning the environment for predators), and flight behaviors (e.g., flapping wings frantically, flying in the opposite direction of the sound). 

After a three-day preliminary trial, data was collected from December 12-28, 2019. Scientists recorded a total of 495 observations across both smaller and larger populations of bean geese. Results showed that the geese were more sensitive to noise when they were part of a smaller group than a larger flock. Ship noises exceeding 70dB at distances of less than 100 meters or greater than 80 dB at less than 200 meters clearly changed the behaviors of the geese. Foraging decreased, while vigilance and flight behaviors increased. However, the duration of the sounds had no effect on behavior. 

The results of this study give insight into the noise tolerance of bean geese. While the birds may be able to adapt to mild noises, the high-intensity sounds of ships may cause important changes in bean goose behavior. The authors recommend further research on other birds to create a database of noise-related behaviors, which could inform waterfowl protection policies. Advocates can also use these results for more immediate mitigation strategies, such as recommending that ships keep a distance of at least 200 meters from bean geese.