Effects of Anthropogenic Noise on Vocal Communication in the Great Kiskadee (Pitangus sulphuratus), Rufous Hornero (Furnarius rufus), and Thrush-like Wren (Campylorhynchus turdinus)

Urban ecosystems and landscapes have increased in size and range since the 20th century, and it is expected that many countries will continue to experience such spikes in the future. With more nations shifting to urbanization, this has become a more significant factor leading to the loss in biodiversity, especially birds. Bird species have been declining since the mid-20th century, and one large reason is through urbanization and the challenges they bring.

One of the main challenges is noise pollution, produced from traffic, aircraft, and construction noise. This negatively impacts birds by inhibiting effective transmission of vocalized songs and calls to potential receivers. In turn, this may lead to reduced reproductive success as vocal communication is essential for protecting territories and resources, for predator awareness and to attract mates. Thus, hampering vocal communication increases vulnerability to more risks, which leaves birds with an ultimatum: adapt or move elsewhere.
To understand how birds are adapting to noise, I examined the effects of noise on song and call characteristics in the Great Kiskadee (Pitangus sulphuratus), Rufous Hornero (Furnarius rufus), and the Thrush-Like Wren (Campylorhynchus turdinus) at 20 study sites. The research took place in Santa Cruz in Bolivia, where recordings began from 7:00 to 9:00 AM. My research predicts that noise will induce changes made to song and call characteristics, indicating that these birds are adapting to noise. By continuing to analyze these effects, this study will not only address a key gap in evidence, but also provide more means to expand our understanding of noise and vocal communication in areas less-documented like Bolivia.

Hello, my name is Anna McElhinny and I will be a senior biology student at George Mason University. I worked with Dr. Luther, my mentor, for this project, in which I assessed the impacts of anthropogenic noise on vocal communication in the Great Kiskadee (Pitangus sulphuratus), Rufous Hornero (Furnarius rufus), and Thrush-like Wren (Campylorhynchus turdinus). All are species commonly found in piedmont and lowland forest near Santa Cruz, Bolivia – where I am doing my research.

What is anthropogenic noise? It is produced through human activities such as through cars running on roadways, construction noise, flying aircraft, and other means of transportation. In this table here, explains the different types of noise I observed during my data collection period in Samaipata and Santa Cruz in Bolivia. 4 noise sources came from buses or large trucks, small trucks, cars and motorcycles. The two upper right headers show the minimum and maximum noise level for each category, which is measured in decibels using my sound meter. Throughout much of the data collection, the noise levels for buses and large trucks ranged from a minimum of 65 decibels to 80 decibels. For small trucks, this range was from 60 to 70 decibels. Cars had a range of 55 to 65 decibels and motorcycles ranged from 80-95 decibels.

So how does anthropogenic noise impact vocal communication? The main issue is that noise can mask or block effective transmission of songs or calls, preventing birds from hearing the information that a vocalization contains. Thus, birds are left with an ultimatum: either adapt or not. For this study, I wanted to assess how birds are adapting to noise, and thus I am predicting that my study species, the Great Kiskadee, Rufous Hornero and Thrush-like Wren will alter their song characteristics in response to noise. Whereas the null hypothesis will demonstrate that there will be no change to song/call characteristics, my study favors the alternative hypothesis, that there is change in order to be heard.
Before we continue, I also wanted to discuss the importance of vocal communication. Since noise acts as a barrier to effective transmission of songs and calls, this can negatively impact all birds involved. Vocal communication is key to assessing quality of territories, to protect food and resources, for predator awareness and to attract mates. Essentially, vocal communication is necessary for survival and to achieve reproductive success, and with noise involved, can make communicating much more difficult.

To show what my study species look like, here are some pictures I took while at the field. This is the Rufous Hornero, which is a type of ovenbird. This is a very common bird in both areas of Samaipata and Santa Cruz. This is the Great Kiskadee and is also a common bird species in these areas. Lastly, I decided to study a third species, such as the Thrush-like Wren since this bird was found in most of the sites that I was analyzing.

To collect the songs and calls, I traveled to the study sites located around Santa Cruz and Samaipata. 9 study sites were located around the area of Santa Cruz. 11 study sites took place in Samaipata.

Recordings began in the morning at each site, from 7:00 to 9:00 AM. I used a camera for all recordings, as well as a shotgun microphone. Noise levels were measured using a sound meter and I recorded for 3-4 weeks consecutively. After recording each day, I would spend a few hours adding data to my database. To analyze the songs and calls for each species, I used RavenLite 2.0, a program that helps to construct spectrograms or visualizations of what each song looks like, which I will show more later in the video.

I’ve included some recordings of each study species. Here, this video was captured at Laguna Guapilo, on an electrical post. From there, you can see a Rufous Hornero building its nest, as it’s applying dirt/clay and some twigs to its dome-like nest. In studying this species, I’ve learned that Rufous Horneros have a diet mainly of insects, but mainly prefer ants and termites. Their habitat range is mostly lowland valleys, especially in areas filled with agriculture and open fields of Samaipata, as well as urban parks in Santa Cruz. Additionally, they are monogamous, meaning they stay with their partners throughout the seasons and even years, which was why they were almost always seen together. One aspect that strengthens their bond is making duets, which are two songs sung at relatively the same time, and I’ll show what it looks like soon as well.

The next recording shows the Great Kiskadee. This was also taken at Laguna Guapilo, where I found this bird sitting on a tire piece near the lagoon. Regarding the life history of the Great Kiskadee, its diet is very generalized. They can eat meat, fruits, insects, mollusks, and even small fish, which is what you can see now. Great Kiskadees prefer habitats such as rural and suburban areas, open fields, and even forest edges. They prefer lowland valleys as well, especially in areas with water. They are also monogamous.

Finally, in the third recording shows a Thrush-Like Wren. Their diet mainly comprises of insects and fruits, though I am not sure what types they prefer. Thrush-Like Wrens vary in habitat, but mostly prefer humid forest and forest edges, pastures and parks. And the pair-bond, I am not quite sure of.

Now, next I will show spectrograms produced from the RavenLite program for each species, to show what each song and call looks like. For the Rufous Hornero Song Duet, it will show two songs from two individuals. The lower portion of the duet, with the lower pitch and frequency from the male. The higher pitched and higher frequency is from the female. Next is the call from the Rufous Hornero as well.

For the Great Kiskadee, these are what the song and calls look like.

And then for the Thrush-like Wren, this is what the song looks like. It was difficult to find a good spectrogram for a call from this bird, so I will only show the song for now.

While I do not have the full results from my project, I do have the estimated count of songs and calls for my sites so far. I have 131 songs from the Rufous Hornero and 26 calls. For the Great Kiskadee, I have 129 songs and 71 calls. And for the Thrush-like Wren, I have 48 songs and 11 calls. This data is only from 10 of the 20 sites I have so far.

Because I am still collecting all of my data into my database as it will take time to perform statistical analysis, I decided to present what I had so far. I will continue to analyze this data during the upcoming semester and hopefully the spring semester as well. I have enjoyed conducting this research in Bolivia and I look forward to continuing this study, and further understanding the impacts of noise on vocal communication in these bird species.