Field Course in Behaviour and Ecology Project Report

2014

The Effect of Anthropogenic Noise Pollution on the Territorial

Song Frequency of the Eurasian Blackcap (Sylvia atricapilla)

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AbstractRecent research indicates that high levels of anthropogenic noise pollution have a significant

impact on the way birds communicate. Low-frequency noise produced by human settlements

masks bird song, which can impair reproduction and courtship between conspecifics. Some

birds have overcome this by altering their song to have a higher minimum frequency, so that

they become distinguishable among the noise. In this report, I observe the effects of moderate

noise pollution on the Eurasian blackcap (Sylvia atricapilla) in order to see if lower thresholds of

background noise still elicit this vocally plastic behavior. I recorded 5 individuals in 3 locations of

differing noise pollution levels, comparing their average minimum frequency. Average maximum

frequency was also taken into account. Overall, the results were consistent with relevant

literature, with blackcaps near a busy town having significantly higher minimum frequencies

than those who lived in more rural locations (p=0.0054). Further experimentation is needed to

isolate anthropogenic noise pollution as the sole cause.

Introduction

Recent research indicates that high levels of anthropogenic noise pollution have a

significant impact on the way birds communicate. Elevated levels of low-frequency noise are a

trademark of human settlements (Katti and Warren, 2004). These low frequencies can mask

communication between conspecific birds, handicapping an important element of sexual

selection (Des Aunay et al., 2014). Some species of bird have been able to adapt to these

conditions with vocal plasticity, singing songs that are less complex, higher frequency, and/or

louder in the presence of background noise (Cardoso & Atwell, 2011). This has been exhibited

in robins, great tits, house finches, and other small songbirds (Dowling, 2012, Huffield et al.

2013, Bermudez-Cuamatzin et al., 2014). Most often observed is a reactionary increase in

minimum frequency when exposed to low-frequency noise pollution, proving that the behavior is

a “short-term acoustic adaptation” (Bermudez-Cuamatzin et al., 2011). Not all birds are capable

of this plasticity however, particularly large birds, which renders otherwise suitable areas

uninhabitable thus decreasing abundance and diversity of selected species in noisy areas

(Proppe et al., 2013, Francis & Clinton, 2011). With a projected human population of 9.6 billion

by 2050 (UN report, 2013) anthropogenic noise pollution is only going to increase, and so it is

vital that we understand its relationship with wildlife in order to preserve biodiversity.

While extensive research has been done to test the effects of urban noise levels on

birds, little has been done on populations which inhabit areas of moderate to low noise pollution,

as is present in the small towns and settlements of the Italian Alps. Passo Pura, located on the

southeast edge of the Alps, is a quiet area punctuated with bouts of noise from cars and

motorcycles. Eurasian blackcaps (Sylvia atricapilla) are very common throughout the area,

males producing a distinct territorial song. I was interested in exploring the effects of moderate

noise pollution on the song of these birds to determine whether vocal plasticity is selected for in

the early stages of urbanization- that is, the increase of minimum frequency in response to

urban noise as mentioned earlier. The nearest permanent human settlement is the town of

Ampezzo, which has a sawmill creating a constant source of noise in addition to passing cars

and agricultural machinery. Birds were recorded in Ampezzo as well as further up the mountain

at the Rifugio Tita Piaz, an area of minimal noise pollution beyond the occasional passing

vehicle. The minimum and maximum frequencies of the male territorial song could then be

compared to assess any differences.

I hypothesized that blackcaps close to Ampezzo would have a higher minimum frequency than

birds in more rural areas up the mountain.

Methods At dawn (5 AM to 6:30 AM Central European Time) I recorded 5 individual birds of the

same species (the eurasian blackcap, Sylvia atricapilla) in 3 locations over a period of 4 days.

The locations included the Rifugio Tita Piaz in Passo Pura, the nearby town of Ampezzo, and a

path in the forest a mile from the Rifugio. The forest represented a rural area, whilst the Rifugio

represented an isolated area of minimal anthropogenic noise pollution. Ampezzo represented

an area of moderate to high noise pollution.

In order to get better recordings from birds which were perched in trees, I created a makeshift

amplification cone for the microphone. I taped the microphone to the end of a long stick so that

it could be as high up as possible. (Fig 1)

I generated a spectrogram of each bird’s song using Bat Scan 9 and noted the lowest and

highest frequency reached during the territorial defense song. (Fig 2)

I used a one-way ANOVA to analyze the average maximum frequencies of each location to see

if there was a significant difference between the groups. I also used a one-way ANOVA to

analyze the average minimum frequencies in the same way.

If my one-way ANOVA results were significant, I analyzed the data further using a pairwise t-test

to compare each location.

Figure 2: A spectrogram of the Eurasian blackcaps’ territorial defense song. Frequency is measured along the Y axis and time is represented on the X axis. The composition remains generally the same in all species within the areas

of testing. Measurements were taken where the spectrogram spikes in three rhythmic “da’s”, denoted by the red square. The blue rectangle shows where the song begins and ends.

Figure 1: Microphone setup. Left shows the makeshift cone, constructed from plastic bottle and stabilized with kitchen towel. Tape was then wrapped around the stem to fix it to the microphone. Right shows the microphone taped to the large stick which will be used as an arm extension.

Results

The difference between the maximum

frequencies of the territorial calls showed a

slight upwards trend (Fig 3a). The minimum

frequencies had a strong, significant difference

from each other (Fig 3b).

To further explore the differences between the

average minimum frequencies I used a pairwise

t-test to compare the means of each location.

The greatest difference was between the

Rifugio and Ampezzo, Ampezzo having

significantlly higher minimum frequencies (p=

0.0054). The difference between Ampezzo and

the forest birds was also statistically significant

(p= 0.044), Ampezzo again having higher

minimum frequencies. Unexpectedly, the

difference between the forest blackcaps and

the Rifugio was stronger than that between

Ampezzo and the forest (p= 0.031). The forest

location showed higher minimum frequencies

than the Rifugio.

DiscussionModerate anthropogenic noise pollution may have an effect of the minimum frequency of

territorial songs of the Eurasian blackcap, however more controlled research is necessary to

isolate it as the sole cause.

My results were consistent with the findings of similar studies done in urban areas, which

could have important implications for bird populations in the future as noise pollution becomes

Figure 3: (a) A scatterplot of the average maximum frequency for individual birds in the 3 locations. A one-way ANOVA showed significant difference (p= 0.068) (b) A scatterplot of the average minimum frequency for individual birds in the 3 locations. A one-way ANOVA showed a strongly significant difference (p= 0.003).

(a)

(b)

more prevalent. An interesting point to note is the elevated minimum frequency in the forest

blackcaps compared to the Rifugio. A possible explanation could be that lower frequency calls

make blackcaps more conspicuous to predators, as high-pitched calls are more difficult to locate

(Dooling, 2000). In the forest there is likely a higher population of predators, which would make

a higher frequency call advantageous; a lightly settled area with humans may create a pocket of

low predation (assuming predators are deterred by human presence). This could explain why

the birds by the Rifugio Tita Piaz had a lower frequency call than those in the forest who may be

at greater risk of predation.

Bird density and species composition may be another factor to consider, as higher bird

density would create noise with which to compete, potentially influencing song frequency. If the

avian population down in Ampezzo consisted of more species with a lower average minimum

frequency than blackcaps, this could explain a shift to a higher frequency in order to be heard

among these birds. By contrast, if the bird population higher up the mountain consists of small

songbirds with high-pitched songs, this would allow the blackcap to maintain a lower-frequency

song. By performing abundance and diversity surveys prior to recording this could be taken into

account. Personal observation at all three sites led me to believe that there were indeed

different compositions of species in Ampezzo compared to the Rifugio and the forest, who

shared a fairly similar composition.

Observing birds in their natural habitat likely provides results closest to natural

behaviour, but caged/capture experiments could be useful in order to prevent recording the

same bird more than once. It would also create an environment in which noise pollution as a

cause could be isolated, particularly if bird calls with differing levels of background noise could

be played to the subjects. This would be the most efficient way of measuring the plasticity of the

behavior, as they would reply with higher minimum frequencies to louder calls if they possess

the plasticity character.

Further experimentation would benefit from high quality recording equipment. If

background noise levels could be quantified rather than estimated based on human population

this could give useful insight to the threshold of noise pollution which triggers selection for vocal

plasticity. I would recommend additional research into other species, such as the great tit

(Parus major), who have been proven to alter song frequency in response to urban noise

pollution, but to observe them in quieter suburban environments to see if a similar behavior is

displayed. It would also be useful to compare song complexity, length, and volume as these are

factors which have also been shown to change with relevance to noise pollution levels.

Bibliography

BERMUDEZ-CUAMATZIN, E., ARIEL RIOS-CHELEN, A., GIL, D. & MACIAS GARCIA, C.

2009. Strategies of song adaptation to urban noise in the house finch: syllable pitch plasticity or

differential syllable use? Behaviour, 146, 1269-1286.

BERMUDEZ-CUAMATZIN, E., RIOS-CHELEN, A. A., GIL, D. & MACIAS GARCIA, C. 2011.

Experimental evidence for real-time song frequency shift in response to urban noise in a

passerine bird. Biology Letters, 7, 36-38.

CARDOSO, G. C. & ATWELL, J. W. 2011. On the relation between loudness and the increased

song frequency of urban birds. Animal Behaviour, 82, 831-836.

DES AUNAY, G. H., SLABBEKOORN, H., NAGLE, L., PASSAS, F., NICOLAS, P. &

DRAGANOIU, T. I. 2014. Urban noise undermines female sexual preferences for low-frequency

songs in domestic canaries. Animal Behaviour, 87, 67-75.

DOOLING, 2000 Sound Localization in Birds

DOWLING, J. L., LUTHER, D. A. & MARRA, P. P. 2012. Comparative effects of urban

development and anthropogenic noise on bird songs. Behavioral Ecology, 23, 201-

209.FRANCIS, C. D., ORTEGA, C. P. & CRUZ, A. 2011. Noise Pollution Filters Bird

Communities Based on Vocal Frequency. Plos One, 6.

HUFFELDT, N. P. & DABELSTEEN, T. 2013. Impact of a noise-polluted urban environment on

the song frequencies of a cosmopolitan songbird, the Great Tit (Parus major), in Denmark.

Ornis Fennica, 90, 94-102.

PROPPE, D. S., STURDY, C. B. & ST CLAIR, C. C. 2013. Anthropogenic noise decreases

urban songbird diversity and may contribute to homogenization. Global Change Biology, 19,

1075-1084.

UN News Service Section, (2013). UN News - World population projected to reach

9.6 billion by 2050 – UN report. [online] Available at:

http://www.un.org/apps/news/story.asp?NewsID=45165#.U8-JxJUg_b0 [Accessed 23

Jul. 2014].