Does wearing a face mask make humans less scary to tree sparrows?

Jiang X, Liu J, Zhang C, Liang W. 2020. Face masks matter: Eurasian tree sparrows show reduced fear responses to people wearing face masks during the COVID-19 pandemic. Glob Ecol Conserv. 24:e01277. doi:10.1016/j.gecco.2020.e01277.

Header image: Eurasian tree sparrow photo by Bengt Nyman wikimedia commons:

Feeling blue 

In December 2019, the world as we know it changed as the global pandemic of COVID-19 spread. Undoubtedly the most important effect of this pandemic has been its terrible cost to human life. Having recognized that, this pandemic has also changed how we (humans) normally venture outside. In particular, the use of mask covering has become the norm. Because of this, scientists in China set out to explore how this change in appearance affects the way a common bird species responds to humans.

Figure 1: Investigator with and without face mask (photo from article; open access)

Animals’ behavioral response to humans 

I’m really fascinated by how animals that frequently encounter humans adjust their fear responses to be able to live among us (you can check out my previous blogs on the topic here)! Theory tells us that if you are too shy, you’re likely to waste energy running away every time a human is nearby. Instead, animals should learn that nearby humans do not pose a direct threat and adjust their response so that the distance at which they run away from us decreases over time. The distance associated with the start of an animal fleeing from an approaching threat is called flight initiation distance (FID). Animals that are bold have very short FID, meaning that approaching humans can get very close to them before they flee. In contrast, a long FID means that the animal is very frightful and begins to flee at greater distances between it and you.

Mask wearing and Eurasian tree sparrows

Xingyi Jiang and colleagues (Hainan Normal University, Wei Liang’s Lab) explored how mask wearing affects the fear responses of Eurasian tree sparrows (Passer montanus; figure 1) in two provinces of Sichuan, China. They evaluated birds that have been exposed to mask wearing for six months since the start of stricter public health requirements. They hypothesized that birds learned to associate masks wearing humans as non-threatening. To test this hypothesis they approached birds with and without face masks (figure 1) and compared their flight initiation response.  

Table 1: Expected outcomes of birds responses to approaching investigators with and without a face mask

Xingyi Jiang and colleagues found that Eurasian tree sparrows responded with greater wariness to the approach of an investigator without a face mask. This result supported their hypothesis that these birds had modulated their responses to humans wearing face masks. What’s interesting is that this finding also suggests that birds had increased wariness to humans without facial covering. Authors suggest that this is evidence of learning, as in the last six months birds would have been exposed to masked humans and as a consequence adjusted their responses to them. To verify that hypothesis, it would have been necessary to test birds closer to the start of mask wearing, to see if mask wearing increased wariness and then after months of exposure if wariness decreased. 

Figure 3: Behavioral responses of birds to the approach of an investigator with and without a face mask. The y-axis shows the flight initiation response in meters. More wary birds will begin to flee at a greater distance and thus have a longer flight initiation distance. Birds responded with greater wariness to the approach of an investigator without a face mask. (Photo from the article; open access)

Bird brained: 

A reason I am passionate about the study of behavioral responses is that it provides insights into how animals learn and adjust to rapidly changing conditions. In the United States, it is common to attribute bird-brained as lacking intellect or complex thoughts. Yet, growing research, such as this one, continues to show us how birds and other animals are smarter and capable of complex learning to problem solve rapid changes occurring in their environment. 

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Kevin Aviles Rodriguez

I am in the process of completing my PhD in Ecology and Evolutionary Biology at the University of Massachusetts in Boston. I am interested in human environmental changes as natural experiments to test hypothesis about the evolution of animals. Specifically, I study small lizards known as anoles and how living near human households impacts their ecology and behavior. I love fieldwork because often it takes me away from the cold and towards the sunny beachy islands that I love the most.

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