"Pavone" Giuseppe venduto a Putifarre. C. 1490-1500. via Bode-Museum, Berlin.

Read the Reflection, written 20 August 2021, below the following original Transmission.

The shelter-in-place orders and the massive drop in human activity in our cities, designed to slow the spread of COVID-19, have given us surprising and unexpected sightings of wildlife species across cities around the world. But beyond general awe — and a brief respite from the gloominess of the news — what can seeing all of this wildlife tell us about human-deprived spaces? 

Although the media has mainly covered unexpected sightings occurring in urban settings as a result of lockdowns, there are other important, more subtle changes that are happening in the world. First, some species, including those currently living in cities and those making the occasional forays into them, are now able to use habitats and resources that they had never before been able to exploit. Second, species in cities are experiencing a less harassing environment — less active, less noisy. An unknown number of adjustments have been taking place within a short window of time, and thus we are experiencing a once-in-a-lifetime opportunity to study how humans affect other animals in our cities. Although many of us had assumed that some of these individuals avoided cities mainly due to changes in habitats, it is clear now that we humans scare many of them out. 

Fear in wildlife has been broadly addressed, and we know that a lack of fear can occur in the wild. Some of the most common examples come from the Galapagos Islands, where many of the animals on the archipelago (particularly as adults) have no natural predators. For example, adult Galapagos tortoises are fearless because they have evolved in an environment with no predators. Indeed, some research has shown that insular systems have tamer animals. Lizards from islands flee from human approach at closer distances than those from mainland habitats, a pattern that has been shown to override phylogenetic closeness (Cooper et al 2014). Although studies are often correlational, evidence points to the lack of insular predators as one of the main causes behind this intriguing pattern. Yet, things are not very straightforward when we add humans to the formula. Empirical findings have shown that there is substantial variation in inland species’ and populations’ responses to human presence. A behavioral study focused on six different Galapagos species has shown that some of them do respond with fear to human tourist activities, but some do not (González-Pérez & Cubrero-Pardo 2010). Furthermore, species such as the small ground finch (Geospiza fuliginosa) still show fear responses to introduced predators years after predators have been exterminated from the island (Gotanda 2020), suggesting that evolutionary changes, and not just phenotypic plasticity related to wildlife behavioral responses, can occur in a relatively short time frame. 

So where does this leave us in terms of understanding responses of animals to rapid increases and decreases in human presence? There are few clear patterns, and even fewer clear results, regarding some key ecological and evolutionary questions: Are the changes we see evolutionary in nature, or due just to phenotypic plasticity? How does the environment an individual is born into reflect future behavior, ecology, and fitness? Do populations adapt as quickly to the sudden absence of humans as they do to their sudden presence? 

In the relatively short time period of the lockdowns, animals could make adjustments that range from the expected relaxation of alarm systems, from a behavioral approach, to changes at the evolutionary level (see Schilthuizen 2018 for amazing examples). In Southern California, we have been conducting a long-term study of several populations of an urban songbird, the dark-eyed junco (Junco hyemalis). Since this woodland species began to move down from the mountains into the cities of Southern California a few decades ago, these birds have adapted remarkably well to the sunny coastal lifestyle (Yeh 2004). Their population numbers are rising, and they have begun to move from college campuses to both dense city centers and leafy residential suburbs. Not surprisingly, these birds are not too scared of humans. After all, if these individuals were to fly away at every human who was approaching or passing by, there would never be enough time to eat, find mates, and feed their offspring! But the sudden quietude in which they now find themselves allows us to examine something very different: how will these birds respond to a rapid decrease in the levels of human disturbance — both the adults birds now, and the offspring born into these much calmer and more serene situations? Will they become more fearful of people or will they change their perception of us as threats? Will we see a decrease in fitness as human chaos starts up again or will our absence pass unnoticed, evolutionarily speaking? 

There are obviously no answers to our questions yet. And that’s why lockdowns constitute a unique and unparalleled opportunity to examine what happens to wildlife experiencing these rapid changes in their living environments. We may expect differences in the behavior of some animal populations, most likely leading to unexpected results. For instance, the newborn chick in human-deprived cities whose parents were not bold enough to use a resource in an urban area (e.g., insects from university campus lawns) may start using them now and continue to do so if they lack the perception of humans as potential threats. 

But besides all of the above, the current scenario leaves us with some more philosophical questions: If many species find our “urban habitat” so stressful, should we reconsider how we urbanize and how we develop cities? Wouldn’t we want to generate scenarios that may attract many of the surprising species that have been sighted after lockdowns as part of our cities in our day-to-day lives? Headline news and social media across the country are stating that “we can’t go back to normal” (Baker 2020). In some senses, we hope this is true! That is, in addition to the health, social, and economic ramifications of this pandemic, which have been fairly catastrophic (Ruiz Estrada 2020), we hope this pandemic allows us to consider how we can have more animals in our daily lives in the city, and more fully share the planet. 

Pamela Yeh
Santa Fe Institute

Ian MacGregor-Fors
Instituto de Ecología, A.C. 


  1. Baker PC (2020) “We can’t go back to normal”: how will coronavirus change the world? The Guardian. March 31, https://www.theguardian.com/world/2020/mar/31/how-will-the-world-emerge-from-the-coronavirus-crisis 
  2. Cooper WE, Pyron RA, Garland T (2014) Island tameness: living on islands reduces flight initiation distance. Proceedings B 281: 20133019 
  3. Gotanda, K. M. (2020) Human influences on antipredator behaviour in Darwin’s finches. Journal of Animal Ecology 89(2): 614-622. 
  4. Ruiz Estrada MA (2020) Economic Waves: The Effect of the Wuhan COVID-19 on the World Economy (2019-2020). SSRN https://dx.doi.org/10.2139/ssrn.3545758 
  5. Schilthuizen M (2018) Darwin comes to town – How the Urban Jungle Drives Evolution. Picador, New York. 290p. 
  6. Yeh P (2004) Rapid evolution of a plumage pattern following population establishment in a novel habitat. Evolution 58:166-174. 


T-027 (Yeh & MacGregor-Fors) PDF

Read “Welcome Back, Animals!” in Nautilus (May 20, 2020).

Read more posts in the Transmission series, dedicated to sharing SFI insights on the coronavirus pandemic.

Listen to David Krakauer discuss this Transmission on episode 32 of our Complexity Podcast.


August 20, 2021


Over a year ago, we discussed a new and unexpected research direction we were taking: looking at how the sudden and dramatic emptying of our cities impacts the animals that have been living there. Will the animals behave the same way? Will they change, and if so, can we make predictions about the directions of change? In particular, we were wondering how dark-eyed juncos—a fairly new urban inhabitant—might change with regards to their fearfulness of humans and in their aggression levels towards other juncos. We also concentrated on the response of bird communities to the much calmer and emptier cities resulting from the strict COVID-19 lockdowns. Additionally, both our labs worked together to keep track of wildlife species that were being recorded by the general public and the media in quarantined cities, underscoring the role that community science could have on unexpected scales. We now have some preliminary answers that we will discuss later, but the bigger surprise for us is how increasing complexity in our natural world requires increasing nimbleness on the part of researchers and educators. Until now, we had rarely thought about the role of the researcher in the research itself.

Science is often considered an impartial pursuit, where we are supposed to take the researcher out of the equation, or at least avoid biases as much as possible. This year we learned that this task is much harder to accomplish than commonly thought. During the pandemic, our labs and those of many colleagues across disciplines were decimated not just by the virus itself, although tragically many of our families were severely affected. Depression, anxiety, fear, anger, confusion, and exhaustion tore through our labs. One of the most talented and promising PhD students of the Yeh lab—a woman of color, who grew up in deep poverty, the child of a single teenage mother—dropped out of graduate school. On and off, together with students and postdocs, we were all stuck at some point; some of us were simultaneously bored by the quarantine and also completely unable to get work done. Others were completely overwhelmed by the extra work the pandemic placed on so many of us, with the academic machinery trying to keep the regular paces going even in the middle of a pandemic. We worked hard to scratch out successes, with some students graduating on time, and interesting work still being published under the pressing circumstances. But more so than at any time in our careers, we were faced with the human part of science, and that part that has proven to be beyond complex!

As we were madly pivoting in an attempt to save future careers (and our own), one of the Yeh Lab graduate students offered this saying: “We have to make lemonade out of lemons.” We have all heard this saying before, but for our decimated and depleted labs, it became a mantra and we clung to it. We also realized how similar we were to our study system: Like humans, birds also had to pivot because of the pandemic. When we started making the connection of the universality of the “pivots,” we had a more intimate connection with the organisms we studied, and I think it was a starting point for our lab to collectively heal.

In retrospect, it should not have been such a surprise to us that who does the research, and how we vary as individuals is a key component of research. The knowledge that who does the research is crucial has been demonstrated in our field of behavioral ecology, where the idea that there is “female-choice” in mating systems rather than “male–male combat” only started being fully understood and fleshed out in the 1970s, when women were finally allowed to join the ranks of men in field research1.

In practice, how do these realizations change how we do our work? We are trying to understand how our own mental well-being affects the work we do, sometimes as individuals, both individually and collectively. This impacts not only our productivity but also the quality of our interactions, the questions we ask, the ability to be open to new directions, and the excitement we have about our work. We are starting to talk with psychologists, sociologists, and even artists to determine how we can measure all these aspects, and how we can work within our own mental, emotional, and physical capacities to produce whole scientists, who can in turn produce whole science—science that considers context and understands that sometimes one cannot take the scientist out of the science.

As for the birds? Well, in California dark-eyed juncos appeared to have a rough couple of years as far as breeding—although it is currently unclear how much of this has to do with the drought and how much of it has to do with a change in human activity. But the juncos pivoted substantially in their behavior, appearing to be less aggressive than the already fairly relaxed prepandemic city juncos. In Colombia, we could see how calmer cities opened an avenue for more birds, both diurnal and nocturnal, showing how our day-to-day activities act synergistically with urbanization in molding the wildlife communities we currently have. We do not yet know if these responses will have long-term effects on the behavior and ecology of urban birds, but we do know that we, as scientists, have learned and are learning more than we have ever imagined from this trying phase for humanity.

Read more thoughts on the COVID-19 pandemic from complex-systems researchers in The Complex Alternative, published by SFI Press.

Reflection Footnotes

1 K. Borgmann, “The Forgotten Female: How a Generation of Women Scientists Changed Our View of Evolution,” All About Birds, June 17, 2019, https://www.allaboutbirds.org/news/the-forgotten-female-how-a-generation-of-women-scientists-changed-our-view-of-evolution