During the COVID-19 pandemic, strict lockdowns in cities led to a drastic reduction in human activities and food resources for urban wildlife. A new study reveals how this affected the behavior and survival of one of the most successful urban-dwelling birds – the carrion crow. The researchers found that young crows struggled to find food, leading to a sharp decline in their survival rates. Meanwhile, adult crows increased their movements outside of their typical territories, likely in search of scarce resources. These findings highlight the strong dependence of some urban species on human-provided food, and how major disruptions can impact their ecology.
Crows Thrive in Cities, But at What Cost?
Many animal species have adapted remarkably well to the urban environments created by human activity. One of the most successful is the carrion crow, a highly intelligent and opportunistic bird that has become a common sight in city centers around the world. Carrion crows are known to rely heavily on food scraps and waste provided by human activities in urban areas.
The Great Lockdown Experiment
The COVID-19 pandemic provided a unique opportunity to study how urban crows would respond to a sudden and drastic reduction in the food resources they typically depend on. When strict lockdowns were implemented in cities across the world in 2020, public spaces, restaurants, and other sources of human-provided food were suddenly closed off or greatly reduced.
Researchers in Paris, France took advantage of this “natural experiment” to investigate the impacts on a population of carrion crows that had been closely monitored since 2015. By tracking the survival and movements of individually-marked birds, the team was able to quantify how the crows’ behavior and demography changed during the lockdown periods.
Juvenile Crows Struggle to Survive
The findings were clear – the lockdowns had a significant negative impact on the crows, especially the young birds. The researchers found that the apparent survival rate of juvenile crows (those in their first year of life) dropped dramatically during the lockdown periods, from 85% in normal years to just 59% in 2020.
This sharp decline in survival is likely due to the sudden lack of readily available food that young crows depend on to grow and thrive. As inexperienced foragers, juvenile crows were hit harder by the reduction in human-provided resources compared to the more experienced adult birds.
Adult Crows Become More Nomadic
While the juvenile crows struggled, the study also revealed changes in the movement patterns of adult carrion crows during the lockdowns. Adult crows increased their movements out of their typical territories in the Jardin des Plantes, the main study site in Paris, and ventured further into the city in search of scarce resources.
This behavioral shift suggests that adult crows were able to adapt to the loss of food in their usual haunts by expanding their foraging ranges. However, the researchers did not find a corresponding increase in adult mortality, indicating that the more experienced birds were able to weather the disruption better than the younger generation.
The Importance of Human-Provided Food
The findings from this study highlight the strong dependence that some urban wildlife species have developed on the food resources provided by human activities. When those resources suddenly disappeared during the lockdowns, it had a significant impact on the crows’ survival and behavior.
This raises important questions about the long-term sustainability of urban ecosystems that have become so reliant on human-derived food sources. As cities continue to grow and expand, managing the availability of these resources may be key to maintaining healthy and resilient populations of urban wildlife.
Author credit: This article is based on research by Perrine Lequitte-Charransol, Alexandre Robert, Frédéric Jiguet.
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