Behavioral Sink: A Cautionary Tale for Animal Populations

Behavioral sink is a phenomenon in animal populations in which the behavior of individuals declines due to overcrowding or other environmental conditions. This decline can lead to both long-term and short-term impacts on the population, including reductions in reproductive success and population growth. In extreme cases, it can even lead to the extinction of a species. This phenomenon is particularly relevant in the context of human-caused environmental changes, such as habitat destruction, climate change, and pollution.

Behavioral sink was first described in the 1970s by David Lack, an evolutionary biologist. In an experiment with house finches, he found that overcrowding caused the birds to show reduced feeding and nesting behaviors, leading to reduced reproductive success. Subsequent research has confirmed and expanded upon Lack’s findings, showing that behavioral sink can occur in a variety of species in response to overcrowding and other environmental changes. For example, studies of wild rats have shown that overcrowding can lead to reduced exploration and foraging behavior, resulting in decreased food intake and reproductive success.

The effects of behavioral sink can be particularly pronounced in species with a high degree of sociality, such as primates. For example, studies of monkeys have shown that overcrowding can lead to reduced social interactions, aggression, and grooming, which can have long-term impacts on the population’s health and well-being. Additionally, overcrowding can lead to increased stress levels, which can have a variety of negative impacts on the health and behavior of individuals.

Behavioral sink is an important consideration for conservation efforts, as it can have significant impacts on animal populations. It is important to consider how environmental changes can affect the behavior of species, as well as their population dynamics. Understanding the impact of behavioral sink can help inform conservation efforts and help ensure that species are managed in a way that minimizes the risk of population decline.


Lack, D. (1974). Ecological adaptations for breeding in birds. London: Methuen.

Reebs, S. G. (2002). Behavioral responses of wild rats to overcrowding. Behavioral Ecology, 13(3), 331–338.

Mendoza, M. S., & Fedigan, L. M. (2013). Crowding effects on behavior in a group of wild black howler monkeys (Alouatta pigra). Behavioral Ecology and Sociobiology, 67(8), 1275–1286.

Wang, Y., & Zhang, Y. (2017). Effects of crowding and density on stress response of animals. Frontiers in Veterinary Science, 4, 48.

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