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How did the study of territorial nesting birds advance the understanding of population regulation?

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Common wildebeest — population ecology A herd of common wildebeest (*Connochaetes taurinus*) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.

The study of territorial nesting birds has been instrumental in advancing the understanding of population regulation by highlighting the role of density-dependent factors.

Ornithologist David Lambert Lack was a pivotal figure in this field. Through his research, most notably on the European robin, he argued that the density of animal populations is a primary determinant of their distribution and numbers, often outweighing density-independent factors like weather.1

In territorial species, individuals compete for limited resources such as nesting sites and food. When a population increases, competition for these resources intensifies, effectively limiting the number of individuals that can successfully breed. This process acts as a regulating mechanism, maintaining population density within a specific range. By observing how birds defend multipurpose territories, ecologists have gained a clearer understanding of how social behaviors and resource monopolization contribute to the natural regulation of animal numbers.234