A new study revisits the classic theory of how ecologically similar birds, such as wood warblers, coexist in the same trees. Led by researchers at Penn State and the American Bird Conservancy, the study suggests that these birds partition their habitat in fine ways, but not through diet differences as previously thought.
Robert MacArthur’s 1958 landmark paper proposed that five species of wood warblers could coexist by foraging in different parts of the same tree. However, a new study using modern techniques has found that these bird species exhibit strong differences in foraging behavior among themselves. The researchers observed birds over 20 years and collected fecal samples to assess their diet, which consists mainly of insects and spiders.
The study reveals that foraging behaviors are strongly linked to the birds’ physical characteristics, such as size and leg bone length. Smaller birds tend to hover more often while foraging, while birds with longer leg bones forage near the ground. Despite these differences in behavior, there is a considerable overlap in their diets, suggesting that MacArthur’s emphasis on diet may have been partially misplaced.
The researchers found that closely related species have more similar diets, and competition has likely shaped how these species forage today. However, other forces, such as migration patterns and stress of wintering locations, may also have influenced warbler evolution.
To further investigate the relationship between diet and foraging behavior, the team plans to analyze the nutritional quality of food sources in their overwintering locations. The study highlights the importance of considering multiple factors when understanding species interactions and how they shape the traits we see today.
Source: https://phys.org/news/2025-04-foraging-wing-ecologically-similar-birds.html