Bird wings have a surprising effect on island biodiversity

The shape of a bird’s wings offers insights into its lifestyle and abilities. Interestingly, bird wings also tell fascinating stories about nature and islands.

For instance, the albatross has wide, sail-like wings built for soaring over oceans, while the antpitta’s short, stubby wings reflect its preference for brief flights near the ground. However, can the shape of bird wings reveal deeper insights about biodiversity and nature’s organization?

Recent research from Washington University (WashU) in St. Louis suggests it can. The study highlights how bird wing shape – a proxy for long-distance flying ability – influences biodiversity patterns on islands across the globe.

“Our results reveal how a key dispersal trait – bird wing shape – can shape fundamental diversity patterns and island biogeography across scales,” said Justin Baldwin, first author of the study. Baldwin recently completed his PhD in ecology and evolutionary biology at WashU.

Bird wings and island biodiversity

Until now, studies on island biodiversity focused mainly on geographic factors, such as an island’s size and its isolation.

These factors significantly affect the number of species found on an island. Larger islands typically host more species due to lower extinction rates, while isolated islands have fewer species because reaching them is challenging.

“To date, most studies have focused on how geographic factors such as area and isolation influence island species-area relationships,” Baldwin said. “Our results highlight the importance of trait differences among species, specifically traits related to dispersal ability.”

The remarkable theory of island biogeography, introduced by Robert H. MacArthur and Edward O. Wilson 50 years ago, described these patterns. They observed that isolation limits species diversity on islands, while larger areas support more species.

However, the theory assumes all species have similar abilities to disperse and colonize new habitats – an assumption modern ecologists have questioned.

Measuring bird wing shape

Baldwin and his co-advisor, Jonathan Myers, explored the potential influence of bird wing shape on island biodiversity.

The researchers utilized a dataset of hand-wing index values, which measure how pointed a bird’s wings are.

Birds with high values, such as swifts and swallows, are excellent fliers capable of covering long distances. In contrast, birds like chickens and wrens with low values are more limited in their flight range.

For their analysis, the experts synthesized data for 6,706 bird species across 3,894 islands. They then calculated species-area relationships for all 11 recognized biogeographical realms and for 248 unique combinations of bird families in specific regions.

Birds and biodiversity patterns on islands

The findings revealed that wing shape significantly influences biodiversity patterns.

“In parts of the world where birds tend to have low dispersal abilities, the species-area relationships were steep,” Baldwin explained.

This means that larger islands in these areas host a sharp increase in species numbers. In regions where birds possess higher dispersal abilities, species-area relationships were flatter, indicating a smaller gain in species numbers with increasing island size.

Additionally, the study identified a phenomenon called diversity saturation. On islands with many bird species equipped for long-distance flights, biodiversity seemed to reach a plateau.

These patterns demonstrate how dispersal traits like wing shape interact with geographic factors to influence biodiversity.

Implications for bird conservation

Understanding how traits like wing shape affect biodiversity has practical applications. Islands often harbor unique species found nowhere else, making them critical for conservation efforts.

“The theory of island biogeography and species-area relationships have important applications for biodiversity conservation, especially on islands, which often harbor large numbers of endemic species found only within a single island or group of islands,” Myers said.

The study’s findings can inform conservation strategies to address challenges such as habitat loss, deforestation, and sea-level rise. By understanding how dispersal traits shape species distribution, conservationists can better predict and mitigate biodiversity loss on islands.

“The ecological and evolutionary processes that determine the steepness of the species-area relationship can be used to predict how and why habitat loss…causes extinctions and biodiversity loss on islands,” Myers added.

Significance of the study

Bird wing shape, a simple yet powerful trait, offers valuable insights into island biodiversity patterns.

This study underscores the importance of considering species-specific traits alongside geographic factors to understand and protect nature.

As researchers continue to explore these relationships, their findings will help guide efforts to preserve the rich and diverse life on our planet’s islands.

The study is published in the journal Ecology Letters.

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