Island bird communities are changing in unexpected ways

The impact of pollution and climate change on global ecosystems remains a complex, underexplored field. A recent study led by the University of Texas at Arlington offers new insights, particularly concerning bird populations on islands, suggesting that our understanding may be more limited than previously recognized. 

“Anthropogenic activities have reshaped biodiversity on islands worldwide. However, it remains unclear how island attributes and land-use change interactively shape multiple facets of island biodiversity through community assembly processes,” wrote the study authors.

Surprising discovery among island birds

By examining bird populations from the Zhoushan Archipelago (China’s largest island chain), the experts were surprised to find more bird species in agricultural areas than in forested regions.

“Usually, one predicts that there should be fewer species of birds living in agricultural areas where trees have been removed and the land manipulated than in natural habitats like forests,”  said co-author Luke O. Frishkoff, an assistant professor of biology at UT Arlington. 

“But strangely, on the islands we studied off the coast of China, we found opposite patterns with the communities of birds under examination – there were more bird species in agriculture than in forested areas.”

Focus of the study

The research team, including collaborators from East China Normal University in Shanghai, the University of Birmingham in the United Kingdom, and the University of Pittsburgh Medical Center, chose islands for their study due to their ecological significance: while islands constitute only 5% of the Earth’s land mass, they support 20% of its animal species.

Over two years, the scientists conducted four surveys during the breeding season across 34 islands, ranging from forested to farmed, and from isolated to more accessible. Their findings challenged preconceived notions about habitat preference among birds. 

“Human activities have extensively modified habitats on three-quarters of all the Earth’s surface worldwide, and islands are no different,” Frishkoff said.

Island bird populations 

The data revealed that bird populations on smaller, more isolated islands were more evolutionarily similar than those on larger, less remote islands. This observation was contrary to the team’s initial hypothesis that forested areas would harbor more diverse and numerous bird species than agricultural settings.

“All this is suggesting that there are some fundamental principles of ecology that we don’t yet understand, and that there is perhaps something special about islands that affects species that can tolerate human environments differently than species that require natural ecosystems for survival,” said Friskhoff. 

“We need additional research to better understand why bird evolution, and the evolution of species in general, is different on islands so that we can better protect and sustain biodiversity in other human-dominated ecosystems,” he concluded.

Island bird diversity

Island bird diversity is a fascinating and unique aspect of ecology, primarily because islands act as isolated laboratories of evolution. 

Endemism 

The limited geographic scope of an island, along with its distinct environmental characteristics, often leads to a high rate of endemism – many species found on islands are found nowhere else on Earth. 

This phenomenon is exemplified by famous examples such as the finches of the Galápagos Islands, studied by Charles Darwin, which have evolved a variety of forms and functions suited to their specific island environments.

Isolation and evolution

The isolation of islands means that birds that arrive, whether by flight or accidental means such as drifting on vegetation, often diverge significantly from their mainland ancestors. 

Over generations, these birds can evolve to exploit different ecological niches. For instance, some may become flightless if there are no predators, or develop unique feeding techniques tailored to the resources available on the island.

Challenges 

However, this remarkable diversity is also coupled with vulnerability. Island birds are often more susceptible to extinction due to limited population sizes, restricted habitats, and a reduced genetic pool. 

Moreover, they are particularly vulnerable to human impacts – such as habitat destruction, introduced species, and climate change – which can rapidly and irrevocably alter their limited habitats. Conservation efforts are therefore critical to preserve the unique bird populations that contribute to the rich biodiversity of the world’s islands.

The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–