Bird species extinctions are far more impactful than we realized

Over the past 130,000 years, human activities have led to the extinction of hundreds of bird species. This has resulted in substantial reductions in avian functional diversity – the range of different roles and functions that birds perform in the environment. 

While humans have been contributing to the global loss of species diversity for thousands of years, the impacts on other dimensions of biodiversity are not yet clear. 

Extinctions impact ecological functions 

New research led by the University of Birmingham highlights the severe implications of the ongoing biodiversity crisis and emphasizes the urgent need to identify the ecological functions being lost through extinction.

From the well-documented demise of the Dodo to the recent extinction of the Kauaʻi ʻōʻō songbird declared in 2023, scientists have evidence of at least 600 bird species having become extinct due to human activities since the Late Pleistocene, when modern humans began spreading across the world. 

Broader implications of species extinctions 

Utilizing the most comprehensive dataset to date of all known bird extinctions during the Late Pleistocene and Holocene, the study examines the broader implications of these losses on the planet.

“Humans have been driving a global erosion of species richness for millennia, but the consequences of past extinctions for other dimensions of biodiversity – functional and phylogenetic diversity – are poorly understood,” wrote the study authors. 

“In this work, we show that, since the Late Pleistocene, the extinction of 610 bird species has caused a disproportionate loss of the global avian functional space along with more than 3 billion years of unique evolutionary history.”

Chopping off a branch of the tree of life

Study lead author Tom Matthews is an expert in global environmental change at the University of Birmingham. 

Matthews noted that while the sheer number of bird species lost is a big part of the extinction crisis, what we also need to focus on is that every species has a job or function within the environment and therefore plays a really important role in its ecosystem.

“Some birds control pests by eating insects, scavenger birds recycle dead matter, others eat fruit and disperse the seeds enabling more plants and trees to grow, and some, like hummingbirds, are very important pollinators. When those species die out, the important role that they play (the functional diversity) dies with them,” said Matthews. 

“In addition to functional diversity each species also carries a certain amount of evolutionary history, therefore when that species becomes extinct, it’s basically like chopping off a branch of the tree of life and all of that associated phylogenetic diversity is also lost.”

Three billion years of evolutionary history lost

The researchers found that the extent of human-induced bird extinctions to date has resulted in the loss of approximately three billion years of unique evolutionary history and a 7% reduction in global avian functional diversity.

This is a significantly larger amount than expected based on the number of extinctions alone. 

Post-extinction aftershocks

Given the wide range of crucial ecological roles performed by birds, the loss of avian functional diversity likely has far-reaching implications. 

These post-extinction aftershocks include reduced flower pollination, diminished seed dispersal, the breakdown of natural control over insect populations – including many pests and disease carriers – and increased disease outbreaks due to decreased consumption of carrion. 

Species extinctions and plant diversity

Moreover, the reduction in global bird populations documented in the research may affect the ability of many plant species to adapt to current and future climate change.

According to Matthews, these results are a timely reminder that the current extinction crisis is not just about species numbers. 

“By identifying declines in avian functional and phylogenetic diversity driven by human actions, our findings highlight the urgent need to understand and predict the impacts of past anthropogenic extinctions on ecosystem function.”

This is needed, said Matthews,  in order to prepare for the magnitude of expected future loss from the projected 1,000 bird species that are expected to die out completely over the next two centuries.

“This information is vital for setting effective targets for global conservation strategies, as well as ecosystem restoration and rewilding efforts.”

The study is published in the journal Science.

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