The World's Birds Warn of a Planetary Ecosystem in Crisis: Did Sparrows and Owls Play the Same Role? The Reality Revealed by a Global Bird Survey

"It's not okay just because there are still many birds"

The narrative that "birds are decreasing" has become more common in recent years. However, many people might think, "Even so, there are still various birds, and nature is surprisingly tough."

A new study published on November 26 poured cold water on that "optimism." An international team, including Imperial College London and the University of Cambridge, analyzed data on about 3,700 bird species collected from 1,200 locations worldwide, reporting that changes in land use are eroding the very "resilience" of ecosystems.Phys.org

The focus here was not simply on the "number of species." The researchers looked at the diversity of roles birds play and the depth of their reserves.

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Birds as generalists in the "ecosystem service industry"

Birds are not just cute creatures.

・Pollination industry transporting pollen
・Transportation industry carrying seeds far by eating fruits
・Pest control industry eating harmful insects
・Cleaning industry disposing of animal carcasses

...and more, they can be called generalists in the "ecosystem service industry" that supports our lives behind the scenes.

The research team quantitatively organized what kind of "jobs" birds perform by combining information on various diets, body sizes, beak shapes, and wing shapes.Phys.org

They then compared bird communities in areas with different land uses, from natural forests to large-scale farmlands and urban areas. The result showed that the more human activity progresses, the more the variety of roles becomes extremely thin.

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Ecosystem "insurance" is being canceled

In highly natural forests, there are many species of birds that play similar roles. For example, if there are multiple fruit-loving birds that disperse seeds, even if one species decreases, other birds can take over the job. This "reserve workforce" is referred to in the study as **functional redundancy**.Phys.org

However, in places where conversion to farmland or urbanization has progressed, this redundancy has been completely lost.

・Only a few "tough birds" that are strong against environmental changes survive
・Other delicate species disappear along with their roles
・The roles of the remaining tough birds become similar

In other words, it became a state where "a certain number of species remain, but there is no overlap in roles."Phys.org

Translating this to human society, it's like a company losing veteran employees and backup staff, with a few employees handling multiple departments. While things may somehow work normally, the risk of the entire system stopping is high the moment a new problem arises.

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Conducting "extinction simulations" on a computer

To verify how dangerous this situation is, the research team also conducted extinction simulations on a computer.Phys.org

When randomly "erasing" bird species,

• in highly natural areas, functional diversity stubbornly persists even if quite a few species disappear

• However, in areas that have already lost redundancy, reducing just a few species causes ecosystem services to collapse significantly

This was the result.

In other words, changes in land use are actions that cut away the "safety margin" from ecosystems. Even if it seems that a decent number of bird species remain, it's possible they are already walking a tightrope.

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Three reactions spreading on social media

When this news was reported, various reactions spread on social media. Here, let's organize these trends into three main categories (the specific posts are summarized and reconstructed by the author and do not refer to any specific individuals).

1. A sense of crisis that "fewer birds = our lives are in danger"

The most noticeable voice was, "Isn't this ultimately self-inflicted by human society?"

"If birds disappear, pests will increase, and we'll have to rely on pesticides"
"If forest regeneration stops, climate change will worsen"

Posts like these are increasing, linking bird issues not only to the environment but also to food security and health risks.

2. Sadness and anger over "changes in familiar landscapes"

There are also many nostalgic posts like "When I was a child, the birds were so noisy."

"Since the nearby rice fields turned into residential areas and solar panels, I haven't seen swallows"
"Since the green space became a parking lot, the morning chirping has disappeared"

Voices like these are common in many regions, including Japan, making people realize that changes in land use are also altering the "soundscape."

3. Positive proposal-type voices that "hope remains"

On the other hand, there are movements to not end with just dark topics.

"Let's support conservation activities in satoyama and agriculture that leaves hedges for birds"
"Even in cities, we can increase places for birds and insects with balcony greening and rainwater basins"

Accounts sharing practical ideas like these are increasing, with hashtags like "#WhatWeCanDoForBirds" suggesting small actions.

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Towards an era where "diversity" alone cannot be protected

This study has significant implications in showing with data that we cannot be reassured even if a "number of species" remains to some extent.Phys.org

Traditional conservation indicators have focused on "how many species there are." However, even if there are the same number of species,

• if they are all birds with similar diets, body sizes, and behavior patterns, they are functionally monotonous

• Even if there are few, if the roles are clearly different, they are functionally diverse

This study has shown a new framework for evaluating ecosystem fragility by combining this "functional diversity" and "redundancy."Phys.org

This provides a significant hint for policy-making. For example, when designating protected areas, it becomes necessary to consider not only "whether there are rare birds" but also "the types of ecosystem services this area provides and the depth of its reserves."

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Thinking about it in the context of Japanese landscapes

In Japan, changes in land use are accelerating, such as the abandonment of satoyama, large-scale residential development, large-scale monoculture farmland, and mega-solar installations.

• Satoyama, where once coppice forests and rice paddies spread in a mosaic pattern

• Willow forests and grasslands along rivers

• Small groves at shrines and temples in urban areas

Such "gaps in nature" were important bases for diverse birds. However, if they are transformed into large residential areas or logistics warehouses all at once, not only will "the number of bird species decrease," but "role bias" may rapidly progress.

If birds responsible for seed dispersal decrease, the rate of forest renewal will slow, and the growth of forests contributing to climate change mitigation will also decelerate. If birds that eat pests decrease, pesticide use will increase, raising the burden and cost on ecosystems. This is an issue directly connected to our daily prices and health.

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Actions we can take to protect "functional diversity"

So, what can ordinary people do?

1. Support "patchwork landscapes" instead of single ones
   Support plans to leave green spaces mixed with native shrubs and flowers rather than large expanses of grass.

2. Secure "bird workplaces" in familiar places
   Plant fruit-bearing trees on balconies or in gardens, place pots that can create puddles, and avoid making outdoor lights unnecessarily bright—these actions can increase small oases in the city.

3. Participate in local conservation activities and citizen surveys
   Bird counts and nature observation meetings are valuable data sources for researchers to evaluate functional diversity.

4. Send messages about land use through consumer behavior
   Choosing products made from certified forest materials or environmentally friendly agricultural products is a voting action that supports land use that "protects ecosystem insurance."
   
   
   

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Can we choose a future where we can hear the birds?

This study can be said to have supported the intuitive slogan "the richer the biodiversity, the better" with more precise data.Phys.org

• What kind of birds are doing what kind of work

• How many reserves are there for that role

• And how human land use is eroding it

By visualizing these, the relationship between ecosystems and human society emerges not just as a "nature conservation" issue but as a problem of "infrastructure risk management."

The reduction of birdsong in the forest holds more meaning than just a lonely landscape. It is a warning that the invisible network supporting our tables, health, and climate stability is thinning.

The voices of crisis and hope exchanged on social media may still be small. However, whether they lead to concrete actions will determine whether we can choose a future where we can hear the birds.

The park we walk next, the products we choose to buy, the policies we vote for—each one decides whether to protect or cancel the ecosystem's "insurance." This bird study quietly but sharply presents such a reality.

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