The silent spread of bird flu and its impact on our ecosystems

Bird flu, also known as avian influenza, is an old acquaintance to animal health experts. It is a viral disease caused by different strains of the influenza A virus, which circulates naturally among wild aquatic birds, particularly ducks, gulls and shorebirds. Most of the time, these animals act as silent carriers, but when the virus mutates or develops more aggressive variants—such as the current H5N1 strain—it can cause severe outbreaks and mass mortality.

In recent months, Spain has once again recorded outbreaks in several autonomous communities, affecting both wildlife and poultry farms. The spread of the virus is not uniform: it intensifies in winter, when thousands of migratory birds arrive from northern Europe and share wetlands, estuaries and agricultural areas. A natural movement that now acts as a highway for viruses. The result is a situation that calls for constant vigilance and ever-closer coordination between animal health, environmental and agricultural authorities.

What sets this wave of bird flu apart from others is not only the number of cases, but its ecological impact. In Spain, as in other European countries, H5N1 has affected particularly vulnerable species such as birds of prey, seabirds and small mammals that come into contact with infected animals. More and more cases are being detected in wildlife thanks to more comprehensive monitoring systems. This allows us to respond more quickly, but it also reveals the true scale of the problem: a virus that no longer threatens just chicken or turkey farms, but also key links in the chain of biodiversity.

Although the virus can occasionally jump to mammals—such as foxes, minks or seals—the risk to the human population remains low. The cases detected worldwide have been very isolated and, in most instances, linked to very close contact with infected birds. Even so, international organisations are not letting their guard down: every mutation raises new questions about the virus’s ability to adapt. For the time being, epidemiological surveillance and biosafety protocols are working, but experience in recent years shows that no country can afford to let its guard down.

Where bird flu does have a direct impact is on sustainability. An outbreak on a farm leads to mandatory culls, financial losses and trade restrictions. For small-scale producers, this can be a severe blow, particularly in island regions where the supply chain is limited. In environmental terms, every mass die-off of wild birds disrupts food web dynamics, affects scavenger species, alters migration patterns and can threaten the balance of already fragile ecosystems.

Furthermore, the climate crisis has introduced a new factor: warmer winters, changes in migratory routes, and wetlands under increasing pressure from drought. All of this helps the virus to persist in the environment and makes it difficult to break the chain of transmission. What was once seasonal is now becoming unpredictable. In this context, wetlands and stopover sites for migratory birds—such as Doñana, the Ebro marshes, and the Mediterranean wetlands—have become critical hotspots where the balance between conservation and disease surveillance is becoming increasingly delicate.

The bird flu pandemic has also spurred scientific innovation. European and Spanish laboratories are working on faster detection methods, genomic analyses that enable the tracking of the virus’s evolution, and field protocols that facilitate sample collection without disturbing protected species. One of the major advances is the use of artificial intelligence to predict migration routes based on weather conditions and anticipate potential outbreaks. These are tools that seemed like science fiction a decade ago and are now at the forefront of prevention.

The preventive measures are well known, but their effectiveness depends on coordination. Spain maintains an active surveillance system that combines on-farm testing, monitoring of wild birds and rapid response protocols. For the public, the message is clear and simple: do not touch dead or sick animals, notify the environmental authorities, and follow health guidelines. The vast majority of people are not at any real risk, but they can help cut off potential routes of transmission.

Bird flu reminds us of something we sometimes forget: animal, human and environmental health are all interconnected. What happens in a wetland in Castile and León can have an impact on a farm in Galicia or a nature reserve in the Balearic Islands. This is the “One Health” approach, a vision that recognises that sustainability also depends on controlling diseases circulating in nature.

And perhaps that is the main lesson to be learnt from this new wave of H5N1: rather than fearing it, we need to understand it. Viruses will continue to be part of the natural world, but our ability to monitor, prevent and manage them can make all the difference. Spain has robust systems and experienced professionals; the challenge now is to keep them up to date in a rapidly changing environment. Because protecting biodiversity also means protecting ourselves.