The threat of avian influenza H5N1 looms over global biodiversity

Worryingly, 16% of wild bird species and 27% of mammal species with known H5N1 infections as of 2024 are already of conservation concern (specifically, listed by the International Union for Conservation of Nature (IUCN) as either near threatened, vulnerable, endangered or critically endangered) owing to other anthropogenic threats (Fig. 1c) (data from WAHIS). In some species, a substantial fraction of global or regional populations was lost to H5N1. For example, over 20% of the Chilean population of Humboldt penguins (listed as vulnerable) presumably died of H5N1 in 2023 (ref. ¹¹). Extremely concerning is the 2024 arrival of the virus in islands surrounding Antarctica, where a large fraction of the population of threatened species live, such as the vulnerable wandering albatross (as recorded by the Scientific Committee on Antarctic Research (SCAR)). Influenza viruses are listed by the IUCN as a threat for only 12% of the threatened species that already been infected, which is something that must be reevaluated now that spatial spread and mortality are increasing.

The unexpected threat of pathogens such as H5N1 can compromise many years of in situ and ex situ conservation efforts. One paradigmatic case is the California condor, a critically endangered species that has been captive-reared for decades to recover its once-almost-extinct global population. H5N1 presumably killed 21 condors in 2023 — more than 6% of the wild population¹². The critical situation of this species led specialists to start vaccinating the birds against avian flu to reduce further mortalities¹². Captive individuals of threatened species (including Andean condors and lions) were infected in zoos and rehabilitation centres that are working on ex situ conservation (data from WAHIS).

It has become evident that remote protected areas cannot shelter species from the threat of H5N1. For example, numerous individuals of several species — including Peruvian pelicans, Peruvian boobies and sea lions — died within just a few weeks during the austral summer 2022–2023 in remote protected areas of Peru⁶ (Fig. 1a). Emerging pathogens such as H5N1, fuelled by anthropogenic drivers, can travel fast and wide around the world to affect wildlife in remote areas that were previously assumed safe.

The persistence of populations of long-lived, low-reproduction species such as albatrosses, penguins and condors largely depends on high survival rates. A sudden threat that eliminates a large proportion of the population can severely hamper persistence. Although mortality is evident immediately, the sublethal effects of the virus (for instance, on movement and breeding behaviour¹³) might only be apparent in the future. The unprecedented speed and scale of such virus-related mortalities leave little time for design and implementation of conservation interventions.

Mass mortality events have repercussions for ecological processes beyond the effects on individual species. The ephemeral resource pulse from animal carcasses produced by the H5N1 virus could modify the abundance, demography and movement behaviour of generalist facultative scavengers, which has downstream effects on species interactions. For example, a higher availability of carcasses can favour the presence and abundance of pests, which also affects interactions with other animals and human health¹⁴.

Losses of top predators and scavengers can be particularly impactful for ecosystem function via trophic cascades (for example, by mesopredator release)¹⁵. H5N1-driven mortalities of carnivores such as sea lions, boobies, penguins and pelicans might modulate prey demography and behaviour, as well as nutrient cycling and ecosystem structure of coastal environments. Scavengers are efficient carcass cleaners, so reduced populations could lead to higher risk of pathogen spillover and an increase in the abundance of pests that take advantage of carcasses¹⁴. These potential ecosystem effects of such sudden, widespread top-predator mortalities caused by H5N1 require further research, such as the implementation of population and community models to evaluate potential cascading effects on ecological interactions.

Apart from the intrinsic value of the wildlife being lost and the potential for concerning changes in ecosystem function, ecosystem services could be compromised by the loss of wildlife. For example, the loss of marine birds could result in lower availability of guano, an important source of fertilizer for some communities^6,9. The potential ecological changes in marine coastal ecosystems¹⁵ could modify food and other provisioning services to local fishers or seaweed collectors. The service of ecotourism could be impaired by the loss of pinnipeds and marine birds (for example, penguins) in some regions, including Antarctica. Cultural services such as recreation, relaxation, leisure and spiritual enrichment could also be affected. Potential effects of ecosystem service losses should be assessed by scientists from the social and natural sciences together with Indigenous people, local communities and other stakeholders who are affected.

The magnitude of H5N1’s direct and indirect effects on species, ecosystems and human health and well-being are uncertain. Progress is needed in both basic research and policy — especially transboundary management. The most critical research need is to address the pervasive knowledge gap about the virus’s actual effects, particularly in understudied and biodiverse regions such as central Africa (Fig. 1a). Monitoring should escalate in marine birds and mammals, as well as terrestrial scavengers, because those groups appear to be infected at the highest rates. Monitoring birds whose flyways include currently unaffected regions is also urgently needed. Mapping the risk of H5N1 infection would help to prioritize surveillance efforts and minimize the effects if the virus eventually spreads to new regions. Vaccination of threatened species against avian flu should be debated and considered, but is only likely to be feasible in specific cases. Knowledge of animal ecology, particularly animal movement, and its influence on H5N1 spread is necessary to predict the evolution of the virus and the potential efficacy of interventions.

In terms of policy, global collaboration is essential for surveillance, early diagnosis, monitoring, sharing of information and provision of financial and technical instruments, particularly in disadvantaged areas. Currently, several international organizations (such as OFFLU, European Food Safety Authority, and SCAR) are working to improve information sharing. However, in many regions, the lack of funds and infrastructure for testing and monitoring are challenges that are difficult to overcome.

The root cause of this pathogen’s emergence, spread and spillover must be addressed through changes to food production systems and consumption patterns². Separating wildlife from existing intensive production systems that boost the virus virulence and transmission would help in the short term. However, deeper transformative changes are required, such as making food production systems healthier and more sustainable. In a globalized and interconnected world, any strategy to deal with threats such as H5N1 must stress the connection between nature and people (namely, a One Health approach), given that disconnection will continue to precipitate biodiversity loss.