Update on the effects of Avian Influenza Outbreak 2022 on Dalmatian pelicans in Greece
The Avian Influenza (AI) wave of 2022 had an unprecedented biological impact on wild birds throughout Europe and caused mass mortality in Dalmatian pelicans (DP) in most of their southeastern European breeding range. However, the effect on the Lesser (Mikri) Prespa Lake colony, NW Greece, the world’s largest colony of the species, was particularly devastating. By the end of April 2022, 1,734 DPs had died, corresponding to ca 58%-67% of the colony (number of apparently occupied nests has varied in recent years, ca 1,300-1,500). A staggering loss, representing the worst wildlife disaster in Greece.
All the dead pelicans were adults in full breeding plumage and the carcasses were located on the nesting islets or close by in the water. Laboratory results in early March indicated the highly pathogenic H5N1 strain of AI, clade 184.108.40.206b.
The first mass mortality event was recorded on February 17th, a week after the first DPs arrived at Prespa from their wintering grounds in NE Greece and W Turkey. In late February, there were already hundreds of dead DPs on the nesting islets and the number of carcasses was massively increasing in the following weeks. The mortality rate progressively slowed down after mid-March and by the end of April the outbreak virtually ceased, resulting in the huge death toll of 1,734 DP breeding individuals.
At the same time, during March and April, the disease was spreading in Greece to other DP breeding sites, as well as to other wetlands used by pelicans for feeding during the breeding period. [Note: Both species of pelicans nesting at Prespa – the DP and the great white pelican (GWP) – travel frequently, throughout the breeding season, to wetlands lying as far as 200 km away, to cover their increased food needs].
News on mortality events were consecutively reported by volunteers of the Hellenic Ornithological Society’s network, as well as by the management authorities of other wetlands. By mid-March, all four colonies of the eastern part of the population in the country had been affected, and DP mass mortality events had been recorded in a total of thirteen wetlands in northern and central Greece (Table 1). Overall, during spring 2022, 2,286 DP deaths were recorded in the country. The high-altitude colonies experienced major die-offs, while the lowland ones recorded much lower mortality, probably because of higher air temperatures which are unfavorable to the virus’ survival. Fortunately, the two colonies in the west coast remained intact. It has been documented that the two population groups, the eastern and the western, have a very low level of mixing/gene flow, which is attributed to a major geographic obstacle, i.e., the Pindus mountain range. This fact could be part of the explanation for the absence of any mortality in western Greece.
Based on information collected through the PELECANUS GROUP – a network of pelican researchers and conservationists, members of the Pelican Specialist Group of IUCN SSC – the H5N1 strain of AI was also confirmed in the Albanian and Montenegrin DP colonies, and in three of the Romanian colonies in the Danube Delta, resulting in a total of 128 DP deaths. As far as we know, no incidents were recorded in the Bulgarian and Turkish colonies. By combining all available data, we estimated that over 40% of the southeastern European breeding population was lost, corresponding to roughly 10% of the global DP population (best estimated at around 24,000 individuals ).
Table 1. DP deaths recorded per wetland in Greece during the H5N1 outbreak in spring 2022. The four colonies of the eastern population group are highlighted with an asterisk.
Site no. DP deaths
- Lesser Prespa Lake* 1734
- Cheimaditida Lake* 181
- Karla Reservoir* 103
- Kerkini Lake* 90
- Kastoria Lake 85
- Zazari Lake 42
- Koroneia Lake 23
- Doirani Lake 15
- Pamvotida Lake 4
- Polifitou Dam Lake 3
- Volvi Lake 3
- Vegoritida Lake 2
- Aggelochori, small coastal wetland 1
TOTAL NUMBER 2,286
Only a handful of GWPs died during the outbreak in Greece, and very few other species were affected, in small numbers, which implied that DPs are particularly vulnerable to this AI strain. Moreover, no GWP mortality was recorded at Lesser Prespa Lake, although the two species nest side-by-side on the same nesting islets. It is important to note that no DPs had ever been reported infected by the AI virus prior to 2015, and all previous mortality events had resulted in relatively minor losses. In particular, the 2021 HPAIV (H5N8) outbreak affected DP populations in Greece, and the 2015 HPAIV (H5N1) outbreak affected DP populations in Romania, Bulgaria and Russia. The 2022 outbreak’s scale and duration were unprecedented and the impact on DPs devastating, raising concerns for the species’ fate in the event of recurrent outbreaks.
Several factors may have contributed to high infection rates and the high vulnerability of DPs, especially at the Prespa colony. The early start of the breeding cycle (early February) combined with the persistent low temperatures at Prespa (around 0oC in February and March) and the large aggregations on the nesting islets may have been crucial factors. Unknown genetic factors may have contributed too. Regarding the virus transmission route, we are considering the hypothesis that DPs were infected at Prespa, since no cases had been reported from their wintering or stopover sites and, moreover, the mass mortality events that took place in other Greek wetlands occurred later. It is suspected that the AI virus may have been transmitted indirectly to DPs via wintering waterbirds at Prespa, especially as record numbers were documented in 2022; three times more than average. Ducks and resident greylag geese roost and defecate on pelican nesting islets prior to the arrival of pelicans, while the first nesting material used by DPs upon their arrival are the old reed canes located on the islets, i.e., the exact ones that are most certainly full of faeces from wintering waterbirds.
During the outbreak, multi-level work was put in place by the Society for the Protection of Prespa (SPP) to accurately document the mortality rate at Prespa and other Greek wetlands, to mobilise the authorities in carcass removal operations and to alert local, regional and international partners. Consultations with researchers in avian infectious diseases were extremely helpful, similarly those with conservationists from other countries, which had recently experienced comparable wildlife disasters, such as Israel. The collection and management of the carcasses at Lesser Prespa Lake was co-ordinated by the regional authorities in collaboration with the local veterinary services and other local bodies, under the auspices of the Greek Ministry of Environment. It was a very challenging task: the huge number of large, heavy carcasses in the middle of the lake, the difficult access, the risks of personnel exposure, and the need to minimise disturbance to the surviving nesting pelicans; a well-posed puzzle that nevertheless demanded rapid solutions. After seven collection days in March and April, 82% of the carcasses – almost 15 tons – were removed from Lesser Prespa Lake, substantially reducing the viral load on the colony.
In the three months after the mass deaths ceased, the situation at Prespa has looked strikingly odd compared to previous years. Most of the few hundred DPs that survived sat around the nesting islets looking indifferent to the breeding process. Yet, the breeding season was extended this year and after a series of nest abandonments and failures, a spark of hope finally emerged. Eventually, around 100 breeding pairs nested and raised their young. This has been the lowest number of nests ever recorded at Prespa since the 1980s, and means that it will take decades for the population recovery, provided that no other incidents occur. At present, there are around 90 DP chicks at different age stages, which appear to be healthy. Concurrently and similarly to previous years, there are now also several hundreds of GWP chicks at Prespa.
In recent days, shortly before pelican young become capable of flight, the SPP carried out on-site visits to the Prespa colony, to sample genetic material from the young of both species. This sampling is part of the research that the SPP is now initiating, in collaboration with academic institutions, to shed light on crucial issues regarding the possible biological and behavioural basis of the high vulnerability of the Prespa DPs, to explore the possible genetic basis of this susceptibility, to investigate the possible involvement of other infectious factors, and to improve our understanding of transmission mechanisms and virus survival and perseverance.
As a future step, the SPP plans to study the genetics of both population groups in Greece, the eastern and western, to shed light on more factors, possibly related to genetic diversity. This laborious sampling is expected to be carried out with contributions from other relevant bodies and organisations. Moreover, the SPP will work towards mobilising other pelican researchers and conservationists in SE Europe to contribute genetic material from all DP colonies in the Black Sea/Mediterranean flyway, with the aim of exploring risks stemming from possible genetic diversity loss, to check for bottlenecks and phylogenetic relationships, as well as to assess gene flow between populations.
Considering recent studies stressing that highly pathogenic AI is viewed as no longer a poultry disease, but as an emerging threat to wildlife worldwide, high vigilance, increased protection measures at colonies and focused research is essential throughout the DP breeding range. This array of actions will ensure an increasing DP population and ultimately its recovery. To this end, the SPP urges awareness and support from different relevant funding sources and initiatives, in the EU or elsewhere.
 Catsadorakis, G. & D. Portolou. (compilers) 2018. International Single Species Action Plan the Conservation of the Dalmatian Pelican (Pelecanus crispus). CMS Technical Series No. 39, AEWA Technical Series No. 69, EAAFP Technical Report No. 1. Bonn, Germany and Incheon, South Korea.