Procellariiformes are among the most threatened seabirds globally, yet viral pathogens affecting this group remain poorly understood. Herpesviruses are widespread in birds and capable of establishing latency, reactivating under immunosuppression, and causing severe disease, particularly in cross-species transmission. We surveyed herpesvirus in 50 individuals (12 species) that stranded along the southeastern Brazilian coast (2017–2023). A nested pan-PCR protocol targeting the DNA polymerase gene detected herpesvirus DNA in 24% (12/50) of the birds. Seven distinct herpesvirus sequence types were identified, all clustering within the genus Mardivirus, including two previously known variants and novel lineages. To our best knowledge, this represents the first herpesvirus report in the Black-browed Albatross (Thalassarche melanophris), Cape Verde Shearwater (Calonectris edwardsii), Manx Shearwater (Puffinus puffinus), and Southern Giant-Petrel (Macronectes giganteus), as well as new host reports for the Yellow-nosed Albatross (T. chlororhynchos) and Cory’s Shearwater (C. borealis). No associated lesions were observed in histopathology. Our findings expand the known host range of herpesviruses in Procellariiformes and reveal possible circulation among colonies and non-breeding areas across the Southern and Northern hemispheres. Our results underscore the need for integrative ecological-, virological-, and population-based studies to clarify how seabird ecology influences herpesvirus transmission dynamics and long-term persistence in this group.

Mass mortality events (MMEs) or ‘wrecks’ represent sudden and large‐scale mortality episodes often associated with extreme environmental conditions. Despite their ecological importance, MMEs remain poorly documented in the South Atlantic, particularly for Procellariiformes, a group highly vulnerable to climate‐driven anomalies. Detecting such events in this region is challenging because baseline mortality levels are unknown, limiting the ability of monitoring programs to identify abnormal mortality episodes. We developed a quantitative framework to detect and characterize seabird MMEs by integrating time‐series decomposition, changepoint analysis and kernel density estimation. The framework was applied to 8 years (2017–2024) of standardized beach monitoring data covering approximately 3320 km of the Brazilian coastline. This approach allowed us to identify anomalous mortality peaks, estimate the temporal duration of mortality episodes and delineate their spatial extent and hotspots along the coast. We detected seven previously unreported MMEs impacting 3779 stranded Procellariiformes. Events occurred primarily during austral autumn in northeastern and during austral spring in southeastern–southern regions, revealing recurrent seasonal and spatial patterns. Cory's Shearwater Calonectris borealis , Manx Shearwater Puffinus puffinus and Atlantic Yellow‐nosed Albatross Thalassarche chlororhynchos were the most affected species, with juveniles disproportionately represented. Kernel density analysis identified recurrent hotspot regions of mortality along the Brazilian coast. We propose mortality thresholds in an early‐warning system to guide monitoring efforts during abnormal stranding events. Synthesis and applications . Our study provides the first systematic assessment of seabird mass mortality events in the South Atlantic and introduces a transferable statistical framework for detecting MMEs in other taxa and regions lacking baseline mortality information. By identifying recurrent temporal anomalies, high‐risk areas and vulnerable species, we could establish quantitative indicators of MMEs. This approach offers a practical tool for monitoring programs to improve early detection of mortality events and to implement rapid response protocols.

Adenoviruses are widespread DNA viruses that infect a broad range of vertebrate hosts and are recognized for their long-term host coevolution, remarkable genetic diversity, and broad pathogenic potential. Coronaviruses circulate among wild birds due to their evolutionary potential and are relevant to animal and public health. However, the diversity and ecological role of these viruses in pelagic seabirds remain poorly understood. This study provides the first molecular survey of adenoviruses and coronaviruses in Procellariiformes from the South Atlantic. Fifty stranded individuals representing 12 Procellariiformes species were collected along the southeastern Brazilian coast, between 2017 and 2023. Adenovirus and coronavirus survey were performed using nested PCR protocols, followed by sequencing, phylogenetic analysis, and histopathology of positive cases. Adenovirus was detected in seven individuals (14%; 95% CI: 5.8-26.7%) from three species: Southern Giant Petrels (Macronectes giganteus), Cory's Shearwaters (Calonectris borealis), and Black-browed Albatrosses (Thalassarche melanophris). Five sequence types were identified, including similar variants in Southern Giant Petrels and distinct adenoviruses in Cory's Shearwaters and Black-browed Albatrosses. All viruses clustered within a divergent lineage with adenoviruses previously detected in New Zealand seabirds and a Chimney Swift from the USA. No intranuclear inclusion bodies were found in histopathological analysis. All specimens were coronavirus-negative. This first molecular detection of adenoviruses in Procellariiformes expands the known diversity and host range of seabird adenoviruses and suggests circulation of genetically distinct viruses across oceanic regions, highlighting the need for genomic and epidemiological studies of their evolution, transmission, and health impacts.