Understanding patterns of pathogen emergence can help identify mechanisms involved in transmission dynamics. Beak and feather disease virus (BFDV) poses a major threat worldwide to wild and captive parrots. Yet data from wild birds on seasonal fluctuations in prevalence and infection intensity, and thereby the potential high-risk times for virus transmission, have been lacking. We screened wild Crimson Rosellas (Platycercus elegans) for BFDV in blood and cloacal swabs. Prevalence in blood samples and cloacal swabs, as well as viral load varied with Julian date and in blood, were highest after the breeding season. Breeding birds had lower viral load and lower BFDV prevalence in blood than nonbreeding birds (10.1% prevalence in breeding vs. 43.2% in non-breeding birds). BFDV prevalence was much higher in younger (<3 years) than older (≥3 years) birds for both blood samples (42.9% vs. 4.5%) and cloacal swabs (56.4% vs. 12.3%). BFDV status in blood and cloacal samples was not correlated within individuals. We show that, at least in P. elegans, BFDV infection seems to occur year-round, with seasonal changes in prevalence and load found in our samples. Our analyses suggest that the seasonal changes were associated primarily with the breeding season. We also discuss age and sex as important predictors of BFDV infection. Emerging infectious diseases of wildlife pose a major threat to the conservation of global biodiversity 1,2. Knowledge of temporal patterns of infection allows improved targeting of management strategies to times when pathogens are most prevalent 3,4. Pathogens are often present in host populations year-round, but prevalence fluctuates seasonally 5. Several mechanisms have been proposed to explain this, including seasonal changes in weather 3,6 , in pathogen virulence and presence 5 , and variation in host susceptibility 7,8. Seasonal breeding can influence host susceptibility, with lowered antibody production and increased parasite load during the breeding season often typical 9 and generally attributed to a weakened immune system during offspring care 3. Only a few wildlife studies have investigated the influence of seasonal changes in host biology on pathogen dynamics, with the available studies finding a peak in pathogen prevalence after the breeding season, and explaining this via an influx of susceptible young into the host population 6,10. Among pathogens, viruses have a particularly severe impact on wildlife, as they can adapt quickly to a wide range of potential hosts and are responsible for a high proportion of emerging infectious diseases 11. Beak and feather disease virus (BFDV) is an ssDNA circovirus with a global distribution that can infect most, if not all, Psittaciformes (parrots, lorikeets, cockatoos) 12. This is concerning, as the Psittaciformes are among the most threatened bird orders 13. Accordingly, BFDV has been declared a 'key threatening process to biodiversity' by the Australian Government and a Threat Abatement Plan has been established 14,15. It has furthermore been found in ...