Cover photograph (Copyright © 2015, American Society for Microbiology. All Rights Reserved.): Black-headed gulls (Chroicocephalus ridibundus, shown in juvenile plumage) are colony-breeding birds and natural hosts for avian influenza A virus subtypes H13 and H16. Influenza outbreaks occur annually in breeding colonies at the end of summer, when juveniles leave the nest. Serial infections of juvenile gulls over a period of more than one year show that reinfection with the same virus results in progressively less virus excretion, implying that the epidemiological cycle of avian influenza in black-headed gulls depends mainly on infection of first-year birds. (Image obtained by Michelle Wille, Uppsala University, Sweden.) (See related article in November 2015, vol. 89, no. 22, p. 11507.)