Increasing avian pox prevalence varies by species, and with immune function, in Galápagos finches

► Avian pox prevalence increased rapidly in Galapagos finches from 2000-2009. ► Lack of a comparable increase in proportion of recovereds suggests high mortality. ► Increase in prevalence and level of susceptibility varies across species. ► Variation in innate immune function appears to underlie these species differences. ► Variation in immune function also appears to underlie annual variation in prevalence. Avian pox virus (APV), a pathogen implicated as a major factor in avian declines and extinctions in Hawaii, was introduced to the Galápagos in the late 1890s. While APV is thought to have increased in prevalence in recent years, no study has carefully evaluated the threat this pathogen poses to the Galápagos avifauna. In this paper, we examine the course of the APV epidemic in seven species of Galápagos finch on Santa Cruz Island (Geospiza fuliginosa, G. fortis, G. magnirostris, G. scandens, Camarhynchus parvulus, Cactospiza pallida, and Certhidea olivacea). We describe temporal changes in the prevalence of the avian pox disease (AP) caused by APV and the proportion of individuals that have recovered from AP from 2000 to 2009. Then we examine species differences in susceptibility to AP and how this variation correlates with differences in innate immune function. We show that AP prevalence has increased dramatically from 2000 to 2009. However, this increase in prevalence varied by species; specifically, we found that prevalence increased rapidly in G. fuliginosa, C. parvulus, G. scandens, and C. olivacea, but not at all in G. fortis. Furthermore, innate immune function varies between years and species, and this variation correlates with increased prevalence and species variation in susceptibility to APV. To our knowledge, this is the first study to demonstrate significant interannual variation in innate immune function in wild birds, and to show that this immune variation correlates with susceptibility to an introduced disease.