Proceedings of the Vertebrate Pest Conference

Axis deer on the Hawaiian Islands of Maui, Lāna‘i, and Moloka‘i simultaneously experienced one of the most dramatic population crashes on record in 2020-2021, which coincided with extended drought conditions and prompted an emergency declaration for these islands. This phenomenon has been anecdotally documented during previous drought events in 2011-2012, but never formally studied. Newspaper articles document abundant deer becoming a nuisance to agriculture and natural resources, and then experiencing high mortality during droughts. This phenomenon fits Caughley’s (1970) operational definition of eruptive (sic) fluctuation “…as an increase in numbers over at least two generations, followed by a marked decline.” We examined available deer population and rainfall records over the time period of interest. Deer may have increased rapidly during favorable years with high survival and recruitment. During moderate drought, young of the year may experience high mortality, with little recruitment to populations. During severe drought, adults may experience noticeably high mortality. When populations are suppressed by large numbers of removals, fluctuations in mortality may be modulated. Abandonment of large-scale intensive agriculture in recent decades may complicate interpretation but understanding these population processes may lead to better management strategies for axis deer in Hawai‘i.