Resistance and resilience of Virgin Islands bird populations following severe hurricanes

Abstract

We analyzed changes in abundance of terrestrial birds on St. John, U.S. Virgin Islands, for a 32 year period during which 3 major hurricanes occurred. Using 1987 as a baseline year, because it followed a 27 year hiatus when no major hurricanes hit the island, we assessed the impact of hurricanes on vegetation structure and bird populations. Bird abundance was determined for 25 m radius circular plots that were surveyed each year of the study along the same transects. Percent cover of trees, shrubs, and herbs was measured in each plot in 1987, 1990, and 2019. All of the survey plots were in moist forest or dry woodland in Virgin Islands National Park. Of 13 common birds, 5 did not show marked and consistent declines in abundance following hurricanes even though the structure of vegetation on the island was heavily modified by storms. Three of these species are insectivores. Seven species declined or showed habitat shifts following Hurricane Hugo in 1989, but 5 of these populations subsequently increased and most recovered to close to their 1987 abundance during the 1990s. Six of these 7 species also declined or showed habitat shifts following Hurricanes Irma and Maria in 2017. The most marked declines in the aftermath of hurricanes in both 1989 and 2017 were for frugivores and nectarivores, especially hummingbirds. Most common bird species in Virgin Islands National Park were either resistant to the effects of severe hurricanes or resilient in the decade following a hurricane. However, more research is needed to assess the status of vulnerable species such as hummingbirds and rare resident species (Bridled Quail-Dove [Geotrygon mystacea] and Puerto Rican Flycatcher [Myiarchus antillarum]).