Wildlife of
United States Minor Outlying Islands

Primary Threats

• Sea-level rise and storm-driven overwash threaten low-lying atolls (e.g., Baker, Howland, Jarvis, Palmyra, Kingman), reducing seabird nesting habitat and affecting freshwater lenses where they exist. Ocean warming drives coral bleaching and reduced reef resilience, while increasing frequency/intensity of marine heatwaves and changing currents can disrupt productivity that sustains seabirds and large pelagic species. Climate-driven shifts also increase disease risk and heat stress for dense seabird colonies (notably on Midway).
• Introduced rats, mice, ants, and invasive plants can devastate ground-nesting seabirds, alter native vegetation, and disrupt invertebrate communities on small islands with few refuges. Invasive insects (e.g., ants) and plants can spread rapidly following ship/aircraft arrivals. Some islands have faced severe impacts historically, prompting intensive biosecurity and eradication campaigns (e.g., rodent eradication and ongoing prevention at remote atolls).
• Marine debris (especially plastics and abandoned/derelict fishing gear) accumulates on remote shorelines due to Pacific gyre currents, entangling sea turtles and seabirds and damaging reefs during high surf events. Several sites also carry legacy contamination risks from past military activities (e.g., fuel spills, PCB-like contaminants, and at Johnston Atoll a history of hazardous materials management), requiring ongoing controls and monitoring even after major cleanups.
• While many monument waters are highly protected, highly migratory fish (e.g., tunas) and shark populations are affected by fishing pressure outside protected boundaries. Illegal, unreported, and unregulated (IUU) fishing risk persists because these islands are far from major enforcement hubs, and poaching can target valuable species (e.g., sharks for fins, reef fish, sea cucumbers) where access is possible.
• Even limited human presence can have outsized impacts: aircraft operations and infrastructure on Wake Island, periodic refuge management/research visits, and vessel visits can disturb seabird colonies and sensitive shorelines. On Midway, concentrated seabird nesting adjacent to managed facilities increases risks of disturbance, aircraft-wildlife hazards, and localized habitat wear.
• High-density seabird colonies can experience periodic disease events (e.g., avian botulism outbreaks recorded on Midway) that cause significant mortality, especially when warm conditions and carcass accumulation facilitate transmission. Disease risk can also increase with climate warming and with invasive vectors.
• Existing runways, buildings, seawalls, and operational footprints (most notably on Wake and Midway, and historically at Johnston) fragment limited terrestrial habitat, create artificial lighting and collision risks for birds, and can alter shoreline processes. Maintenance and emergency repairs can introduce invasive species or contaminants if biosecurity is not stringent.
• Historical alterations (dredging, shoreline armoring, habitat conversion associated with past military use, and introduced vegetation for stabilization) have changed dune/beach dynamics and native plant communities on some islands. Recovery can be slow because soils are thin, native seed sources are limited, and recolonization is constrained by isolation.
• Because ecosystems are small and productivity can be episodic, even low levels of extraction (e.g., opportunistic take of seabirds/eggs historically, or localized harvest of reef species by unauthorized visitors) can depress populations. The remoteness makes detection difficult, increasing the incentive for occasional illegal take.