A Tour de Force by Hawaii's Invasive Mammals: Establishment, Takeover, and Ecosystem Restoration through Eradication

Abstract

Invasive mammals, large and small, have irreversibly altered Hawaii's ecosystems in numerous cases through unnatural herbivory, predation, and the transmission of zoonotic diseases, thereby causing the disproportionate extinction of flora and fauna that occur nowhere else on Earth. The control and eradication of invasive mammals is the single most expensive management activity necessary for restoring ecological integrity to many natural areas of Hawai'i and other Pacific Islands, and has already advanced the restoration of native biota. Science applications supporting management efforts have been shaped by longstanding collaborative federal research programs over the past four decades. Consequently, feral goats have been removed from >1,358 km 2 , and feral pigs have been removed from >723 km 2 of lands in Hawai'i, bringing about the gradual recovery of forest ecosystems. The exclusion of other non-native ungulates and invasive mammals is now being undertaken with more sophisticated control techniques and fences. New fence designs are now capable of excluding feral cats from large areas to protect endangered native waterfowl and nesting seabirds. Rodenticides that have been tested and registered for hand and aerial broadcast in Hawai'i have been used to eradicate rats from small offshore islands to protect nesting seabirds and are now being applied to montane environment of larger islands to protect forest birds. Forward-looking infrared radar is also being applied to locate cryptic wild ungulates that were more recently introduced to some islands. All invasive mammals have been eradicated from some smaller islands, resulting in the restoration of some ecosystem processes such as natural forest regeneration, but changes in other processes such as fire regimes and nutrient cycling remain more difficult to reverse at larger landscape scales. It may soon be possible to manage areas on larger islands to be free of invasive mammals at least during seasonally important periods for native species, but at the same time, new mammal introductions continue to occur.

Fire as a driver and mediator of predator–prey interactions

“…McGregor et al ., 2016b; Hradsky et al ., 2017a). However, there is strong potential for this dynamic to play out in other locations where fire occurs and naive prey are vulnerable to invasive predators, such as Madagascar (Farris et al ., 2017), New Caledonia (Palmas et al ., 2017), and Hawaii (Hess, 2016). Management approaches for reducing invasive predator impacts in relation to fire include conducting low‐severity burns that retain natural refuges (Leahy et al ., 2015; Shaw et al ., 2021), providing artificial refuges post‐fire (Bleicher & Dickman, 2020; Watchorn et al ., 2022), and conducting lethal control of predators, either through long‐term landscape‐scale suppression, or through targeted control at high‐priority sites pre‐ or post‐fire (Comer et al ., 2020; Hradsky, 2020).…”

Interpreting Feral Goat (Capra hircus) Movement to Guide Management in a Mesic Watershed on Oʻahu, Hawaiʻi

“…The largest driver of extinction globally is habitat modification and loss (Brooks et al 2002), with nonnative mammal introductions also playing an important role (Blackburn et al 2004). Introduced ungulates (hard-hooved browsing mammals), in particular, are universal ecosystem transformers (Chynoweth et al 2013, Hess 2016, with typically negative impacts on native species and ecosystems. No ungulates are native to Hawaiʻi, which resulted in plants losing at least some defenses against large herbivores (Hess 2016).…”

“…Introduced ungulates (hard-hooved browsing mammals), in particular, are universal ecosystem transformers (Chynoweth et al 2013, Hess 2016, with typically negative impacts on native species and ecosystems. No ungulates are native to Hawaiʻi, which resulted in plants losing at least some defenses against large herbivores (Hess 2016). Domestic goats (Capra hircus) were introduced to Hawai'i by Captain Cook, in the late eighteenth century, quickly becoming feral (Tomich 1986).…”

“…Domestic goats (Capra hircus) were introduced to Hawai'i by Captain Cook, in the late eighteenth century, quickly becoming feral (Tomich 1986). Feral goats lack natural predators in Hawaiʻi, intrinsically growing into large herds that browse and trample vegetation, denuding native ecosystems resulting in severe soil erosion and coastal sedimentation (Chynoweth 2013, Hess 2016. Feral goat removal is prerequisite to the protection of diverse endemic Hawaiian ecosystems (Burt and Jokiel, 2011, Cabin et al 2000, Hess 2016).…”

“…Feral goats lack natural predators in Hawaiʻi, intrinsically growing into large herds that browse and trample vegetation, denuding native ecosystems resulting in severe soil erosion and coastal sedimentation (Chynoweth 2013, Hess 2016. Feral goat removal is prerequisite to the protection of diverse endemic Hawaiian ecosystems (Burt and Jokiel, 2011, Cabin et al 2000, Hess 2016). With that, there is a need understand feral goat behavior and movement ecology across these diverse landscapes (Chynoweth et al 2015), that could tailor management strategies to specific locations.…”