Guam National Wildlife Refuge Comprehensive Conservation Plan

Guam National Wildlife Refuge Comprehensive Conservation Plan
Migratory Waterfowl and Waterbirds
With no standing water sources present, migratory waterfowl and waterbirds are rare
observations on the Ritidian Unit. However, migratory waterbirds using open field regions of the
Refuge include cattle egret (Bulbulcus ibis), little egret (Egretta garzetta), and intermediate egret
(Egretta intermedia) (Pratt et al. 1987). Two resident breeding waterbirds that are documented
in forest edge and exposed coral reef regions on the Ritidian Unit are yellow bittern (Ixobrychus
sinensis) and Pacific reef-heron (Egretta sacra) (Pratt et al. 1987).
Migratory Shorebirds
Guam serves as an important stop-over location for migratory shorebirds during the non-breeding
season. Shorelines, exposed coral reef, and open field habitats are common observation locations
for shorebirds on the Ritidian Unit. Sightings during the fall migration have been recorded on the
Refuge for Pacific golden-plover (Pluvialis fulva) and wandering tattler (Heteroscelus incanus).
5.4 Pest and Nonnative Species
Pest Species
Invasive species are infiltrators that invade ecosystems beyond their historic range and threaten
biological diversity. Introductions are usually human-mediated and cause harm to the economy,
environment, or human health (Executive Order 13112). Direct competition with native species
for resources such as food, water, and space has a major impact on the environments to which the
species is introduced. Invasive species may also destroy or modify crucial habitat leading to
greater exposure of native species to predators, competition for food resources, and removal of
important Refuge attributes (Priddel and Carlile 1998). In addition, invasives are often vectors
for the spread of pathogens and disease (Geering et al. 1995; Dickman 1996).
Island ecosystems are exceptionally fragile and adversely impacted by invasives due to their
intricate trophic structure (Fritts and Rodda 1998b). Endemic island species that have evolved in
the absence of a particular invasive predator are at risk because they lack the necessary defenses
to impede their predation (Dickman 1996, Fritts and Rodda 1998a) or survive resultant ecosystem
imbalance. Guam is a notable example of island invasion success, with the introduction and
establishment of at least 9 mammal and 32 amphibian and reptile species since European
settlement (Savidge 1987; McCoid 1993; 1999, Stinson 1994; Christy et al. 2007). However, not all
species establish and are considered invasive. There are currently over 80 invasive species listed
for Guam (Appendix A), and the number is growing rapidly (e.g., the recent discovery in
September 2007 of the coconut rhinoceros beetle Oryctes rhinoceros; A. Moore, University of
Guam, personal communication). However, only a subset is present on Guam Refuge (Table 4).
Chapter 5. Refuge Biology and Habitat 5-27