Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
emphasized in the lower portions of the HFU and KFU to minimize and halt the spread of
mosquitoes into higher elevation forested areas (Van Driesche and Van Driesche 2000).
Other ecosystem effects can be attributed to pig activity. Rooting and compaction can deplete the soil
of needed oxygen (Van Driesche and Van Driesche 2000). The behavior of pigs causes erosion of
cliff and stream banks. As a result, the quality of both fresh and brackish water system can be
degraded (USFWS 2008).
Most of the fenced portions of the HFU are pig free. Pig removal began at the HFU in 1988;
however, the 5,001.4 ac enclosure was not completed until 1992. The estimated density of this area
in 1992 was 4.7 pigs/mi 2 . The unmanaged area of Middle Maulua and Unit 3 had predicted densities
2.5 times greater. The population of Unit 3 was 118 ± 36 in 2004, while Unit 6 contained 24 ± 20
pigs (Hess et al. 2006). The lowland area of the HFU (which is not fenced) most likely supports a
high-density pig population (Jeffrey, pers. comm.). Within this area, the highest pig densities occur in
the closed canopy forest (USFWS 1996b). In addition, the adjacent State-owned Pīhā Game
Management Area contains a high pig population.
The efficacy of the pig removal program at HFU from 1987-2004 is described by Hess et al. (2006).
During this study it was determined that greater than 41-43 percent of the population at HFU must be
removed annually in order to effect a decline in pigs. To reduce the population by 50 percent in
following years, roughly 70 percent of the population must be removed annually; otherwise there is a
sustained population. Eradication at the HFU with dogs was estimated to require 11.8 worker-hours
per pig; this number is similar to estimates generated for the Hawai„i Volcanoes National Park,
which required 20 worker-hours per pig. Hunting with dogs is expensive because of intensive labor
costs and high maintenance and veterinarian costs. In addition, hunting dogs were killing nēnē on the
Refuge (Jeffrey, pers. comm.). In contrast, the eradication rate at HFU using snares was estimated at
4.9 worker-hours per pig. After the first 9 years of staff pig hunting in HFU, pig activity remained
between 25-30 percent. Within 18 months of first setting pig snares, no pig activity was observed by
Refuge staff through ungulate surveys. Pig snares were first tested at HFU in 1999 (Van Driesche
and Van Driesche 2000) and are now permanently deployed throughout the units. Snares have been
determined to be cost efficient. The snares are usually set in groups of 10, and average about 1 snare
per acre with a unit and cost roughly $17 each. Snares are anchored to trees and placed in areas of
high pig activity. Subsequently, the snare sets are inspected every 6 months, and replaced and reset as
needed. Pig carcasses are not removed, but are left in the forest as the cost of removal is high and the
carcasses often act as bait (Jeffrey, pers. comm.).
Pigs are abundant on the KFU, with recent estimates suggesting up to 1,000 pigs freely roaming the
property. They are found at all elevations of the unit (USFWS 2007A, 2008). The Refuge plans to
remove these animals once an ungulate proof fence is completed.
Rats (Rattus)
Three rat species are found throughout the Hawaiian Islands. Polynesian rats (Rattus exulans) arrived
from the central Pacific approximately 1,500 years ago as stowaways on canoes of the Polynesians
colonizing Hawai„i. Norway rats (Rattus norvegicus) reached the Hawaiian Islands after the arrival
of Captain Cook in the 1770s; and black or roof rats (Rattus rattus) most likely arrived in the 1870s.
It is estimated that these three species have populated nearly 82 percent of the major islands and
island chains throughout the globe (Tomich 1986, Tobin and Sugihara 1992). Black and Polynesian
4-88 Chapter 4. Refuge Biology and Habitats