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NON-NATIVE LAND VERTEBRATES
People ner.11t o bcrome more a w a r e o j p r o h f c m s caused by ,yIicti
~,cnebroresin narurul areas in ikuivai i. They musr cilso rcnhze t h a t
something can and s h o u l d be done,
Charles P. Stone
Vertebrates (anin~olswith hackhones) includs mammals, hirds, reptiles,
amphibians, and fishes. Recause Harai'l is located soma 1,500 nii (4,000 km)
froni continents, some oi these groups are not well rcpresentcd by specie5 thar
arrived without the help of humans. Hauai'i has no native amph~hisn\or lard
reptiles. and onlv one land ~imnrnnl(the Hawaiian or h o : q b~t(La~iunrc
cinereus), 'upe'up,,'~),
six specie? of native nun-marlnc fishes. and 57 s p c k s of
native land hirds. Yet natursli+ed (hwing estahlishcd populations) 5pecicl of
vertchrate. ~includinrPoltncsian introducrionil incluc!:. 19 mammal>. 45
birds, and I? reptilesvand amphibians.
I N I T I A L INTRODUCTIONS BY MAN
With the initial arrival of Polynesian people in ahout 400 A.D., vertehrate
introductions began. The early settlers deliheratel brought what is generally
considered the Polynesian triad--pig, dog, and chic en (Sus scrofa, Canis
familiaris, Ga1lu.sgallus). But they also brought some stowaways--the Polynesian rat (Ratfirserulans) and some r e ~ t i l e skeckos and skinksl Most of
the 5 crrehcires introducr;l by l'olynesih delGnded on hurimsand prohahly
did not seriously in\;ide nmve ecosystems. Thc! Ilkel!, frequented
llawaiian setrlements m d clld not do as much darnnge U I the n;,tive biota ar
tlie nctiviries of Pol!ncian humans (clearing l o ~ l ; ~ fore\[.
~ i d killing flightl e u hirds, selling i:res, and so forth). 'fhz rat w y have been a n eweprion.
as elwvherc it is known tc)r.at rhc eggs of seabirds. S~udiesin Hawai'i ha\e
shown that it was prohnbly quite a threat 1 0 flighkcs insects and grounddwelling mails. Rut until Ca t i n James Cook arr~vedin 1778, thr introtliiced
vertehrate most harmful to tk'c'nntlve biota u a j ~ r o h s h l ythe hunim a n i n d ,
rather than the species that arrived with him.
i;
THE SECOND PHASE-THE HOOFED M A M M A L S
The arrival of Captain Cook and other sea captains shortly thereafter
inaugurated a second group of vertehrate introductions. Animals that would
be useful to future visitors and which were appreciated by the Hawaiians were
brought ashore. These included cattle, goats, European pigs, sheep, and
horses
(Bos IUUIUS. Cauru hircus. Sus scrofa. OviE mie.s. Ermr~rcaballus).
The
..-~ ~ a w a i i a n favored
s
these ipecies so much that ~ l l & ~ ~ l : ~a rknpu
e d (tahoo) on
many of h e m , allowing numhers 111 huild up tremendously. ASa result, native
pl?ni community structure and cpmposition deteriorated in forests where the
nnmals fed. Unlike the Polmeslan introductions.
these
became
feral~~,
~ animals
~
~
..-~..~.
~
(dqmestic animals no longei dependent on man) over much of Hawai'i. Feralizahon was helped, of course, by increasing exploration bv man, clearing
of forests, and settlement bv immigrants. LaFlre numhers ofintroduced hoofed
mammals (ungulates) ate pal:rt:~hienative plants, rctluced p l a ~ t ~ o p & t i o ~ s ,
and caussd the c.\tinctions of numerow plant \ p e w s unadspted to hrowsiny.
gazing, trampling, and erosion.
But more than olants were destroved. Native birds and invertebrates
(such as insects nndland mall,), depsndent on the hahitat providcd bythe
plant?. were also reduced. Opening oi the forei~sby the feral nngulates albo
changed normal light, moisture, m ~ dnutrient cvcling pattern.. For c w n ~ l c .
in
some areas drahaee natterns of water were ilter&l because there was'lit-'
..~
tle native veget:,tion'ird to catch rain or to hold soil. Soils c&np:~credby
animal hooves favored rapid r ~ r o f ofwater.
f
As P . ~ I I I Sfronl elsewhere in the
world were :ntrodu;cd to 1iou.ai'i. h o o i d marnm:lls crested ~ l a c e Isvnrabk
r
for them in native ecosvsterns hy rcmovine natlve plant,. Un&~tes distributed alien plant seeds c!~rigingto their hair and carrlcd in t h c ~ digesrive
r
tracts. Alrm ~ l n n t ziurttrer altered n;lti\.e ~larilsuccession bee Smith. NonNative Plants: this volume).
By the 1i,ic~~~i800s.
foresters arrd nthera in Haw4i.i had beconie concerned
ahout the destruction of watersheds (area? which amtrihute to cctmmon water
collection and runoff downslone) caused bv feral uneulates. A oroeram to
reduce ungulate pupula~ionsk l make run'ofi patte&s morc c&si$cnt and
water less turhid (muddy) eventuallv resulted. I t included the planting of
introduced s ~ c c i e of
s trees, creation and fencing of Forest Resenes, removal
of animals through huntin and poisoning, and bounty system (payment for
evidence of animals killedf. This p/rilosoph of ungulate reduction to protect
watersheds and soil continued untd 1959, w en responsibility for feral ungulates was transferred from the Hawai'i Department of Agriculture to the
Hawai'i Department of Land and Natural Resources (DLNR). At this time,
hunting seasons and hag limits for ungulates were established and !he
p,hilosophy became one of sustained yield management (perpetuation of consistent numbers of animals) for hunting, rather than reduction of animals to
protect ecosystems and watersheds.
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THE THIRD PHASE
SJIALL MAJIMAIS, BIRDS, AND AIORE UNGULATES
Black Rats and Mon ooses
d
In the late 1800s an into the mid 1900s. transportation, settlement, and
visitation to the Islands continued to increpse. The black rat (Ruthls
ratha) probably arrived by accident some!tme between 1870 and 1890 in
Hawai'i and began to severely impact natlve blrds and probably mollusks).
The last Laysan rails (Ponanulapalmen) were era lcated on Midway
Islands, as was a population of the Laysan finch (Telespyza cantans). Other
species, especially colonial-nesting seabirds, were updoubtedly also easy
prey for black rats, and predation on tree-nesting birds such as H a w a i m
6
.
mosquitoes, may have reduced native bird populations prior to the arrival of
malaria.
Un dates
%roblems caused by cattle, pigs, and goats were aggravated by the inuoduction of additional hoofed anlmals. Although sheep had been ~ntroduced
by Vancouver in the 179k, sheep-raising began in the late 1800s. Once feral
cattle were controlled, feral sheep became a serious problem in mamane
(Sophora chysopltylla) forests of Mauoa Kea, for example. A court order to
remove the sheep from the mountain was issued in 1979 to protect the Endangeredpalila (Loxinides bailleui), and most feral sheep are now gone
in the
Gpperelevations.
Axis deer (Rrir mis) were introduced to the island of MolokaT in 1868
and became a pest within 30 years (Tomicb 1986). They were also released on
Maui and Lana'i, where they inhabit private lands, and they are now managed
hv the State for hunting on Moloka'i and Lana'i. A nonulation in Moanalua
valley on O..~huu m r&md or clim1n8tedhy deveiol;ment, predation hy
~ ~ j released on Lana'i
doer, and ponshins. hlm:lon sIicr.ii (OIL!r n u s i ~ wuere
in 19.54 and are st81 hunted there. Releases on Mauna Kea on Hawai'i Island
have hvhrid~zcdt t l \onlr. J c i r ~ , with
c icral h c p . M~,ufl~in
are now heing
were
removed f r m i tlauna Kea fur thc \:me rcswnt feral ,hcep. previouslv
.
removed.
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THE FOI'KTH 11H:4SF.-CONTINL'IN(; I'KOI{LERIS
Increasing resident human populations, especiallv on the outer islands
[)c~r~pectivc~.
i ~ i l ~ i ,anJ
t ~ .touiim hive ~ntensifiedthe mro(from s n 0 jli~
~ Il:an:~~'i.
Opening and fragmentation
d~ctionand yirrsd a!f dien ; ~ n i n i ; t l111
~ ~ : ~ : u r i :are;,.
tl
111mn\that nlien animals have more oouorof the feu reni:~irii~~~!
tunitv, to oenetrate
:reas which once were resistant to them. Smaller and' '
,
more irregular ar~.:l. haw more edge jun..tions of different vegetation types)
for alien snimalc ro c m t x t n;~tivetore\[.
Animal invaswm d!en includc an irruotive oeriod when Iarne numbers of
aliens survive and increase in numbers. A jlopulHtion of much l&er numbers
usuallyfollows the peak and persists at that level. During the peak, the
effecti on native ofev s ~ e c i e i o~r l a n t can
s be ereat and even result in their
extinction. ~ach'ne&a'nim:d in&i~in can ha\*;effects on different native
species in a natural area at peak po[rulxion levels, and eventually many
sbecies of native olants and-animdican become rare or extinct i s a result of
siuccessivc alien i;ruptions. ([:or cxarnplr, common myna, (Acndolheres
trirrk), although not resident in native forests now, once were abundant in
them in their ~rnmtivephase i n the IXWs. The harmful effects of omnivorous
myna%on forest plants ind anim;ds were probably great for a short period and
may have done lasting damage in forests.)
Introduced wecies of venehrates such as the domestic eat (Fdis catus).
often released dc'lihcrately in natural areas, and the house mouse ( M u s d o k fim)are now widcsliread in Hawai'i and undoubtedly have more effects
on native soecies thin we know. In contrast to the moneoose. the feral cat
hunts at niiht and i\ ahle to prey on roosting or nestinglbirds when the are
most vulnerahlc. Also in contrast to the mongoose. cats are readily ah e to
r
climb trees to atrnck oirds. M c c are abundant enough to reduce significantly
the numbers of cceds produced hy some native plants, thus inhibiting production of voune ~lants.Mice also serve as an im~ortantand consistenifbod
hase fo; SII& ipecles as mongonres, cats, and ham owls, thus supporting
Ii~chernumber\ of species nhrch .
prev. on n a h c vertcbratcs than ~ t ~ u <itherld
wiie be possible. Populations of some introduced species may still be expanding in numbers
and distribution. Mongooses reach higher population dens~tieson Caribbean
islands than they have reached on simdar-sized Hawaiian islands. Feral pigs
have invaded areas like Kipahulu Valley on Maui since the 1950s. and the
bogs in u per Hana Rain Forest and new areas in the West Maui Mountains
as recent v as the 1980s. The reasons for this are not well understood. but in
some csses. mutitalistic relationchips with introduced pl:ints may rerult in
of b u ~ hp i y anJ plsnts. Introduced
llicreased densities and di~~ributions
:~nimxls(sttch as r l u s and earthworms) mav also favor increaced densities and
distribution of pigs. -Adjustments in rai popidations may still be in progress,
with black rats becoming more abundant than Polynesian rats in some areas
for unknown.reasons. It is possible that these situations may not represent
long-term trends as much as shifting advantages resulting from climatic
patterns or other factors, but significant damage to the native biota may
occur either way.
The introduction of new species of vertebrates to Hawai'i is a constant
threat. In 1987, two brown tree snakes Buga meguluk) from Guam were
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discovered in Honolulu and destroyed ( Engbring,
personal communication).
This species is responsible for elimination of nearly all of the forest bird
species on Guam \Savidge 1987). An Animal Species Advisory Committee
and an Aquatic Li e and Wildhfe Advisory Commission for each Hawai'i
countv are charged with reviewine deliberate im~ortationsof new s~ecies.
Ilowever, the clkncer of ilccidenhl intrducti rn's and of rnovcmenis o i
species from place to place within 1l;iwai'i arc gre:it (rec Smitl~,Controlline
the Flow. .. ithis volume).
P
f.
MANAGING INTRODUCED VERTEBRATES
There are five hsically different objectives in managing introduced
icrtelirateh in 1I:wdi'i. TI:ey are: 1) Su\tsined \ield; 2) I:'rad:cati,~n:3)
Long-term population reduction; 4) Short-term population reduction; 5 )
Natural regulation.
The Hawai'i Department of Land and Natural Resources vractices sus[:liner1 vielJ man:igekenr for feral ungul:~tesand gnme birds oh moct StnK
~
point \r herc p~~pulzunn
properly. The ltitent 1s to hunt anim;~lsonly t t the
levels can be maintained for future hunting. An exceotion is Stateland on
113una Kes, whcre thc mmagcment goal For i d h e e p and mouilor. i. no\%
cradicntion to protect palila h3hitat.
On lands on ned hv the Nblionbl Park Senice snd 1 h e Yarurc Con3crvan? of Hawaii, the goal for feral ungulate management is kmg-term reductit~nor era.lica!ion tu prorsct native sco\!.ten~>. Er:,di~:ttror~L I S U ~ I I V rcquires fencing of areas to seuamte them from outside area, for which other
~3nagcme~it-ohjccti\cs
have been e'tablibhed, or 10 crexte rnme niann<eablc
areas within which animals can be eradicated. Re(luctton or eradicmon rrithi n fences i, hy hunting uith rifles (go:tts): hunting nith dugs (pigs): or sn:~rin$.
tr:lppit~g,;lnJ h~~nti:lg
in c~mhir~;~rion
(pig<). \lun:torin(: o f ; ~ n i n ~ps ~l ~ p u l s ~ e Jur~n,:w m r d snd cradicjti~tnprogrunic olid
tion, I11 d c t e r n ~ : ~sI:ttu,
s t t p 111
cnllccr~n; of d:11:1 from atlini;tls ;I\ the! arc rcmo\ed are ~nip~rt;lnt
dcterminin~.the Cit'Cai\~llc~\
tliprtl&m\ and i n iniproving their r.iiiilr.n.y.
Slonitoring u i \,egetatiorl resow!. i\ a l w useful. Counting the numhcr of
:mimaI\ rcmovcd mitv m:.n
little, ~ L Ii In i h n m o n on thc rate OI' rcn1ov;t.
ner
' unit area is i m ~ o i t a n t
Short-trrm r e d u i t d ia u\usll) the i ~ h i e c r i ~inc rn;rnagemcnt of manI
or I . Ihe h ~ r hpopl.l;diun dr~i>itlr.\.
widespread tli\tr~hutions.and
r 3 ~ l dr e ~ r o d ~ ~ c t rate,
i v c t ~ tf k \ c m ; J tnan1111:1limake r.r:tdic;lrion or lonui n import:lnt nLrllte;ni rcductiort ~~xtrenicl)
~tnlikrl,. )'el, reducing n~~rnhers
ral arm\ prlctr 10 or during hreeJing ~ e : w nfor~ cndsngercd bird,. or during
vulnerable fruiting or seeding periods for native plants,may be possible. Aii
anticoagulant poison called diphacinone is being developed in Hawai'i to
reduce mongoose numbers in breeding areasused by eight Endangered bird
s~ecies.Testing the effectiveness of oredator reduction on the survival of
$ung birds hasnot yet been atternpied, and we do not yet know the best
tlmes for and intervals between treatments with diphacinone.
Research on t r a m i n s anticoamlants. and acute toxicants for black rats
determined. Short-term reduction of some alien bird populations in some
high-value areas ma] also be possible, but this has not been attempted in
Hawai'i. For example, mynas are social birds and may b e subject to decoy
tramine. in which a few birds lure others into tram. Reduction of kalii
(Lopl~uraleucornelanu) by shooting or'trapping may be pos$ble and
ph&&
is desirable to reduce dispersion of the alien vine banana poka (Passiflora
mollissirnu) in some areas.
aeement ohiective. The numbers of ~ i g s alien
.
birds. fats. insects. and so
-
humans can alleviate some of the neeative effects of alien vertebrates on the
n:ltiw hiold 111 < t m c > I ~ I I ; ~ ~ InJccd,
~ I I I I A11. can hc argued th:,r, iinie human.
~ I I C problem.; either kt~~i\in&,d!
or unknoisingly i n the fir31 {11;~e.
we
in~ti.t~ecl
have vnne rcm~n>il~ilitv
to elimin:~tethen1 where othcr value5 are ~ m v u r t a n ~ .
In any event, tb allow natural regulation to result in high numbers of aliens
is really "management by default." Management,of introduced species by natural regulation or sustained yield to "non-damagmg" levels in ecosystems
where they have not evolved is "biologically meaningless" (Gagnk 1988). Rare
and vulnerable native species and ecosystems are put at risk by lack of human
concern and action.
FUTURE NEEDS AND RECOMMENDATIONS
Considerable information is available for managing hoofed animals.
native ecosystems need attention, especially on Natural Arca Reserves and
some other conservation lands owned by the State.
The feasibility of short-term reductton of mongooses, rats, and alien birds
still requires research. However, reduction of human disturbances (roads,
trails, housing developments, food sources, and so forth) in native ecosystems,
and less fragmentation of remaining natural areas, will result in fewer alien
bird species and lower numbers of alien birds there (Scott et al. 1986).
Education of the general public, teachers, and important decision-makers
in political and business communities is critical. People need to become more
aware of problems caused by alien vertebrates in natural areas in Hawai'i.
They must also realize that something a n and should be done. A minimum is
to avoid introducing alien vertebrates to new ~ l a c e s .There is a need to out
ting io long-term action programs for natural areas are given elsewhere
in this volume and in the literature (see especially Myers 1986).
Important References
Bergcr, A.J. 1974. History of exotic birds in Hawaii. 'Elqaio 35(6):60-65.
Berger, A.J. 1975. History of exotic birds in Hawaii. 'Elepuio 35(7):72-79.
Gagnb, W.C. 1988. Conservation priorities in Hawaiian natural systcms. Bioscience
38(4):264-271.
Juvik, J.O., and S.P. Juvik. 1984. Mauna Kea and the myth of mulliple use: endangered
species and mountain management in Hawaii. Mo~omirtResearch orid Developrurrtt
4191-202.
Moulton. M.P.. and S.L. Pimm. 1983. The introduccd Hawaiian avifauna: biaeeoeraohic
u
.
evidcnce far competilion. American Nonmlist 121(5):669-6!M
Moullan, M.P., and S.L. Pimm. 1986. Species introductions to Hawaii. Pp. 231-249 IN H.A.
,
,
Springer-Verlag, New York.
Myers, N. 1986. Tockii,~Mr?ss&ti,,&
of Snccies: A Great Crpotiw Cilallerqe
Horace M. ~ l b r i g h < ~ c c t u r e s in
h i C&s&atian
~
26. Univ. California, ~ e r k c l c ~ .
Savidge, J.A. 1987. Extinction of an island forest avifauna by an introduccd snake.
Ecology 68(3):660~668.
Scott, J.M., S. Mountainspring, F.L. Ramsey, and C.B. Kepler. 1986. Forex1 Bird
Co,mmnities of tile Howuiim Islands: 771cirDymmics, Ecology, m d Consewotion.
Studics in Avian Biology 9. Cooper Ornithological Socicty, Berkeley, California.
Smith, C.W. [this volume] Controlling thc flow of non-native species.
Smith, C.W. [this volume] Non-native plants.
Stone, C.P. 1985. Alien animals in Hawai'i's nativc ecosystems: toward conlrolling the
adverse effects of introduccd vertebrates. Pp. 251-297 IN C.P. Stone and J.M. Scott
(eds.), Howois!r TemsIn'oI Eco~yxfms:Pwswwlion and M a n o p t e m . Unir. Hawaii
Press for Univ. Hawaii Cooperative National Park Resources Studies Unit, Honolulu.
Stone, C.P., and J.O. Keith. 1987. Control of feial ungulates and small mammals in Hawaii's
national parks: research and management. Pp. 277-287 IN C.G.J. Richards and J.Y. Ku
(eds.), Conlrol of Momn~olPests.Supplcrnent 1, Tropical Pest Management 32. Taylor and
Francis, Ltd., London.
Stone, C.P., and L.L. Loope. 1988. Reducing impacts of introduced animals on native biota of
Hawai'i: what is being done, what needs doing, and the role of national parks.
Envimntnental Conservation 14(3):245-254.
stone, C.P., and J.M. Scott (eds.). 1985. HawoiS's TerreslrialEcovStems: Preservation
nndManogemen1. Univ. Hawaii Press for Univ. Hawaii Cooperative National Park
Resources Studies Unit, Honolulu.
Tornich, P.Q. 19%. Mon~malsin Hawaii: A Syftopsis and NotorionnlBib,iograPhy.
2nd edition. Bishop Museum Special Publ. 76. Bishop
press, ~~,,,,l~l,,.
van Riper, S.G., and C. van Riper, 111. 1982. A Field Guide to flte Mamntols in Howoii.
The Oriental Publ. Co., Honolulu.
Vitousck, P.M., L.L. Loope, and C.P. Stone. 1987. Introduced species in Hawaii: biological
effects and opportunities for ccolagical research. Trends in Eco/omondEvoltrtion
2(7):224-227.