Establishment of the Invasive White-tailed Deer in Portland,
Jamaica.
Published Date: August, 2007
Author: Shauna-Lee Chai,
Conservation Science Officer, Jamaica Conservation & Development Trust
Address: 29 Dumbarton Avenue, Kingston 10.
Jamaica W.I.
Email:
jcdt@cybervale.com
PDF Version
Summary
A small
population of white-tailed deer (Odocoileus virginianus) was
introduced to Jamaica in the 1980s through the accidental
release of captive-held animals. This article is based on a
2003 investigation carried out on their distribution,
population size, and socioeconomic impacts of the
introduction. The investigation also sought to ascertain
whether the deer represent a threat to biodiversity in the
remaining natural forests of the Blue and John Crow
Mountains.
O. virginianus
in Jamaica is restricted to Portland, where it occupies a
relatively small area of approximately 19 km2 in
and around the communities of Mt. Pleasant, Industry,
Shrewsbury, Content, Darley, Little Spring Garden, Eden
Wood, Paradise, and, Swift River. These areas are
characterized by low altitudinal edge habitat interspersed
with small agricultural fields growing cash crops like
pumpkin, carrot, yam, and corn.
Interviews with
local residents indicate that O. virginianus is a serious
agricultural pest in the communities in which it occurs.
Farmers in the area complained of deer damaging agricultural
crops, and claimed average monthly losses of J$10,000.
By
incorporating deer defaecation rate and dung decay rate into
line transect surveys of deer dung, the total deer
population in Portland was estimated at 182 individuals.
This alien
invasive does not appear to have penetrated the forests of
The Blue and John Crow Mountains, and at present, poses more
of a threat to small scale agriculture.
Key-words:
Odocoileus virginianus, alien invasive, deer dung
transects, agricultural pest, introduced species
Introduction
One of the
greatest challenges facing wildlife professionals, and
indeed, native ecosystems world wide, is the increasing rate
at which human activities are causing a homogenization of
the earth’s species. Jamaica is no exception to this
unfortunate trend, and it is threatened by 52 known invasive
plant and animal species (IABIN, 2003).
Introduced species
cause billions of dollars in damages each year. Their
impacts include herbivory, predation, disease, parasitism,
competition, habitat destruction, and hybridization with
native species (Simberloff, 2000). The devastating effects
of biological invasions are rivaled only by habitat
destruction, with the latter being the greatest cause of
species decline (Wilson, 1992).
Island systems are
especially vulnerable to exotic species, due in large part
to the absence of entire groups of species in insular
communities (e.g. terrestrial mammals); hence island
invaders may encounter resource rich environments that are
free from competitors and predators, and such ecological
release greatly enhances their prospects for successful
establishment (Simberloff 1995).
Odocoileus
virginianus Species Description
Odocoileus
virginianus
Z. (white-tailed deer) is the most widespread and abundant
member of the deer family (Cervidae). There are
approximately 38 subspecies of O. virginianus
recognized in America (Smith, 1991).
White-tailed deer are so named because when alarmed, they
hold their tails erect, exposing their white underside.
Adult males
weigh from 90-135 kg, and attain a height (at shoulder) of
53.3-106.7 cm, and a length of 104.1-240 cm. The length of
the tail averages 10-36.5 cm, and the hind foot averages
27.9-53.8 cm in length. In general, females weigh 20-40%
less than males (Taylor, 1956).
In the northern
hemisphere, this species demonstrates seasonal variation in
pelage. Their summer coat consists of short, thin, wiry
hairs and varies from red-brown to bright tan. The coat is
darker along the mid-dorsum and paler on the face, throat
and chest. The winter coat develops in late summer to early
autumn, and is a blue-gray to gray-brown colour with longer,
thicker, and more brittle hairs. Adults have a white
nose-band, orbital region, and throat patch. The
underparts, including the lower tail, insides of legs,
venter, and chin are also white (Guthrie, 1971). Fawns have
a red-brown coat, with white dorsal spots that disappear at
3-4 months of age (Hesseleton and Hesseleton, 1982).
Adult males
possess antlers (rarely found on females), and male fawns
have small bumps or “buttons” in their first year, and
unbranched spikes or branched antlers thereafter. The size
and shape of antlers is a reflection of age, nutrition,
heredity and heterozygosity (Hesseleton and Hesseleton,
1982).
Reproductive
Capacity
Deer have very
high rates of reproduction, and given optimum conditions and
low mortality rates, their populations can expand rapidly.
McCullough (1979) reported that a population of 6
white-tailed deer (2 bucks and 4 does presumed to be
pregnant) introduced to the Edwin S. George Reserve, a 1,146
acre reserve in southeastern Michigan, grew to a size of 180
individuals in six reproductive seasons (6 years), and
reached a maximum of about 222 head in 7 years. Later, the
population was reduced to 10 deer, and in a period of 6
years, it grew to a size of 212 individuals. The population
growth rate in these examples was found to be over 50% per
year (McCullough, 1983). Although remarkable, this
population growth rate was not thought to represent the
maximum rate of increase attainable by the population, as
the growth rate of the herd decreased with increasing
population size. An unimpeded rate would have yielded over
300 individuals, compared to the estimated 222 and 212
(McCullough, 1982).
In addition to
their high reproductive capacity, white-tailed deer are
among the most genetically variable mammals studied, and
this high genetic variability is very advantageous,
especially when a small number of these animals are
introduced to an area, as it reduces the magnitude of
potential founder effects.
Natural
Range and Habitat Preference
White-tailed deer
range from southern Canada throughout most of the
coterminous United States, southward to northern South
America (Smith, 1991). The animal has been introduced to
many places, including The British Isles, Czechoslovakia,
Finland, Yugoslavia, New Zealand, Cuba, The Virgin Islands,
Curacao, and other Caribbean islands.
Deer prefer
ecotone or edge habitats where fields and forests come
together, producing an area with abundant shrubs and low
growing trees. This habitat provides them with adequate
vegetation for concealment and ample food; deer tend to
avoid mature forests where the undergrowth, and hence food
supply, is limited (Severinghaus and Cheatum, 1956).
Radio-teleometry studies in Scotland showed that deer used
agricultural land primarily at dusk and dawn, and woodland
areas were highly preferred in between these times (during
the day and at night) (Idris, 1990).
Deer Impacts
Both native and
introduced deer are considered pests in many parts of the
world. Deer are known to pose a threat to native forests
(Marquis & Brenneman 1981, Kay 1993, Relva & Veblen 1998,
Manchester & Bullock 2000, Wardle et al. 2001, &
Fuller & Gill 2001). Through predation of seeds, browsing,
and trampling of seedlings, deer may exert a profound
negative impact on forest regeneration. Deer also damage
forests through browsing of the lateral branches or terminal
buds of developing trees, bark-stripping of more mature
trees, and fraying of bark from the main stem of small trees
by rubbing them with their antlers (Putman and Moore,
1998).
In Pennsylvania,
the disappearance of highly palatable plants was found to
adversely affect other wildlife that rely on these plants
for food and cover, resulting in a dramatic reduction of
biodiversity in forests. deCalasta (1994) found that deer
altered forest structure and composition by eliminating much
of the intermediate canopy, which led to the local
extinction of many intermediate canopy dwelling
songbirds.
In its native
range within the United States, for example, O.
virginianus is a serious agricultural pest. Because of
their large size and associated dietary needs, these
ruminants are able to consume virtually all the foliage of
the plants they prefer (Nugent, 2001). White-tailed deer
allocate more time to feeding than to any other activity,
and select the most nutritious forage available (McCullough,
1982).
In agricultural
areas, farm crops are an important year-round source of high
quality forage for white-tailed deer, representing up to 78%
by mass of the total diet (Gladfelter, 1984). As a result,
deer can pose a serious threat to agriculture, and can
inflict considerable economic losses. Damage to farmland
occurs in many forms, including grazing, flattening by
rolling, lying, or trampling of crops, damage to fences or
hedges, and damage to trees (Scott and Palmer, 2000). Doney
and Packer (1998) report from a survey carried out in
lowland England that the most common type of damage was
grazing, followed by damage to trees, flattening of crops,
and damage to fences.
Conover et al.
(1995) estimated crop damage in the United States
agriculture industry at almost US$500 million per annum, and
deer are responsible for much of these damages. In one
survey conducted by the Pennsylvania Farm Bureau (2002), the
average farmer lost over US$9,000 per year due to damages
caused by deer.
Deer also affect
the water quality of river systems through erosion and
faecal contamination, and they carry diseases and parasites
which can be transmitted to humans.
About 29,000
people are injured and over 200 people die each year due to
deer-vehicle collisions in the U.S. (Conover, 1995).
Deer
Introduction to Jamaica and its Implications for
Biodiversity Conservation
The white-tailed
deer was introduced to the island in the 1980’s. There are
conflicting reports about the year and the number of deer
that were introduced. One confirmed report is that in 1988
during hurricane Gilbert, 6 captively held deer escaped into
the wild from their holding at Somerset Falls - a local
tourist attraction in the parish of Portland. These 6
individuals were comprised of 3 males and 3 females (Shaw,
pers. comm.). There was, however, probably more than
one instance of deer escaping from this location, as
residents in the area maintain that some of the animals
escaped in 1980 during hurricane Allen.
The Blue and John
Crow Mountains National Park is located in relatively close
proximity to areas where white-tailed deer have now become
established. Jamaica has been recognised as a biodiversity
hotspot, and much of its biodiversity is contained within
this park. The park is the largest remaining area of
natural primary forest, and contains some 923 endemic
species of vascular plants (NEPA, 2003). The area also
serves as an important watershed that is vital for the water
supply to the eastern end of the island, including
Kingston. The possible penetration of O. virginianus
into these forests is cause for considerable concern.
The already
threatened state of the Blue and John Crow Mountain forest,
due to charcoal burning and hillside farming renders this
ecosystem more invasible, and coupled with these
pre-existing threats, the establishment of an introduced
herbivore like the white-tailed deer could have serious
implications for biodiversity conservation in the area.
Study area
This study was
conducted near the centre of Portland, about 8 km west of
the capital Port Antonio. The area is approximately 20 km2,
and is characterized by ecotone or edge habitat,
interspersed with agricultural land (Figure 2.1). Many of
the farms in the area are small (<0.5 km2), and
do not show up on the land use map in Figure 2.1.
Altitude ranged
from 50 m near the Swift River to 350 m on surrounding
hilltops. There are some areas of secondary forest
containing native trees and climbers like Zygia latifolia
and Entada gigas respectively, while other areas are
covered by introduced species of bamboo (Bambusa vulgaris),
fern (Nephrolepis sp) and pine trees (Pinus
caribea) (Plate 2.1). Much of the area is under
cultivation, with carrot, pumpkin, banana, yam, and cocoa
being the predominant crops.
The parish of
Portland receives an average of 367 cm of rainfall per year,
and 27.8 cm of rainfall in the month of June (Meteorological
Service of Jamaica, pers comm., 2003). Numerous
watercourses like the Swift River, Daniels River, Kelly
Brook, and the Black River permeate the area, and there are
several small farming communities along the roads. The
study was concentrated in and around the communities of
Content, Mt. Pleasant, and Shrewsbury, as these communities
appeared to contain the highest densities of the introduced
deer.
METHODS
Field work for the study was carried out
in the summer months of June and July, 2003. Visits were
made to communities within Portland where deer presence had
been reported. Initially, surveys were conducted over a
broad area in order to map the full extent of the
distribution of O. virginianus (Figure 2.1).
Subsequent surveys and field work were conducted in areas
identified as containing deer. A questionnaire was
administered to community members (concentrating on
farmers), and using this method, the presence of deer, and
their impacts in different communities were ascertained.
Deer
abundance was estimated using line transect surveys of deer
dung, as described by Buckland (1993).
RESULTS
Odocoileus
virginianus distribution
Survey results
show that deer are present on the outskirts of the following
communities: Mt. Pleasant, Shrewsbury, Content, Darley,
Little Spring Garden, Eden Wood, Industry, Paradise and
Swift River (Figure 4.1). The animals were found to occupy
a total area of approximately 19 km2, but they
were not distributed evenly over this area, as there were
core areas with relatively high density, and areas where
only occasional sightings were recorded.
Figure
4.1 Study area showing survey points and area occupied by
white-tailed deer in Portland
Twenty eight farmers
and thirty two other residents, within the area occupied were
interviewed. Many people living in towns or larger communities
within the area occupied by O. virginianus had never
heard of deer occurring in Portland; and, as expected, farmers
were the most knowledgeable about the animals, as they had had
the most encounters with the creatures through crop raiding
(Figure 4.2).
Figure 4.2 Percentage
of farmers and other survey respondents within the area occupied
by O. virginianus who had knowledge of deer presence in
Portland.
Crop Damage
Farmers reported deer
in their crops at dusk and especially at dawn. Herd size
according to farmers is 2-3 individuals, often consisting of a
doe, and one or two fawns. This is the characteristically small
herd size of Odocoileus (Anderson & Wallmo, 1984).
Grazing damage was the only type of perceived damage reported by
farmers. They complained that crop damage from deer has
escalated in the past 5-6 years, and estimate loosing on average
$10,000 per farmer per month from crop damage due to deer.
Crops that received the most damage include pumpkin, carrot,
yam, okra, pepper, peas, and corn (Figure 4.3). Crops like
banana, plantain, coco, and dasheen were generally not taken
during deer raids. For some crops such as carrot and pumpkin,
only a few bites of individual fruits are taken, and many more
crops are damaged than are actually consumed. As a consequence,
deer are able to destroy entire fields of crops overnight. Such
extensive damage can apparently overwhelm small-scale
agricultural operations, as some small farmers have reportedly
gone out of business as a direct result of losses attributable
to deer (Plates 4.1 & 4.2).
Figure 4.3. Chart
showing crop types preferred by deer according to the number of
farmers that reported damages in particular crop types. This
pattern probably reflects both the availability of various crops
and deer crop preference.
To
deter deer from raiding crops, farmers have employed a number of
measures. Some have hung makeshift scarecrows sprayed with
perfume in their plots (Plate 4.3). Others have rubbed the
fence posts surrounding their crops with bath soap, hoping that
the scent will deter raiders. And some farmers have left lit
lanterns burning in their plots overnight.
Plate 4.1. Farmer
from the community of Content showing damage to pumpkin by
white-tailed deer
Plate 4.2. Only a few
bites of individual immature pumpkins were taken on this farm in
Content, resulting in the destruction of the entire plot.
Plate 4.3. Makeshift
scarecrow on farmland near the community of Mount Pleasant,
Portland.
Damage to Woodland
Areas
Although damages to
woodland areas were not directly investigated, there were some
obvious signs of antler damage to trees within the area occupied
(Plate 4.4). The damages trees were observed in highly degraded
woodlands interspersed with agricultural fields. There were no
reports of deer presence within the forest reserve of the Blue
and John Crow Mountains National Park
Plate 4.4. Bark
fraying of a young tree near Mount Pleasant, caused by deer
thrashing the antlers up and down against the stem during
territorial displays.
Deer hunting
Some farmers set rope
snares for the animals, but deer are very trap wary, and have
seldom been caught using this method. Deer hunting with the
help of hunters from the Kingston area is becoming increasingly
popular, and deer are tracked and shot on a weekly basis with
the help of tracking dogs. Only one community member (a farmer)
is involved in leading deer hunting expeditions, and he reports
seeing approximately 300 deer killed over the last 3-4 years.
Income from deer
Economic gain from
deer presence has been negligible. Only one community member is
actively involved in leading deer hunting expeditions, from
which he receives a small financial gain for his services as a
guide. This only offsets the losses he receives through crop
damage. Hunters return home with their catch, and either sell
it or consume it. Local catch is rare, and only used for
subsistence. One local touring organization conducts the
occasional deer-photographing outing, charging $1500 per
person.
Deer Abundance
Five dung piles were
recorded along 20 transects (Plate 4.5). Density calculations
were done for the core areas totaling approximately 7.6 km2,
within the total 19 km2 area occupied (Figure 4.4).
Plate 4.5. O.
virginianus dung pile in an area dominated by bamboo near
the community of Content
Using DISTANCE
(Buckland et al., 1993), a dung density (T) of
23914.86/km2 was estimated, based on the number and
distances of the dung piles from the transects. Deer density
(D) was estimated at 23.90 deer/km2, and deer
abundance (N) was estimated at 182.
DISCUSSION
The distribution of
O. virginianus in Portland was smaller than
anticipated. Given that the animal has been established in the
island for approximately 15-20 years, its dispersal has been
fairly minimal, and its range has been confined to a relatively
small area. Marchinton and Hirth (1984) found that movements
and home range in deer are variable, and are influenced by age,
sex, density, social interactions, latitude, season, and habitat
characteristics. Therefore any number of factors could be
influencing the distribution of O. virginianus in
Portland.
O. virginianus’
distribution in Portland is characterized by relatively low
altitudinal areas (50m-300m) permeated by streams, and set apart
from towns and communities. Areas occupied consist of degraded
forest in close proximity to the animal’s preferred agricultural
crops.
The area occupied by
O. virginianus appears to be constrained by a number of
factors. In the southern region of the range, they are probably
constrained by crop type, as coffee, banana and plantain (which
are not the animals’ preferred crop types) are the main crops
grown. To the east of their range, the species is probably
inhibited by more densely populated towns and communities like
Mount Pleasant and St. Margaret’s Bay. These towns also
probably have a greater occurrence of dogs, the presence of
which will work to deter deer. In those communities occupied by
O. virginianus, farmers rarely keep dogs, for fear that
they would prey on goats and other reared animals. The Swift
River, and a change in crop type (from pumpkin and carrots, to
plantain, banana and coffee) probably restricts the animals to
the west of their range.
It appears that deer
have not managed to establish themselves in the Blue and John
Crow Mountain forests. These mature forests are probably
unsuitable habitat as they contain little undergrowth which deer
need for cover and browsing.
The density of O.
virginianus (23.9 deer/km2) in the core areas
occupied, was found to be relatively high. Aulak and
Babinska-Werka (1990) note that in small wooded areas surrounded
by agricultural fields, the abundance of roe deer is 3 times as
high as the density levels for woodlands in Poland. The animals
were found to temporarily leave the shelter of the woodland,
move into nearby fields, and use the vegetation as an additional
food source. In their study of a small forest area (200 ha) in
Poland, surrounded by agrocoenoses, they found a high roe deer
density of 45-62 deer/km2, and not surprisingly, the
agrocoenoses bordering the forest were intensively used by
deer. Areas with numerous small agricultural plots in
Quercus-Carya forests in North Carolina were found to support
high densities of 80 deer/km2 (Torgenson and Porath,
1984).
My O. virginianus
density estimate is limited by a number of factors. Ideally,
defecation rates and dung decay rates should have been estimated
from independent studies done on the population under
consideration. These parameters are highly variable and habitat
specific, but such investigations were not practical given the
scope of this study. In addition, the relatively small number
of dung piles found (5) resulted in large confidence limits.
Nevertheless, the abundance estimate of 182 deer in the core
areas occupied, with an upper 95% confidence limit of 373 deer
appears to be reasonable, based on (1) the relatively small, yet
high quality habitat occupied, and (2) farmers’ estimate of 500
– 1000 deer. Farmers’ estimates are however, based on sightings
and crop damage, but the same group of deer could be returning
to raid crops in each instance, and as such, a population size
of 500-1000 individuals is likely to be an overestimation.
Using the population growth rate of white-tails on the George
Reserve (McCullough, 1982 and 1983), with a founding population
of 6 individuals (Shaw, pers. comm.) growing over a
period of 15 years, the result is a potential population size of
12, 416 individuals in Portland. The population size in
Portland would probably approach this value if it was
uninhibited, and this is an indication that there are inhibiting
factors to deer population growth in Portland, one of which
might be hunting.
A more accurate deer
population size estimate could have been attained if a larger
sample size (number of transects), with longer transects was
taken, and if the area occupied was divided into strata
(woodland versus cropland).
Odocoileus
virginianus and the Portland farmer
Portland is primarily
an agricultural parish, and the vast majority of farmers operate
relatively small farms (<0.5 km2). The small farm
sector is the country’s largest source of employment, supporting
an estimated 150,000 rural families (NEPA, 2003). It is these
small farms in Portland that receive the highest damage levels.
Smaller farms have a larger perimeter to area ratio, which
leaves them more susceptible to damage from deer entering the
edges of plots, from adjacent woodlands. Smaller farms also
have fewer crops, and so the effect of deer raiding can be
catastrophic.
Farmers
reported that deer raiding had intensified over the past 5-6
years, suggesting that the deer population has been increasing.
On the other hand, some farmers reported that deer raiding had
lessened in the past 1-2 years, perhaps reflecting reduced
density attributable to hunting mortality.
In general, farmers
have apparently met with little success in their measures to
deter crop raiding by deer. After a few weeks, the animals
usually become accustomed to the scarecrows and other
frightening devices employed by farmers. Further, none of the
farmers interviewed had switched crop types to those less
preferred by O. virginianus; they explained that this
would not be feasible, given the local market conditions.
Some farmers
experienced losses in certain crop types, while others did not.
This was probably due to the location of the crops within the
field, or the location of the field itself, as fields located
closer to woodland areas are more likely to be raided than are
fields further away from wooded areas (Aulak & Babinska-Werka,
1990).
CONCLUSION
Odocoileus
virginianus
in Portland is a serious agricultural pest, causing thousands of
dollars in damages to small farms. Given their present
distribution, the animals seem to pose more of a threat to small
scale agriculture than to forested areas. Their presence may,
however, have implications for forest restoration in edge
habitats.
Future numbers and
geographical expansion of O. virginianus are strongly
dependent on land use patterns and hunting regimes. As is the
case in lowland Britain (Putman and Moore, 1998), farmed
woodlands create refuges for deer, and serve both to increase
densities in those areas already occupied, and to provide
migration corridors to new areas. If such migration corridors
containing the right crops continue to be made in The Blue and
John Crow Mountains National Park, it will only be a matter of
time before O. virginianus invades this unique and
vulnerable ecosystem.
To better assess the
status, and impending threat of O. virginianus to the
Blue and John Crow Mountains National Park, additional research,
survey work and monitoring is clearly warranted, in particular,
along the northern foot hills of the Park.
RECOMMENDATIONS
-
O. virginianus is an
alien invasive species, and the population in Portland
should be eradicated or controlled in an effort to safeguard
the native biota, and to spare agricultural losses. Since
this is largely the view of community members, control
efforts are not likely to be met by opposition, as is often
the case with introduced animal control programmes. The
most suitable method of control would probably be to have
hunters or members of the Jamaica Defense Force come into
the area at prescribed times (set during community
consultations) to shoot deer. This could be regarded as a
community service, and the meat could be divided up among
community members. In the meanwhile, farmers should be
compensated in some way for deer damage, to ensure that
immediate losses do not result in unemployment and social
disruption.
-
Farm owners should
be given technical support to help prevent deer raiding.
One potential method of deterring deer on farms in the
Portland area is to keep dogs around crop beds, although
such an approach would not come without potential negative
consequences (example, adding to the feral dog problem and
risking predation of reared animals).
-
There is currently
no legislation that addresses the issue of bringing alien
animals and plants into Jamaica, nor is there a coherent,
national strategy aimed at ameliorating the deleterious
impacts of introductions that have already occurred. More
stringent laws should be established that prevent the
importation of any non-native species except under special
circumstances identified by the relevant authorities. An
alien watchdog group should be established that would be
contacted on the first sign of a newly introduced species,
and the government and other relevant organizations should
mobilize to control or eradicate alien invasives wherever
they occur.
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