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Sloths in the city: unexpectedly high density of pale-throated three-toed sloths (Bradypus tridactylus) found in an urban forest patch in Paramaribo, Suriname

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In October 2012 individuals associated with the Green Heritage Fund Suriname organized a rescue of arboreal mammals displaced during deforestation of a 6.8 ha plot in northwest Paramaribo. Rescued or observed animals included 137 pale-throated three-toed sloths (Bradypus tridactylus), eight two-toed sloths (Choloepus didactylus), three Brazilian porcupines (Coendou prehensilis), and three silky anteaters (Cyclopes didactylus). In addition, two lesser anteaters (Tamandua tetradactyla) – a mother and baby – were seen but not rescued. Due to their lack of speed and inability to escape, it is likely that almost all of the pale-throated sloths in the forested plot were captured during the thirty-day period of clear-cutting. Comprising 91% of the total rescued animals, the 137 B. tridactylus included 61 males, 56 females, 15 juveniles, and ve adults that could not be sexed. Data on body mass, length, and other features reveal a population of reasonably healthy but smaller animals at a population density of 20.1 animals/ha that far exceeds any previous reports for this species.
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M. Pool et al. : Sloths in the city: unexpectedly high density of pale-throated three-toed sloths (Bradypus tridactylus)...
Edentata 17 (2016): 25–33
DOI: 10.2305/IUCN.CH.2016.EDENTATA-17-1.5.en
Electronic version: ISSN 1852-9208
Print version: ISSN 1413-4411
http://www.xenarthrans.org
Sloths in the city: unexpectedly high density of pale-throated three-toed
sloths (Bradypus tridactylus) found in an urban forest patch in Paramaribo,
Suriname
Monique Poola, Ruby boatenGb, ann-MaRie ako-aDounvob,
Rachelle allen-McFaRlaneb, Diana elizonDob, henRi PatuRaultb, haiFa alhaWaSb
anD GeoRGe MiDDenDoRFb,1
A Green Heritage Fund Suriname, Paramaribo, Suriname
B Department of Biology, Howard University, Washington DC, USA 20059
1 Corresponding author. E-mail: gmiddendorf@howard.edu
Abstract In October 2012 individuals associated with the Green Heritage Fund Suriname organized a rescue
of arboreal mammals displaced during deforestation of a 6.8 ha plot in northwest Paramaribo. Rescued or
observed animals included 137 pale-throated three-toed sloths (Bradypus tridactylus), eight two-toed sloths
(Choloepus didactylus), three Brazilian porcupines (Coendou prehensilis), and three silky anteaters (Cyclopes
didactylus). In addition, two lesser anteaters (Tamandua tetradactyla) – a mother and baby – were seen but
not rescued. Due to their lack of speed and inability to escape, it is likely that almost all of the pale-throated
sloths in the forested plot were captured during the thirty-day period of clear-cutting. Comprising 91% of
the total rescued animals, the 137 B. tridactylus included 61 males, 56 females, 15 juveniles, and ve adults
that could not be sexed. Data on body mass, length, and other features reveal a population of reasonably
healthy but smaller animals at a population density of 20.1 animals/ha that far exceeds any previous reports
for this species.
Keywords: habitat fragmentation, Pilosa, population density, urban mammal, urbanophilic, Xenarthra
Inesperada alta densidad de perezosos de tres dedos (Bradypus tridactylus) en un parche de bosque urbano en
Paramaribo, Suriname
Resumen En octubre de 2012, voluntarios asociados a Green Heritage Fund Suriname organizaron un res-
cate de mamíferos arbóreos desplazados durante la deforestación de una parcela de 6,8 ha situada al no-
roeste de Paramaribo. Los animales rescatados incluyeron 137 perezosos de tres dedos (Bradypus tridactylus),
ocho perezosos de dos dedos (Choloepus didactylus), tres puercoespines brasileños (Coendou prehensilis) y tres
hormigueros sedosos (Cyclopes didactylus). Además fueron vistos dos osos meleros (Tamandua tetradactyla) –
una madre y su cachorro – aunque no fueron recogidos. Debido a su baja velocidad y su incapacidad para
esconderse, es probable que prácticamente todos los animales de la parcela fueran capturados durante el
período de tala de 30 días. Bradypus tridactylus representó el 91% del total de los animales rescatados; de los
137 individuos, 61 eran machos, 56 hembras, 15 juveniles y cinco adultos que no pudieron ser sexados. Los
datos colectados sobre peso corporal, longitud y otras características muestran una población de animales
razonablemente sanos pero más pequeños, con una densidad poblacional de 20,1 animales/ha que excede
con creces a la de cualquier reporte previo de esta especie.
Palabras clave: densidad poblacional, fragmentación de hábitat, mamíferos en áreas urbanas, Pilosa,
Xenarthra
26 Edentata 17: 25–33 (2016)
Introduction
Although well known for their “slothful” nature,
it is only recently that more research has been con-
ducted on aspects of the natural history of three-toed
sloths, and in particular the subject of this study, the
pale-throated three-toed sloth, Bradypus tridactylus.
Of the four extant species of three-toed sloths only
two are widely distributed. These are the brown-
throated three-toed sloth, B. variegatus (Soares &
Carneiro, 2002; Bezzera et al., 2008; Hayssen, 2010),
and the pale-throated three-toed sloth, B. tridactylus
(Hayssen, 2009a). The other two species, the maned
sloth, B. torquatus (Hayssen, 2009b), and the pygmy
sloth, B. pygmaeus (Hayssen, 2008), have very lim-
ited distributions. In their reevaluation of the dis-
tribution of B. tridactylus and B. variegatus, Moraes-
Barros et al. (2010) restricted the distribution of the
pale-throated three-toed sloth, B. tridactylus, to the
Guiana shield region (from middle Venezuela across
the coast of the three Guianas to the northern side
of the Amazon River; see Fig. 1 in Moraes-Barros et
al. 2010).
Because they are generally stationary, freeze in
response to loud sounds, avoid predators by mov-
ing slowly, and are extremely silent when mak-
ing rare and careful movements (Chiarello, 2008),
sloths are dicult to locate, even when they are
gregarious in anthropogenic habitats (Silva et al.,
2013). Consequently, studies of the ecology, abun-
dance, and density of B. tridactylus are lacking.
However, rescue operations may provide the best
and most realistic estimates of B. tridactylus pop-
ulation density (Laufer et al., 2012), and provide a
unique opportunity to inventory, sample, and study
species normally hard to observe or capture (Vié,
1998). A rescue eort in Paramaribo, Suriname in
October 2012 presented a unique opportunity to col-
lect data on the numbers and demography of pale-
throated three-toed sloths. Being able to collect all
of the individuals present in the study area allowed
us to assess demographic and physical attributes of
an entire B. tridactylus population in an urban, con-
tiguous, relatively undisturbed, and isolated forest
patch.
Materials and Methods
Between 22 October and 22 November 2012
volunteers associated with the Green Heritage Fund
Suriname rescued sloths from the Theo Stolk prop-
erty, a 6.8 ha forest patch, which was being clear-cut
to establish a pasture for cattle. Located in the north
of Paramaribo, the capital city of Suriname (5°50’N,
55°10’W), the typical coastal swamp forest was sur-
rounded on all sides by recent housing develop-
ments and pastureland (Fig. 1). Notable vegetation in
Figure 1. Sloths and other arboreal mammals were rescued from a forested plot (Land of Theo Stolk) in Paramaribo, Suriname that was
clear-cut in 2012. Surrounding areas are either developed or pastureland. Satellite photo via Google Earth.
27
M. Pool et al. : Sloths in the city: unexpectedly high density of pale-throated three-toed sloths (Bradypus tridactylus)...
the forest included the trees Hura crepitans, Triplaris
surinamensis, and Virola surinamensis, as well as
Cecropia spp., found particularly at the forest edges,
Inga spp., Ceiba pentandra, and dierent types of
vines, among which Ipomoea spp. dominated.
The patch of forest was cleared using a
Caterpillar 215B hydraulic excavator that pushed the
trees over. When an animal was spotted, the opera-
tor would proceed slowly so that the animal would
not be hurt and could be removed by volunteers
from the treetop that was now on the ground. The
animals were either placed in cloth bags or kennels.
Although every eort was made for the safety of the
animals, stress was undoubtedly an issue. This was
addressed after animals were transported to a tem-
porary holding site. There we recorded the hydra-
tion condition of all rescued animals (Table 1) and
each animal, regardless of condition, was oered
water with Rescue Remedy drops (Bach, Thousand
Oaks, CA, USA), using pipettes or injection syringes
without needles to reduce stress. All rescued animals
were given a unique identication code that identi-
ed the species, the date, and a sequential number
indicating the order in which the animal was rescued
that day. Although eight two-toed sloths (Choloepus
didactylus), three Brazilian porcupines (Coendou pre-
hensilis), and three silky anteaters (Cyclopes didac-
tylus) were rescued, the only species for which ex-
tensive data were recorded was B. tridactylus. Those
data are presented and discussed here.
Adult male pale-throated three-toed sloths have
a dorsal marking or speculum, as it is called, that
consists of an orange–yellow patch combined with
a black central streak and sometimes black spots
(Beebe, 1926; Anderson & Handley, 2001; Hayssen,
2009a; M. Pool, pers. obs.). At about one year of
age the development of an apparently individually
unique speculum allows for dierentiation of the
sex of individuals (M. Pool, pers. obs.). Prior to this,
gender assignment is particularly challenging be-
cause of the lack of any sexually dimorphic charac-
teristics (Martinelli et al., 2010). Because the smallest
identiable male in our study weighed 1.3 kg, any
animal below that mass was classied as a juvenile
and not sexed. Because of uncertainty about the
presence of a speculum, two animals that exceeded
1.3 kg were classied as adults of unknown sex and
not included in the demographic analysis.
Animals considered juveniles were weighed
using a Plateau digital kitchen scale (Soehnle,
Backnang, Germany) while adult body mass was
determined using a calibrated analog shing scale
(Salter Model 235, West Bromwich, UK). Animal
body length was determined by laying a measuring
tape along the spine from the tip of the tail to the tip
of the nose. The reported sample sizes vary in the
results because we were unable to collect full sets of
data for one juvenile, two adults of unknown sex, 15
adult males, and 12 adult females. Although one an-
imal (BT2303) was injured during the clear-cutting,
no injuries occurred during the data collection pro-
cess. Two animals (one male and one unidentied)
were found dead at the end of the rescue eort; we
noted their presence in the population but did not
record other measurements. Each animal was pho-
tographed with its unique identication code to pro-
vide a complete record of all animals rescued (135)
or found dead (2). Pictures taken, either during data
collection or upon release, included at least one fron-
tal face picture, one side face picture and one dorsal
picture of the complete animal.
Because of the numbers of animals that had
to be quickly processed and because of the lack of
experience of many volunteers, we were unable to
take measurements from all animals and limited
the number of body-size measurements to a set that
could be rapidly and accurately measured. Skull
size was determined using calipers to measure
width from ear to ear. Thorax width was measured
on the dorsal side of the sloth; the arms of the ani-
mal were slightly lifted so that the calipers could be
placed from armpit to armpit. The fore palm length
of one arm was measured from Carpal I to the inset
of the nails. Finally, the back palm of one leg was
measured from the posterior edge of the heel bone
to the inset of the nails. Because of handling dicul-
ties, we did not attempt to ensure that an equal num-
ber of the latter two measurements were measured
on the right and left sides. Recorded data sets were
transcribed and entered into an Excel (Microsoft
Table 1. Determination of hydration condition. Hydration condition was assessed by checking the animal’s tongue, nose, and eyes, as
well as whether it was willing to drink.
Descriptor Denition
Hydrated Skin on nose looks smooth, healthy and warm, and has a dark black shiny color.
Eyes are clear and edges of eyelids are smooth. Mouth is hydrated and tongue is wet.
Slightly dehydrated
Skin on nose looks smooth with thin white cracks in the black skin, which pulls on the edges. Eyes are clear
and edges of eyelids are slightly cracked and dirty.
Mouth is hydrated and tongue is wet.
Dehydrated
Skin on nose looks dry and is cracked, and black skin has whitish appearance. Skin pulls at the edges. Eyes
are foggy and edges of eyelids are cracked, and contain dark brown mucus. Mouth is dry, and tongue is
covered in whitish lm.
28 Edentata 17: 25–33 (2016)
Corporation, Redmond, USA) spreadsheet for anal-
ysis. Signicance for statistical tests using chi-square
and t- tests was determined at the p=0.05 level.
Urbani & Bosque (2006) proposed a standard-
ized framework (updated by Silva et al., 2013) for
categorizing the behavior of sloths in their natural
habitat. Because we recorded behaviors during the
wildlife rescue operation as animals were handled
and measured, our behavioral categories are not di-
rectly comparable. Based on extensive experience
with sloth behavior in rescue situations, animal re-
actions to capture and handling were recorded prior
to and during handling, but not afterwards when
animals were housed together until release (approx-
imately two to three days for healthy animals). The
behavior of each animal was categorized as calm,
restless, afraid, or aggressive. Calm corresponded to
normal behavior, in which a sloth did not show any
signs of agitation and would just sit calmly looking
around in a stationary, resting position (similar to
the huddle position used by Urbani & Bosque, 2006;
Silva et al., 2013). Restless was assigned to animals
moving around in the cage, observing the surround-
ing area, or trying to stick either forearms or head
through the cage in an apparent attempt to escape.
Animals categorized as afraid moved away from
handlers, ducked their heads in between their fore-
arms, or wailed. Aggressive animals tried to hook,
bite, hued or blew at handlers.
Results
Of the 135 rescued and two deceased pale-
throated three-toed sloths (B. tridactylus), 61 were
males, 56 females, 15 juveniles, and ve adults of
unknown sex. Only one mother – ospring pair was
captured. All remaining juveniles were found alone.
Overall population density of the pale-throated
three-toed sloths at the site was 20.1 animals/ha,
comprised of 7.0 males/ha, 8.2 females/ha, and 2.2
juveniles/ha. The ratio of males to females, 1.09:1
(N=117), was not signicantly dierent from 1:1
(X2=0.21, df=1, p=0.644).
Average adult female body mass was signi-
cantly greater than that of adult males (t=2.06, df=88,
p=0.042; Table 2). Average adult body mass was more
than three times that of juveniles (Table 2). Female
body length was also signicantly greater than that
of adult males (t=2.16, df=89, p=0.034; Table 2), and
both females and males were larger than juveniles
(Table 2). The relationship of body mass to body
length did not appear to dier between males and
females (Fig. 2).
Adult females did not dier signicantly from
adult males in the size of the skull (t=0.39, df=97,
p=0.69), thorax (t=0.46, df=80, p=0.64), fore palm
(t=0.09, df=87, p=0.36), or back palm (t=0.22, df=97,
p=0.83; see Table 3).
For two-thirds of the animals (72) hydration
condition was considered good; 14 were reported as
slightly dehydrated, and 18 as dehydrated. No data
on hydration were collected for 26 animals that were
only photographed and not measured, as well as for
three others.
Of the 108 behaviorally assessed sloths, almost
two thirds were calm upon capture (68; 31 males, 26
females, 10 juveniles, 1 unknown). Of the remaining,
Table 2. Body mass and length of rescued pale-throated three-toed sloths, Bradypus tridactylus, by sex and age (Mean±sd and range are
shown). Data were not recorded for all rescued animals.
Mass (kg) Length (cm)
N Mean (sd) Range Mean (sd) Range
Male 46 3.23 (0.68) 1.30–4.80 56.40 (4.33) 44.5–65.0
Female 44 3.52 (0.65) 2.20–4.95 58.23 (3.70) 49.5–66.0
Juvenile 15 0.98 (0.32) 0.55–1.87 36.35 (3.06) 30.5–40.5
Unknown 2 3.00 (1.41) 2.00–4.00 55.75 (6.72) 51.0–60.5
Table 3. Mean, standard deviation (sd), and minimum and maximum size of skull, thorax, fore palm and back palm (cm) of rescued
pale-throated three-toed sloths, Bradypus tridactylus, by sex and age. Data were not recorded for all rescued animals as well as
for the fore and back palm for one rescued female and one rescued male.
Skull Thorax Fore palm Back palm
N Mean (sd) Range Mean (sd) Range Mean (sd) Range Mean (sd) Range
Male 46 4.54 (0.30) 3.7–5.4 8.31 (0.95) 5.6–10.6 6.80 (0.88) 4.9–8.7 8.76 (0.94) 6.0–10.2
Female 43 4.58 (0.37) 4.0–5.7 8.44 (0.71) 7.0–9.5 6.91 (0.63) 5.5–8.0 8.97 (0.90) 6.5–10.5
Juvenile 15 3.49 (0.33) 3.0–4.2 4.79 (0.71) 3.5–6.2 3.91 (0.82) 3.0–6.0 5.71 (0.73) 4.5–7.0
Unknown 2 4.45 (0.07) 4.4–4.5 8.40 (1.13) 7.6–9.2 6.00 (0.71) 5.5–6.5 6.75 (1.06) 6.0–7.5
29
M. Pool et al. : Sloths in the city: unexpectedly high density of pale-throated three-toed sloths (Bradypus tridactylus)...
six were categorized as restless (2 males, 4 females,
0 juveniles), 17 as afraid (7 males, 7 females, 2 ju-
veniles, 1 unknown), and 17 as aggressive (7 males,
7 females, 3 juveniles). Behavioral assessment of
males (N=47) and females (N=44) was not signi-
cantly dierent (X2=1.01, df=3, p=0.799). Because of
small sample size, juveniles could not be compared.
Discussion
Studies reporting abundance and density esti-
mates of B. tridactylus are scarce, perhaps because
stationary sloths are hard to detect in the forest can-
opy (Laufer et al., 2012), even by trained observers
(Chiarello, 2008). Our estimate of 20.1 animals/ha
represents the greatest documented population den-
sity of this species. The highest densities previously
reported were 12.7 animals/ha (Réus & Martins
de Souza, 2007) and 2.2 animals/ha (Carmo, 2002),
both for urban populations in Manaus, Brazil. Other
estimates are considerably lower (Table 4). For ex-
ample, a rescue operation during the lling of the
Petit Saut dam yielded 0.02 animals/ha along the
Sinnamary River in French Guiana (Taube et al.,
1999). Unfortunately, because juveniles and their
mothers were recorded as single individuals, and
because the number of maternal-ospring pairs was
not provided, exact comparison with our data is
not possible. However, recalculation of our data to
match Taube et al.’s (1999) methodology by “pairing”
juveniles with females yields an estimate of 108 an-
imals and a density of 17.9 animals/ha—still orders
of magnitude higher. Taube et al.’s (1999) comment
that approximately 23–24% of both B. tridactylus and
C. didactylus were females carrying young does not
substantially aect the density.
Other studies provide density estimates that
are similarly low. For instance, a non-rescue study
in Guyana by Beebe (1926) reported a density of
0.3 animals/ha. The results of the Conservation
International Rapid Biological Assessment in south-
ern Suriname (Gajapersad et al., 2011) did not in-
clude any mention of sloths—a surprising absence
given that the mammal surveys included a variety
of methods, e.g., camera traps, scat, and animal track
searches, and visual and aural observations. Laufer
et al. (2012) reported a density of 0.002 animals/
km along three rivers in the northern Amazonia of
Brazil near French Guiana. Although river transect
methodology may not be directly comparable, if
we generously allow a 100 m visual eld along the
river’s edge, the results translate to densities of 2
animals/ha. A perhaps more realistic visual eld of
10 m would result in a much lower density of 0.2
animals/ha. Population densities for the closely-re-
lated brown-throated three-toed sloth, B. variegatus,
range from 0.0001 animals/ha (applying the same
translation to the river transect date of Haugaasen &
Peres, 2005) to 26 animals/ha (Table 4). Interestingly,
densities for both B. tridactylus and B. variegatus
were higher in urban areas than in natural habitats
(Table 4).
Laufer et al. (2012) argued that wildlife rescue
operations will always provide a better estimate of
sloth density because the majority of animals are seen
Figure 2. Body length by mass correlations for pale-throated three-toed sloths, Bradypus tridactylus, by sex and age.
30 Edentata 17: 25–33 (2016)
and rescued, whereas the cryptic nature of sloths will
likely result in underestimates of density under natu-
ral conditions. Similarly, Núñez-Regueiro et al.’s (2015)
report on detection issues for large, more mobile, and
presumably less cryptic mammals in mixed forest-ag-
ricultural areas in Argentina further underscores the
problem of accurately estimating population density.
In our study, the unique opportunity oered by the
animal rescue eort to determine the density of the B.
tridactylus population by capturing or observing vir-
tually every animal present might, by itself, have re-
sulted in the “higher than normal” estimate. If so, then
perhaps earlier studies simply missed large numbers
of these extraordinarily cryptic animals (Chiarello,
2008; Voirin et al., 2009) or perhaps the paucity of com-
prehensive eld studies just did not include such an
aggregated population. Regardless, our results sug-
gest that past studies may have substantially under-
estimated pale-throated three-toed sloth population
densities. If true, then the present study in Paramaribo
may provide a much more realistic estimation of sloth
densities than those previously published. However,
we cannot discount several alternative possibilities
that alone or together might have generated this
high population density, especially given similarly
high densities observed in other urban areas (Réus
& Martins de Souza, 2007; Manchester & Jorge, 2009;
Silva et al., 2013; Queiroz et al., 2015).
First, it is possible that historical clear-cutting of
the surrounding region may have provided oppor-
tunities for the establishment of early successional
plant species like Cecropia and sweet potato vines
(Ipomoea spp.)—both of which were seen on the site.
The presence of these preferred food species of pale-
throated three-toed sloths could provide greater
than normal food resources and, in turn, lead to
higher than normal densities (Réus & Martins de
Souza, 2007). However, we noted that the site was
mostly an intact swamp forest with Cecropia located
only along the edges. Thus, Cecropia was neither
abundant in the forest interior nor more abundant
than usual in the surrounding areas. We also noted
that individuals of this population were slightly
smaller than those observed elsewhere, suggesting
the possibility of limited food.
Table 4. Summary of studies with population density estimates (individuals/ha) for Bradypus tridactylus and B. variegatus for a variety
of eld methodologies and habitats. * Density estimated from linear conversion; see text for details.
Species/Location Density
(ind/ha)
Method/habitat Reference
B. tridactylus
Kwamalasamutu Region, Southwestern
Suriname 0Rapid Biological Assessment/ Lowland
rainforest Gajapersad et al. (2011)
Petit Saut dam, French Guiana 0.02 Rescue/ Primary lowland rainforest Taube et al. (1999)
Floresta Nacional do Amapá (FLONA),
Northern Amazonia, Brazil 0.2* River transect/ Rainforest Laufer et al. (2012)
Kartabo, Bartica District, Guyana 0.3 Observations/ Lowland rainforest Beebe (1926)
Universidade Federal do Amazonas,
Manaus, Brazil 2.2 Grid/Urban forest fragment Carmo (2002; cited in Réus &
Martins de Souza, 2007)
Bosque da Ciência, Manaus, Brazil 12.7 Transect/Urban forest fragment Réus & Martins de Souza (2007)
Paramaribo, Suriname 20.1 Rescue/ Urban coastal swamp forest
fragment This study
B. variegatus
Rio Puru, Brazilian Amazonia 0.0001* River transect/ Terra rme and varzea
forests Haugaasen & Peres (2005)
Gorgona Island, Colombia 0.026 Transect/Rainforest Garcés-Restrepo et al. (2014)
Arboletes, Antioquia, Colombia 0.6–4.5 Transect/Tropical dry forest Acevedo-Quintero et al. (2011)
Isla Palma, Valle, Colombia 0.7 Transect/Rainforest Carvajal-Nieto et al. (2013)
Mamirauá Ecological Station, Ama-
zonas, Brazil
2.2–6.7 Transect/Rainforest Queiroz (1995; cited in Mo-
raes-Barros et al., 2014)
Barro Colorado Island, Panama 8.5 Observations/
Lowland rainforest Montgomery & Sunquist (1975)
Praça Tiradentes, Teólo Otoni City,
Minas Gerais, Brazil 10–12 All animals identied/Urban park Manchester & Jorge (2009);
Queiroz et al. (2015)
Botanic Garden Benjamin Maranhão,
Paraiba, Brazil 26 Observations/Urban forest fragment Silva et al. (2013)
31
M. Pool et al. : Sloths in the city: unexpectedly high density of pale-throated three-toed sloths (Bradypus tridactylus)...
A second possibility is that the lack of predators
in this “urban” location, e.g., harpy eagles, arboreal
cats, large snakes, etc. might allow for a substan-
tial increase in population size (Réus & Martins de
Souza, 2007). While this hypothesis may be possible,
the loss of natural predators could be oset by an
increase in non-natural predators (Grant et al., 2011).
More data are needed to resolve this issue.
Third, density may be linked to rates of encoun-
ters and matings between males and females. Thus,
higher density may foster population growth, espe-
cially in the absence of limiting resources or preda-
tors (Réus & Martins de Souza, 2007). The fact that
the population at Paramaribo was comprised of
slightly smaller, perhaps younger, individuals could
support this. However, demographic data, includ-
ing growth rates, encounter rates, mating success,
and population density, are needed to determine
whether animals are smaller because of age or re-
source limitation.
Fourth, high density may have resulted from
contraction and migration of animals from sur-
rounding areas—an artifact of urbanization collaps-
ing a more dispersed and less dense sloth popula-
tion inward to the only remaining forested refuge.
The forested areas immediately east and west of
the Stolk property were clear-cut between 2004 and
2009. It is certainly plausible that animals moved
into the remaining undisturbed forest and survived
until the present study.
It is also possible that all of these factors could
operate together. Thus, sloth densities in the wild
may be much higher than previously recorded, and
urbanization processes may have the potential to
articially increase them further. Regardless of the
causal factor(s), the density of this sloth population
is orders of magnitude higher than previously re-
ported for this species, suggesting that sloths may
be an interesting and important component of trop-
ical urban landscapes. Indeed, given their densities
in urban areas (Table 4), sloths may well be consid-
ered a tropical, urbanophilic species (Grant et al.,
2011). The existence of this high population density
of B. tridactylus in an urban forest strongly arms
the need to recognize that the establishment of green
spaces in cities in the tropics is likely to encourage
species conservation. Further investigations are
warranted.
The 1.09:1 sex ratio at Paramaribo is similar
to that reported by Hayssen (2009a) and Jorge et
al. (1985). We found adult males to be smaller than
adult females, also as others have reported (Beebe,
1926; Richard-Hansen et al., 1999; Hayssen, 2009a).
However, both males and females were smaller at
our study site than those reported from elsewhere.
For example, Wetzel (1985) reported weights of 3.93
kg for males and 4.62 kg for females, both of which
are higher than our observations of 3.23 and 3.52 kg,
respectively. This dierence may be a function of
better sampling in our study, with more individuals
measured, but could result from reduced availabil-
ity of resources (food, space, etc.) at high density, or
a dierence in age structure such that our popula-
tion consisted of more young individuals. Another
reason for greater female body mass could also be
pregnancy. Because of injury, one female that had to
remain for a longer period at the shelter was found
to be pregnant when she miscarried at the end of
December. However, we were unable to determine
the reproductive status for any of the other females.
Similarly, like mass, body length and skull size of
Paramaribo pale-throated three-toed sloths were
generally less than that reported for other popula-
tions. Again, these dierences could be either age or
nutrition related.
Males, when they can see one another, are often
aggressive (Greene, 1989). Likewise, females with
young tend to be aggressive and protective when
sharing the same tree (Soares & Carneiro, 2002). The
fact that we did not observe dierences in the be-
haviors of newly-captive males and females could
reect similarities in their natural behavioral pro-
les, but it could also be a result of disturbance due
to clear-cutting of the forest. Thus, clear-cutting, fol-
lowed by collection, may have resulted in behavior
not typically observed in the wild. While Silva et al.
(2013) utilized a similar framework to ours, we are
hesitant to compare their wild and our captive ani-
mals because they studied B. variegatus. Use of our
framework to assess the behavior of B. tridactylus
in wildlife rescue situations may aid in assessing
individual captive animal responses to disturbance
and to interaction with humans, thereby providing
a means to evaluate the animal’s suitability with re-
spect to translocation in the short or medium term,
and improving subsequent survival at the new site.
Acknowledgements
We thank all the many GHFS volunteers for
their obvious eort and dedication to this sloth
rescue project, but also for their long-standing and
largely unrecognized eorts to promote conserva-
tion and preservation throughout Suriname. We
also thank Natuurbeheer for permission to work
with the animals (Suriname Forest Service – Nature
Conservation Division Permit 10593).
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