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Distance sampling is a widely used technique. However, the influence of several factors on the observations when using this technique, such as speed of the observers, microhabitat, weather, and method of detection, are still unknown. We aimed to evaluate the effect of various factors in the encounter rates and frequency of detection of mammalian species using the distance sampling technique with transects in an Atlantic Forest area, Ilha Grande, state of Rio de Janeiro, Brazil. We evaluated the effects of the forms of detection, sighting time, and the climate conditions on mammals samplings. Between December 2003 and May 2005, 128 transects were undertaken by a single observer, totalling 401.3 km and 382 hours. We recorded 163 individuals of nine species of mammals. Several factors affected our study using the distance sampling by linear transects, which include the animal activity period (i.e., object of study), followed by climate conditions, and transect location. We also found lower encounter rates in transects located in the north part of the island, because of the interference of tourists and the poaching pressure, which must be associated with the higher human densities in the north of the island that would inhibit the presence of certain species. This study highlights the importance of considering these variables when estimating mammal population sizes using distance sampling technique. © 2017, Universidade Federal do Rio de Janeiro (UFRJ). All rights reserved.
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Oecologia Australis
21(4): 422-430, 2017
10.4257/oeco.201 7.2104.06
Bruno Cascardo Pereira1, Átilla Colombo Ferreguetti2* & Helena Godoy Bergallo2
1 Instituto Chico Mendes de Conservão da Biodiversidade (ICMBio). Parque Nacional Serra das Lontras, Ilhéus, BA, Brasil. CEP:
45 653-970
2 Universidade do Estado do Rio de Janeiro (UERJ), Instituto de Biologia Roberto Alcantara Gomes, Departamento de Ecologia. Rua o
Francisco Xavier, 524, PHLC 220, Maracanã, Rio de Janeiro, RJ, Brasil. CEP: 20559-900
E-mails: bruno.pereira@ ib, atilla.ferreguetti@g,
Distance sampling is a widely used technique. However, the influence of several factors on the observations when
using this technique, such as speed of the observers, microhabitat, weather, and method of detection, are still
unknown. We aimed to evaluate the effect of various factors in the encounter rates and frequency of detection of
mammalian species using the distance sampling technique with transects in an Atlantic Forest area, Ilha Grande,
state of Rio de Janeiro, Brazil. We evaluated the effects of the forms of detection, sighting time, and the climate
conditions on mammals samplings. Between December 2003 and May 2005, 128 transects were undertaken by a single
observer, totalling 401.3 km and 382 hours. We recorded 163 individuals of nine species of mammals. Several factors
affected our study using the distance sampling by linear transects, which include the animal activity period (i.e.,
object of study), followed by climate conditions, and transect location. We also found lower encounter rates in
transects located in the north part of the island, because of the interference of tourists and the poaching pressure,
which must be associated with the higher human densities in the north of the island that would inhibit the presence
of certain species. This study highlights the importance of considering these variables when estimating mammal
population sizes using distance sampling technique.
Keywords: Atlantic Forest; distance sampling; linear transects; poaching.
Estimates of population size and density are
fundamental to any effort of conser vation of
endangered species. These estimates provide basic
support for several purposes related to conservation
programs and political decisions, such as to evaluate
habitat loss, to identify priority areas for conservation,
to evaluate minimum viable populations, to determine
the conservation status of a target species, among
others. (e.g., Tomas et al. 2004, Cardillo et al. 2006,
Cunha & Loyola 2011, IUCN 2015, Buckland et al.
2016). However, long-term studies that monitor
population sizes are rare for most taxa, including
endangered species, especially in the Neotropics
(Cardillo et al. 2006, Cunha & Loyola 2011, IUCN
Among the many existing techniques to estimate
density and population size (e.g., Capture-Mark-
Recapture methods; Seber 1986, Sutherland 2006), the
distance sampling technique is one of the most
frequently used (Buckland et al. 2001, 2004). This
technique is based on the detection of animals along
transects (e.g., linear transects; Buckland et al. 2001).
This method is often used to assess populations of
medium and large mammals in tropical forests (Peres
1999, Chiarello 2000, Gonzalez-Solis et al. 2002, Galetti
et al. 2009, Desbiez et al. 2010, Gopalaswamy et al.
2012, Norris et al. 2012, Ferreguetti et al. 2015, 2016,
2017). The distance sampling is a simple and
inexpensive method that can cover large areas in a
short period of time (Cullen Jr. & Valladares-Pádua
1997, Cullen Jr. & Rudran 2004), with the assumption
that target species can be directly observed and there
are no misidentifications (Buckland et al. 2001). In
the distance sampling technique, the main estimated
parameter is the density of a population in a given study
area. Furthermore, this method is also considered more
Mammalian Detectability in Transect Surveys 423
Oecol. Aust., 21(4): 422-430, 2017
accurate than methods that do not account for imperfect
detection, even if the assumption that there are no errors
in the distance measurements is violated (Buckland et
al. 2001).
Distance sampling considers the imperfect
detection of individuals of the target species during
trans ect surve ys (Ma ckenzi e et al. 200 6),
considering that not all individuals are recorded. The
individuals that are exactly on the transect line are
recorded, so that the detection probability decreases
as the object distance increases from the observer
(Buckland et al. 2001, 2004). In general, distance
sampling involves a series of models, which adjust
detection functions for the observed distances, and
uses these functions to estimate the proportion of
objects missed during sampling (Buckland et al.
Despite being a technique widely used over the
years, information on how different factors (i.e., speed
of observers, microhabitat, weather, method of
detection) influence observations while using distance
sampling are still scarce. Mateos (2002) noted that
altitude was the only variable that influenced the
distribution of mammalian species in the Atlantic
Forest. However, factors such as sighting time and
speed of the observer had a quantitative effect on the
encounter rate.
We aimed to evaluate the effect of various
factors on the observations of mammalian species
when conducting distance sampling technique using
transects in an Atlantic Forest area. We tested how
the way in which and when (sighting time) the study
objects were detected affected the encounter rates of
mammals. We also tested the effects of climate
conditions (weather and wind) on the frequency of
detections. We tested four hypotheses: (1) encounter
rates will be higher for larger species during daytime
observations, because it is easier to detect large
individuals; (2) climatic conditions will negatively
influence the detection of species, because individuals
would avoid extreme weather conditions; (3) encounter
rates will be higher in southern than northern parts of
the island, because the northern side of the island is
more densely populated; and (4) mid-sized mammals
will be more abundant in less-disturbed areas in the
island’s south than in the north.
Study area
Our study was carried out in the Ilha Grande
State Park (PEIG hereafter) and in the Biological
Reserve Praia do Sul (ReBio hereafter), in Ilha
Grande island off the southwestern coast of Rio de
Janeiro State, Brazil (Figure 1). PEIG is the second
largest insular Biological park in Brazil and covers
120 km², over half (62%) of the island, which has
193 km². ReBio covers an area of 35.02 km² (INEA
2010). The climate is hot humid tropical without a
dry season. Ilha Grande is the top of a submerged
mountain and has two dominant types of topography,
mountain and coastal plain (INEA 2010). Mountain
peaks occur in the center of the island. Almost half
of the area (47%) is covered by dense, relatively
pristine Atlantic rainforest. Disturbed forests, in an
advanced successional stage, are the second major
habitat type (43%). The remaining areas comprise
rocky outcrops with herbaceous vegetation (7%), salt
marshes, mangroves and beaches (2%). Human
settlements occupy 1% of the island (Alho et al. 2002)
and is concentrated around the northern coastline of
Ilha Grande Bay and in Abraão village. These areas
are undergoing much anthropic disturbances due to
tourism development, with new buildings, port
facilities and expanding infrastructure (Alho et al.
Sampling design
During the period between December 2003
and May 2005, 128 transects were performed,
totalling 401.3 km walked in 382 hours of effort.
The transects were surveyed in five existing dirt
trails in Ilha Grande in order to minimize the impact
of opening new trails (Figure 1). Two of those trails
were located in the northern part of the island,
connecting Abraão Village to Palmas and Feiticeira
beaches (respectively T01 and T02). The other three
trails were on the south side of the island, connecting
Dois Rios Village to Caxado and Parnaióca
beaches, and to Jararaca locality (respectively T03,
T04 and T05). Transects ranged in length from 2.1
424 Pereira et al.
Oecol. Aust., 21(4): 422-430, 2017
Figure 1. Transect locations (T01 to T05) of the mammal sampling in Ilha Grande, state of Rio de Janeiro, Brazil. The black
triangle indicates the location of Abraão Village.
Table 1. Characteristics of transects, number of times each transect was walked (N samples), total kilometers walked in Ilha
Grande, state of Rio de Janeiro, Brazil.
to 6.7 km (Table 1). All transects were marked at
50 m intervals. We recorded for each transect the
evidence of poaching (e.g., hunting traps), and a
Human density index (measured by the number of
inhabitants in the nearest village divided by the
distance to the neares t human settlement) to
compare transects located in each region of Ilha
Grande (north and south) (Table 1).
Transect T01 T02 T03 T04 T05 Total
Extension (km) 2.1 2.3 2.7 6.7 2.1 15.9
N samples
27 23 27 24 27 128
Total Km walked 56.7 52.9 72.9 160.8 56.7 401.3
Island region North North South
South South
Evidence of poaching Yes Yes Yes No No
Human density index 405 412 444 134 103
Minimum altitude (m) 0 10 10 0 20
Maximum altitude (m) 190 160 170 170 250
Average altitude (m) 125.1 106.3 106.4
81.3 136.9
Mammalian Detectability in Transect Surveys 425
Oecol. Aust., 21(4): 422-430, 2017
Transects were walked by the observer during
the activity time of the animals at dawn and twilight
(Chiarello 2000). Transects were walked at an
average speed of 1.1 km/h (± 0.5), and under different
climatic conditions divided into three categories by
weather (clear sky, cloudy or rainy) and four
categories of wind speed (no wind, weak, medium
and strong). For each transect walked, the following
information were recorded: sample size, number of
transect, date, start time, end time, weather, and wind
The A/T (animal x transect) perpendicular
distance was measured considering the exact location
where the animal was first detected. In the case of
animals that used the tree layer, the distance was
measured from the trunk of the tree where the animal
was observed. When a group was observed, we
considered the first animal detected in the group.
Whenever an animal was observed, the following
information was recorded: sighting time, species, A/
T distance, number of individuals (group size), location
in the transect, and form of detection (visual or
hearing). Hearing detections were registered by
vocalizations (warning cries), noise caused by
movements in the vertical strata (movements in twigs
and branches), and noise caused by movements in
the litter (movements on the ground). Visual
detections were registered for animal movements
without any associated noise and by the reflection of
light from flashlights in their eyes at night. Sighting
time was divided into six groups: group 1 (4:00 to
6:00 h), group 2 (06:01 to 08:00 h), group 3 (08:01 to
10:00 h), group 4 (16:00 to 18:00 h), group 5 (18:01 to
20:00 h) and group 6 (20:01 to 23:00 h).
We used the encounter rate as the dependent
variable to evaluate the differences between the forms
of detection and the sighting time of the mammalian
species. Encounter rates were calculated using the
number of individuals (or groups) by the total length
walked in the transects, and were expressed as the
number of individuals or groups every 10 km walked.
We used the frequency of detection (i.e., which
consists of presence and absence data, that is 1 for
detected or 0 for not detected) of each species as
the dependent variable to evaluate the effects of the
climate conditions, because it was not possible to
estimate encounter rates for each time that the
transect was walked.
Data analysis
We assessed the relationship between the
forms of detection on mammalian species encounter
rates with a two-way analysis of variance (ANOVA)
(forms of detection x species). When our models
were significant we used Tukey post-hoc tests ( =
0.05) to compare means. We used Kruskal-Wallis
test when the ass umptions of normali ty and
homoscedasticity were not met, which was the case
of the sighting time of each species. We used a chi-
square test to evaluate the effect of climate conditions
on the frequencies of detection for the most frequent
species using each time that the transect was walked.
As there were cells with values below five, we used
the Cochran correction in this analysis (Cochran
1977). All statistical analyses were performed in
SYSTAT 11® program.
We recorded 163 individuals of nine species
of mammals in 382 h of observation: the common
opossum Didelphis aurita (Wied-Neuwied, 1826)
(Didelphimorphia, Didelphidae; n = 21), the nine-
banded armadillo Dasypus novemcinctus Linnaeus,
1758 (Cingulata, Dasypodidae; n = 13), the brown
howler monkey Alouatta guariba (Humboldt, 1812)
(Primates, Atelidae; n = 16), the common marmoset
Callithrix jacchus (Linnaeus, 1766) (Primates,
Callitrichidae; n = 25), the spotted paca Cuniculus
paca (Linnaeus, 1766) (Rodentia, Cuniculidae; n =
35), the agouti Dasyprocta leporina (Linnaeus,
1758) (Rodentia, Dasyproctidae; n = 4), the
southeastern squirrel Guerlinguetus brasiliensis
(Thomas, 1901) (Rodentia, Sciuridae; n = 36); the
capybara Hydrochaeris hydrochaeris Linnaeus,
1766 (Rodentia, Caviidae; n = 2), and the orange-
spiny hairy dwarf porcupine Coendou spinosus (F.
Cuvier, 1823) (Rodentia, Erethizontidae; n = 10).
The number of species stabilized around an effort
of 167 h. The T04 transect was the only one where
all nine species were observed. T01 and T02
426 Pereira et al.
Oecol. Aust., 21(4): 422-430, 2017
transects had the lowest richness, with only three
species observed: D. aurita, G. brasiliensis, and
C. jacc hus (Ta ble 2) . Th e tota l avera ge of
mammal’s encounter rate was 4.06 encounters every
10 km walked, and the highest encounter rate was
for G. brasili ens is (0.92 en count ers/10 km),
followed by C. paca (0.87 encounters/10 km). The
T05 transect presented the highest encounter rate
(5.29 encounters/10 km; Table 2). Transects located
on the south area (T03, T04 and T05) had higher
richness than the northern area (T01 and T02). In
T01 and T02, both located nearby Abraão Village,
we only observed three species that were present
in all transects (D. aurita, C. jacchus, and G.
brasiliensis). During this study, tourists were found
with some frequency in transects T01 and T02, and
with less frequency in transects T03 and T04. No
tourist was found in T05, since the access is
prohibited. Signs of poaching were observed in
transects T01, T02 and with less evidence in T03
and T04.
Eye reflection and movement were the two
most frequent forms of detection, with eye reflection
restricted to nocturnal species. Warning cries were
mostly restricted to diurnal species such as G.
brasiliensis and C. jacchus. Significant differences
were found in encounter rates among the five forms
of detection (F = 3.432, p = 0.011) and among species
(F = 4.115, p = 0.009). The Tukey test a posteriori
indicated that there was a difference between
detections by eye reflection and by movement on the
ground, with higher encounter rates for the common
opossum and for the spotted paca by eye reflection
(Table 3).
Table 3. Total number of observations for each species according to the form of detection and significance level of the two-
way ANOVA in Ilha Grande, state of Rio de Janeiro, Brazil.
Table 2. Encounter rates of each mammal species per transect in Ilha Grande, state of Rio de Janeiro, Brazil.
Species T01 T02 T03 T04 T05 Total
Alouatta guariba 0 0.94 1.23 0.74 0.18 0.92
Callithrix jacchus 1.05 0.75 0.1 0.5 0.89 0.53
Coendou spinosus 0 0 0 0.06 0.18 0.05
Cuniculus paca 0 2.26 0.41 0.18 0.18 0.62
Dasyprocta leporina 0 0 0 0.5 0.89 0.33
Dasypus novemcinctus 0 0 0.14 0.37 1.58 0.39
Didelphis aurita 0.52 0 0.28 0.12 0 0.09
Guerlinguetus brasiliensis 1.76 0 0.41 1.62 1.06 0.87
Hydrochoerus hydrochaeris 0 0 0.41 0.31 0.35 0.25
Total 3.35 3.97 3.13 4.42 5.29 4.06
Species Warning
in branches
on the ground
Alouatta guariba
- 6 - 10 -
Callithrix jacchus 10 9 - 6
Coendou spinosus - 3 - 2 5
Cuniculus paca 1 - 12 4 18
Dasyprocta leporina
- - 4 - -
novemcinctus - - 5 2 6
Didelphis aurita
- 2 3 4 12
Guerlinguetus brasiliensis 11 10 5 11 -
Hydrochoerus hydrochaeris
- - - 2 -
Total of observations 22 30 29 41 41
Mammalian Detectability in Transect Surveys 427
Oeco l. Aust., 21(4): 422-4 30, 2017
Only D. aurita and C. jacchus had their
frequencies of detection affected by the weather,
which were more detected under cloudy days (X2 =
5.608, p = 0.018 and X2 = 6.862, p = 0.008; Table
4). Cuniculus paca was more detected in days with
no wind and D. aurita in days of weak wind (X2 =
4.154, p = 0.042 and X2 = 17.757, p = < 0.001; Table
4). Only two species were detected on days of
strong wind: D. aurita and A. guariba. (Table 4).
In relation to the sighting time, the Kruskal
Wallis test indicated the existence of significant
differences between the encounter rates among the
groups of sighting time (KW = 11377, p = 0.044;
Table 5). Most of the records were made between
06:01 to 08:00 h (Tukey test a posteriori: p = 0.03)
an d be t w e en 18 : 0 1 to 20:00 h (Tukey test a
posteriori: p = 0.04). Cuniculus paca was detected
only after 16:00 h, and even then, only one out of 35
obs e rvat i ons w a s b e fore 18 : 00 h . Dasy pus
nove m cinct us an d D. aur ita a l so pre s ent e d
crepuscular and nocturnal habits, but were also
recorded in the period close to dawn. Pri mate
species showed activity time between 06:00 and
18:00 h, and only one record of A. guariba occurred
before 6:00 h. This case was a single individual found
in the ground.
Table 5. Number of observations for each species according to the sighting time and encounter rates (individual or group
/ 10 km) in Ilha Grande, state of Rio de Janeiro, Brazil.
Table 4. Frequency of detection of each species and chi-square test results with p values according to different climate
conditions. df = 1 for all the analyses in Ilha Grande, state of Rio de Janeiro, Brazil. Significant values for the chi-square test
are in bold.
06:01– 08:00
16:00- 18:00
Alouatta guariba
1 9 0 6 0 0
Callithrix jacchus 0 16 5 4 0 0
Coendou spinosus 2 1 0 0 4 3
Cuniculus paca 0 0 0 1 18 16
Dasyprocta leporina
0 1 3 0 0 0
novemcinctus 5 0 0 0 3 5
Didelphis aurita
4 0 0 0 13 4
Guerlinguetus brasiliensis 0 22 11 4 0 0
Hydrochoerus hydrochaeris
0 0 1 1 0 0
Total of observations 12 49 20 16 38 28
Encounter rate 0.29
Species Weather Wind
Clear Cloudy Rainy X
(p) No
wind Weak Medium Strong X
Alouatta guariba 7 7 2 0.268 (0.604) 4 9 2 1 1.801 (0.180)
Callithrix jacchus 9 15 1 6.862 (0.008) 8 15 2 0 0.198 (0.656)
Coendou spinosus 4 5 1 - 5 4 1 0 -
Cuniculus paca 19 14 2 1.294 (0.255) 25 6 4 0 4.154 (0.042)
Dasyprocta leporina 1 2 1 0.001 (0.982) 3 0 1 0 2.77 (0.096)
Dasypus novemcinctus 10 3 0 0.569 (0.451) 8 3 2 0 3.077 (0.079)
Didelphis aurita 8 10 3 5.608 (0.018) 8 9 3 1 17.757 (< 0.001)
Guerlinguetus brasiliensis 16 19 2 6.862 (0.008) 12 18 7 0 0.198 (0.656)
Hydrochoerus hydrochaeris 1 1 0 - 1 1 0 0 -
428 Pereira et al.
Oecol. Aust., 21(4): 422-430, 2017
The tree species present in all transects (D.
aurita, C. jacchus, and G. brasiliensis) are considered
as generalist or opportunistic species. Didelphis aurita
is a generalist species (Cáceres 2003) as well as C.
jacchus (Cunha 2005). Both are able to live in altered
habitats and under the most different conditions,
including near human habitations. In addition, C. jacchus
is an invasive species introduced in southeastern Brazil
(Cerqueira et al. 1998), and its presence has been
reported in both urban and preserved forest areas. In
Ilha Grande, we had higher encounter rates of C.
jacchus in the northern area of the island (near Abraão
Village). Guerlinguetus brasiliensis is an opportunistic
species (Alvarenga & Talamoni 2006), easily detected,
with high encounter rates (Chiarello 2000, Marques
2004), and may occur in secondary forests, farms and
parks (Emmons & Feer 1997).
The lower encounter rates observed in T01, T02,
and T03 (south) when compared to T04 and T05 (north)
may be due to human population densities, tourism, and
poaching. Although considered an alternative for
sustainable use in some protected areas, tourism can
have an impact on habitat and natural populations
(Rocha et al. 2012, Habibullah et al. 2016), and Ilha
Grande receives a considerable amount of tourists
throughout the year. The island has a network of trails
that consists of 16 units used by tourists to reach the
various parts of the island. However, since Abraão
Village is the largest settlement in Ilha Grande (i.e.,
located in the north), where most of the hotels are
located, the nearby trails are more frequently used by
tourists. On the other hand, the southern trails are more
isolated and less frequented. Despite a large portion
of Ilha Grande is inserted in protected areas, such as
the Ilha Grande State Park, poaching is also a common
activity in the region. In fact, mammals species whose
meat are much appreciated for food by the local
people have become rare nearby the village, such as
C. paca, D. leporina, and D. novemcin ct us.
Several studies have shown changes in the
abundance of species, and even behavioural changes
in some animals due to poaching pressure (Galetti et
al. 2015, Ferreguetti et al. 2015, 2016, 2017). In fact,
some species may become more skittish and difficult to
see in environments where the practice of poaching is
frequent (Peres & Lake 2003, Ferreguetti et al. 2015,
2016, 2017). This may even affect their activity time,
because some species tend to forage at night in areas
with human presence (Cullen Jr. et al. 2001, Di Bitetti
et al. 2008, Ferreguetti et al. 2015). Thus, the encounter
rates could be lower in T01 and T02 transects because
of the interference of tourists and the poaching pressure,
which must be associated with the higher human densities
in the north of the island, which would inhibit the
presence of certain species.
The form of detection affected encounter rates.
A higher detectability related to eye reflection and
movement was expected, since eye reflection is
restricted to nocturnal species, and the movement
detection (visual) is facilitated for diurnal species. This
may also explain the differences between the
encounter rates depending on the time of observation.
If we add up the six sighting time groups into two,
day and night, night observations would have a higher
number of records. Morgia et al. (2015) defend the
benefits of distance sampling at night, mainly because
the estimates generated in the analysis can be more
precise and accurate, due to the easily detection of
the animals by eye reflection. On the other hand,
Duckworth (1998) mentions the difficulties in
performing distance samplings at night, especially to
detect more cryptic species, with weak eye reflection.
In this study, the detection by eye reflection was very
effective for nocturnal species. The night samplings
in the south area provided data on species that
occurred only or mostly in this period, such as D.
novemcinctus and C. paca. Cuniculus paca is a
highly poached species by the local population, so
few observations were expected, but it was the
second most sighted species and easily detected even
over long distances by its intense eye reflection. On
the other hand, the night samplings on the north side
showed a low success of observations, where the
only sighted species was D. aurita. According to Di
Bitetti et al. (2008), some species change their
behaviour when under poaching pressure because of
the flashlights used by hunters, acquiri ng a
“photophobia and running away before being
detected. This could explain the low frequency of
observations or even the non-detection of certain
Mammalian Detectability in Transect Surveys 429
Oecol. Aust., 21(4): 422-430, 2017
species in the north transects. This supports the
hypothesis that low species richness in the north area
transects may be due to poaching pressure. On the
other hand, on the southern area, where poaching is
lower, hunted species were more frequently observed
(C. paca, D. leporina, and D. novencimctus).
Although some authors avoid collecting data
at night (Duckworth 1998, Marques 2004), this study
has shown that they provide a good amount of data
for species that are generally less frequently
observed. Since most of the Neotropical mammals
have predominantly nocturnal habits, a higher sampling
effort during the night is required to obtain sufficient
data to estimate the density of these species. Thus,
we did not corroborate the hypothesis that the species
are less detected at night samplings because of the
limitation of the observer’s view (i.e., limited by the
flashlight range). All nocturnal species recorded here
were mainly detected by the light reflection in their
eyes, and were less dependent on motion or noise
for detection. We observed that even species of small
mammals, such as arboreal marsupials, could be
detected at night by the eye shine.
Climate and wind also affected the frequency
of detection, as expected. Peres (1999) does not
recommend transects on rainy days because the
weather would affect the ability of the observer to
detect animals, both visually (i.e, animals tend to
decrease their activity), and acoustically (i.e., difficulty
in hearing noises caused by animal motion or alert).
The same may apply in days of strong winds. The
number of observations on rainy days was, as expected,
much lower than on cloudy days, with few observations
of A. guariba and D. agouti. Weather, however, did
not affect the observation of nocturnal species, because
it is possible to see the eye shine even under rain.
Several factors can affect the encounter rate
estimates in studies using distance sampling by linear
transects. In the present study, we detected the
influence of animal activity period (i.e., object of study),
followed by climate conditions, and transect location
as important variables for estimating encounter rates
in mammals. This study hopes to call attention of these
variables when using this methodology widely applied
in the study of mammals and to contribute to the
experimental design of similar studies.
We than k th e Centr o de Estudo Ambi e ntais e
Desenvolvimento Sustentável (CEADS) and the Rio de Janeiro
State University for the logistical support during the execution of
this research. We also thank the Instituto Biomas for financial
support. BCP is also grateful to Coordenação de Aperfeiçoamente
de Pessoal de Nível Superior (CAPES) for a graduate scholarship.
Alho, C. J. R., Schneider, M., & Vasconcellos, L. A. 2002. Degree
of threat to the biological diversity in the Ilha Grande State
Park (RJ) and guidelines for conservation. Brazilian Journal
of Biology, 62(3), 375-385.
Alvarenga, C. A., & Talamoni, S. A. 2006. Foraging behaviour of
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Corumbá: EMBRAPA. 34p.
Submitted: 30 March 2017
Accepted: 03 October 2017
Associate Editor: Rosana Gentile
... small feline species). These observations suggest that encounter rates should be examined with a degree of caution, because several factors can affect species registration, such as the animal activity period, climate conditions and transect location 25 . Thus, whenever possible, the methods used to estimate species abundance should consider the probabilities of detecting individuals. ...
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The aim of the present study is to calculate the encounter rate and estimate the density of medium and large-sized mammals with nocturnal habits in the Cristalino region of northern Mato Grosso, southern Amazon, Brazil, using distance sampling method. Eight species were detected with encounter rate varying from 0.09 at 1.68 encounters 10 km–1, and three population densities were estimated: Cuniculus paca (7.75 individuals km–2), Potos flavus (7.08 individuals km–2) and Mazama americana (4.23 individuals km–2). Our data help expand the information about density of nocturnal mammals in the southern Amazon region, in the transition between the Amazon and the Cerrado biomes, and can contribute to management and conservation of these species.
... We sampled the medium-and large-sized mammals through active search, within a radius of 100 m centred in each sampling site, for five consecutive days in each visit. The two observers walked during two different times of the day, namely, in the early morning from 0630 hours to 0830 hours, and at the end of the day period from 1530 hours to 1730 hours, according to other studies that had performed active search Pereira et al. 2017). During the active search, we sampled medium-to large-sized mammals by direct observation (in part, by using binoculars), vocalisations (e.g. ...
ContextUrbanisation and human population growth can generate conflicts, threatening biodiversity. Resource availability and vegetation complexity owing to human influence may increase the potential that a habitat would lose its species. Conservation biology aims to understand how to soften human influence and maintain viable insitu populations. AimsWe evaluated the non-volant mammal’s richness and abundance in an Atlantic Forest protected area. Specifically, we tested (1) the effect of distance from water resource and vegetation (canopy and understorey cover) on richness and abundance and (2) the effects of anthropogenic pressure such as domestic dog abundance, distances from human settlements, and from the road on the community of non-volant mammals. Methods We collected the data from January through December of 2017 in 20 sampling sites by using live traps (for small mammals), active search, sand plots and camera traps. Key resultsWe recorded 22 species of non-volant mammals, among them four endemic, two endangered and two invasive exotic species. The main covariates that affected the structure and composition of the non-volant mammal’s assemblage was the domestic dog abundance, which repels most of the species into the forest and water resources, which attract the species to forest edges. Conclusions Our results indicated that the negative impact of domestic dog presence in the non-volant mammal’s community is so evident that it could generate changes in the composition, richness, and local distribution of the species. ImplicationsWe suggest that management action in this protected area must initiate a control of domestic dogs to minimise their impact.
... Traps are commonly used to capture small rodents to collect information about their population sizes (Rood, 1972;Streilein, 1982a;Asher et al., 2004;Salvador and Fernandez, 2008). However, some species have a low capture rate, and the density of these populations can be estimated effectively by recording observations of individuals along a line transect (e.g., Freitas et al., 2011;Pereira et al., 2017); this is known as distance sampling (Buckland et al., 2015). ...
Population density and use of space by the rodent, Kerodon rupestris, were investigated in a semiarid area in Brazil. Distance sampling was used along line transects to estimate population density. Observations of K. rupestris were recorded on rocks, open ground, and in vegetation. The air temperature and the height of the vegetation were recorded for each observation. The frequencies of these observations were analyzed using generalized linear models. A total of 612 observations were made for K. rupestris (in 23,172 m traveled), resulting in an estimated population density of 12.45 individuals/ha. Individuals were mostly observed on rock (71%), reflecting a dependence on rocky outcrops in the environment. The rodent was observed to be active when temperatures ranged between 23 and 45 °C, but was most active at temperatures ranging from 31 to 34 °C. Kerodon rupestris varied in its use of vegetation of different heights, preferring vegetation of up to 2 m in height. Our results indicated high density of K. rupestris in the study area, due to the preference for refuges formed by the prevalent rocky outcrops. The rodent displays characteristics typical of the island syndrome, namely being active on rocks and in vegetation, with activity influenced by temperature.
... Information for A. g. clamitans on the island named Ilha Grande is restricted to its occurrence and there are no systematized works on the ecology and behavior of the species (Alho et al. 2002, Pereira et al. 2017. Estimates of population size indicators are critical to any effort to conserve endangered species. ...
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Alouatta guariba clamitans Cabrera, 1940 is an endemic species of the Atlantic Forest that occurs from south Bahia, Brazil, extending south to the province of Misiones, Argentina. In Rio de Janeiro state, the species was classified as threatened, indicating that attention is needed for the conservation of this taxon. Additionally, an outbreak of yellow fever spread throughout the southeastern states of Brazil from January 2017 until March 2018 seriously threatening Rio de Janeiro populations of the species. Herein, we aimed to provide the first estimates of A. g. clamitans encounter rate, density, and population size in the Ilha Grande State Park (PEIG), which is part of the Atlantic Forest biome of Brazil. Data were collected in two different periods, the first between December 2003 and May 2005, and the second from August 2009 to May 2010, and information on encounter rates and behavior was collected to better understand aspects of species’ ecology. The estimated encounter rate in the first period through the distance sampling method was 0.04 ± 0.01 individuals per kilometer. Nine groups were recorded in the second period of the study, with 47 individuals along 3 km. Our estimates of encounter rate, density and population size were low and reinforces the need to initiate species monitoring and assess the impact that yellow fever outbreaks may have on PEIG populations. The results presented here can be a starting point to support future strategic actions for the species, to measure impacts and to the management of the species, and for a conservation program.
... It is worth mentioning that in the zero-distance perpendicular to the transect, the probability of detection is lower than in the first meter as showed in Fig. 2. This is due to the fact that for nocturnal animals, eye brightness is the most important detection method (Pereira et al. 2017). Therefore, if the animal is too close, the angle may not allow you to have the vision of the eye glow. ...
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The spotted paca, Cuniculuspaca (Linnaeus, 1766), is a Neotropical, opportunistic, frugivorous caviomorph rodent, that inhabits primarily broadleaf forests. We aimed to provide the first estimates of density of C.paca for the Ilha Grande, an island located in the Atlantic Rain Forest biome of Brazil. Density and population size were estimated using the total number of individuals observed along each trail through the program DISTANCE 7. Our estimates of density and population size reinforces the importance of the Ilha Grande as an important reservoir of the species. Therefore, the results presented herein can be a starting point to support future action plans for the species, making predictions regarding the ecosystem and management and conservation of the spotted paca. Furthermore, the results can be used as a surrogate for other regions in which the species occurs.
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Most information available regarding domestic dogs in natural reserves comes from developed countries, particularly North America and Europe, where dogs are usually well managed and cared for. Conversely, in developing country reserves information about dogs are comparatively scarce, particularly in terms of their interactions with local wildlife and their management, despite their high abundance and widespread distribution. We aimed to characterize domestic dog spatial distribution using occupancy modelling and estimate abundance in the Mata das Flores State Park (MFSP). We collected data from January to May 2017. We divided the survey into two sampling protocols: (1) interviews and active search on trails and roads in the region and (2) sand plots to detect the presence of dogs in the MFSP. We recorded a total of 132 individually identiied domestic dogs between interviews with surrounding residents and records through active search. We recorded an average of 2 ± 1 dogs per household interviewed. Of this total, we recorded 89 individuals inside the MFSP, through 213 detections in the eve months of sampling. Both the spatial distribution map and occupancy models for the species, indicated a higher occurrence in the side of the park faced to the urbanized area of Castelo municipality, totaling about 53% of the records. We also obtained a high number of records in the areas near the road that intercepts the park, with about 36% of the records. The remaining 11% of the records occurred in areas close to human settlements around the park. Our results of abundance and spatial distribution together with occupancy modeling could serve to assist conservation planning and management in the MFSP. RESUMO. Invasão por Canis lupus familiaris (Carnivora) em uma área protegida na Mata Atlântica, Brasil: distribuição espacial e abundância. A maior parte das informações disponíveis relacionadas a presença do cachorro doméstico em reservas naturais são provenientes de países desenvolvidos, particularmente América do Norte e Europa, onde essa espécie geralmente é bem manejada e controlada. Por outro lado, nas reservas localizadas nos países em desenvolvimento o conhecimento sobre essa espécie doméstica é escasso, particularmente em termos das suas interações com a fauna nativa local e seu manejo. Nós objetivamos caracterizar a distribuição espacial do cachorro doméstico utilizando a modelagem de ocupação e estimar a abundância da espécie no Parque Estadual Mata das Flores (PEMF). Nós coletamos dados de janeiro a maio de 2017. Nós dividimos a amostragem em dois protocolos de amostragem: (1) entrevistas e busca ativa em trilhas e estradas da região do parque e (2) parcelas de areia para detectar a presença do cachorro doméstico no PEMF. Nós registramos um total de 132 cães domésticos identiicados individualmente entre entrevistas com moradores e registros ao redor através de busca ativa. Registramos uma média de 2 ± 1 cães por domicílio entrevistado. Desse total, registramos 89 indivíduos dentro do PEMF, através de 213 detecções nos cinco meses de amostragem. Tanto o mapa de distribuição espacial quanto os modelos de ocupação da espécie, indicaram Recibido 3 abril 2018. Aceptado 31 octubre 2018. Editor asociado: M. Kittlein 2 Mastozoología Neotropical, en prensa, Mendoza, 2019 hhp:// M. M. AAAAAAAA AA AA. uma maior ocorrência no lado do parque voltado para a área urbanizada do município de Castelo, totalizando cerca de 53% dos registros. Também obtivemos um alto número de registros nas áreas próximas à estrada que intercepta o parque, com cerca de 36% dos registros. Os 11% restantes dos registros ocorreram em áreas próximas a assentamentos humanos ao redor do parque. Nossos resultados de abundância e distribuição espacial, juntamente com a modelagem de ocupação, poderiam servir para auxiliar o planejamento e a gestão da conservação no PEMF.
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Biodiversity inventories contain important information about species richness, community structure and composition, and are the first step in developing any conservation and mitigation strategies. The Atlantic Forest of South America is home to around 334 species of small, medium and large‐sized mammals, and is currently restricted to less than 12% of its original cover. Here we present the ATLANTIC MAMMALS, an open data set on information on medium and large‐sized mammal assemblages in the Atlantic Forest of Brazil, Paraguay and Argentina. A total of 129 studies were compiled, including published and in press peer‐reviewed papers, book chapters, theses and unpublished data. We mapped 244 assemblages, eight orders, 63 genera and 94 species (24 of which are classified as threatened by the IUCN Red List) distributed in 128 protected and 116 unprotected areas. Species richness of the mammalian assemblages varied from 1 to 39 species (mean 15). The most recorded species in the entire biome was Dasypus novemcinctus, followed by Cerdocyon thous and Procyon cancrivorous. These data can be useful in support of macroecological studies and conservation planning strategies. Please cite this data paper when the data are used in publications. We also request that researchers and teachers inform us of how they are using the data. This article is protected by copyright. All rights reserved.
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The lowland tapir (Tapirus terrestris, Linnaeus 1758) is one of the surviving members of the Neotropical megafauna. In Brazil, lowland tapirs are considered vulnerable according to the IUCN Red List of Threatened Species and endangered within the Atlantic Rain Forest biome. We aimed to provide the 1st estimates of density and population size for T. terrestris for Vale Natural Reserve (VNR). We predicted the relationships of 6 covariates to habitat occupancy. Density was estimated by the use of distance-sampling techniques, while occupancy, detectability, and activity patterns were assessed with camera-trap monitoring at 39 sample sites over a 1-year period. Density for T. terrestris was 0.8 ± 0.2 lowland tapirs/km 2 and population size was 200 ± 33 individuals. Occupancy probability was described by 2 covariates (density of palm trees and distance to water resources) and detectability by those same 2 covariates plus 2 more (distance to road and density of poaching). The species showed the 3 highest peaks of activity at 1900, 2300, and 0400 h. We concluded that VNR still harbors a viable population of lowland tapirs. However, anthropic impacts in the reserve such as poaching and road kills could already be directly affecting the lowland tapir population and producing indirect effects for the whole ecosystem. Results presented herein can be a starting point to support future work in the region and to make predictions regarding the ecosystem relationships, management, and conservation of lowland tapirs. A anta brasileira (Tapirus terrestris, Linnaeus 1758) é considerada uma das espécies sobreviventes da megafauna neotropical. No Brasil, a anta é considerada vulnerável de acordo com a lista vermelha de espécies ameaçadas da IUCN e considerada em perigo para o bioma da Mata Atlântica. Nosso objetivo foi fornecer as primeiras estimativas de densidade e tamanho populacional de T. terrestris para a Reserva Natural Vale (RNV). Além disso, nós testamos o efeito de 6 covariadas para modelar ocupação do habitat. Estimamos a densidade e o tamanho populacional com a técnica de amostragem de distância por transecção linear. A detectabilidade, ocupação e período de atividade foram estimados com o uso de armadilhas fotográficas em 39 sítios amostrais por um período de 1 ano. Estimamos uma densidade de 0,8 ± 0,2 antas/km 2 e um tamanho populacional de 200 ± 33 indivíduos. A probabilidade de ocupação foi representada por 2 covariadas (i.e. densidade de palmeiras e distância do recurso hídrico), e a detectabilidade pelas mesmas covariadas anteriores com a adição de outras 2 (i.e. distância da rodovia e densidade de caça). A população presente na RNV apresentou 3 picos de atividade, às 19:00, 23:00, e 04:00 horas. Nós concluímos que a RNV ainda pode apresentar uma população viável de anta. Porém, os impactos antrópicos presentes na reserva (como a caça ilegal e morte por atropelamentos) podem já estar diretamente afetando a população de anta e produzindo um efeito indireto em todo o ecossistema. Os resultados aqui apresentados podem ser o ponto inicial para o desenvolvimento de futuros estudos na região e também para predições sobre medidas de manejo e conservação da anta e de todo o ecossistema.
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The purpose of this study is to investigates the impact of tourism on biodiversity loss in a sample of 141 countries. In the analysis, we measure tourism using the numbers of international tourist arrivals, while biodiversity loss is proxy using the numbers of threatened species – birds, fishes, mammals and plants. We also include GDP per capita, population growth, protected areas, and crop production, which act as the control variables. We find that using robust standard error estimator the number of international tourist arrivals, population growth rate, protected areas and crop production increases the numbers of threatened species, while GDP per capita reduces the numbers of threatened species. One policy implication of this study is that since businesses in the tourism industry depend on the very existence of biodiversity, then biodiversity conservation should become the essential factor for business sustainability.
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We provide the first estimates of density and population size of two sympatric species of armadillos (Euphractus sexcinctus and Dasypus novemcinctus) for the Vale Natural Reserve, evaluating how poaching would be affecting their habitat use (i.e. detectability and occupancy probability) and also describing their activity patterns. Abundance and density were estimated using a distance sampling technique. Occupancy, detectability, and activity patterns were assessed using camera-trapping during a one-year period. Estimated population densities were 0.06 individuals per hectare (ind/ha) and 0.05 ind/ha for D. novemcinctus and E. sexcinctus, respectively. Occupancy probability of both species was affected by the distance to forest edge. D. novemcinctus showed a positive relationship with increasing distance from the edge, whereas E. sexcinctus showed an opposite relationship. D. novemcinctus also showed higher occupancy rates in sites closer to a water resource. Additionally, occupancy and detectability of both species were negatively affected by historical poaching intensity in the reserve. Activity patterns varied between species, with D. novemcinctus being mostly nocturnal and E. sexcinctus being diurnal. We conclude that despite the two armadillo species sharing several niche dimensions, they showed spatial and temporal segregation. These differences may be an adaptation to reduce interspecific competition but may also be affected by the need to avoid poaching pressures. This study contributes to increase the knowledge and conservation of these two little-studied species.
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The red brocket (Mazama americana) and gray brocket deer (Mazama gouazoubira) are sympatric in the Atlantic Forest and present a number of ecological similarities in their diet and habitat use, although interspecific competition in these species is poorly understood. This study aimed to compare abundance and produce evidence of niche partitioning between these species. We estimated population density, activity patterns, habitat occupancy, and detection probabilities for the 2 species in a large remnant of the Atlantic Forest of Espírito Santo, Brazil. Abundance was estimated using the distance sampling technique, and occupancy, detectability, and activity patterns were assessed using camera-trap monitoring at 39 sample sites over a 1-year period. During surveys, we obtained 44 sightings of M. americana and 74 of M. gouazoubira, with 199 records in which the species was not discriminated. We applied a correction for the unidentified sightings to avoid underestimating density. The corrected population size estimates were 3,668 individuals (confidence interval [CI] 95%: 2,989–4,601) for M. americana and 6,701 (CI 95%: 5,857–7,667) for M. gouazoubira. Occupancy probability for M. americana was best described by the large trees density (diameter at breast height > 50cm) and the edge forest distance, while M. gouazoubira did not present any habitat preferences based on the covariates used for modeling. M. americana was mostly nocturnal, whereas M. gouazoubira was active mainly during the day. We conclude that, despite the abundance of these sympatric species, and their occupation of the same habitats, they may avoid competing for habitat and feeding resources through differences in their activity patterns. Os veados mateiro (Mazama americana) e catingueiro (Mazama gouazoubira) são espécies simpátricas na Mata Atlântica, e apresentam várias semelhanças ecológicas tais como o uso do habitat e dieta. A hipótese de competição interespecífica entre essas espécies ainda não foi testada. Este estudo teve como objetivo comparar a abundância e verificar evidências de separação de nicho entre essas duas espécies simpátricas. Estimou-se a densidade, o padrão de atividade, e a probabilidade de ocupação das duas espécies em um fragmento de Mata Atlântica no estado do Espírito Santo, Brasil. A abundância foi estimada utilizando a técnica de amostragem distância (esforço total: 908 km), e o padrão de atividade e a probabilidade de ocupação foram avaliadas usando armadilhas fotográficas em 39 locais de amostragem durante o período de um ano. Na transecção linear obtivemos 44 observações de M. americana e 74 observações de M. gouazoubira, com 199 registros em que as espécies não foram discriminadas. Nós aplicamos uma correção para a falta de discriminação de espécies para evitar subestimar a densidade. As estimativas corrigidas de tamanho de população foram 3.668 indivíduos (95% CI: 2.989–4.601) e 6.701 indivíduos (95% CI: 5.857–7.667) para M. americana e M. gouazoubira, respectivamente. A probabilidade de ocupação de M. americana foi melhor descrita pela densidade de árvores com diâmetro altura do peito > 50cm e a distância da borda da floresta, enquanto M. gouazoubira não mostrou preferência de habitat com base nas co-variáveis utilizadas para a modelagem. M. americana foi principalmente noturna, enquanto M. gouazoubira mostra um padrão de atividade diurno. Podemos concluir que, apesar destas duas espécies serem simpátricas, abundantes, e ocupando os mesmos habitats eles não compartilham o mesmo período de atividade. Esta separação no tempo poderia ser uma adaptação para evitar a competição direta, uma vez que as espécies do gênero Mazama apresentam um nicho muito semelhante quando o habitat e a dieta são considerados.
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Defaunation can trigger cascading events in natural communities and may have strong consequences for plant recruitment in tropical forests. Several species of large seed predators, such as deer and peccaries, are facing dramatic population collapse in tropical forests yet we do not have information about the consequences of these extinctions for seed predation. Using remote camera traps we tested if defaunated forests have a lower seed predation rate of a keystone palm (Euterpe edulis) than pristine areas. Contrary to our expectation, we found that seed predation rates were 2.5 higher in defaunated forests and small rodents were responsible for most of the seeds eaten. Our results found that defaunation leads to changes in the seed predator communities with potential consequences for plant–animal interactions.
Occupancy Estimation and Modeling: Inferring Patterns and Dynamics of Species Occurrence, Second Edition, provides a synthesis of model-based approaches for analyzing presence-absence data, allowing for imperfect detection. Beginning from the relatively simple case of estimating the proportion of area or sampling units occupied at the time of surveying, the authors describe a wide variety of extensions that have been developed since the early 2000s. This provides an improved insight about species and community ecology, including, detection heterogeneity; correlated detections; spatial autocorrelation; multiple states or classes of occupancy; changes in occupancy over time; species co-occurrence; community-level modeling, and more. Occupancy Estimation and Modeling: Inferring Patterns and Dynamics of Species Occurrence, Second Edition has been greatly expanded and detail is provided regarding the estimation methods and examples of their application are given. Important study design recommendations are also covered to give a well rounded view of modeling.
Reliable estimates of the size of natural populations are required by national and regional governments for management and conservation, by international commissions that manage natural resources, and by NGOs. Distance sampling, in which distances of detected animals from a set of randomly located lines or points are recorded, is the most widely-applicable technique for obtaining such estimates. Almost all users of distance sampling methods use software and methods developed at St Andrews. Software Distance [5] is the industry standard and has over 30,000 registered users from around 115 countries. The methodological developments and associated software have allowed better-informed decisions to be made in the management and conservation of populations as diverse as whales, seals, fish, elephants, apes, deer, birds, ants, trees and flowering plants.
Estimating the size of ungulate populations dwelling forested habitats is technically difficult and expensive. In particular, population assessment via conventional distance sampling (CDS) at landscape scales is challenging and often discarded for its high costs. The development of a framework for its methodological optimization is mandatory. To tackle this issue, we used survey simulations. For arbitrary-distributed populations, we compared the following: (i) systematic random transect allocation, (ii) random selection of footpaths, and (iii) two-stage sampling selection of footpaths (2, 5, 10 blocks). The performance of two-stage sampling and random footpath selection estimators was similar. Then, we applied previous results to estimate the size of a red deer (Cervus elaphus) population in the Italian Apennines. Using data from a pilot survey, we estimated density via CDS and density surface modeling (DSM), and we quantified survey costs per unit effort. Considering our deer distribution, we finally simulated and evaluated the cost-effectiveness of the abovementioned designs for a range of realistic efforts (25–65 transects). CDS produced a negatively biased and less precise estimate than the corresponding DSM. For an effort of 65 transects, design (ii) estimates were unbiased (coefficient of variation = 0.31), while design (iii) provided negatively biased estimates (coefficient of variation = 0.27). Two-stage sampling designs with few blocks were less expensive than other designs in attaining the same level of precision, and they emerged as a cost-effective survey design. Our simulation approach thus provided managers a readily available tool to improve the estimate of ungulate abundances at a landscape scale.