A Study of Bat Diversity in Campanario’s Primary Forest
Cameron Incognito
Kyle Hovey
Julianne Pekny
Annie Krichten
Tramond Baisden
Introduction
Costa Rica is home to over eleven percent of bat species in the world, with 108
species observed thus far. Furthermore, over half of the mammalian species in Costa Rica
are bats. Hollow trees, their bark, buttress roots, and some leaves are common roosting
places for bats in Costa Rica due to the relative scarcity of buildings and caves. While
roosting, multiple species of bats may be observed, but when foraging it is most common
for single-species flocks.
Bats consume a wide variety of food sources, but individual species are classified
into different guilds including frugivores, nectarivores, insectivores, carnivores, and
omnivores. Frugivores, whose diets consist of mainly fruits, may supplement such
protein-poor diets with insects when necessary. Captured examples in the present study
include Carollia perspicillata and Carollia castanea. They are frequently observed in
both primary and secondary forests since many fruiting plants (e.g. Piper and Cecropia)
grow there. Nectarivores consume nectar from flowers, thereby promoting the pollination
of a number of flower species, and obtain protein from pollen. In the wet season when
nectar becomes scarce, nectarivores consume insects and fruit. Glossophaga soricina, a
nectar-eating bat, was captured this year. Insectivores, like the Pteronotus gymnonotus
captured this year, feed on insects. Pteronotus is observed to forage in open areas, for
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example over roads and near beaches, for insects. They are commonly known to roost in
caves, but still benefit from visiting fruit trees where many insects may be found (LaVal
K, Rodriguez-H B, 2002). Omnivores have a diverse diet, including fruits, insects, nectar,
and small animals. Phyllostomus discolor was found this year and is essential as a
pollinator as shown in a Guanacaste study in which eighty-two percent of captured bats
carried pollen (LaVal K, Rodriguez-H B, 2002). Carnivores consume small animals, and
the first carnivore in this study, Lophostoma silvicola, was caught this year. Lophostoma
silvicola’s diet consists mostly of frogs and lizards, though it may consume small
amounts of fruit if necessary. It forages at levels of low vegetation exclusively in primary
forests and roosts in hollow trees and termite nests. This species is an indicator of a highquality, healthy environment because it relies on primary forests (Mora JM, 2013).
This study aimed to sample bat diversity in the primary forest located at
Campanario Biological Station in an effort to determine relationships between the
presence of bats and the density of plants and fruits. Comparisons between 2013 primary
forest data and previous years’ data in both the primary and secondary forests were used
to determine any correlations between bat populations in different habitats. Lastly, the bat
richness, abundance, and spread were compared to the data obtained from a similar 2013
primary forest bird study in an effort to determine any correlations between bird and bat
feeding and living conditions.
It was hypothesized that a higher abundance and richness of bats would be found
in close proximity to their respective food sources. In an area of high plant and fruit
density that may attract or serve as bat food sources, a higher number of bat captures
would be expected. It was also expected that there would be similar trends between bird
2
and bat captures; in areas of high bird captures, it was expected that there would be a high
amount of bat captures. Finally, due to the fact that bats’ peak feeding periods are at dusk
and dawn, it was expected that bat captures would be highest just after dusk (LaVal RK,
Rodriguez-H B, 2002.).
Methods
Nine mist nets were assembled along the Bauhinia trail in the primary forest of
Campanario Biological Station to capture both birds and bats. The first net was
positioned closest to the field station at 3:20 pm, with net nine positioned at the furthest
end of the trail at 5:00 pm. The mist nets, consisting of thin mesh netting divided into
four panels with a pocket in between each layer, ranged from ten to fifteen meters long
and were hung on 3 meter poles of various material. The poles were anchored to nearby
trees in order to provide stability and to keep the net tense enough to capture bats and
birds, but prevent bat ricochets, potentially freeing them. Once assembled, the nets were
patrolled periodically (approximately every 30 minutes) for captures. In the event of a
capture, the bat was untangled and classified according to time, net number, species, and
gender. The length of the tibia and forearm were recorded, as well as age (adult or infant)
and the presence of parasites for species identification purposes. Fecal samples were also
collected from captured bats if possible to identify any seeds and plants that they
previously fed upon. The captured bats were then released back into the forest. Bat
captures took place between 6:00 pm and 9:00 pm.
Plant density and fruit density surrounding each net were also measured. At each
net, plant density was measured at six locations by finding the number of leaves,
3
branches, and stems that touched a 2 meter long bamboo pole at a distance of two meters
on both sides of the net. This was carried out at both ends of the net and also in the
center. Later, plants were classified by family. Fruit density was measured by counting,
collecting, and classifying all berries within three meters of each side of each net. The
total berry count was divided by the area surveyed to yield the fruit density for each net.
All statistical analyses were carried out using Microsoft Excel and the JMP program.
Results
Table 1: Detailed measurements and calculations from bat capture at Campanario
primary forest. 2013
Bat
Genus and
Gender
Adult
Tibia
Forearm
Number
Species
(y/n)
Length
length
(mm)
(mm)
1
Glossophaga Female
Y
n/a
n/a
Soricina
2
Carollia
n/a
Unknown n/a
n/a
perspicillata
3
Glossophaga n/a
Unknown n/a
n/a
soricina
4
Carollia
Female
Y
21
43
perspicillata
5
Pteronotus
Female
Y
n/a
54
gymnonotus
6
Phyllostmus Female
Y
n/a
65
discolor
7
Carollia
Female
Y
21
44
perspicillata
8
Glossophaga Female
Y
n/a
37
soricina
9
Carollia
Female
Y
17
37
casteanea
10
Carollia
Female
Y
16
37
castenea
11
Lophostoma n/a
Unknown n/a
n/a
silvicola
4
Figure 1: The number of individuals of each bat species captured at Campanario primary
forest (2013) and the secondary forest (2005).
Number of Bat Individuals Captured (N)
5
Bat Captures in Primary vs. Secondary
Forests
4
3
Primary
2
Secondary
1
0
Bat Species Captured
Table 2: The number of bat individuals captured at Campanario primary forest, their
respective dietary guilds, and their capture location. 2013
Net
number
Total
number of
Individuals
Number of
Insectivores
Number of
Frugivores
Number of
Nectarivores
Number of
Omnivores
Number of
Carnivores
1
2
3
4
5
6
7
8
9
2
1
5
2
0
1
0
0
0
0
0
0
1
0
0
0
0
0
2
0
2
0
0
0
0
0
0
0
0
2
0
0
1
0
0
0
0
1
0
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
5
Figure 2: Comparison between the number of captures per net between bats and birds in
Campanario primary forest. 2013
Number of Bat Individuals (N)
Number of Individuals Caught per
Net
10
8
6
Total number of Bat
Individuals
4
Total number of Bird
Individuals
2
0
1
2
3
4
5
6
Net Number
7
8
9
Figure 3: The number of bats captured in select time intervals in Campanario primary
forest. 2013
Time Capture Intervals
20:30 – 21:00
Time Intervals
20:00 – 20:30
19:30 – 20:00
19:00- 19:30
18:30 – 19:00
18:00 – 18:30
0
1
2
3
Number of Bat Indivduals (N)
4
6
Figure 4: The number of bat individuals captured as function of plant density in
Campanario primary forest. 2013
Number of Bat Individuals (N)
Number of Individuals Captured
versus Plant Density
6
5
P-value=0.8907
R² = 0.0029
4
3
2
1
0
0
1
2
3
4
Plant Density (number of plants, N)
5
6
Figure 5: The number of bat individuals captured as a function of fruit density in
Campanario primary forest. 2013
Number of Bat Individuals (N)
Number of Individuals Captured
versus Fruit Density
6
5
4
P-value=0.4206
R² = 0.0916
3
2
1
0
0
2
4
6
8
10
2
Fruit Density (berries/ m )
12
14
7
Richness of Bats (N species)
Figure 6: The richness of bats as a function of plant richness in Campanario primary
forest. 2013
5
Bat Richness vs. Plant Richness
4
P-value = 0.3950
R² = 0.105
3
2
1
0
0
2
4
Richness of Plants (N species)
6
Number of Bat Individuals
(N)
Figure 7: A comparison of the number of bat individuals captured in both the Campanario
primary and secondary forests. 2013 and 2005
8
2013(Primary)
2005(Secondary)
6
4
2
0
18:00 – 18:30 – 19:00- 19:30 – 20:00 – 20:30 –
18:30 19:00 19:30 20:00 20:30 21:00
Time Intervals
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Discussion
As seen in Figure 1, there was very little overlap between species found in
Campanario’s primary and secondary forests. There was also a higher bat richness (total
bat species captured) found in primary forests compared to secondary forests, a likely
result of primary forests’ capability of providing more cover for the bats from predators
and their higher abundance of resources due to maturity. Similar capture success rates
were also observed in the primary forests (0.055) and in secondary forests (0.07). While
more nets were used in the primary forest than the secondary forest, the capture success
rates were similar, suggesting that perhaps extra nets and the extra time are not necessary
to have the same capture success.
Figure 2 shows that the captured bat individuals were located in the earlier nets
(1-4) while the birds captured by peers ranged across all nets except 4. To determine why
this was the case, the plant and fruit density surrounding each net was compared to the
number of bats and birds captured to look for possible correlations and relationships.
While a direct relationship was found between bird richness and plant richness by
peers, this relationship was not observed with bats. As seen in Figure 6, there is no direct
correlation between these two variables as exemplified by the insignificant P-value
(0.3950) and low R2 value (0.105). Plant diversity and richness surrounding the nets
included five different genera of Melastomata and four different genera of Psychotria.
Neither Piper nor Cecropia, both of which are pioneer species known to be consumed by
some species of bats caught in this study, were observed in close proximity to the nets.
Alternatively, the number of birds captured was inversely proportional to the plant
density surrounding the nets suggesting that birds preferred the more open areas. As seen
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in Figure 4, there is no correlation between the number of bat individuals and the
surrounding plant density. The large P-value (0.8907) indicates that the relationship is not
significant and the small R2 value (0.00289) indicates that there is no linear relationship
present. Therefore no conclusions can be made about the habitat or feeding area
preferences of bats in the primary forest.
Thirdly, the number of birds captured was positively related to the fruit density
surrounding the nets suggesting that the areas of more fruit are more populated by birds.
This is to be expected as the more fruit available, the more birds will be able to be
sustained. As exemplified in Figure 5, no correlations were able to be determined
between the number of bats captured and the surrounding fruit density. The plot
possessed a large P-value (0.4206) and a very small R2 value (0.0919) showing that the
points were insignificant and that a linear regression was not appropriate.
In summary, a higher abundance and richness of bats was not observed in
proximity to the food sources near nets. Additionally, locations with higher fruit and plant
densities did not indicate higher bat abundance, contradicting several of the original
hypotheses.
This data also disproves the hypothesis that birds and bats would possess similar
trends regarding captures and factors such as net location (Figure 2), abundance, richness
(Figure 6), plant density (Figure 4), and fruit density (Figure 5). Several species of bats,
using echolocation, are capable of avoiding mist nets easier than birds, which may have
been a factor in the lack of trends.
As exemplified by Figure 7, the highest bat capture rate was after dusk for both
primary and secondary forests. This is most likely observed because bats are beginning to
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leave their roosting sites to forage. Foraging is also important to consider when thinking
about why some of our hypotheses were disproved, why there were so many differences
between the bird and bat capture data, and why there were so few correlations between
bat capture and the factors analyzed. While bats are known to roost together, it has been
observed that they do not forage together (Wainwright, M. 2002). This is not the case for
birds, which are known to forage in flocks of multiple species ultimately providing
protection during feeding. This may explain why there was a higher richness of birds
captured in comparison to bats.
Bats are known to travel several kilometers per night in order to find their
respective food sources. This may indicate that the bats captured in this study may have
been captured en route to their foraging sites. Therefore the bats captured may not have
been near the nets for the resources around, unlike the birds. This rationale is supported
in this study as some of the collected bat feces were found to contain Piper seeds, a
common food source for Corollia. Piper was not found near our net sites indicating that
the particular bat had been traveling while foraging for food. In addition, the mist nets
were originally placed in areas containing plants known for bird foraging, not bat
foraging, such as Melastomata and Psychotria.
Admittedly, there are some potential sources of error present in our study. First,
fruit may have been located near the nets but not within our sampling distance of three
meters. Thus, abundance of fruit may have been underrepresented for some nets.
Additionally, bats may have been caught near their roosts or at another point of a
potentially long journey towards food sources other than those surrounding the net, such
as Piper or Cecropia. It is possible for captured animals to escape from mist nets and,
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while incredibly unlikely, individuals can be captured more than once. Lastly, due to
collaboration with a group studying birds, mist nets were set up in spots likely for birds to
flock (e.g. those near Psychotria and Melastomata fruit sources) rather than bats, which
may account for the relatively low number of individual bats captured.
Additional experiments, which would likely involve a significant amount of
addition labor and cost, would be able to remove many of the sources of error and biases
found in this experiment. Bat detectors, which have been show to record over 30% more
captures than alternative means such as mist nets, can be utilized to provide a more
accurate sample for measuring bat diversity and abundance. The time intervals for
capture can also be increased to possibly provide a larger sample size and a more
accurate comparison to the bird study conducted by peers. The larger sample size
obtained would make it possible to examine the relationship between frugivore and
nectarivore bats and the fruit density surrounding the nets where they were captured. This
was carried out for this study; however there were only four data points available to
produce a plot of the number of frugivore bats captured versus fruit density. The plot
contained an insignificant P-value (>>o.o5) and a relatively low R2 value (0.66262). If
there was a larger bat sampling size, which may become available after several years
worth of data, a trend may become evident. Lastly, it would be interesting to study
richness and abundance of bats in different seasonal and geographical conditions as they
may differ greatly.
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Conclusion
In this study a higher abundance and richness of bats was not observed in
proximity to the food sources near nets. A higher plant density and higher fruit density
also did not correspond to a higher bat capture number as predicted in the original
hypothesis. No parallel trends were observed between birds and bats at the sampling
locations as predicted. However, the frequency of bat captures was found to be highest
just after dark as originally predicted. Lastly, the primary and secondary forests were
found to contain different species of bats, with the primary forest being more diverse.
References
Carlo, T. Pers. Comm. 2013.
LaVal RK, Rodríguez-H B. 2002. Murciélagos de Costa Rica: BATS. 1 ed. Santo
Domingo de Heredia, Costa Rica: Instituto Nacional de Biodiversidad, INBio,
2002.
Mora, JM. Pers. Comm. 2013.
Wainwright, M. 2002. The Natural History of Costa Rican Mammals. Ed: David
Featherstone. Distribuidores Zona Tropical, S.A. Miami, FL. 2002.
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