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\begin{document}

\title{A portable Raspberry Pi-based camera setup to record behaviours of frogs
and other small animals under artificial or natural shelters in remote
locations}



\author[1]{Jordy Groffen}%
\author[2]{Conrad Hoskin}%
\affil[1]{James Cook University}%
\affil[2]{James Cook University - Townsville City Campus}%


\vspace{-1em}



  
  \date{May 21, 2024}


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\selectlanguage{english}
\begin{abstract}
Here, we describe a Raspberry Pi-based camera system that is portable,
robust, and weatherproof, with a close-up focus (2.5 cm). We show that
this camera system can be used in remote locations with high rainfall
and humidity. The camera has an Infrared LED light to film in dark
places and can continuously record for 21 days. We also describe how to
make concrete artificial shelters to mount the camera in. One of the
great strengths of this shelter/camera setup is that the animals choose
to take up residence and can then be filmed for extended periods with no
disturbance. Furthermore, we give examples of how shelters and cameras
could be used to film a range of behaviours in many small cryptic
amphibian species, but also other small vertebrates and invertebrates
globally.%
\end{abstract}%



\sloppy


\textbf{Introduction}

Understanding animal behavioural responses to environmental variation
and change is a frequent goal in animal ecology and has important
implications for conservation (e.g., Hopkins \emph{et al.} , 2023;
Kays\emph{et al.} , 2015; O'Brien \emph{et al.} , 2023a). However,
collecting behavioural data on animals, especially in remote areas, is
very time-consuming and requires a lot of effort and resources. Camera
systems are increasingly used to remotely monitor wildlife because they
can record behaviour over long and continuous periods and are generally
non-invasive (see reviews: Cutler \& Swann, 1999; Jolles, 2021;
Trolliet\emph{et al.} , 2014). Camera systems can be commercially built
systems (e.g., Meek \emph{et al.} , 2014; Trolliet \emph{et al.} ,
2014), which are ready to use and generally compact but can be expensive
and have less flexibility in program settings, battery life and data
storage (Cox\emph{et al.} , 2012; Prinz \emph{et al.} , 2016; Reif \&
Tornberg, 2006). Alternatively, they can be do-it-yourself assembly,
which can be more flexible and cheaper (e.g., Cox \emph{et al.} , 2012),
but can be time-consuming to make and harder to use.

Self-assembled camera setups generally use a microcomputer, typically
Raspberry Pi (www.raspberrypi.org) or Arduino (www.arduino.cc) (Allan
\emph{et al.} , 2018; Greenville \& Emery, 2016; Johnston \& Cox, 2017).
Raspberry Pi-based video recorders have been used in animal behavioural
studies; for example, behavioural studies of the waggle dance of
honeybees (Ai\emph{et al.} , 2017), the spacing of foraging fruit flies
(Churchill\emph{et al.} , 2020), nematode behaviour (Nu\selectlanguage{ngerman}ñez \emph{et al.}
, 2017), monitoring of mammal populations (see review Swann \emph{et
al.} , 2004), respiration and pupil dilation in laboratory mice
(Kallmyer \emph{et al.} , 2017; Privitera \emph{et al.} , 2020), avian
studies assessing nest box use, parental care and other behaviours (e.g.
Hereward \emph{et al.} , 2021; Prinz \emph{et al.} , 2016; Zárybnická
\emph{et al.} , 2016). The use of Raspberry Pi units to collect video
data on behaviour in amphibians has, to the best of our knowledge, only
been conducted on Hellbender salamanders (\emph{Cryptobranchus
alleganiensis} ) in the United States (O'Brien \emph{et al.} , 2023a,b),
where cameras were used in artificial aquatic shelters to described
courtship and parental care behaviours and nest outcome. Self-assembled
cameras can also be combined with other sensors; for example,
temperature and humidity sensors (McBride \& Courter, 2019).

Artificial shelters have been proven to be a successful tool to monitor
amphibian populations. They have an advantage over labour-intensive
trapping and observation methods (Sutherland \emph{et al.} , 2016) and
reduce disturbance to the animals and their environment (Hesed, 2012).
Artificial shelters built with the option of camera observation are a
good way to obtain important behavioural data while minimising impacts
on animals or their habitat. Once an animal is using a shelter, it can
be observed for extended periods using a small camera that is serviced
without any disturbance to the animal or the shelter. However, many
amphibian species are small, so cameras need to focus on small subjects
at close range. Furthermore, many amphibian species live in remote areas
(e.g., mountain tops), so shelters and associated camera setups need to
be small and transportable and have long recording periods. Previous
studies have made portable camera setups, but the minimum focal distance
is 15--25 cm (Hereward \emph{et al.} , 2021; O'Brien \emph{et al.} ,
2023a, b) and the recording time is limited to a maximum of 96 hours
(O'Brien 2023a, b). These cameras are of limited use for the study of
small animals under shelters, and need to be serviced regularly or
recordings need to be short and/or well-spaced in time.

In this study, we describe and test a Raspberry Pi camera setup that is
portable, robust to weather, can continuously record for 21 days (504
hours), and has a focal distance of 2.5 cm. The camera setup was tested
on a small (approximately 3.5 cm long) microhylid frog species that
lives among leaf-litter, logs and rocks on remote mountaintops in north
Queensland, Australia. We also describe two artificial shelters to mount
the cameras in. The combination artificial shelter/camera setup we
present could be used to collect natural history and behavioural data on
any small, cryptic vertebrate or invertebrate species.

\textbf{MATERIAL AND METHODS}

\emph{Camera set up}

For the camera setup, we used a Raspberry Pi 4 microcomputer circuit
board~with a 5-megapixel 1080P camera (25 mm x 24 mm x 17 mm) with a
130\selectlanguage{english}0 adjustable night vision fisheye lens (focus 2.5 cm) and a single 5
mm infrared LED light (Fig. 1). We removed the round part of the
infrared LED light using a belt sander and added a small
semi-transparent piece of sticky tape to diffuse the light throughout
the filming chamber (Fig. 1). A Rpi-RTC DS1307 clock module keeps
accurate time while not connected to the internet. The microcomputer was
placed in an IP65 waterproof electrical junction box (158 x 90 x 60 mm)
with four 1 g silica gel desiccant packets. Three holes were drilled in
the junction box: two on the long side for waterproof cable glands (fits
cables between 3--6.5 mm) and one on the bottom for the PVC male adaptor
(SKU 436-010; 3 cm). The power source cable (USB type C) and the USB
extension cable were inserted individually through one of the two cable
glands and together into a 1.5 m long stainless-steel shower hose to
prevent damage by rodents (which chew exposed rubber or plastics). On
the side of the stainless-steel hose, the cables were inserted
individually through cable glands in an IP67-rated waterproof PVC box
(38.8 x 28.9 x 24.3 cm). In this box, the USB power cable is connected
to a power converter (12 V to 5 V) connected to a 130 Ah LiFePO4 lithium
battery (10 kg).~A 1 TB USB drive is connected to the USB extension
cable (Fig. 1).

Trials by (Mouy \emph{et al.} , 2020) have found that USB storage used
more energy than SD card storage, therefore lowering battery life, and
USB storage was less reliable because of its more fragile connection.
However, O'Brien \emph{et al.} (2023a, b) and Kallmyer \emph{et
al.}(2017) successfully used 64 GB and 32 GB USB storage in their study,
respectively. In this study, we chose a 1 TB USB storage~because the USB
drive and battery are separated from the microcomputer; which has the
benefit that the USB drive and battery are replaced in the field after
21 days (often during rain and 90\%\textgreater{} humidity), we do not
have to open the box with the microcomputer and camera to potential
damage by moisture. The total cost for the 21-day camera setup is
AUS\$790.75 (Table 1).

The camera length can be easily adjusted for different habitats. For
example, when filming animals under leaves or artificial shelters (Fig.
4), we used the camera setup with the camera directly placed in the PVC
male adaptor (4 cm width) and the lens focusing at 2.5 cm. To ensure
that water could not enter the PVC male adaptor, a PVC coupling was
placed with a glass lens glued inside and a rubber O-ring was placed
between the connections. This way, if necessary, we could still change
the focus of the camera by removing the coupling. For filming under
natural or artificial wood shelters (`logs'; see paragraph ``artificial
shelters'' below), we use a 20 cm long and 4.2 cm wide PVC pipe in the
converter, which goes over the male adaptor. The camera and the infrared
LED light were held in place at the end of the PVC pipe with a
3D-printed holder against the glass lens. Both the camera and battery
box were covered with square mesh (mesh size 1~x 1 cm) to protect the
plastics from chewing by rodents. To record the temperature and humidity
a datalogger (Hygrochron iButton) was placed in the chamber when the
camera was recording (Fig. 5).

The Raspberry Pi was coded to start recording when it powered on, and
for continuous video recordings of 15 minutes each. These recordings run
back-to-back but a 15-minute duration was chosen to keep the file size
of each recording manageable (O'Brien \emph{et al.} , 2023a). The
`continuous' recording stretched for 21 days. Videos were saved to a 1
TB USB drive, creating folders of the month followed by folders of the
day. The videos themselves were labelled with time (hour.minute.second)
(Appendix 1; for detailed instructions on how to program the Raspberry
Pi see e.g. Hereward \emph{et al.} , 2021; Youngblood, 2019).

\emph{Artificial shelters}

We designed the artificial shelters based on the preferred
nesting/sheltering microhabitat of microhylid frogs, as described by
Felton \emph{et al.} (2006) for \emph{Cophixalus ornatus} (now \emph{C.
australis} ; Hoskin, 2012). Sheltering and nesting microhabitats are
essentially small crevices or holes in soil or wood, or under leaf
litter, logs or rocks. The objective was to make artificial shelters
that contain small spaces and can have a camera inserted to film any of
these spaces (i.e., a `chamber') that is in use.

Two artificial shelter types were constructed, one using wood and one
using concrete. The wooden shelters were made by splitting logs found at
the site (e.g., from a tree fall near a road or path) (Fig. 2A). By
splitting the log in half, we produce a flat surface to place against
the ground (Fig. 2B). The resulting log size (i.e., surface in contact
with the ground) was an average of 60.4 cm in length x 18.5 cm in width.
When a frog occupied the shelter and we decided to film, a 42 mm wide
hole was drilled through the log to fit the camera. The diameter of the
drill hole reflected the size of the end of the camera so that it can be
neatly inserted. We also sourced sink plugs of approximately 40 mm
diameter and filled these with concrete, so that these could be used to
block the hole when the camera was ultimately removed. The concrete was
used to add weight to the plug and to add thermal buffering to the
chamber.

The concrete artificial shelters are rectangular concrete blocks of
(29.5 x 22.5 x 4.5 cm), with six rounded (42 mm diameter) nesting
chambers, each with two entrances/exits (Fig. 3B).~A~plug hole is
present above each nesting chamber so that the plug can be lifted to
inspect the nesting chamber. The plug sits atop a 40 mm wide and 35 mm
long piece of PVC pipe. The plug has concrete packed into it to better
buffer the nest chamber. We constructed concrete artificial shelters
using a four-two-one concrete mixture (four parts crushed rock; two
parts sand; and one part cement). One-third of the concrete was poured
in a 4 L Tupperware container, and then six 42 mm-wide plastic-wrapped
PVC pipes were equally distributed in the concrete, placed vertically to
make chambers and a galvanized 1 x 1 cm mesh hardware cloth was placed
around them. The other two-third of the concrete was then poured into
the Tupperware container around the PVC pipes. Pieces of garden hoses
(each 3 cm) were placed in the concrete where the entrances/exits going
to be (Fig. 3A). The whole Tupperware container was then placed on a
vibrating plate to remove air bubbles. After drying for at least 48
hours, the PVC pipes and garden hose pieces were taken out of the
concrete. The shelters were then soaked in water for 3 days and then
dried completely in the sun before being deployed in the field. The cost
of making the shelters was AU \$20, per mould (4L Tupperware, 42 mm x
100 mm PVC pipe, and 10 pieces of 3 cm garden hose), AU\$3 for the
concrete shelter (concrete, sand, crushed rock, and galvanized mesh
hardware cloth) and about AU\$18 for the six lids per shelter (sink
plugs, PVC pipe, screws, concrete mixture) (Table 1). So, once you have
the moulds, which are reused, the total cost per shelter is around
AU\$21 (US\$14), with potential labour costs not included (Table 1).

\emph{Testing the cameras and artificial shelters}

The camera setup and artificial shelters were tested in the Paluma Range
(north-east Queensland, Australia), where a small (3.5 cm body length)
microhylid frog (Robust Whistling Frog \emph{Austrochaperina robusta} )
occurs at high abundance. This species is restricted to mid-elevation
and upland rainforest, living among the leaf-litter and under logs and
rocks (Hoskin \& Hero, 2008). It is extremely cryptic, other than the
loud whistling calls of males calling after rain. \emph{Austrochaperina
robusta} is a terrestrial breeding frog, with direct development
(tadpoles develop within the eggs), and the small clutch is laid in
leaf-litter and under logs and rocks and is attended by an adult frog
(Hoskin, 2004). Details of breeding biology, including the role of the
adult in caring for the eggs and metamorphs, as well as their year
around microhabitat use are unknown due to the small size and cryptic
lifestyle.

Thirty artificial concrete and 30 wooden shelters were placed in a known
high-density \emph{A. robusta} area between November 2022--January 2023.
To test the most risk-prone parts, switching out batteries and USB drive
in the field, we used 30 mAh 12V batteries that can run up to 5 days.
Cameras were deployed 14 times during the subsequent breeding season (21
November--23 February), with a minimum deployment of a camera being 3
days and a maximum deployment being 30 days at a shelter. During this
period, the batteries and USB drives of the cameras were changed every
3--5 days. This involved a total of 62 battery and USB changes.

\textbf{RESULTS}

Twenty-four out of the 30 concrete shelters and 19 out of the 30 wooden
shelters were occupied at least once by \emph{A. robusta} during the
field test period. Cameras were placed in 11 shelters, each of which had
a different \emph{A. robusta} individuals. The film quality was
generally excellent, including good lighting (Fig. 5), and a total of
850 hours of video footage with an \emph{A. robusta} in view was
generated. Eight individuals stayed longer than 5 days in a chamber that
was being filmed, while three stayed over 30 days. This suggests that
the camera was accepted by the frogs, and not a source of disturbance.
In addition to frogs, various other species sought refuge under the
artificial shelters and were captured in the video footage. These
included other small vertebrates (skink species) and invertebrates such
as ants, earthworms, velvet worms, cockroaches, and millipedes.

Although the cameras were thoroughly tested before being deployed in the
field, a few issues arose during field testing. In two camera setups,
the dates and times displayed on the video files were inaccurate after
batteries were replaced. To resolve this issue, we reran the codes for
the clock, which successfully fixed the problem for one camera. However,
we had to replace the clock module in the other camera. In one camera
setup, the brightness of the Infrared LED light decreased in some videos
before eventually turning off. This occurred towards the end of the
expected video duration and was likely due to the lower voltage
available. The issue was resolved by changing the battery and always
using fully charged batteries. The final issue was that despite
adjusting and testing each camera's focus before deployment, some
cameras produced out-of-focus video. This was primarily attributed to
the camera sliding down too deep (and hence out-of-focus) in the shelter
setup. This was sometimes due to the camera hole in the artificial
shelters being slightly wider than the camera PVC pipe, causing the
camera to slide down too far. In other cases, it appeared that the
camera had been moved during filming, probably due to disturbance from
wildlife such as brush turkeys or feral pigs. To address these issues,
we applied multiple layers of Duct tape around the camera PVC pipe to
secure it in place and prevent any sliding or moving. Another common
cause of unfocused videos was the gradual elevation of the soil beneath
the camera due to the burrowing behaviour of earthworms, but this could
not be prevented.

We initially envisaged that the camera setup could be damaged by
moisture. They were sitting in a wet rainforest environment with regular
heavy rain, and the 62 battery and USB drive changes were all performed
in \textgreater{}90\% humidity and sometimes during rain. However, no
water damage was observed on the cameras, batteries, or USB storage
drives. This was even the case for one of the cameras which spent time
with its lens end underwater when one of the chambers was flooded during
heavy rain. The camera kept recording and was not damaged.

\textbf{DISCUSSION}

In this paper, we have described and demonstrated the successful
building and testing of a Raspberry Pi-based camera that produces high
quality close-up (2.5 cm) videos and is portable and weatherproof. The
camera setup can record continuously for up to 21 days in remote
locations, and we have demonstrated how they can be used in natural
settings or paired with artificial shelters. The cameras could be used
for many different research topics, in many different species and
settings. Collecting long-term continuous behavioural data, especially
in the field and from small species, is very intensive and often
logistically not possible (for example, at night or when the animal is
in their shelter). This camera setup will enable behavioural data to be
collected on the natural history of small and cryptic species.

A benefit of the camera is that you have control over programming when
to record. In this trial, we programmed the camera to continuously
record for 21 days. We recommend starting with this method to get an
idea of the species daily time budget. However, the camera can be coded
to record whatever data is required for the specific research questions;
for example, for 30 minutes every four hours, or only day- or
night-time. Specific recording periods will increase battery life and
increase the camera data collection time. The self-assembled camera
setup could be combined with sensors such as temperature and humidity
loggers (McBride \& Courter, 2019). We deployed the cameras on a
mountain in the tropical rainforest which has high rainfall (average
annual rainfall of 2534.7 mm) and humidity during the summer months of
\textgreater{}90\% 24 hours a day. We therefore did no attach
temperature and humidity sensors because adding these would have
required extra holes to be drilled, increasing the chance of moisture
entering the setup. Adding sensors would also decrease the battery life.
The goal of this study was to build a camera setup that is robust,
extremely weatherproof, with as long as possible recording time, and
relatively cheap to make. We did use separate temperature and humidity
sensors (Hygrochron iButtons), which are robust and don't connect to the
camera setup or battery (Fig. 5).

The artificial shelters proved to be very successful because they were
voluntarily occupied by the frogs in high numbers and enabled filming at
optimal distance. Importantly, they also enabled extended behavioural
observations without influencing the frog's behaviour. Obtaining
sheltering and breeding information in a species like this would
otherwise require regular turning of logs and other cover, disturbing
(and potentially injuring) the frogs and damaging the micro-habitat. Due
to this success, we now have increased the number of shelters and
expanded the research to other upland areas, with the objective of
recording the breeding behaviours and breeding success of Critically
Endangered microhylid frog species. While both artificial shelter types
(concrete and log) were successful, filming and maintenance of the
concrete shelters was easier, due to the sturdier and stable material,
and the predrilled holes. In addition, the log artificial shelters will
disintegrate and fall apart with time and will need to be replaced. In
contrast, the concrete shelters will last and will increasingly
`integrate' with the environment (e.g., moss growing on them,
leaf-litter falling on them).

During our trial many other species of small animals occupied the
chambers and were filmed. Of particular interest were cockroaches
(\emph{Periplaneta australasiae} ) that occupied the shelters for short
periods of time. We discovered that the infrared LED light used in the
camera setup illuminate through the exoskeleton of the cockroaches,
showing the internal organs (Fig. 4C). In one set of filming, the
infrared LED light showed that one of the cockroaches had a gut parasite
that could clearly be seen moving internally. This shelter/camera setup
could be used to study, for example, the prevalence of gut parasites in
cockroaches in different habitats, the development of the gut parasite,
and the effect on the cockroach.

A strength of this shelter/camera setup is that the animals choose to
take up residence and were then filmed with almost no disturbance.
Servicing of the batteries and storage cards does not impact the camera
end or shelter. We suggest these shelters and cameras could be used to
film a range of behaviours, for example, parental care behaviour,
shelter use, species interactions, and courtship behaviour, in many
cryptic amphibian species and also other small vertebrates and
invertebrates, globally.

\textbf{Acknowledgements}

We would like to thank Sam Pratt (Virginia Tech), and Russell Warburton,
Wayne Morris and Dean Frendon (James Cook University) for their help
with development of the camera software and hardware. Furthermore, we
like to thank Amendra Perera (James Cook University) for access to the
workshop and equipment to build the concrete shelters. We also like to
thank the many volunteers who participated in fieldwork. This research
was conducted under James Cook University animal ethics approval A2857
and Queensland Government scientific research permits WA0046995 and
P-PTUKI-100306983-1.

\textbf{Funding information}

This work was funded by the Holsworth Wildlife Research Endowment Grant
(Ecological Society of Australia), the Skyrail Rainforest Research Fund
(Skyrail Rainforest Foundation), and a Ric Nattrass Research Grant
(Queensland Frog Society Inc.).

\textbf{Data availability statement}

All data and code are available in the main text or the supplementary
material: Table 1. and Appendix 1.

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\textbf{Table and Figures}

Table 1. Items, and their costs, required to build a camera setup that
can record continuously for 21 days.

Figure 1. Circuit diagram of the camera setup (A.), and a photo of the
camera housing (the Raspberry Pi unit is inside the black electrical
junction box; B.).

Figure 2. Wooden ``natural'' shelter in place (A.), and photo showing
the underside of the natural shelter installed in the field, the ground
is cleared from leaves before the shelter is being placed (B.).

Figure 3. Construction of an artificial concrete shelter (A.), and photo
showing the underside of the resulting concrete shelter, with the six
chambers and associated entrances/exits (B.).

Figure 4. Example of how the camera is placed in an artificial concrete
shelter (A.), a natural log (B.), and in leaf litter (C.).

Figure 5. Video screenshots of animals in chambers of the concrete
shelters. (A.) Two \emph{Austrochaperina robusta} next to the
temperature and humidity data logger (Hygrochron Ibutton). (B.)
An\emph{A. robusta} showing defensive behaviour against an intruding ant
(red arrow). (C) A cockroach, and (D.) a millipede grooming itself.\selectlanguage{english}
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\textbf{Hosted file}

\verb`Table 1.docx`  available at \url{https://authorea.com/users/661133/articles/664342-a-portable-raspberry-pi-based-camera-setup-to-record-behaviours-of-frogs-and-other-small-animals-under-artificial-or-natural-shelters-in-remote-locations}

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