Camera monitoring

Cameras that are suitable for wildlife monitoring are now widely available for affordable prices. Developed and designed for relatively large animals that are the prey of hunters, their usefulness and ease of use for small arboreal animals however vary greatly and all have considerable limitations. 

The range of camera brands and models on the market is gigantic and new models arrive while others are taken off the shelves too quickly to keep track.

Camera trapping has increased our ability to study the behaviour of animals in the wild under ‘natural’ conditions and continuously for long periods without large manpower. They operate in most habitats, day and night and withstand extreme weather conditions. The quality and reliability of the results is a different issue though.

Motion-sensitive, remotely triggered camera traps are useful to confirm species presence, to compile a species inventory, measure population status over time and detect changes early in the process and to a lower degree investigate the behaviour of animals.

There are 2 major types of cameras - white flash and infrared. 
The advantage of white flash cameras is that they show colours even in the dark, which is very useful if the animal in question is hard to identify (e.g. various types of mice) or if attempting to identify individuals by their markings. The bright flash however tends to scare wildlife away and can even cause harm by short-time blinding animals. Wildlife also learns quickly to avoid these cameras.
We are only using infrared cameras for our monitoring work.

Every technology has its own jargon and these cameras are of course no exception. Terminology can even vary between brands which makes reading and comparing manuals a bit tricky.
My problem here is also the fact that all major features work in connection with each other and it is hard to write about one without mentioning others. Confusion is guaranteed.

Camera features

PIR (passive infrared) motion detector
This is the most commonly used infrared system in camera traps.
Sensors on the front of the camera detect the difference between the air temperature and a moving animal’s body temperature and trigger the capture of an image - the greater the contrast between the temperature of the animal and the ambient temperature, the more reliable the output.

The sensitivity of the sensors can be adjusted and needs to be high in summer when air and body temperature are not far apart and if the target species is small.
Cameras claim to detect movement – and take photos – even if the animal is 19 to 30 metres away; however this relates to large animals emitting a lot of heat. If the animals are small, expect a far smaller detection zone. Increased sensitivity also does not guarantee detection of a target.
The detection zone is the area in which the camera will detect motion and heat differences.

The sensors usually form detection bands and the target object must move in or out of the so-formed detection zones. Only Reconyx gives a diagram with the positioning of their sensor bands in their manual. However, even here the detection zone changes with the choice of resolution. For all other cameras I used I could not find any information on the positioning of the sensors which makes it even harder to position the camera according to needs.

A key weakness of PIR sensors is their poor detection of animals if the temperature differential between the background and the animal is low. Observations on a beach (high reflection) can be very problematic and cold-blooded reptiles are also very challenging as they need to be significantly colder than the surrounding environment – which they avoid by warming themselves up in the sun.
Ambient temperature ranges above 31°C seem to limit the reliability of detection of animals for all cameras. This also seems to apply to heavy rain and high humidity.

Auto PIR (also called sensitivity):
It monitors the ambient temperature and automatically adjusts the trigger signal.

Field of View
This is not synonymous with a camera’s detection zone. Usually only a small proportion of the field of view is within a camera’s detection zone. The area captured in the image varies between 35°-50°.

Illumination
All our cameras are low glow or no glow infra-red. Some claim to have ‘black light‘, however that just seems to be another name for no glow as the LEDs are only painted black.

Around 40 built–in infrared LEDs function in the way as a flash would – if flashing wouldn’t have to be avoided in order to be as clandestine as possible. They illuminate the area with infra-red light so that there is enough light to take a photo. The LEDs’ range determines the quality and clarity of the photo. On high sensibility, the illumination range can be up to 19 m.

If an object is very close to the camera, the illumination often results in a loss of recognisability or even a total ‘white-out’ of the object.
Newer camera models have a LED control function (low-normal-high) to reduce the strength of the illumination and to prevent overexposed photos; however that can lead to dark photos during day light.
When using an older model masking tape can be put over some of the LEDs.

Some of the cameras we are using (Bushnell Natureview 119439/40 and 119740) provide close focus lenses (46 and 60 cm) which at least render an animal that is very close to the camera still identifiable.

LEDs are battery powered. If taking videos, illumination for long periods (up to 60 seconds maximum video length) is needed which would draw the batteries down fast.

Trigger speed (also called response time or trigger latency)
This is the time between the camera’s first detection of heat in motion and a photo taken. The faster the trigger speed the more likely a quickly moving animal is captured in the photo. Slow trigger speeds lead to ‘false positives’ - photos without the triggering object captured. 
If observing slow moving objects that stay in one spot – for instance a feeding station – for an extended time, low trigger speeds are adequate, however faster trigger speeds will in general increase probability of detection.

Technology has improved greatly in this regard. Our oldest camera has a trigger speed of 1.344 seconds while the newer models have 0.2 seconds. However, in the field also those new models often do not live up to the factory claims as other features such as the distance of the object have an influence.

Trigger interval (or recovery time)
This is the time needed between successive triggers.
The fastest setting is 1 second while in our experience older models take 3 to 7 seconds. The default for this interval is usually set to 10 seconds but it is programmable to up to 60 minutes if a high number of photos of an animal that spends considerable time in one spot is to be avoided..

The fastest camera we use is Reconyx which can produce up to 2 frames per second in ‘rapidfire mode’ when switched to low resolution (wide and narrow photo).

Night Vision Shutter (NV)
This shutter controls the speed during night triggers. Higher speed leads to more clarity of the image and will reduce the blur caused through movement, however this does not increase detectability.
Newer, more expensive camera models can be set to high, medium or low shutter speeds.

Resolution
A choice of 3, 5 or 8 Mega Pixel is the usual standard for older models, while some new models have added 14 MP.

Reconyx is different and hard to compare with other brands as they offer a choice between 1080 pixel and 3.1 MP.

The higher the resolution, the lower is the shutter speed which can result in blurred images.  As in all cameras long exposures carry the risk of blurred photos.

Field Scan
This is a time-lapse feature that allows to choose a time span when the camera is to operate – for instance only between 9 pm and 6 am, or only once every hour. If there is any activity outside the set time frame, some cameras would nevertheless take those photos in addition.
Most new cameras can also be set to day or night use only.

Capture Number
Most cameras offer a choice of how many photos are taken in sequence per trigger – usually 1 to 3 exposures. Reconyx, which has no video function, can take 10 photos in fast succession which comes close to video recording. Several photos in a row increase the likelihood of successful identification of a target.

False triggers
Slow trigger speeds, moving vegetation, rain, movement of light, they can all trigger photos without a discernable reason. Some brands/models are more prone to this then others and the more expensive cameras usually produce less ‘false positives’. 

A ‘false negative’ would accordingly occur if no photo is taken despite of the clear presence of an animal. False negatives cannot be verified or quantified unless someone (or another camera) is watching.
They are however the most frustrating feature of all cameras we use - ringtails seem to wear invisibility cloaks!

Covert cameras
The illumination caused by infra-red cameras is invisible to our human eyes – just as the marketing claims. However, according to newer research (Meek et al, 2015) predators not only detect the presence of camera traps; they modify their behavior in response.
This clearly applies to kangaroos as well and l would assume that for most wildlife species our cameras are far from clandestine and non-intrusive.

SD - SDHC cards
This kind of camera can use SD cards that store up to 32 GB, which means masses of single photos. Only if videos are recorded, this can fill up quite quickly.
We mostly use 16 GB as we never leave the cameras unchecked for longer than a fortnight.

Most cameras have a formatting feature that would delete all existing files and prepare the card for reuse. For control what is deleted or not, this function should be switched off but then the contents of the card needs to be manually (selectively) deleted.

Reconyx (800 and 900) are different as camera features can be set via a SD card ‘pre-programmed’ in the computer. Even though the SD card will be reformatted by the camera, the chosen settings will stay active until they are altered again via SD card or directly in the camera.

SD cards have a ‘write protection switch’ which, if in locked position, will stop the camera from recording photos. They usually come switched to ‘unlocked’ but in case of a problem, the position should be checked.
Also, if cards are used in several camera brands, the formatting should be checked as some devices can alter the formatting of the card. 

In addition to capacity, card ‘speed’ is an important feature. The higher the speed the quicker data (photos) can be transferred to the card from the camera.

Speed class C10 and U3 are supposedly only important for videos but our comparison of C10, 8 and 4 cards showed quite different results also for still photos - from no photos at all (4), few photos (8) to a high number of photos (10). We tested this with 2 or more cameras of the same brand/model in a row with the same settings but different class sd cards. 
U3 seems to make a difference only when transferring data to the computer but not in the field.

We also compared write/read speeds 30-45-60 and 90. The differences were too small to quantify. It only makes a difference when hundreds of photos are to be transferred to a computer fast.

We also tried to investigate whether the number of false positives/negatives is strongly influenced by the SD cards but there seem to be far more complex relationships at work between several components - the camera features and quality, SD card and batteries. 

Most cards claim to be waterproof, shockproof and x-ray proof. However changing cards during rain sometimes caused their failure.

There are some extremely cheap cards on the market, but the incidence of failure seems higher particularly in long-term usage.  Extremely cheap could also mean fake.

We have no experience so far with micro cards that need an adapter.

Some brands (e g SanDisk) offer data recovery programs which make it possible to recover deleted files.  This can be very useful if working simultaneously with several cameras or several operators transfer data and there is a risk of confusion what has already been transferred to the computer.
However, if the ‘format’ option is switched on (camera set-up), recovery is impossible!

Photos can also be downloaded straight to a Mac or Windows computer without swapping the SD card over. This can extend the longevity of the cards.
Lt Acorn is not compatible with Mac computers.

Batteries
4 batteries are the minimum requirement for any camera to work, however, 8 or if possible 12 batteries produce the best longer term results.

Lithium AA batteries are recommended for infra-red cameras but they are very expensive and their use borders on environmental vandalism if using high numbers of cameras over long periods of time.

Rechargeable batteries (NiMH) are not recommended but for financial and environmental reasons we use Eneloop and rarely had any problems.
Reconyx HC 600 and PC 900 only operate on NiMH rechargeable batteries or Energizer 1.5 AA Ultimate Lithium batteries.

Alkaline batteries will not provide the quality performance and are badly affected by hot and cold weather. High temperatures can however also reduce run-time of rechargeable batteries by up to 50%.

The claim that batteries will last up to a year cannot be verified by us for any camera we use. The suggestion to recharge batteries every 3 months if in constant use might reduce their life span but as 2100 recharges are reportedly possible, this should not be an issue. 

In our experience some cameras tend to take more day photos when battery power gets low, which then draws them down even faster. Photos also can get darker when batteries are low.

Batteries have to be fitted carefully as movement of the camera can lead to a loss of contact if there is no proper barrier holding them in place. Even if the loss of contact is only temporary, settings such as day/time stamps will be lost.