Survey guidelines for Australia’s threatened non-flying mammals

3.3.3Spotlighting

Spotlighting is a survey method used at night to detect nocturnal species while they are active. It is effective for both arboreal and ground-dwelling species of all size classes, although arboreal mammals are most easily detected by this method. Spotlighting is conducted in a similar manner as a diurnal survey (Section 3.3.1), in that an investigator searches for active fauna, but in this case the target species are nocturnal and the investigators search area is defined by a spotlight. The survey is conducted at night with the aid of a spotlight to detect the animals in the dark, usually as a result of their eye shine, but night-vision scopes can also be used for sightings from stationary or hidden observation points (not discussed further here as a survey method).
Spotlight surveys are of limited use in dense vegetation as the light cannot penetrate far enough from the observer. In habitats with dense understorey vegetation, spotlighting can be conducted along clearings or tracks either by an observer on foot, or from a vehicle. Investigators must consider, however, that species may avoid road verges or other habitat edges that are suited to spotlight surveys. Where surveys are carried out in these areas species may go undetected.
The distance that fauna can be detected from the observer will vary depending on the nature of the subject site and an investigator’s experience. Lindenmayer and colleagues (2001) indicate that the probability of detecting arboreal mammals during spotlight surveys is similar for distances up to 50 metres from the transect line. Therefore, transects placed 100 metres apart are optimal for arboreal mammal spotlight surveys, as the area surveyed between adjacent transects does not overlap.
Weather conditions are also known to influence the success of spotlight surveys as extreme temperature, rainfall or wind can reduce animal activity and also make it more difficult for an observer to see fauna. Laurance (1990) found that arboreal mammals in a North Queensland tropical forest were significantly less active when the temperature became cooler, which indicates the importance of climatic conditions during surveys. Temperature has not quantitatively been related to activity for most species but investigators should take a cautious approach by avoiding conducting surveys during inclement conditions such as heavy rain, strong wind or extremely hot or cold temperatures. To reduce the potential that climatic conditions may influence the survey outcome, surveys should be repeated over two nights and across all seasons if it is possible. Goldingay and Kavanagh (1988) found the detectability of feathertail gliders using spotlighting changes with the visibility of the moon.
The equipment and methods used for spotlight surveys are as follows:

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  use of a light hand-held spotlight (minimum of 30 watt for open forests and woodlands; minimum of 50–75 watt in tall or closed forests) that is easily carried and is powered by a suitable battery (for example, portable, sealed lead acid rechargeable batteries). Extra batteries and globes are advisable to overcome equipment failure
  
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  the spotlight should be held near the observer’s line of vision to maximise the chance of detecting eye shine (light reflected from animals’ eyes). If the spotlight is held beyond the direct line between the observer’s eye and the eye shine of the animal, then the eye shine reflection is difficult to detect
  
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  the spotlight beam should be moved slowly at a consistent speed over the relevant habitat (for example, ground level for ground-dwelling species)
  
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  binoculars should be used once an animal has been spotted to confirm the species identity and to record any distinguishing features
  
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  the direction of travel should be decided in advance, either by locating a track or by marking out a transect with flagging tape. In this way the observer moves a known distance at a set speed (for example, 10 metres per minute walking [Van der Ree & Loyn 2002], or approximately 5 kilometres per hour in a vehicle along a forest track) to ensure that the planned survey effort is achieved
  
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  spotlighting should be conducted as quietly as possible. This is so that animals are less likely to be disturbed and carry on with their normal activities rather than hiding or fleeing before they can be seen. It also means that the observer is more likely to hear any calls or other noises that may indicate the species presence and location.
  

Light type, such as a White V redfitter, and light strength are important when spotlighting. Most ecologists recommend 30 or 50 watt, as 100 watt is too bright and most animals will look away, making it difficult to detect species using eye shine.

Recommended survey method

Survey effort will vary according to factors such as size and shape of the subject site and density of understorey vegetation. However, as a general guide, the following recommendations are suggested for spotlight surveys conducted on foot (per person) for a 5 hectare subject site (that is, 50 000 square metres) (Note: transect distances are indicated as a guide only and are expected to vary according to the size and shape of the subject site):

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  use a hand held spotlight (50 or 75 watt) and adhere to the method described above
  
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  survey at least two 200 metre transects per 5 hectare site (or longer transects for larger sites)
  
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  maintain an interval of at least 100 metres between the two transects in order to maximise the area surveyed, which is usually 1 kilometre
  
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  the location of transects must be selected to sample appropriate habitats (see species profiles) occurring within the subject site. It is important to note, however, that transects will go through many habitats
  
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  move at a speed of 10 metres per minute, hence a 1000 metre transect will take 100 minutes (1 hour and 40 minutes) (this is a conservative estimate that is expected to vary according to the observer’s experience and the vegetation density at the site). It is also beneficial to spend time standing still or searching trees with binoculars
  
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  spotlight surveys along transects should be repeated on two separate nights where possible
  
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  avoid very windy or rainy nights as these conditions can reduce fauna activity and the observers' ability to detect fauna
  
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  investigators must be adequately experienced with the technique, and be able to distinguish species using a combination of detection of eye shine and close-up examination using binoculars.
  

Vehicle based spotlighting is only recommended for some macropods and considered a poor alternative for most other species.

Animal care and ethics considerations for spotlight surveys

Spotlight surveys must also be conducted according to the relevant animal care and ethics requirements, with as little interference inflicted on the animal’s wellbeing as possible. This includes minimising the amount of time that a spotlight is shone directly on fauna, using a light with a narrow beam to reduce the blinding effect that the light may have on the animal’s vision and, when practical, using a red or preferably a dimmer switch to reduce light intensity for prolonged observations once the animal has been spotted.