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Spotlight and Daylight Cruise Survey of Deer: Collecting and Interpreting Data

Methods and Materials

Russell Stevens

By Russell Stevens
Strategic Consultation Manager and Wildlife and Range Consultant

Posted Jan. 1, 1999

Why Conduct Spotlight Surveys

Intelligent natural resource management is based on an inventory of the resource in question. Harvest quotas are used when the deer population is managed via intensive hunting, are specific for quantity, sex, and sometimes age, and are intended to shape the herd's composition. In general, quotas are based on results of the deer population surveys from the current year, deer harvest records from the previous year, and long-term trends from both.

Many deer population estimation procedures requiring various amounts of time and money have been developed. Each method has unique strengths and weaknesses; none is always accurate. The spotlight survey is accepted widely as a practical method of estimating deer population trends in areas with openings in timber and brush. Deer density and buck : doe and doe : fawn ratios obtained from spotlight surveys are merely estimates, deer density being the most useful.

Selecting Spotlight Survey Routes

Permanent survey routes (figure 1) should be selected after a careful examination of the ranch's habitat types and follow all-weather roads so that inclement weather will not prevent sampling of particular areas. The selected route should sample each area only once and traverse habitat types (upland brush, bermudagrass pasture, cropland, bottomland timber, native range, etc.) in proportion to their existence on the ranch. Do not include a route leg only because it crosses known deer concentrations; the survey is only a sample of a portion of the habitat on the ranch and must be as representative as possible. Longer routes are better if they can be completed within three to four hours. Observer fatigue and weather changes (fog, rain, etc.) can be a problem on longer routes. The same route should be used each year so that data will be comparable among years.

figure 1

When to Conduct Spotlight and Daylight Cruise Surveys

To minimize sampling bias, choose a consistent time to begin each spotlight survey, but start no earlier than one-half hour after sunset. A minimum of five surveys conducted within a two- to three-week period minimizes the influence of weather and other factors on deer activity. Ideally, wind speeds should not exceed 15 to 20 miles per hour, there should be no rain, and the temperature should not be excessively high.

Always notify the local game warden before each spotlight survey is conducted.

Sample size for buck : doe and doe : fawn ratios can be supplemented by mobile or cruise surveys conducted just after daylight. Daylight cruise surveys should be conducted at the same time of the year as spotlight surveys. Ideally, a minimum of 100 deer should be identified for data interpretation. The spotlight and daylight cruise survey and visibility estimate forms are shown in attachments A, B, and C, respectively.

Equipment Used to Conduct Spotlight Surveys

A large Rubbermaid storage container can be used for seating and holding equipment: two magnetic antennas to serve as "spider web catchers" when placed on the vehicle's cab, spotlights powered by a battery attached to homemade cable, tape to secure the cable to the vehicle, and extra batteries and spotlights.

Spotlights with 400,000 candlepower work best; those with less intensity sometimes are too weak, while those with more may lack field of view.

The data recorder can use a small flashlight so the dome light can remain off and reduce windshield glare for the driver.

Two-way headsets are a convenience that can enhance communication between the driver and observers, reducing the need for loud talking or tapping.

Conducting Spotlight Surveys

Use a vehicle with an open bed so observers have an unobstructed view while traversing ranch roads. Ideally, surveyors include a driver, two observers and a data recorder. Duties of personnel are as follows:

  1. The driver should travel five to eight miles per hour and tell observers when to take visibility estimates.
  2. Ideally two observers, one on each side, are located behind the cab. They should scan the area constantly, covering an arc from the front center to the rear center of the vehicle to look for deer or their eyes' reflection (figure 2). Incidental sightings of other animals may need to be recorded, depending on the surveyors' objectives.
  3. Visibility estimates (table 1) should be taken every 1/10th mile. Observers estimate the distance in yards at right angles to the vehicle. Deer detection and identification is questionable beyond 250 yards, where the maximum visibility is arbitrarily set. Visibility estimates should not be taken across canyons, through trees, or past other objects or topography that may conceal deer.
  4. The data recorder registers pertinent pre- and postsurvey information, visibility estimates, and deer sightings. This information (attachment A) should include the ranch name, starting and ending time, weather conditions, names of personnel conducting the spotlight survey, and number of fawns, does, bucks, unknown deer, and other animals observed.
Figure 2

figure 2A doe and fawn spotted on the 9/15/95 spotlight survey. If you look closely, you can see the fawn standing behind the doe. The fawn's ear can be seen above the doe's rump.

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