Spotlight and Daylight Cruise Survey of Deer: Methods and Materials
Agricultural Division In this Publication: |
Part 2: Methods and Materials
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 (click figure to enlarge)
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When to Conduct Spotlight and Daylight Cruise Surveys
Spotlight surveys conducted in late August or in September allow the observer
to identify the sex and age of deer more accurately. Earlier in the season,
fawns are more difficult to see because they are smaller and less mobile,
and bucks' antlers may not be well developed. Later in the season, fawns
may be large enough to confuse with does. Surveys generate information that
helps determine harvest quotas and is most useful before deer hunting season.
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.
Figure 2 A 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. (click figure to enlarge) |
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 - PDF file) 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 - PDF file) 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.
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Next: Interpreting the
Data
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