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Wolves of the World

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Methods for Estimating Wolf Abundance

With the advent of radio-telemetry, and because wolves are territorial pack animals, estimating their abundance is relatively straight-forward compared to most other species of free-ranging wildlife.

When it is necessary to accurately estimate the number of wolves in a particular area, wildlife biologists will radio-collar at least one individual in each pack. This is accomplished by either live-trapping wolves or darting or netting them from a helicopter. Though the initial step of capturing and collaring wolves is time consuming, estimating abundance afterward is comparatively easy.

A biologist will locate the radio-collared individual from an airplane and count the number of other wolves traveling with it. This is usually done during winter when snow provides excellent background and tracking conditions for observing wolves. Because the pack often splits as they hunt, multiple observations are needed to determine pack size. Neighboring wolf packs that do not have collared individuals are often located, mapped, and counted. Thus fairly large areas can be censused for wolf abundance. Radio-telemetry can also give biologists an estimate of wolf mortality, territory size, dispersal rates, and the number and type of prey being consumed. The reliability of these estimates is related to the number of wolves and wolf packs collared as well as the number of times they are located and accurately counted.

Radio-telemetry is the ultimate method, but other techniques are used to estimate wolf population size and trends. For example, computer modeling is sometimes used to project baseline estimates that were originally determined from radio-telemetry. This helps keep estimates current but side-steps the continual need for expensive and time consuming radio-collaring studies. In large areas, such as an entire state, it is not feasible to radio-collar a wolf in every pack. In these cases population trend surveys are often used. Trend surveys include: ground and aerial tracking for wolf sign in snow, counting visits to scent stations, soliciting responses to simulated howling, interviewing hunters, trappers and resource professionals, and keeping track of depredation complaints.

Wolf abundance and distribution are monitored annually by the Wisconsin and Michigan Departments of Natural Resources. Both states use a mix of radio-telemetry and surveys for sign and incidental observations.

The Minnesota Department of Natural Resources (MN DNR) uses a method of estimating state-wide abundance which incorporates surveys of wolf sign (questionnaires to resource professionals, scent stations, and depredation complaints) from across the state combined with intensive radio-telemetry studies in smaller areas. MN DNR used this method to obtain state-wide wolf population estimates of 1,235 during the winter of 1978-79 and 1,500 - 1,750 during the winter of 1988-89. The 1988-89 estimate was expanded to 2,000 - 2,200 in 1996 using population modeling combined with new estimates of wolf range, recruitment, and mortality. MN DNR's 1997-98 state-wide survey/census, a technically advanced version of previous techniques, estimates MN wolf population to be 2,450 wolves and was used again in 2004-2005 with an estimate of 3,020 wolves. The MN DNR plans to conduct a wolf survey during the 2007-08 winter season.

Selected References
Fuller, T.K., W.E. Berg, G.L. Radde, M.S. Lenarz, and G.B. Joselyn. 1992. A history and current estimate of wolf distribution and abundance in Minnesota. Wildlife Society Bulletin, Volume 20, pages 42 - 55.

Updated 2007