From the Wisconsin Department of Natural Resources
-- Deer researchers have succeeded in capturing a total of 187 deer in two study areas as part of a multi-year effort designed to answer concerns hunters have voiced over population estimates. Capture efforts continue through March 2011.
Population estimates are used in part to determine deer hunting season structure.
Spread across two study areas, one centered around Sawyer County representing a northern forest habitat, and one centered in Shawano County representing a farmland-forest habitat, the studies take the closest look yet at the actual percentage of deer taken by hunters compared to all other causes of death. Reproductive rates and causes of death in fawns are also being explored.
"The outpouring of offers to help and assist with providing access to land and deer trapping activities from hunters, landowners and conservation groups has been phenomenal," according to research scientist Chris Jacques. "Without their help it would be very difficult to pull this off and with that help, we can make this a better study that will accomplish more in answering their questions and addressing their concerns."
Captured deer have been fitted with radio collars and ear tags so that researchers can follow them to determine cause of death. New born fawns will also be located and collared for the same purpose. One important question hunters and researchers are trying to learn more about is the percentage of deer, both adult and fawns that are lost to predators such as black bear, bobcat, coyote and wolf.
Two primary methods have been used to date for capturing deer. Ground traps, which are either wooden boxes or netted frames, both with trap doors, and recent efforts to capture deer using nets shot from a low flying helicopter.
Like any statistical survey, as the size of the sample increases-the number of deer captured in this example-the more confident researchers can be that what they observe in the sample accurately represents the population as a whole.
"Capturing as many deer as possible at the start of this project is important," said Jacques, "and helicopters have proven to be the most efficient way to capture large numbers of deer in a short amount of time."
Capturing wild deer can result in unintended mortality. Every animal captured represents an investment in the project in time, effort and expense so researchers take every possible precaution to keep mortality as low as possible. In the case of helicopter capture, keeping pursuit times and transport distances short and limiting handling time from the moment the net drops till the animal is released are important to survival.
Usually, less than 5 percent of captured animals die. Death can be from physical injury such as broken bones or to capture myopathy, a disease resulting from capture-related stress. Mortality rates currently are running at 7.3 percent (9 mortalities in 123 captures) at the Shawano County study site and 4.5 percent (8 mortalities in 179 captures) at the Sawyer County site.
Eight of the 17 mortalities to date have been related to helicopter capture. Necropsies will be performed on the eight to determine cause of death.
"We try very hard to handle deer carefully to minimize stress, but there is really no other way to answer the questions hunters are asking about our population estimating process that doesn't involve capturing and marking these deer and then following them to determine how they die," said Jacques. "We will continue ground trapping efforts through the end of March and at that time we'll review all our notes and data related to both ground and helicopter trapping efforts to increase our deer trapping efficiency and reduce mortalities in future years."
More information on deer research studies is available at http://dnr.wi.gov/org/es/science/wildlife/deer/.