Spotlighting deer in the name of science

Email to a Friend  Print this Article

Creeping slowly along the back roads of Redwood County, spotlights slicing through the darkness from either side of the pickup cab, the man and woman were on a mission: Find deer.”Last night we counted 54 deer, but the night before we only saw eight,” the woman noted. “The weather is better tonight so we hope to see quite a few more.”

They were nearly an hour into their search before the driver’s spotlight reflected off the eyes of a deer in a field. “There, right there, see it?” he said quietly to his female companion. By the time they called it quits three hours later, they would catch another 28 deer in the glare of their spotlights.

Wendy Krueger, Minnesota Department of Natural Resources (DNR) wildlife manager at Slayton, and Dick Tuszynski, retired Mille Lacs Area DNR wildlife manager and currently a temporary DNR Wildlife employee, were the shiners on this recent night in southern Minnesota.

Armed only with spotlights, a range-finder, clipboard and protractor, they are part of an ongoing DNR study to determine deer densities through the use of spotlighting and distance sampling.

Counting deer from a helicopter in the winter, along with deer harvest registration data and other biological information, have been the standard methods for estimating deer populations. However, aerial surveys are expensive and highly dependent on having sufficient snow on the ground to be able to accurately count deer.

Marrett Grund, a deer research scientist at the DNR farmland populations and research station at Madelia, said distance sampling is about 10-15 percent of the cost of aerial surveys. It’s also thought to be a more accurate barometer of deer numbers largely due to the “visibility bias” of aerial surveys. Visual impediments due to thick ground cover can obscure deer from observers in the air, especially when snow cover is inconsistent.

In 2005, the DNR began to look more closely at spotlight surveys and distance sampling in the state’s farmland zone state. As do agencies in other states, the Minnesota DNR has traditionally used both aerial surveys and deer harvest information to estimate white-tailed deer density and set hunting seasons.

The research is finding that population estimates derived from distance sampling can be used to recalibrate, or correct, population models, Grund said. “Often the population models were giving us population estimates three times higher than the estimates from distance sampling,” Grund said. “The population model might have been telling me that there were nine deer per square mile, but in fact there were only three deer per square mile. These findings have considerable implications for wildlife managers.”

If, for example, deer density is under estimated, the harvest regulations might be set too low. That could unwittingly result in an overabundance of deer with a commensurate increase in deer depredation problems and vehicle-deer collisions. It would also decrease hunter opportunity to harvest deer.

Krueger and Tuszynski are one of eight two-person DNR teams that have been spotlighting deer around the DNR’s southern region this spring. Each team drives a different 20-mile route each night with instructions to travel it at between 10-15 miles per hour. When deer are spotted, the driver stops, a range-finder determines the distance to the deer, and a protractor is used to measure the angle of the deer from the vehicle. That information, along with the number of deer seen and the time, are promptly recorded on a chart.

Once Grund receives the recorded information, it is analyzed in mathematical computer models to determine deer densities. By applying geometric calculations and other proven science to analyze the data, Grund said, “We are confident the results will be more reliable than previously and that will help us to more effectively manage the deer population and set hunting seasons.”

Reader Comments

Would you like to comment?

Sign up for a free account, or sign in (if you're already a member).