Greater appreciation through increased knowledge
The rut can be a particularly exciting time to be afield. Bucks and bulls have one thing on their mind. The intense focus on breeding dramatically changes their behavior. Bachelor groups break up, feeding becomes a distraction, and being secretive and discrete is no longer an advantage. Bucks and bulls come out of cover and into the open to chase, court, and guard females. Wild spaces ring with bugles, grunts, and rattling antlers.
To gain greater insight into the world of a rutting male, scientists at the Caesar Kleberg Wildlife Research Institute have been fitting white-tailed deer bucks with collars that contain a GPS unit. These GPS collars record the buck’s location every 20 minutes from the beginning of November through the end of February. This period encompasses the peak of the rut, which is mid to late December in the South Texas study area.
Over the past three years, collars have been placed on over 60 bucks. By analyzing the thousands of locations obtained for each buck, a picture of buck movements before, during, and after the rut becomes clear. To date, we have analyzed data from 33 bucks and the home range of these deer during the 4-month monitoring period averaged 2,967 acres. Although home ranges of over 4.5 square miles seemed large, what was a greater surprise was the huge variation among individual bucks. The smallest home range was 332 acres and the largest was 13,648 acres! There was a general decrease in home range size as deer aged from yearlings to 3 years of age and then an increase in mature bucks.
Daily movements in November averaged just less than 3 miles per day. That movement rate jumped to over 5 miles/day during December and over 6 miles per day at the peak of the rut. Again, there was a great deal of variation amongst individual bucks. For example, during December daily movement ranged among bucks from 2.5 miles to over 8 miles per day.
Excursions, defined as short term (usually less than 24 hours) trips that occurred outside of the home range, peaked in December. In fact, every one of the 33 bucks we have analyzed so far has made at least one excursion in December. Fewer than half the bucks made excursions in other months. Some excursions during the rut covered extraordinary distances. For instance, one buck made an 18-mile, round-trip excursion in early December, then 10 days later made another excursion that covered 11 miles.
So what? There are several lessons that this gee-wiz GPS technology can impart:
- The great increase in movements during the rut explains why hunters are often successful hunting trophy bucks during the breeding season. It also explains why bucks that have not been seen before suddenly show up during the rut, and why they can just as quickly disappear.
- The high rate of daily movement, coupled with bucks focusing on breeding instead of eating, explains why they lose up to 30% of their body weight in a 4-6 week period. The stress of the rut helps explain why 80% of non-hunting mortality in bucks occurs from December to March in southern Texas.
- The large movements of bucks during the rut make it imperative that white-tailed deer are managed at a large scale. One property, even if it is small, can harvest so many bucks that few reach maturity, denying nearly everyone in the region a shot at a trophy buck.
David G. Hewitt is the Stuart Stedman Chair for White-tailed Deer Research at the Caesar Kleberg Wildlife Research Institute. Collaborators on the researched discussed are Aaron Foley, Randy DeYoung, Mickey Hellickson, and Mitch Lockwood.
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