By Jared Hedges, MIT Wildlife Specialist

Each year when winter arrives, the Wildlife Program begins gearing up for one of our biggest events of the year – mule deer captures on the eastern slope of the Cascades. This year, based on pilot and Wildlife Program staff availability, capture dates were set for February 21-24. 

The Program had previously conducted a 2-day capture effort in December resulting in 8 deer captures, but this February effort was the culminating event. At 5:00 a.m. on a Wednesday morning, with all of the gear checked, packed, and checked again, Wildlife Program staff headed east for four days of deer captures.

Wildlife biologists have several methods of capturing deer for research: ground darting, using netted box traps, and helicopter net gunning. The Wildlife Program uses all three methods, but where deer spend the winter in more open landscapes, helicopter net gunning is the clear winner.

Three crews are necessary for an effective net gunning operation.  Crew One consists of the pilot, a “gunner” and a “mugger.” When a group of deer is located, the pilot swoops in to within shooting distance, in constant communication with the gunner on how to best position the helicopter. 

When the opportunity feels right, the gunner shoots the 12 x 12-foot net from the open door at the deer below and the deer’s forward momentum causes it to tangle itself immediately. With the capture confirmed, the pilot finds a place to land, allowing the gunner and mugger to run out and secure the deer and begin the sampling process. 

With Crew One busy with the captured deer, the pilot flies back to the Landing Zone (LZ) to pick up Crew Two. This two-person crew is shuttled to Crew One’s location, where they take control of the deer and continue the sampling, collaring, and release process. 

The gunner and mugger then get back to the helicopter to resume their search. When deer number two is captured, Crew One (remember, the gunner and mugger) secures the deer while the helicopter returns to the location of the first deer to pick up Crew Two, who should be done processing deer number one. 

This leap-frog method continues as more deer are captured, or until the helicopter needs to refuel – usually around the 2-hour mark. Crew Three, the LZ Crew, has an equally important (albeit less glamorous) role. They act as ground support, maintaining radio contact with the pilot and crews at periodic intervals, repacking nets, and outfitting biological sample kits as needed.

Once the deer is secured, the sampling process begins. The first step when handling the animal is to put a mask on them to reduce their stress level. There is a threat of what’s called “capture myopathy,” which is exertion-induced muscle damage associated with extreme exhaustion, struggle, or stress during capture. For this reason, our biologists take every precaution to reduce stress on the animals while handling them. 

The rest of the process is actually quite simple – outfitting the deer with a GPS collar, taking a blood sample to assess pregnancy, completing the data sheet, and untangling the deer from the net before release. The entire process, from initial netting to release, takes anywhere from 5 to 15 minutes per deer, depending on the specifics of the scenario. 

Terrain, degree of entanglement, and body position of the deer all factor in, making each capture a unique experience. The most important piece here, after staff and animal safety, and the main reason for these captures in the first place, is the GPS collar. 

The data collected from GPS collars are immensely valuable from a management perspective. To give some context as to how much data can be obtained from one collar, a deer was collared in 2013 and went on to live at least until 2019 when its collar battery was exhausted and went off air, providing the program with 6.5 years of data and 2,375 locations. And that’s just one deer! 

The data from the deer are being used for survival analyses, causes of mortality, home range delineation, migration routes and migratory behavior, age structure of the herd, pregnancy rates, and many more valuable population parameters. 

Pregnancy rates obtained from blood serum are an indicator of animal condition and habitat quality, herd productivity, and hunting opportunity. Low pregnancy rates usually indicate poor-quality habitat or low buck-to-doe ratios, and high pregnancy rates usually indicate higher-quality habitat and an adequate number of bucks. Biologists then use that information to help them make decisions on how to improve the habitat deer rely on.

This year, overcoming persistent low-lying fog and a few greenhorns on the team, the crew was able to capture 51 deer over 6 capture days. The data collected from these 51 new individuals, and 107 already marked deer still on air, will provide additional insight into the health of the deer herd we have studied since January 2013, helping the Wildlife Program to better understand their current status, as well as any future needs.

Saturday, February 14, signaled the end of this year’s mule deer capture effort. Under overcast skies, the crew packed up and headed back west, feeling both exhausted and contented, grateful to be doing our part to ensure the sustainability of one of the Tribe’s most valued natural resources – the mule deer.