High losses documented during U.P. fawn mortality study

Marquette, Mich. — If fawn mortality during the second year of a fawn survival study in Iron County is any indication, U.P. hunters are not likely to see many yearling whitetails this fall, at least in the northern half of the region. Seventy-six percent of the 50 fawns that were captured for the study during 2013 are known to have died, and the fate of the remaining fawns is unknown because they lost the radio collars they were wearing.

Iron County is in what is normally considered the U.P.’s medium snowfall zone, but snowfall has been heavier than normal U.P.-wide the past two winters. The 9-year study is designed to compare fawn survival in low, medium, and high snowfall zones of the U.P.

To gather data in each zone, pregnant does and primary deer predators such as wolves, coyotes, black bears, and bobcats are captured and fitted with radio collars. When does give birth, as many fawns as possible are captured and fitted with radio collars, too, to determine how many survive and the causes of mortality among those that die.

Besides monitoring the survival of collared deer, researchers monitor collared predators and try to determine how many deer they prey on.

The first three years of the study were spent in Menominee County, which is in the low snowfall zone. Another year of research is planned for the Iron County study area before moving to the high snowfall zone.

Twenty-six (52 percent) of the fawns that were part of the Iron County study during 2013 were lost to predators, according to Dean Beyer, DNR wildlife research biologist. He reported that nine fawns were killed by coyotes, five by black bears, three by wolves, two by bobcats, and one by a fox. Predation accounted for the deaths of six fawns where it was impossible to determine which predator was responsible.

Other causes accounted for the deaths of another dozen fawns (24 percent). Two were dead at birth, for instance, and the deaths of three more were attributed to “weak fawn syndrome.” Another fawn died from maternal neglect, and three suffered trauma. What caused the trauma in two of those cases was unknown, and a vehicle struck one.

One fawn died of an illness that resulted in its lungs filling with fluid. Two fawns died of starvation and exposure during the recent winter. The radio collars fell off of the remaining 12 fawns (24 percent).
“We are no longer monitoring any fawns that were captured last year,” Beyer wrote in an email March 18. “This does not mean no fawns captured this summer are surviving, as there have been 10 known collar failures (mostly due to faulty locking mechanism) and an additional two collars found that may have fallen off. It is important to note that the collar failures occurred between July 3 and Oct. 9, 2013, while most fawn mortalities occurred during the month of June.”

Twenty-two (46 percent) of the 48 adult does that were fitted with radio collars last winter also have died, according to Beyer, and only two of those deer were hunter kills. One of the two hunter kills was unrecovered by the hunter. The unrecovered doe was found near a road on Oct. 8, 2013, with an arrow in its chest. A third doe was killed illegally.

Predators were responsible for killing 13 (27 percent) of the does. Coyotes pulled down eight, wolves got four, and a bobcat claimed one of them.

Capture myopathy (stress related to capture) was responsible for three doe deaths within 10 days of being handled. The cause of death was unknown for two does, and one died as a result of birthing complications related to malnutrition. That doe was found dead on April 30, 2013 – one of the many thousands of deer that died of malnutrition in the U.P. last winter.

“To gauge malnutrition, we looked at both the general body condition and the bone marrow,” Beyer said. “We gave that doe a body condition of 1 (our lowest score), indicating that there were no fat deposits along the ribs, shoulders, or rump. The marrow was also red and very soupy, indicating poor condition.”

Even though that doe’s fawns were underdeveloped due to her poor condition, one was in the process of being born when she died. A second underdeveloped fawn was in her uterus.

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