Mortality

 

Of the fifteen radio-collared bobcats tracked over the 23 months of study, by the time the study ended on December 26, 1997, only seven remained alive (M02, F03, M04, F05, F06, F12, and M15). Though the sample size is too small to generate any useful statistics on causes of deaths or sex and age-dependent mortality rates, some inference about causes of death can be made as detailed in what follows.

It is not fully known what killed M01 or how it was that he died. His collar was located in the mortality mode at the bottom of a drainage canal that paralleled a forest road on the extreme western side of the center of his lifetime range on September 27, 1997. The canal was seven meters wide and estimated to be at least four meters deep, based on depth measurements with a measuring pole. The signal of the collar was emanating from the bottom of the canal. With the use of the pole as a probe to locate the collar, it was determined that there was a large fallen tree lying just above the canal bottom just above the collar. The collar could not be retrieved. It is possible that an alligator might have killed M01 and cached the body, with collar intact, under the tree. But this is mere speculation. Equally true, he could have been killed by a hunter and the collar tossed into the canal by the hunter. Regardless, cause of death in his case was deemed as undetermined.

F07 was found dead in the middle of a large mixed cypress and hardwood swamp on June 4, 1997. Her body was floating in one meter of water, still intact. The only apparent wound or injury detected was a 4-cm wide hole on the right side of her abdomen. No clues about how the hole came to be were evident. Despite a slightly advanced state of decay, flesh around the wound was intact and did not provide any indication of its origins. Cause of death was undetermined.

M08 was shot by a hunter on the opening days of general gun hunting season in the fall of 1996. His body, with his collar in mortality mode, was found on November 14, 1996 inside a den located within tree fall that had been covered with briar vine. Extensive examination and necropsy took place with the help of Florida Fish and Wildlife Conservation Commission then-veterinarian assistant Mark Cunningham. His wounds included an entry wound to the back of the left thigh, a large exit wound to the front of the thigh, a fractured femur near the hip joint, and injury to his left upper jaw, canine, pallet, and surrounding soft tissues. Bullet fragments were found embedded within the wound to the mouth. They consisted of lead fragments sheathed with copper. This indicated that the round that struck M08 was a full metal jacketed round and likely fired from a high powered rifle typical for use with deer hunting. Since general gun hunting season had begun on November 9, this is all the more plausible. Bullet fragments were also recovered from the thigh area. Given the location and nature of these wounds, it is surmised that the round first struck the back of the thigh, then broke apart as it struck the femur, shattering the femur on impact. Bullet fragments then exited the front of the thigh, taking with it massive amounts of muscle and skin. A fragment then proceeded forward to strike the jaw [his head was likely rotated to the left at the time], incurring the damage there as secondary injury to the main wound on the thigh.

Internal organs were examined for state of decay at necropsy and indicated that the time between when he had died and when his body had been recovered was short, likely within 8 hours. He was found at 10 AM on November 14. Thus, M08 expired sometime on the night of the thirteenth or early morning on the fourteenth. The lower digestive tract and stomach was removed an examined for food material and parasites. A few blades of grass were found in the stomach as well as a number of maggots. The stomach was not damaged by the gunshot wound, nor were any internal organs. Nor were any organs or interior spaces of the abdomen necrotic except for the liver, which merely possessed a slight discoloration (darkened). There were no entry points into the chest or abdominal cavity through which entomological agents could gain access. Thus, it was determined that the presence of maggots in the stomach was the result of ingestion, likely because M08 was licking or grooming his wounds. The thigh exit wound did possess a moderate maggot load. The exit wound was rather large, about 10 cm across. The muscle tissue was heavily damaged and necrotic, as was the surrounding skin in that area of the thigh. Necropsy also indicated that M08 was severely dehydrated and on the verge of starvation. Given all these factors, it was concluded that M08 received the gunshot wound around the ninth or tenth of November (Saturday or Sunday). He apparently lived with the wound for a few days until he died on the 13th as a result of a combination of starvation, blood loss, septicemia, and infection by the ground-borne bacteria, clostridia, which is known to lead to gangrene in compound fractures and gunshot wounds.

F09 was found, with her collar in mortality mode, within the hollowed trunk of a dead oak tree within a hydric hammock in the middle of her range on February 20, 1997. The tree was standing upright of its own accord. The trunk was about 5 m tall. The hollowed out portion existed in the upper 2 m of the tree. There was a hole through a knot at the top of the trunk through which she apparently gained access into the tree. Her body was found resting on the interior bedding at the 2-m level. She was extremely emaciated and dehydrated. Her stomach contents consisted of a small woody twig and about 50 ml of fluid. Her body was sent to Dr. Melody Roelke at the National Cancer Institute in Frederick, Maryland for post-mortem evaluation. Due to the advanced state of decay, cause of death could not be determined. There were no visible wounds on her body.

M10 was found lying in the open on the ground in a mixed conifer and hardwood stand in an advanced state of decay on October 9, 1997. Scavengers had fed on his abdomen and hind legs prior to recovery, thereby making determination of death difficult. No gunshot wounds or other causes of death could be found or determined.

M11’s body was not recovered upon detection of his collar’s mortality signal on December 26, 1997. The collar was found in the middle of an old field. The leather had been ripped apart on the portion opposite the transmitter housing. There were no signs of a struggle or fight with another bobcat or other animal. The collar’s leather material did not possess any bite marks. The rip did not appear to be the result of anything but that caused by a human being. It is speculated that M11 was shot by hunters while moving through the field, who then removed the collar by tearing it apart. This was likely done so that the hunters could take the body for taxidermy mounting without the risk of being tracked and found with the use of the collar. Thus, the cause of death for M11 was deemed due to be the result of hunter activities.

F13 was killed by a hunter just prior to September 27, 1997. Her body was found on the 28th located within a palmetto thicket adjacent to the end of a rectangular clearing that had a hunting tree stand located at the opposite end. The length of the clearing was about ten meters. Her wounds consisted of a penetrating wound to the upper abdomen that went all the way through from her left side to the right. The stomach and liver were in the pathway of this hole and each was sliced transversely along this path. The path of the wound was triangularly shaped in cross section. The shape of the lacerations to other tissues along the path of this wound, as well as those inflicted to the stomach and liver indicated that it was a tri-tipped broad head arrow that killed her. Thus, hunting activity wad deemed as the cause of death.

F14 was killed by an automobile on County Road 349 on June 5, 1997. During the course of tracking F14, she had never come close to this paved high-speed roadway and always remained deep within the forest to its west.

Of the eight cats that died in the study, three (38 %) deaths were due to hunters, four (50%) were due to unknown causes, and one (12 %) was due to automobile collision (Figure 67). Thus, a total of 50 % of the deaths were known to be human related. Due to hunting alone, three of fifteen (20 %) of the bobcats in the study population were killed by hunters. Thus, despite the scant data, hunting pressures in the Mallory Swamp were present and appeared to be a major factor in bobcat mortality. However, it is not known what effect hunting imposed on population demographics or what level of harvest occurred annually over a statistically larger sample size. According to local hunters in the area, bobcats appeared to be only opportunistically hunted as trophy sport and the demand for fur by trappers did not seem to be a major factor in hunter related deaths. Deer, hog, and turkey were the chief game for hunters in this part of Florida.