In one study, 27% of natural mortality of the puma was related to injuries sustained while trying to capture prey. The study was published in 1995 and is called Fatal trauma sustained by cougars while attacking prey in southern Alberta. It was conducted by P.I. Ross, M.G. Jalkotzy and P.-Y. Daost.
This is approaching one third of mountain lion attacks on prey which result in injury to the cat which at some time in the future ends up with the injury killing them. It’s quite a remarkable statistic. The problem is that an attack on a prey animal can be inherently dangerous especially if the prey is large. I suppose it is common sense but, for example, deer and elk have sharp antlers and hooves. And if a puma attacks an animal and struggles with it on a steep slope or on unstable terrain they can fall. One study found the carcass of a puma and mule deer lying together. The puma had apparently died of a broken neck sustained in the struggle.
In another puma death it was found that the cat had broken its skull. One puma had died because a piece of wood had pierced its brain. It is speculated that the injury occurred during a struggle with a prey animal.
There are accounts of pumas dying from very bad chest injuries, impalements on branches and toxaemia (in this instance blood poisoning by toxins from a local bacterial infection caused by an injury). It is believed that these kinds of fatalities are more likely to occur to inexperienced cats or old and infirm ones.
Another factor worth taking into account is that if a puma is injured and incapacitated even to a fairly low level it may prove fatal because they are solitary hunters. If they can’t hunt effectively they starve to death. One study reports an adult female injured during an attempt to capture an elk. Both cat and deer had slid down a steep slope and struck a tree. The puma was captured about three weeks later. Her jaw was broken and her two lower canine teeth had been torn out. She also had puncture wounds on her shoulder and hip. She was, as can be imagined, in very poor condition and had lost 30 pounds in weight over those three weeks.
Porcupines can also present a genuine hazard to pumas. They have been found with porcupine quills embedded in their faces and lips. Porcupine quills can be fatal to dogs. I don’t know whether they can be fatal to mountain lions. Perhaps not because, astonishingly, puma faeces sometimes consist almost entirely of porcupine quills which suggest that they have swallowed them without being harmed!