Figure 16.—Injury to left front foot of specimen M-196. (Photo courtesy of L. D. Mech).
Figure 17.—Healed fracture of left hind leg of specimen M-227. (Photo courtesy of University of Minnesota Veterinary Diagnostic Laboratory.)
Because the data show that wolves in our study area tend to kill a disproportionate number of older deer, it is not surprising to discover that wolves also tend to capture a disproportionate number of individuals with abnormalities and pathological conditions ([table 8]). The explanation for such selection is obvious in regard to the abnormalities of the lower limbs ([figs. 14]-[17]): deer with injured or abnormal limbs simply cannot run as fast or as agilely as normal animals ([table 7]). Our observations show that deer usually depend on their alertness and speed to escape approaching wolves (Mech 1966b, Mech et al., p. 1). Any trait or condition that tended to interfere with either alertness or speed would decrease an individual's chance of escape.
It is more difficult to explain how dental abnormalities or pathological conditions of the mandible ([figs. 8]-[10]) would predispose an individual to wolf predation. However, in the case of dental abnormalities the genetic or environmental conditions that caused the abnormality might also have caused some other trait that increased the animal's vulnerability. Or the abnormal condition itself may have caused a further, more critical, disruption of the animal's physiology or behavior, which in turn predisposed it to wolf predation.
The finding of several wolf-kills with poor fat stores could indicate that primary or secondary malnutrition was a factor in the animals' deaths. However, it would take a statistical comparison between the fat stores of the deer at large and those of the wolf-kills to establish this.
The discovery that 13 percent of the fawns and 84 percent of the yearlings killed during January, February, and March had not yet shed their deciduous incisors and premolars, respectively, also fits well with the rest of our information. Evidently some unusual factor had caused the delay in tooth development and replacement. One possibility is that the animals were born in August or September, much later than normal. Although most deer in Minnesota are born in May and June, there are records of births in July and August. In addition, a fetus 181 to 200 days old was found in a doe killed on September 26 (Erickson et al. 1961).
An alternate explanation for the delay in tooth replacement is that the animals were suffering from malnutrition or nutrient deficiency. Severinghaus[35] has evidence that yearling bucks that have not replaced their deciduous premolars during November, and thus are aged at 17 months (Severinghaus 1949), generally have shorter, narrower antlers and fewer points than 18-and 19-month-old individuals. Degree of antler development in turn is considered related to nutritional state (Latham 1950). Thus it is reasonable to conclude that animals behind in tooth development and replacement, whether this is caused by age or diet, are physiologically inferior.