This page is archived as part of Mississippi State University's history. It may refer to situations which have changed or people who are no longer affiliated with the university.
Mississippi State University

Bobcat (Lynx rufus)

Survival and Mortality


Results


We used 68 bobcats (28 male, 40 female) to estimate survival and cause-specific mortality. Of 31 bobcat mortalities, causes of death were as follows: 14 (45%) were incidental harvest (shot), 10 (32%) were unknown, 4 (13%) were to vehicle collisions, 2 (6%) to other bobcats, and 1 (4%) to feline panleukopenia. Half of unknown deaths occurred during fall-winter; thus, incidental harvest was potentially causal.

Mean annual survival was 0.75 for males (range = 0.62-1.00) and 0.84 (range = 0.44- 1.00) for females. Annual survival did not differ between sexes (P = 0.182), nor did annual survival differ among years (P = 0.865). Survival did not differ between the breeding-gestation (1 February - 31 May) (0.98) and parturition-young rearing (1 June - 30 September) (0.95, P = 0.176) or between the parturition-young rearing and fall-winter (1 October - 31 January) (0.86, P = 0.915). However, survival was lower in breeding-gestation than fall-winter (P <0.001).

Survival during breeding-gestation (P = 0.09) and fall-winter (P = 0.073) did not differ between sexes, although both tests approached significance with males having lower survival. However, survival during parturition-young-rearing differed between sexes (P = 0.019), with females (0.92) having lower survival than males (0.99). Lastly, males experienced higher probabilities of incidental harvest than females (P = 0.011), whereas only females died from vehicle collisions. Females were more likely to experience mortalities during parturition-young rearing (P = 0.042) than males. However, males and females were equally likely to experience mortalities during breeding-gestation (P = 0.812).

Using fall-winter harvest probabilities and hunter effort recorded on TWMA by year, we detected no relationships between deer hunter effort and incidental harvest probabilities for females (P = 0.110) or males (P = 0.799). Probability of mortality from human-related factors (incidental harvest, vehicle collision) was not correlated to hunter effort for males (P = 0.799) but was for females (P = 0.046).

Mean distance moved between consecutive locations in diurnal periods during fall-winter was 444 m for males and 312 m for females. Distances moved between consecutive locations in diurnal periods did not differ (P = 0.153) between sexes. Movement rates during diurnal periods averaged 450 m/hr for males and 369 m/hr for females, and movement rates did not differ (P = 0.492) between sexes.

During crepuscular periods, distances moved between consecutive locations averaged 541 m for males and 368 m for females. Distances moved between consecutive locations did not differ (P = 0.136) between sexes. Movement rates during crepuscular periods averaged 489 m/hr for males and 446 m/hr for females and did not differ (P = 0.736) between sexes. Probability of incidental harvest was correlated with crepuscular distances moved (P = 0.049) and movement rates (P = 0.058) for females. We also detected correlations between diurnal distances moved and probability of incidental harvest for females (P = 0.054). For males, we detected no relations between crepuscular distances moved (P = 0.272) or movement rates (P = 0.280) and probability of incidental harvest, nor were diurnal distances moved (P = 0.462) or movement rates (P = 0.478) correlated with probability of incidental harvest.

Summary

Annual survival rates of adult bobcats on TWMA and GP were similar to those reported in other southeastern studies, but considerably higher than in northern latitudes. Incidental harvest accounted for substantial proportions of bobcat deaths, although legal trapping pressure was absent. Temporal patterns in mortality were similar between our study and others, with peak exploitation of bobcat populations occurring during trapping-hunting seasons.

In exploited bobcat populations, male survival is generally lower than females. However, exploitation rates on TWMA and GP were lower than in most other studies. Because of physiological demands placed on solitary female felids, such as those required for lactation and kitten rearing, we hypothesized that female survival during parturition-young-rearing might be lower than for males. Our data supported this hypothesis, indicating that parental care responsibilities may influence female survival and fitness. For bobcats, energetic requirements of females during lactation may increase by 2-3 times. Thus, lower female survival in our study during parturition-young-rearing may be a direct consequence of parental care responsibilities, influenced by increased energetic requirements relative to males.

Male bobcats typically maintain larger home ranges and core-use areas than do females and exhibit greater movement rates than females, particularly during fall-winter, coinciding with fall white-tailed deer hunting seasons and early breeding. Given these differential life- history characteristics, we hypothesized that male bobcats would be more susceptible to incidental harvest, and that male movement patterns would be correlated to probability of incidental harvest. Our data rejected the hypothesis that no sex-specific differences existed in incidental harvest probability, indicating that male bobcats had higher probabilities of incidental harvest, and although not statistically different, lower survival rates during fall-winter relative to females.

We observed a relationship between female movement patterns and susceptibility to incidental harvest, which suggested susceptibility increased during years with higher mean movement distances and rates. Female bobcats likely locate home ranges to ensure sufficient resources for their survival and survival of their kittens, and they must hunt their home ranges more intensively, which requires large amounts of prey from smaller areas relative to males. If higher movement rates indicate increased hunting activity, our data suggest females hunting extensively within their home range are more susceptible to mortality from human-related factors. However, the relations between prey availability, hunting patterns, and subsequent susceptibility to harvest on TWMA and GP is unknown.

Management Implications

Legal trapping did not occur during the long-term project and in the absence of legal trapping, incidental harvest was the dominant cause of mortality. We suggest that managers consider the magnitude of incidental harvest when implementing harvest limits on bobcat populations. Our data indicate that male bobcats are more susceptible to incidental harvest than females. However, female mortality appears to increase during kitten-rearing periods, likely a function of parental care responsibilities.