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Mississippi State University

Raccoon (Procyon lotor)

Survival and Mortality


Results


TWMA

We used 176 raccoons (131 males, 45 females) to estimate survival and cause-specific mortality patterns. Of 69 known raccoon mortalities, 5 (7%) were attributed to human-related factors, 11 (16%) died from natural causes, 22 (32%) were legally harvested by raccoon hunters, and 31 (45%) causes of death were unknown. Eight of 31 raccoons (26%) classified as dying from unknown causes were near (within home range) individuals confirmed as dying from canine distemper; thus, distemper possibly caused mortality in those instances. No raccoons were taken by trappers during the study.

Annual survival was higher (P = 0.031) for males (0.63) than females (0.50). We detected no differences in survival between sexes during breeding-gestation (P = 0.439) or during fall-winter (P = 0.349). However, we detected differences in survival between sexes during parturition-young rearing (P = 0.023), with females (0.93) having higher survival than males (0.83).

Within sexes, male survival during breeding-gestation (0.82) did not differ (P = 0.887) from survival during parturition-young rearing. However, male survival during parturition-young rearing (0.83) differed (P = 0.048) from survival during fall-winter (0.91). Similarly, male survival during fall-winter was greater (P = 0.022) than survival during breeding-gestation.

Female survival during breeding-gestation and parturition-young rearing did not differ (P = 0.191 and P = 0.184, respectively) from survival during fall-winter. However, female survival was less (P = 0.012) during breeding-gestation (0.65) than parturition-young rearing (0.93).

Cause-specific mortalities did not differ among years (P = 0.978) or between sexes (P = 0.116). Most (58%) confirmed deaths resulted from legal harvest. Confirmed deaths from canine distemper occurred during 1991, 1992, 1996, and 1997. Raccoons were more likely (P = 0.025) to experience mortality from natural causes during breeding-gestation than parturition-young rearing.

GP

We used 31 raccoons (23 males, 8 females) to estimate survival and cause-specific mortality from 1 January 1996 - 31 December 1997 on GP lands. Of 7 known raccoon mortalities, 1 (14%) was attributed to vehicle collisions, 1 (14%) was illegally harvested, 2 (29%) died from natural causes (canine distemper), and 3 (43%) causes of death were unknown. No raccoons were taken by trappers during the study.

Mean annual survival was 0.81 for males and 0.94 for females. Annual survival did not differ between sexes (P = 0.17). Survival did not differ (P = 0.847) between breeding-gestation and parturition-young rearing. However, survival differed (P = 0.057) between breeding-gestation and fall-winter with greater survival during fall-winter. Similarly, survival differed (P = 0.039) between parturition-young rearing and fall-winter with greater survival during fall-winter.

Cause-specific mortalities differed among years (P <0.001), seasons (P <0.001), and between sexes (P <0.001). Unknown causes and disease accounted for most (71%) confirmed deaths whereas harvest was non-existent. Unknown deaths comprised a substantial proportion of mortalities due to accelerated decomposition rates during spring and summer when unknown deaths occurred. Both confirmed deaths from canine distemper occurred during 1997 by males sharing large portions of the same home range.

Summary

Annual survival of adult raccoons on TWMA was similar to rates reported in previous studies in the southeastern United States. However, temporal patterns in mortality on TWMA differed from other studies. Peak exploitation of raccoon populations often occurs during fall-winter trapping and hunting seasons. However, on TWMA low exploitation prevailed during fall-winter across the study and no harvest occurred on GP. Annual variations in survival across the study period were a function of differential effects of epizootics and varying temporal exploitation regimes. Likewise, the observed lack of survival differences between sexes during breeding-gestation and fall-winter was from low exploitation, particularly with no legal trapping occurring during the study.

Patterns of mortality differed across seasons, although survival did not differ between sexes during breeding-gestation. Canine distemper was most prevalent during breeding-gestation. Based on raccoon necropsy, distemper affected raccoon populations on TWMA during late fall-winter 1991, breeding-gestation 1992, and breeding-gestation 1996-97. Male raccoons maintain larger home ranges and predominately exhibit greater movement rates during breeding periods. High movement rates, coupled with increased home range size during breeding, could increase the likelihood of males contracting epizootics through increased social interactions, during breeding versus other seasons. Additionally, increased interactions between males and females during breeding periods likely results in increased susceptibility of contracting epizootics for both sexes. On GP, male survival was lowest during parturition-young rearing periods, due to death of 3 males that exhibited grouping behavior. These points support our findings that cause-specific mortality rates over the long-term study did not differ between sexes.