Northern Prairie Wildlife Research Center
Fifty-one percent of the recovered foxes were trapped, 28% were shot, and 21% died from other causes (e.g., collision with vehicles). Foxes were recovered up to 8.6 years after being tagged. Twenty-two foxes were recovered as pups and three of those (1 F, 2 M) had dispersed. Those pups were recovered 12, 14, and 24 km from their release sites on 6 June, 15 August, and 24 September, respectively. Two of 4 foxes (3 F, 1 M) recovered ≥7 years after being tagged had not dispersed; both were females.
|Table 1. Number of red foxes tagged as pups in eastern North Dakota and recovered, 1969-73.|
|Year||Sex||No. Tagged||No. Recovered||Recoveries by age-classa (yr) as a percentage of number tagged|
|< 0.5||0.5 < 1.0||1.0 < 2.0||> 2.0b|
Years after tagging; year starts annually on 1 April and ends on 31 March.
b Includes 1 male and 1 female that were 7.7 years old and 2 females that were 8.6 years old.
Straight-line recovery distances were determined for 322 adult foxes tagged as pups (Table 2). Recovery distances ranged from 0 to 302 km. Thirty foxes were recovered >80 km from release sites; there was no difference (χ² = 0.189, 1 df, P = 0.66) in proportion of males (9.9%) and females (8.5%) recovered >80 km from release sites. Three foxes recovered >200 km (246, 274, and 302 km) from release sites were females. There was no interaction (F = 0.27; 2, 316 df; P = 0.76) between age-class and sex for recovery distances. Recovery distances increased as age-class increased and was greater for males (Table 2). Recovery distances increased linearly with age-class (F = 21.6; 1, 316 df; P < 0.001). No quadratic trends were detected (F < 0.01; 1, 316 df; P = 0.99).
Table 2. Dispersal and straight-line recovery distances of 322 adult red foxes tagged as pups in eastern North Dakota and recovered as adults, 1969-73.
|Recovery distance (km)|
|Males||0.5 - <1.0||128||24||12||1-153||64|
|1.0 - <2.0||35||35||21||0-147||77|
|2.0 - <8.0||29||46||26||8-131||97|
|Females||0.5 - <1.0||72||19||3||0-302||29|
|1.0 - <2.0||25||24||5||1-246||36|
|2.0 - <8.0||33||33||9||0-274||52|
|a Years (Apr-Mar)
b An additional 7 males and 12 females were recovered by recovery location was insufficient to calculate recovery distance.
c Recovery distance increased with age-class (F = 11.5; 2, 316 df; P < 0.001) and was greater for males (F = 26.6; 1, 316 df; P < 0.001).
Proportion of Foxes Recovered That Dispersed
One hundred eighty-four (57%) foxes, for which recovery distances were available and which were recovered as adults, dispersed. However, the proportion of recovered foxes that dispersed varied by sex and age-class (Table 2). Sixty-four percent of males and 29% of females recovered as adults during their first year after tagging had dispersed (χ² = 22.5, 1 df, P < 0.001). Of foxes that were recovered as adults, 77% of males and 36% of females had dispersed the second year after tagging (χ² = 10.3, 1 df, P = 0.001), and 97% of males and 52% of females had dispersed during years 3-8 after tagging (χ² = 15.7, 1 df, P < 0.001). For males, proportionally more recovered from older age-classes had dispersed (χ² = 12.9, 2 df, P = 0.002); a similar but weaker relationship was found for females (χ² = 4.9, 2 df, P = 0.09).
Recovery directions of the 137 males that were recovered as adults and were known to have dispersed were: east (34%), south (18%), west (16%), or north (32%) of the release sites. This distribution was not uniform (χ² = 13.7, 3 df, P = 0.003). Recovery directions of the 47 females that were recovered as adults and were known to have dispersed were: north (43%), east (26%), south (6%), or west (26%) of the release sites. This distribution also was not uniform (χ² = 12.3, 3 df, P = 0.006).
We evaluated the hypothesis that littermates dispersed in similar directions. Eighty-two pairwise combinations of recovered littermates involving 102 foxes from 43 litters were used in the analysis of within-litter similarities in direction of dispersal. Pairwise dispersal angles of 39% of recovered littermates were ≤45° of each other and 65% were ≤90° of each other compared with expected values of 27% and 53% for nonlittermate tagged foxes recovered as adults, respectively (χ² = 6.43, 3 df, P = 0.09).
We hypothesized that I-94 affected fox dispersal directions. Seventy-five pups tagged and released north of 1-94 and 64 pups tagged and released south of 1-94 in the 2 physiographic regions and recovered as adults were used in the analysis. We found no differences in the dispersal direction between physiographic regions among foxes tagged north (χ² = 1.33, 3 df, P = 0.72) or south of 1-94 (χ² = 3.04, 3 df, P = 0.39). Therefore, we combined data from the 2 physiographic regions on each side of I-94 to compare dispersal directions between foxes released north and south of I-94. Analysis of combined data revealed a difference (χ² = 16.8, 3 df, P = 0.001) in dispersal directions of foxes tagged north compared with those tagged south of I-94. Inspection of data revealed the most logical explanation for the difference was in the percentage of recoveries in the direction toward I-94. Sixteen percent of recoveries of dispersing foxes tagged south of I-94 were north of respective tagging sites compared with 22-39% in each of the other quadrants. For foxes tagged north of I-94, 7% of recoveries of dispersing foxes were south of respective tagging sites compared with 24-43% in each of the other quadrants.
Effects of Population Size
We could not evaluate the actual proportion of all foxes tagged that had dispersed because tag recovery rates were undetermined, and duration of the harvest season and harvest intensity varied annually. However, the annual fur harvest season always included November through January. We found only small monthly differences in annual distributions of first-year recoveries for November-January for males (χ² = 6.67, 8 df, P = 0.57) and females (χ² = 9.24, 8 df, P = 0.32), and large differences in annual distributions for males (χ² = 35.0, 20 df, P = 0.02) but no differences for females (χ² = 22.0, 20 df, P = 0.34) when first-year recoveries from portions of other months were included. To avoid the problem of unequal harvest periods, we limited our evaluation of effects of population density on dispersal to the percentage of foxes recovered during November-January of their first year that had dispersed, and to distances dispersed during November-January. There were 69 male and 19 female foxes in these recovery class cohorts. We found a strong inverse relationship between fox density and the proportion of recovered males that had dispersed but no indication of a similar relationship for females (Table 3). Proportions of foxes that had dispersed and were recovered during November-January of their first year ranged from 76% (1969) to 50% (1973) for males, and from 88% (1970) to 0% (1973) for females (Table 3).
We evaluated average straight-line dispersal distances of male and female foxes recovered during November-January of their first year relative to fox population density during spring of tagging. Correlation coefficients (weighted by the no. of foxes to account for unequal sample sizes) for males (r = 0.53, 3 df, P = 0.36) and females (r = -0.03, 3 df, P = 0.96) indicated no relationship between population density and dispersal distances.
|Table 3. Relationship between fox population density in spring and corresponding percentages of foxes that dispersed and were recovered as adults during November-January of their first year, eastern North Dakota, 1969-73.|
Families/km2 for 6 townshipsb
|% dispersed||76||64||65||55||50|| 0.94|
|% dispersed||33||88||7||27||0|| 0.49|
|a Pearson correlation
coefficient weighted by n to account for unequal sample sizes.
For males P = 0.02 (3df); for females P = 0.40 (3 df).
b Density during spring when foxes were tagged (Allen and Sargeant 1975).