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Movements and Habitat use of Franklin's
Ground Squirrels in Duck-Nesting Habitat

Results


We recorded 10,381 radio locations of 49 (27 M, 22 F) Franklin's ground squirrels during 1981-82; 9 squirrels were tracked for portions of both years. We captured 45 (27 M, 18 F) ground squirrels from all trapping efforts on the WPA in 1981 and 48 (28 M, 20 F) in 1982. Based on the ratio of marked:unmarked captures, we surmised that approximately half the adult ground squirrel population was radiomarked each year. Annual monitoring periods for individual ground squirrels were 12-127 days (Mean of X = 72). In 1981, 8 females were tracked during gestation and lactation periods and all had young. In 1982, 7 of 9 females tracked during these periods had young. Seven (5 M, 2 F) radiomarked ground squirrels in 1981 and 8 (5 M, 3 F) in 1982 were killed by predators (primarily red foxes [Vulpes vulpes] that cached the squirrels or brought them to a den). One male traveled regularly between the WPA and an abandoned farmsite 0.6 km away, and was often off the study area; it was omitted from further analysis.


Daily Activity Patterns

Data from tracking and activity recorders revealed ground squirrels were strictly diurnal. Activity data from both sexes were combined because similar percentages of male and female squirrels were active during each hourly period (P > 0.10). Ground squirrels typically became active between 0600 and 0900 hours (approx 1-2 hr after sunrise), remained active throughout most of the day, and entered burrows and became inactive between 1900 and 2100 hours (approx 1-2 hr before sunset). Data from 100 activity recordings of 19 ground squirrels revealed that the latest any squirrel entered its burrow was 2125 and the earliest any squirrel left its nighttime burrow was 0705 hours. Monthly variation in daily activity patterns was slight and associated with changing length of day.


Daily Movements

Daily movements of individual ground squirrels began when they emerged from their nighttime burrows and ended when they retreated into burrows for the night. The mean daily total distance traveled by males was greater than the mean daily total distance traveled by females (P < 0.05) (Table 1). Biweekly differences were significant during one 2-week period in 1981 and 3 2-week periods in 1982 (P < 0.05). Females traveled least during gestation (late May-early Jun) and during the 2-week period just before immerging for the winter (Aug). Distances traveled daily by males decreased during the 2-week period before immergence.

Table 1.  Mean daily distance traveled (m) by adult Franklin's ground squirrels during biweekly sample periods on a study area in North Dakota, 1981-82.
Yr
    Period
M F
na Mean of X SD na Mean of X SD
1981
    10-23 May 13 219 138 7 140 78
    24 May-6 Jun 17  139b 77 16  82b 34
    7-20 Jun 15 223 104 16 167 49
    21 Jun-4 Jul 16 213 77 15 205 76
    5-18 Jul 16 210 135 12 214 88
    19 Jul-1 Aug 11 152 37 18 148 76
    2-13 Aug 8 134 57 15 152 53
    Mean of X biweekly 96 188   99 157  
1982
    25 Apr-8 May 9 282 147      
    9-22 May 23  263b 123 13  110b 56
    23 May-5 Jun 34  234b 126 23  96b 38
    6-19 Jun 26  205b 142 24  100b 52
    20 Jun-3 Jul 18 197 139 17 169 64
    4-17 Jul 26 259 155 27 197 86
    18-31 Jul 33 241 132 45 184 92
    1-13 Aug 19 137 72 24 149 55
    Mean of X biweekly 188 227   173 150  
    Mean of X annual 284 213   272 153  
a No. daily records.
b Significantly different means between M and F (P < 0.05).


Home Ranges

Biweekly home-range sizes did not differ between years (P = 0.2418). Biweekly home-range sizes of 21 males averaged 7.2 ha (range = 0.5-38.4 ha) and were greater than those of 20 females that averaged 2.7 ha (range = 0.3-14.1 ha) (P = 0.001) (Table 2). The largest mean biweekly home-range sizes of males in 1981 were in early May during the breeding season, and in 1982 in late July. Biweekly home ranges for males were smallest before the males entered hibernation in 1981 and 1982. During both years, mean biweekly home ranges of females remained relatively small throughout gestation and lactation, then gradually increased during the post-lactation period, and decreased shortly before immergence. Mean activity radii of males during biweekly intervals (Mean of X = 1,106 m) were greater than those of females (Mean of X = 67 m) (P = 0.0001). Shifts in geometric centers of activity over biweekly intervals were also greater for males (Mean of X = 97 ± 103 [SE] m, n = 91) than for females (Mean of X = 59 ± 5.4 m, n = 86) (P = 0.0015).

Annual home-range size did not differ between years (P = 0.977). Annual home ranges of 21 males averaged 24.6 ± 11.5 ha and were greater than those of 20 females that averaged 8.7 ha (range = 2.5-22.7 ha) (P = 0.0001). Annual home ranges overlapped within and between sexes. The annual mean activity radius of males (Mean of X = 147.9 69.4 m) was greater than that of females (Mean of X = 87.7 ± 35.4 m) (P = 0.0014).

Table 2.  Mean biweekly and annual home-range sizes (ha) of adult Franklin's ground squirrels on a study area in North Dakota 1981-82.
Yr
    Period
M F
n Mean of X SD n Mean of X SD
1981
    27 Apr-9 May 6 9.7 2.7      
    10-23 May 8 8.4 2.9 8 2.9 1.6
    24 May-6 Jun 8 4.7 2.8 9 1.3 0.7
    7-20 Jun 6 8.4 4.9 8 3.1 1.8
    21 Jun-4 Jul 8 6.0 2.8 7 3.9 0.9
    5-18 Jul 7 6.0 3.2 7 3.6 1.7
    19 Jul-1 Aug 6 4.2 3.4 9 4.0 4.0
    2-13 Aug 6 3.6 2.2 6 2.2 1.3
    Mean of X biweekly 55 6.4   56 3.0  
    Mean of X annual 10 19.3   11 9.4  
1982
    25 Apr-8 May 8 6.1 3.0      
    9-22 May 8 8.4 6.1 4 0.8 0.7
    23 May-5 Jun 8 5.5 5.5 6 1.7 1.4
    6-19 Jun 8 5.3 4.4 8 1.1 1.0
    20 Jun-3 Jul 8 7.0 9.0 8 2.7 1.1
    4-17 Jul 10 11.6 3.6 9 3.6 2.5
    18-31 Jul 8 14.8 8.1 9 4.0 3.0
    1-13 Aug 6 3.6 2.7 8 2.2 1.3
    Mean of X biweekly 64 8.4   52 2.5  
    Mean of X annual 11 29.4   9 7.9  
 


Habitat Use

The distribution of 4,430 telemetry locations of active ground squirrels during both years combined showed unequal use of habitats on the WPA (Fig. 1). The most intensively used portion of the WPA comprised the northern portion of TB and adjacent portions of UN19 and DC6. Two-thirds of the radio-marked ground squirrels were located in TB at least once. The least used portions of the WPA upland were DC5, the center of DC8, and the southeastern part of DC6.

When inactive at night, ground squirrels were underground in what appeared to be abandoned burrow systems of northern pocket gophers (Thomomys talpoides). Because burrows were also used for refuge during the day, above ground movements of the ground squirrels were influenced by the location of suitable burrows. The spatial distribution of burrows used at night by habitat block was similar to the distribution of locations of squirrels during the day (Table 3).

Table 3.  Percent availability, percent use, and electivity index of upland habitats used by active adult Franklin's ground squirrels and percent of burrows within habitats in North Dakota,1981 and 1982 combined.
Habitat
block
Yr
since tillage
Habitat
composition (%)
Active locations Inactive
locations
% Electivity
index
% of
burrows
    TB 14 1.5 14.2 +0.82 7.2
    UN19 19 14.3 28.6 +0.33 29.4
    DC9 9 18.5 23.2 +0.11 29.0
    DC6 6 20.3 18.7 -0.04 15.7
    DC3 3 15.1 10.0 -0.20 10.6
    NP a 1.6 0.8 -0.37 2.5
    DC8 8 14.1 4.1 -0.55 5.6
    DC5 5 14.6 0.4 -0.94 0
a Native prairie was never cultivated.

Electivity indexes calculated for the 8 habitats using only active locations showed that TB and UN were used greater than expected and that DC3, NP, DC8, and DC5 received less use than expected (Table 3). During each year, analysis of visual obstruction and litter depth measurements on the 7 habitats dominated by herbaceous cover (TB excluded) indicated some difference among habitats during each of the 3 sampling periods (ANOVA, P < 0.001), but when least square means were examined, no pattern to the differences among sampling periods or habitats was evident.

All habitats differed in age of the stand and frequency of cultivation after the initial seeding of the WPA in 1963. The 2 habitats that received greater use than expected were characterized by relatively long periods of no disturbance to vegetation or soil. Although the vegetation and soil on NP were undisturbed longer than in any other habitats, that area was often surrounded by water that deterred use by ground squirrels and accounted for its relatively low electivity index. The 3 habitats that received less use by ground squirrels than expected had relatively recent disturbances to the soil and vegetation. Habitat block DC3 and DC5 were farmed for ≥2 years between 1974 and 1979. Habitat block DC8 was farmed continuously from 1966 to 1975. Although DC6 received less use by ground squirrels than expected, avoidance was not as great as anticipated based on cultivation history. However, most use of that block occurred adjacent to heavily used TB and an adjacent sunflower stubble field often visited by squirrels in spring 1981.

The electric fence probably had little effect on the low relative use of DC8 because the portion of UN19 enclosed by the fence received heavy use similar to that portion of UN19 outside the fence (Fig. 1). A previous study (Lokemoen et al. 1982) and telemetry data and observations obtained during our study showed that ground squirrels moved freely through these fences.

Ground squirrels used only the fringes of the cropland adjoining the WPA (Fig. 1). The most intensively used cropland was located immediately northeast of TB. A narrow band of trees extending north of TB provided the ground squirrels with a source of protective cover at the field edge. Nineteen of the radio-equipped ground squirrels used that area at least once. Most use occurred in April 1981 when waste sunflower seeds from the previous year's crop were available, and during late summer 1982 when wheat planted in the field was ripening. Use of other fields adjoining the WPA and containing the same crop was limited to < 1 % of the locations. These fields were not close to shrub cover on the WPA. Seven of 49 ground squirrels used the uninhabited farmstead adjacent to the WPA.

Mowing and burning of portions of the WPA affected ground squirrel movements. Habitat block DC5 was mowed the summer preceding this study. Ground squirrels avoided habitat block DC5 throughout the study. In contrast, DC3 was mowed in late summer 1981 and burned the following spring. Ground squirrels used habitat block DC3 extensively before it was mowed and burned but used it infrequently until the vegetation regrew to a height of about 30 cm in mid-May.


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