Northern Prairie Wildlife Research Center
|Table 1. Frequency of occurrence (F) and percent frequency of occurrence (%) for swift fox prey items in cropland (Crop) and rangeland (Range) areas in western Kansas in spring (1 Mar.-30 May) 1996, summer (1 Jun.-31 Aug.) 1996 and fall (1 Sep.-31 Dec.) 1993|
|Spring 1996||Summer 1996||Fall 1993|
|Soricidae (Blarina hylophaga)||1||3||6||9||1||5||0||0||8||16||6||15|
|Geomyidae (Geomys bursarius)||0||0||8||13||0||0||0||0||3||6||6||15|
|Zapodidae (Zapus hudsonius)||0||0||1||2||1||5||0||0||1||2||3||8|
|Felidae (Felis catus)||1||3||2||3||0||0||0||0||0||0||0||0|
|Sunflower (Helianthus spp.)||9||26||3||5||2||10||0||0||17||34||0||0|
|Wild Plum (Prunus spp.)||0||0||0||0||0||0||0||0||1||2||0||0|
|Prickly Pear Cactus (Opuntia spp.)||0||0||0||0||0||0||0||0||0||0||1||3|
|Bovidae (Bos taurus)||7||20||20||31||4||20||0||0||6||12||6||15|
|Didelphidae (Didelphis virginiana)||1||3||1||2||1||5||0||0||0||0||0||0|
|Procyonidae (Procyon lotor)||0||0||2||3||0||0||0||0||1||2||0||0|
|1 The overall frequency of occurrence of plants does not include the grass category. Grass was excluded because its nutritional value in a carnivore diet is questionable (Fichter et al., 1955) and it occurred in trace amounts|
Mammals were the most frequently occurring prey ingested by swift foxes in cropland and rangeland in the spring, and in cropland in the summer (Table 1). Overall, 11 families including 21 species of mammals were identified in the scats from both areas. In cropland and rangeland murid rodents were the most common mammals occurring in swift fox diets in summer and fall, but not in spring, when rabbits occurred more frequently. Within the Muridae family, white-footed mice (Peromyscus spp.) and voles (Microtus ochrogaster) consistently occurred in high frequency in all seasons and in both areas.
We detected no variation in overall frequency of occurrence of mammals in scats between cropland and rangeland in any season (P ≥ 0.123). We did, however, detect differences between study areas in frequency of occurrence of plains pocket gophers (Geomys bursarius) and heteromyid rodents in scats. In spring samples, we detected more pocket gophers in rangeland (13%) than in cropland (0%; P = 0.026) and more heteromyid rodents in rangeland (23%) than in cropland (9%; P = 0.067).
Arthropods were the most common food item in the swift fox diet in cropland and rangeland in fall, and in rangeland in summer (Table 1). In both study areas, the estimated percent volume of arthropods in scats was second only to mammals (Fig. 2). Five orders and five families of the class Insecta were identified in scats from both cropland and rangeland, as was one family of the class Diplopoda in cropland. In both areas, the most common arthropod class present was Orthoptera in fall samples and Coleoptera in summer samples. In spring samples, the most common arthropod class present in cropland was Lepidoptera and in rangeland Coleoptera.
|Fig. 2. Percent of total volume of prey items in 215 swift fox scats collected in cropland and rangeland landscapes in western Kansas in spring and summer 1993 and fall and early winter 1996. Estimates of volume were used to evaluate whether identified items were food or were ingested incidental to consumption of other prey.|
We detected no difference in frequency of occurrence of arthropods overall between cropland and rangeland in any season (P ≥ 0.438), but frequency of occurrence was different between areas for the three most common insect orders. Lepidoptera was more frequent in scats from cropland (54%) than from rangeland (9%) in spring (P < 0.001) and in fall (cropland 20%, rangeland 3%; P = 0.011). Coleoptera was more frequent in scats from rangeland (58%) than from cropland (37%) in spring (P = 0.049) and in fall (rangeland 80%, cropland 60%; P = 0.042). Orthoptera was more frequent in scats from rangeland (55%) than from cropland (31%) in spring (P = 0.027).
Bird remains were present in scats collected from cropland and rangeland in all seasons (Table 1). Bird remains consisted of egg shells, small broken feather shafts, partial legs of passerines and in one case, a leg spur from a ring-necked pheasant. Bird remains overall occurred more frequently in scats from cropland (30%) than from rangeland (8%) in fall (P < 0.008). Adult birds also occurred more frequently in scats from cropland (26%) than from rangeland (8%) in fall (P = 0.023). Eggshell fragments from all three size categories were found in scats from both areas, but in small, relatively similar proportions. Eggshell fragments were found more frequently in scats from rangeland (33%) than from cropland (0%) in summer (P = 0.046).
Wild plum (Prunus spp.), prickly pear cactus (Opuntia spp.) and commercial sunflower (Helianthus spp.) were the only plants found in sufficient volume to be considered food items. In 47% of 32 scats containing seeds of wild plums, prickly pear cactus, or commercial sunflowers, the seed residue constituted ≥25% of the volume of each scat. In the fall, wild plum seeds were found in one scat from cropland and prickly pear cactus seeds were found in one scat from rangeland. Sunflower seed husks were present in scats from both study areas but not in all seasons (Table 1). We did, however, find more commercial sunflower seed husks in scats from cropland (26%) than from rangeland (5%) in spring (P = 0.004) and fall (cropland 34%, rangeland 0%; P < 0.001).
Reptiles occurred infrequently and in trace amounts in swift fox scats. Only scales were found and we were unable to identify species. Reptile remains were present in scats collected from cropland and rangeland in fall and from rangeland in spring (Table 1). In the spring reptile remains were more frequent in scats from rangeland (11%) than from cropland (0%; P = 0.042).
Carrion occurred in scats from both cropland and rangeland in spring and fall and in cropland in summer (Table 1). The majority of carrion were identified as domestic cattle; a small proportion of scats contained hair of unidentified deer (Odocoileus spp.), raccoon (Procyon lotor) and opossum (Didelphis virginiana). We detected no difference in frequency of occurrence of carrion between scats found in cropland and rangeland in any season (P ≥ 0.099).
Observation rates using spotlight survey data were 0.88 and 0.44 for Ord's kangaroo rats, 0.16 and 0.08 for cottontail rabbits and 0.56 and 0.48 for black-tailed jackrabbits in rangeland and cropland, respectively. Observations rates for all rabbits combined were 0.72 in rangeland and 0.56 in cropland.