An occupied house normally has several runways radiating from it. These are well worn paths, smoothed by use, and cleared of obstructions, and the rat tends to keep to them in its foraging expeditions. Usually a trail leads to a bush or tree showing evidence of heavy use by the rat. Ordinarily such a trail cannot be traced more than 30 feet from the house, and it seems that the most concentrated foraging occurs within this short radius. Experience in live-trapping has indicated that the distance covered by a woodrat in its normal foraging for food is ordinarily less than 75 feet in any direction from the house.
Usually the rats can be caught in traps only at their houses or nearby places that they frequent, as indicated by their sign. When travelling, woodrats make use of overhead cover as much as possible. Storing of food seems to be associated with the animal's reluctance to wander far from home. When a rat is gathering preferred food for storage the home range may be enlarged (or the animal may travel beyond the limits of its regular home range). In any case the rat may find it necessary to traverse an additional area in order to reach the food source. This may involve, in part, extension vertically, as when the rat obtains food from trees directly over the house. The home range is thus somewhat three-dimensional; both trails and feeding places are often above ground. Because of dependency on cover, woodrats do not forage randomly in all directions from the house.
Although the house and its immediate environs are defended as a territory by the occupant, possession may be soon relinquished. A woodrat may shift frequently from one house to another, especially if unoccupied houses are readily available. Because woodrats had undergone drastic reduction in numbers, as discussed on p. 505, unoccupied houses in various stages of disrepair were numerous throughout the woodland in 1948 and 1949, and the rats that were present then seemed especially inclined to wander. Even old houses that are collapsed and disintegrating may be used temporarily, or may be taken over and repaired. Houses that are in sites exceptionally favorable in that they provide food and shelter may be occupied more or less permanently, with a succession of woodrats over many generations.
Shifts to new areas are perhaps most often motivated by a search for mates. Such shifts are, on the average, longer and more frequent in males. Males must range farther in search of females when numbers are low. On the other hand, when numbers are high and most of the best sites are occupied, newly independent young and displaced adults are forced to travel greater distances in search of homes. Some of the larger and more powerful males move far greater distances than smaller males. The longest distances recorded were mostly for large adult males in breeding condition. The average maximum distance between successive points of capture for 27 adult males was 345 feet. For 39 females (adults and subadults) the corresponding figure was 143 feet. The extremes for males were 0 to 1080 feet and for females, 0 to 650 feet. Of the 27 males, five moved the maximum distance in a single night. Most of the long movements by males did not constitute clear-cut shifts in home range, and many returned to their original locations.
The average distance between points of first and last captures for 72 subadult and adult males was 165 feet. A similar figure for 72 subadult and adult females was 133 feet. Of the males 23.7 per cent were at the same place at the first and last captures; for females the percentage was 36.1. These figures are from the combined data of our trapping records, but the trends differed sharply in the two sets of records. In Fitch's records, movements averaged longer and difference between the sexes was much less: 189 feet for 41 males and 178 feet for 42 females. Corresponding figures from Rainey's records were: 141 feet for 31 males and 74 feet for 30 females. In Fitch's field work, opportunities to record exceptionally long movements obviously were better because the trap line encompassed a larger area, approximately half a square mile, whereas Rainey's live-trapping was concentrated on relatively small areas. The reason for the greater vagility of females in Fitch's records is less evident. However, the data were obtained within the period of drastic population reduction, at a time when there were numerous empty houses throughout the woodland, facilitating travel, and shifts from one home range to another where conditions were, temporarily at least, more favorable. Rainey found that the females in the small colony in woodland where he trapped, moved much less than did those that lived along the hilltop outcrop, which provided a natural travel route.
Following are several examples of males and females with long histories showing individual variation in frequency and distance of movements.
Males
(1.) First captured October 14, 1951, and last captured 327 days later on September 6, 1952. He was taken 12 times. For the first seven captures (October 14, 1951, to July 15, 1952), no movements were recorded. In the following seven days he moved 367 feet. Within the next 21 days he returned to within 114 feet of the site of original capture. Less than one month later he was caught for the last time, at this same site.
(2.) This large male was captured twelve times over a period of 827 days (March 16, 1952, to June 21, 1954). He tended to wander more than other males and was absent from the trapping area from early 1952 to May 1953. One round trip made in a two-weeks period, amounted to a linear distance of 1894 feet if the rat followed natural cover. The return trip of 947 feet was the greatest distance traversed in a single night in any of the woodrats we recorded. Other movements between successive captures were: 722, 397, 356, 293, 253 and 144 feet (the latter shift made three different times). Sexual urge probably motivated most of his wandering, since numbers of females were low.
(3.) For this male the span of records was 143 days, with 18 captures. For the first eight recaptures, extending over a period of 39 days, he was still at the original location. Four days later he had moved 120 feet and was visiting a female. A week later he returned. In the following month he was recorded as making two more moves, of 115 feet and 215 feet. He was last recorded at the hilltop outcrop.