Part 3

The long-tailed weasel is considered to be a potentially important enemy of the woodrat. Weasels have been seen on the Reservation on only a few occasions, but they may be more numerous than these records would indicate. Two were caught at the hilltop outcrop, at different times and places, in funnel traps put out to catch snakes. The weasel seems to prefer this rocky habitat, which is also favored by the woodrat. Because of its ferocity and willingness to attack relatively large prey, and because it is an agile climber and able to squeeze through any openings large enough to accommodate a woodrat, it would seem to be a formidable enemy.

The pilot black snake (Elaphe obsoleta) is an important enemy of this woodrat on the Reservation and probably throughout the rat's geographic range except for the extreme western part. Although this snake occurs in every habitat of the Reservation, it has been found most often along rock outcrops of wooded hilltop edges in the type of habitat most favored by the rat. Most often pilot black snakes have attempted to escape into crevices of the outcrop. These snakes are also skillful climbers and often have escaped by climbing out of reach along branches or even vertical tree trunks. On several occasions these snakes have been found on or beside woodrat houses, or have escaped into them. Over a seven-year period 143 pilot black snakes have been recorded, 53 of which were adults.

On September, 1948, a large pilot black snake found basking on a rock ledge, distended by a recent meal, was palped and contained a subadult female woodrat. On June 19, 1953, one of us, approaching a live-trap set under an overhanging rock ledge, saw a four-foot pilot black snake on top of it. The snake struck repeatedly at the rat in this trap, but was unable to reach it. At each stroke the rat would dash about the trap frantically.

These snakes hunt by stealth, and might catch woodrats by entering their nests, or by lying in wait along their runways, but are not quick enough to catch them in actual pursuit. Young in the nest would seem to be especially susceptible to predation by the pilot black snake. These snakes hunt by active prowling, either by night or by day, and much of their food consists of the helpless young of birds and mammals found in the nests. While only well-grown or adult pilot black snakes would be able to swallow an adult woodrat, any but first-year young probably would be able to overcome and swallow the small young. The female woodrat's habit of dragging the young attached to her teats as she flees from the house at any alarm must save many litters from predation by the pilot black snake. First litters of young, born in early March, are already well grown, and past the age of greatest susceptibility to predation before the snakes emerge from hibernation in late April or early May.

The timber rattlesnake is another potentially destructive enemy, but on the Reservation, and throughout much of its original range it is now relatively scarce. The genus Neotoma largely coincides in its over-all distribution with the genus Crotalus, of the rattlesnakes. For most kinds of woodrats, the larger species of rattlesnakes are among the chief natural enemies.

The timber rattlesnake has habitat preferences similar to those of the eastern woodrat. Of 30 timber rattlesnakes recorded on the Reservation over an eight-year period, all but one were at or near hilltop rock ledges in woodland. The woodrat is probably one of the most important prey species for the timber rattlesnake. Like the woodrat, the rattlesnake is mostly nocturnal in its activity. Unlike the pilot black snake, it hunts by lying in wait, striking prey which comes within range, and waiting for it to die from the venomous bite, rather than by active prowling. Therefore, it is probably less of a hazard to young in the nest than is the pilot black snake. Even young rattlesnakes too small to eat woodrats are potentially dangerous to them, as they may strike and kill any that come within range.

Commensals

Rainey (1956) listed many kinds of small animals that use the houses of the eastern woodrat and live in more or less commensal relationships with these rodents.

A situation unusually favorable for observing woodrats and their associates was discovered on the Reservation where, in July, 1948, two old strips of sheet metal, each covering an area of approximately 25 square feet, were used as shelter by a lactating female with three young. This was on a brushy slope just below an old quarry site. A rock pile and remains of an old rock wall were nearby. Woodrats had carried many sticks back under the metal strips, filling the spaces beneath their edges. There was a nest and a system of runways beneath the strips. In the following seven years this site was seldom deserted for long and was used by a succession of individuals. The strips of metal could be easily raised and then lowered into place with little disturbance. Because the situation was not entirely natural, the findings may not be typical of other rat houses. Animals found over a period of years beneath these metal strips include: several dozen each of the ring-necked snake (Diadophis punctatus), five-lined skink (Eumeces fasciatus), and ant-eating toad (Gastrophryne olivacea); several individuals each of cottontail (Sylvilagus floridanus), white-footed mouse (Peromyscus leucopus), short-tailed shrew (Blarina brevicauda), least shrew (Cryptotis parva), American toad (Bufo americanus), Great Plains skink (Eumeces obsoletus), pilot black snake (Elaphe obsoleta); and one each of bull snake (Pituophis catenifer), spotted king snake (Lampropeltis calligaster), red milk snake (L. triangulum), and timber rattlesnake (Crotalus horridus). The snakes which were potential predators on the rats seemed to be merely utilizing the shelter in these instances, but they may have been lying in wait for prey there.

Among mammals, the cottontail and the white-footed mouse are the most persistent users of the woodrat houses, especially those that are no longer occupied by the rats. On one occasion five white-footed mice were caught simultaneously in a trap set beside a house at the base of an osage orange tree. Subsequent trapping showed that this house was no longer occupied by a rat, but that the mice lived in it. Occupancy of such an old woodrat house by white-footed mice may continue long after abandonment of the house by the rat, even after the house has partly decayed and settled to a small part of its original volume.

Cottontails often have their forms under the edges of houses, either occupied or deserted. These situations offer protection overhead and on three sides. Abandoned houses having one or more of the entrance holes enlarged, as by predators breaking through the side of the house to gain access to the nest, are especially well adapted for occupancy by the cottontail. The rabbit may make its form inside the house structure.

The opossum, also, finds the type of shelter that it requires in abandoned houses that have had the entrances sufficiently enlarged. On various occasions opossums or their remains have been found in such old houses, and opossums released from live-traps have been known to seek shelter in abandoned woodrat houses.

At the old quarry on the Reservation woodrat sign was especially abundant. A wooden bin approximately seven feet square, used to store crushed rock before quarrying operations were abandoned, was inhabited by one rat. At the base of a rock crusher on the top of a bank a few yards from the bin was an accumulation of sticks and other debris brought by woodrats. A rock wall at the top of the bank between the crusher and the bin had many crevices providing shelter for the rats, and projecting rocks were littered with their droppings. In the spring of 1949 the bin and rock crusher were removed, but at least one rat continued to live in the rock wall. In the summer of 1951 several tons of corn ruined in the flood were dumped on the top of the bank above the wall. By autumn, Norway rats, either brought in with the corn or attracted by it, had taken possession of the wall, evidently displacing the woodrats, which were no longer present. Although this Old World murid rat is much different from the woodrat in habits, it seemingly can compete with it and replace it where habitat conditions are otherwise favorable for both.

Movements

The woodrat is dependent on the stick houses that it constructs for shelter. For each individual the house constitutes a home base to which it is attached, and about which its movements revolve. The area within which routine daily movements are confined constitutes the home range, which is variable in size and shape. An individual may, and usually does, alter its home range over periods of time. The home range is somewhat nebulous because the rat may at any time move far beyond the small area to which its activities are largely confined. It may be motivated by sexual urge or other voluntary wandering; it may be enticed by a food supply or some other specific attraction not available near its house; or it may be forcibly displaced by an intruder or may abandon in favor of an offspring.

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.

(4.) The records of this male extended over 465 days, with 13 captures. For the entire period only one movement, of 163 feet, was recorded. Twelve of the 13 captures were at the same house.

(5.) This male was captured 16 times over a span of 130 days. After the second capture he moved 144 feet along the outcrop and was caught there for the next 14 times, having developed a "trap habit."

(6.) This male was in the area 210 days (13 captures) and shifted his range. He was first captured on August 17, 1952, at a house at the rock fence 433 feet from the outcrop. Between this date and October 12, 1952, he moved to the outcrop and established residence in a vacant house. He was recorded as making six more moves, the longest of which was only 40 feet.