Woodrat

“ Food of the eastern woodrat consists chiefly of vegetation; many kinds of leaves, fruits, and seeds are eaten. For many individuals foliage and seeds of the osage orange are the staple; hedge rows and dense trees of osage orange provide favorable sites for the houses. Woodrats are attracted to meat baits, and have been known to feed on flesh of carcasses, even on one of the pilot black snake which is a predator on the rat. ”

“ On various other occasions two or more rats have been caught in the same trap simultaneously but in every instance these were either: a pair of adults, the female appearing to be in oestrus; a lactating female and one or more of her young; or young less than half-grown, that were obviously litter mates. Older woodrats, especially males, often have their ears torn and punctured from fighting. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ One male who stayed in the maternal house all summer, and reached adult size there, later moved several times, and was last recorded 900 feet away. One young female shifted 110 feet. In several instances juveniles appeared abruptly in houses known to have been unoccupied previously, and some of these houses were in poor repair. These young had wandered from their maternal houses, for unknown reasons. On one occasion a young woodrat was caught in a mouse trap set in a meadow, a habitat into which adult woodrats would scarcely be expected to venture. ”

“ 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. ”

“ In the autumn of 1948 the population of woodrats was far below the level it had attained in 1947 or earlier, but the rats were still abundant and distributed throughout a variety of habitats. Almost every part of the woodland was occupied by at least a sparse population. Also, many rats lived beyond the limits of the woodland proper, in such places as deserted buildings, thickets, roadside hedges, and tangles of exposed tree roots along cut banks of gullies. ”

“ Our study was made at a time when populations were shrinking and disappearing, and obviously individual spans would have been longer if we had been working with a stable population. In most instances the spans of our records represent only small parts of the life spans of the individuals involved. Nevertheless, our records emphasize the potentially greater longevity of the woodrat as contrasted with the various smaller rodents living in the same area. ”

“ The number of individuals living along any particular stretch of ledge could be determined only by intensive live-trapping, whereas residences of individuals could be more readily identified in most other situations away from the ledge. Stick houses of woodrats are, characteristically, large and dome-shaped in woodland, but along the ledges they usually lacked this typical form and consisted of a much smaller accumulation of sticks, often merely filling a small crevice. ”

“ To a greater degree than any other kind of mammal on this area woodrats show intraspecific intolerance. On various occasions when captives were placed in the same or adjacent cages, they focused their attention on each other with evident hostility, the more powerful or aggressive individuals attacking or pursuing. Several times the confinement of two rats in the same live-trap or cage resulted in the death of the weaker individual, and seemingly this is the normal outcome unless the attacked rat is able to escape. ”

“ Many kinds of predatory mammals, hawks, owls, and snakes probably take woodrats occasionally, but the spotted skunk, long-tailed weasel, horned owl, timber rattlesnake and pilot black snake are considered to be by far the most important predators because of their habits and prey preferences. Few actual records of predation on woodrats were obtained because of their scarcity during most of the period covered by our study. ”

“ Some individuals grow to maximum adult size at an age of one year. Unusually large individuals are not necessarily those that are unusually old. Longevity is greater in woodrats than in most smaller rodents. One female of adult size when first trapped was last captured 991 days later when she must have been well over three years old, and others are known to have survived more than two years even though populations were shrinking so that few of the rats were able to survive for their normal life span. ”

“ An almost continuous canopy of foliage has developed, shading the understory and thinning it by killing shrubs and saplings. In those situations where the canopy is most dense, as on north slopes having stands of young hickory averaging twenty feet high, the understory is now largely lacking, but in other situations, particularly on south slopes, the understory thickets are still dense. On the whole, however, habitat conditions have become less favorable for the woodrat.
Within the woodland the population of woodrats was not evenly distributed even at its maximum density ”

“ Ordinarily sleet would not seriously damage woodrats living in houses in woodland habitats and less suitable hedge rows because it usually freezes as it falls and coats only the surface of the house. Gradual thawing would allow normal runoff without much penetration. Because the sleet during the storm described above did not form a glaze as it fell, the ice particles penetrated many houses. It has been observed many times that captive woodrats refused food that was frozen or were unable to eat it. Woodrats in live-traps in winter rapidly weaken unless a large supply of food is available. ”

“ That most of these first-litter young may have been eliminated by the unfavorable extreme of weather at the most critical stage in the life cycle may be readily imagined although definite proof is lacking. However, the mortality must have extended beyond newborn young. Loss of first litters ordinarily would be compensated for by the end of the season, since a female usually breeds more than once in the course of a season. In any case, by autumn, when the actual field study of woodrats was initiated, many houses were already deserted and in disrepair. ”

“ In October, 1948, live-trapping was begun on a heavily wooded slope facing northwest, and a ten-acre area was trapped rather thoroughly in the succeeding weeks. Because few traps were then available, this was the only area that was well sampled in 1948, although diffuse trapping was carried on over some 200 acres. On the ten-acre tract a total of 17 adult and subadult woodrats were caught, four along the hilltop rock outcrop, six along the gully at the bottom of the slope, and seven at intermediate levels on the slope. ”

“ 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. ”

“ Typical growth curves for male and female woodrats; early stages are based on the litter of a captive female, later stages on average gains of recaptured juveniles and subadults, excluding those that seemed to be stunted. Solid line represents males and broken line represents females.
Young weighing less than 100 grams are rarely caught in live-traps. Four young, all males, first caught at an average weight of 80 grams, gained on the average, 1.39 grams per day over intervals that averaged 44 days. ”

“ By November 21, 1951, at a probable age of 15 months, he weighed 350 grams having attained almost the maximum size. Other exceptionally large individuals were known to be less than two years old, while those rats that survived longest on the study areas did not much exceed average adult size. These records seem to show that exceptionally large woodrats are usually not those of advanced age, but are individuals which have grown most rapidly through fortuitous circumstances, probably depending upon both innate and environmental factors. ”

“ 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. ”

“ An adult female that appeared to be in oestrus on February 3, 1952, was imperforate on February 10.
Growth
At birth woodrats weigh approximately 10 grams or a little more. In a litter born in captivity and kept by Rainey, the average gain amounted to a little more than 1.5 grams per day during the first two months, but in the third month it was somewhat less. As this was an unusually large litter, of five young, one more than the female's teats could accommodate, their growth may have been a little less rapid than in most of those under natural conditions. ”

“ At one cabin in the mountains of New Mexico where I lived one summer several mountain rats made free of the place and at night persistently tried to add our shoes to their nest under the floor. An hour or so after retiring we would hear our shoes scrape slowly across the floor, and in the morning they would be found stuck toe down in the broad crack where the floor ended near the wall. In the woodrat country when small articles are missed from camp it is always worth the trouble to investigate the nearest rats’ nests. ”

“ As a rule each nest is occupied by a single rat, but sometimes several may be found in one, and the well-worn trails that so often connect the entrances of neighboring nests bear evidence that woodrats have a social disposition. ”

“ The presence of woodrats is generally indicated by accumulations of odds and ends filling the crevices of the rocks about their retreats or piled about the entrances of their burrows, such accumulations including small sticks, pieces of bark, leaves, cactus burrs, bones, stones, and any other small objects which may be found in the vicinity. ”

“ As may be surmised from their habits, woodrats are skillful climbers, both in trees and on 517 the rough rock walls of the cliffs they inhabit. Their only notes appear to be shrill squeaks and squeals when quarreling among themselves at night. ”

“ Woodrats are plentiful on the Mexican table-land, making their nests under cactuses or thorny agaves, where they are persistently hunted as game by the natives, who prize them as a special delicacy. I saw them regularly sold in the markets of the cities of San Luis Potosi and Aguas Calientes, where the method of marketing them was unique. As soon as they were dug from their nests, their lower incisors were broken off close to the jaw to render them powerless to bite, and then the rats were placed alive in a strong sack and carried to town. ”

“ In most localities woodrats are distributed sparingly, but occasionally become so abundant in favorable places on brushy plains that colonies containing hundreds of nests may be found in limited areas. They sometimes become so plentiful about ranches as to make serious inroads on grain and other crops. They also give the Forest Service much trouble by digging up the pine seeds planted in their great reforesting nurseries. ”

“ They are a shrewd set of fellows, these rats. Some years ago, the cellar of the house in which I resided was greatly infested with them. They devoured potatoes, apples, cabbages, and whatever came in their way; for they are not very particular about their diet, you know. Well, we set a trap for them. It was a flat stone set up on one end, with a figure four. We scattered corn all about the trap, and placed a few barrels on the end of the spindle under the stone. The first night these midnight robbers ate up all the corn around the trap, but did not touch a morsel under it. ”