No. 6. In hilltop woods, 30 feet from a corner adjoining a pasture and a corn field, at the base of an osage orange tree of one foot DBH, and also over a hollow cottonwood log one foot in diameter and three feet from the osage orange tree. Suspended mats of grape and smilax vines, and the thorny, dead, lower branches of the tree provided additional shelter. The house was composed of sticks and twigs, mostly of osage orange, with spines still present; slabs of bark, wood chips, and dry leaves also made up part of it. Materials on the exterior of the house appeared old and weathered, but the house was conical and solid. Seven fresh corn cobs were on the house or near its base, suggesting that corn from the nearby field had figured importantly in the diet of the occupant. A well beaten path led from the base of the house alongside the log, to a large cottonwood tree 15 feet from the house. This evidence that the house was occupied was verified by live-trapping the occupant. Late in 1948, also, the house was occupied by another individual, but seemingly was deserted for a period of months thereafter.

No. 7. On upper part of north slope where a hickory seven inches in diameter had fallen across an old sunken log approximately one foot in diameter. The house, composed mainly of hickory twigs 1/4-inch to 1/2-inch in diameter, mixed with bark, wood chips, and leaves, was partly decayed, with no fresh sign and was in a thicket of greenbrier, saplings of hickory and hackberry, and cut tops of hickories. The top was flattened to less than four inches above the level of the supporting hickory log. There were large cavities in the side of the house. When first discovered in the autumn of 1948, this house was occupied by a subadult female rat, but she moved away permanently, and the house had been deserted for approximately a year when these observations were recorded.

No. 8. In middle of northwest slope, in thick branches of broken top of a black oak. This house had become flattened by decay and settling to form a mound approximately one foot high and five feet in diameter. Only the top protruded through the carpet of dry leaves. Once well protected and partly concealed by the branches and twigs of the oak top, this house was now fully exposed by the disintegration of the top. The house consisted chiefly of oak twigs. In October, 1948, a woodrat was live-trapped at this house, but probably it was a wanderer. The house had then already undergone much deterioration.

Natural Enemies

Some 56 species of animals that regularly prey on small vertebrates live on the Reservation. Many of the larger kinds may take woodrats occasionally. Because of size, habitat preferences and the time and manner of hunting, five species stand out as the more formidable enemies—the horned owl (Bubo virginianus), prairie spotted skunk (Spilogale putorius), long-tailed weasel (Mustela frenata), pilot black snake (Elaphe obsoleta) and timber rattlesnake (Crotalus horridus).

Throughout the study horned owls were common on the area, but their numbers were highest in 1948. Samples of pellet collections have shown that the cottontail is the staple food, being represented in almost every pellet. Various rodents also are important in the diet, the cotton rat, prairie vole, or white-footed mouse being most prominent according to the time and place of collection. The woodrat is approximately optimum size for prey, and it constitutes one of the most preferred food sources. Remains of only two woodrats were found in the pellets examined, but at times when the pellets were collected woodrats were so scarce that they constituted only an insignificant percentage of the biomass of potential prey. On several occasions woodrats in live-traps were attacked by horned owls, as shown by the overturned and displaced trap and quantities of fine down adhering to them and to nearby objects. The horned owl lives in the same habitat as does the woodrat. In other regions woodrats are known to figure prominently in the diet of the horned owl. At the San Joaquin Experimental Range in California, for instance, N. fuscipes was found 240 times, more frequently than any other kind of prey, in 654 pellets of the horned owl, and this owl was shown to be the one most important natural enemy of the rat, although many kinds of carnivores, raptors and snakes also took toll from its populations. On the Reservation the population of horned owls has been fairly stable from year to year, with roughly one pair to 100 acres of woodland. Some territories have been maintained continuously throughout the eight-year period of observation, though changing to some extent in size, shape and area included. In 1948, when livestock grazed on the area, and the ground cover of herbaceous vegetation was relatively sparse, cottontails were much less abundant than they were later when the vegetation was protected. Small rodents including voles, cottonrats, and deer mice, were also less abundant then, and the numerous horned owls may have been supported in part by the high population of woodrats.

The spotted skunk may be an even more important enemy of the woodrat, although the evidence is circumstantial. No records of these skunks preying on woodrats have been found in the literature, nor were any such instances recorded by us except for attacks on woodrats confined in live-traps. This skunk is a formidable enemy of small and medium-sized rodents, as it can climb, dig, and squeeze through small openings. That it may prey on rat-sized rodents and may even be a limiting factor to their occurrence is well shown by Crabb's (1941:353) studies in Iowa. He found that Norway rats (Rattus norvegicus) ranked third in frequency (cottontail, mostly carrion, ranked first) in the winter food of the spotted skunk. Crabb observed that about farmyards and farm buildings where the skunks had been eliminated by persistent persecution, rats were abundant, but that about others where the skunks were present, the rats were scarce or absent. On several occasions he noted that heavy populations of rats about farm buildings in summer and autumn nearly disappeared in winter if a skunk was in residence.

Sign of spotted skunk was noted frequently on various parts of the Reservation, especially along the hilltop ledges which were the best woodrat habitat. On several occasions skunks released from live-traps took shelter in woodrat houses which appeared to be unoccupied. According to a local fur dealer, C. W. Ogle, spotted skunks reached a peak of abundance in Douglas County in the winter of 1947-1948, and many pelts were brought in for sale then. The concentration of skunks may have had detrimental effect on the population of woodrats, especially when extremes of weather had already made conditions critical for them, as in early March, 1948, and in January, 1949, when snow and sleet made their usual food supply unavailable.

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