Ecological Observations on the Woodrat, Neotoma floridana Part 3

_Longevity_

The longest span of records for an individual woodrat recorded was 991 days in a female, already adult when she was first caught on November 18, 1948. Other relatively long spans of records were: 827 days in a male, adult when first caught on March 16, 1952; 754 days in a female, also adult when first captured; 649 days in a male first captured as a juvenile; 465 days in a male, adult when first captured; 409 days in a male, juvenile when first captured; 399 days in a female, juvenile when first captured; 395 days in a female, adult when first captured; 390 days in a female, adult when first captured; 366 days in a male, adult when first captured. Of these eleven individuals (six females and five males) whose records cover more than a year, eight were already adult when first caught. These eleven rats represent only 4.3 per cent of the total number captured. 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. Of several thousand individuals of the genera _Mus_, _Zapus_, _Reithrodontomys_, _Peromyscus_, _Sigmodon_, and especially _Microtus_, none is known to have survived so long as two years, and only a few individuals are known to have survived so long as one year after being marked.

_Summary_

Plant succession resulting from land use practices created habitat conditions especially favorable for woodrats in the late nineteen forties in northeastern Kansas, and particularly on the University of Kansas Natural History Reservation. With protection from prairie fires, woody vegetation had encroached onto areas that were formerly gra.s.sland, and, later, fencing against livestock permitted dense thickets of undergrowth to develop. In this region the woodrat usually lives in a forest habitat, and requires for its house sites places that are especially well sheltered, as in matted thickets of undergrowth, root tangles exposed along eroded gully banks, hollow stumps or tree trunks, bases of th.o.r.n.y trees with multiple trunks for support, thick tops of fallen trees, or, especially, rock outcrops with deep crevices.

At the time of their maximum population density in or about 1947, woodrats probably averaged several per acre on the woodland parts of the Reservation. In the autumn of 1948, 17 were caught on the ten-acre tract of woodland that was live-trapped most intensively. By then, however, the population had already undergone drastic reduction, as shown by the fact that there were many unoccupied and disintegrating houses throughout the woodland. While the time and manner of mortality was not definitely determined, circ.u.mstantial evidence suggests that the downward trend began in early March, 1948, when record low temperatures and unusually heavy snowfall coincided with the time when parturition normally occurs. The rigorous weather conditions then may have been injurious, not only to the newborn litters but to the females comprising the breeding stock. Nevertheless, the population remained moderately high through 1948, but by early spring of 1949 more than three-fourths of the adults and subadults present in late autumn had been eliminated.

Again, unusually severe winter weather seemed to be the underlying cause, as in January precipitation was the heaviest on record in 81 years, with penetrating sleet storms, persistent ice glaze, and occasional brief thawing followed by sudden drops to extremely low temperature.

After the drastic reduction in the winter of 1948-49, the population did not recover. Although no further sudden reductions due to extremes of weather were noted, the trend seemed to be one of gradual, progressive decline throughout the following period of years. Deterioration of the habitat, as the developing forest shaded out undergrowth, and inroads of certain predators may have been important in preventing recovery of the population. 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.

Of the animals which share the woodrat's habitat, many small mammals, reptiles, amphibians, and invertebrates use its houses and live in a somewhat commensal relations.h.i.+p.

Woodrats are somewhat territorial, each defending its house and an indefinite surrounding area against intrusion by others. Houses tend to be s.p.a.ced at intervals of at least 40 feet; occasionally they are closer together. Most foraging for food is done within 75 feet of the house.

However, woodrats often wander far beyond the limits of the usual home range. On the average, males travel more frequently and more widely than females, and the larger and older males travel more than the smaller and younger. Search for mates provides the chief motivation for wandering.

Extent of wandering is controlled to a large degree by availability of natural travelways, such as rock ledges, by shelters for temporary stopping places, such as old deserted houses, and by population density of the rats themselves.

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 carca.s.ses, even on one of the pilot black snake which is a predator on the rat.

Woodrats are born blind, naked, and helpless, at a weight approximately four per cent of the adult female's. They gain at a rate of at least 1.5 grams per day in the first two months. When they have reached a weight of 100 grams, the gain averages somewhat less than one gram per day, but individual variation is great. Males gain more rapidly than females, especially in the later stages of growth, as adult weight is greater by approximately one-fourth in the male. 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.

_Literature Cited_

CRABB, W. D.

1941. Food habits of the prairie spotted skunk in southeastern Iowa.

Jour. Mamm., 22:349-364.

FITCH, H. S.

1947. Predation by owls in the Sierran foothills of California. Condor, 49:137-151.

RAINEY, D. G.

1956. Eastern woodrat, Neotoma floridana: natural history and ecology.

Univ. Kansas Publ. Mus. Nat. Hist., 8: No. 10, in press.