September 26, 1949 230 gms.
September 27, 1949 230 gms.
October 18, 1949 260 gms.
October 27, 1949 250 gms.
October 29, 1949 220 gms.
November 8, 1949 235 gms.
November 15, 1949 245 gms.
November 24, 1949 240 gms.
November 26, 1949 240 gms.
November 30, 1949 240 gms.
December 20, 1949 260 gms.
February 18, 1950 230 gms.
April 5, 1950 290 gms.
April 7, 1950 300 gms.
October 7, 1950 320 gms.
November 29, 1950 345 gms.
March 23, 1951 340 gms.
Another example, showing winter cessation of growth in a male at even
smaller size is shown below. This was in the winter of 1950-1951.
November 9 145 gms.
November 28 175 gms.
November 29 165 gms.
January 10 180 gms.
January 11 175 gms.
March 1 225 gms.
March 23 200 gms.
_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 grassland,
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 thorny 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, circumstantial 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 relationship.
Woodrats are somewhat territorial, each defending its house and an
indefinite surrounding area against intrusion by others. Houses tend to
be spaced 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
carcasses, 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.
_Transmitted March 12, 1956._