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.