Fifty-year trends in a box turtle population in Maryland

摘要

A survey conducted in 1995 investigated long term declines reported in a population of box turtles Terrapene carolina monitored each decade since 1945 in bottomland hardwood forest at the Patuxent Wildlife Research Center, Maryland. Methods duplicated past surveys in most respects, but were supplemented by radiotelemetry and a survey of dominant vegetation. Seventy different turtles were found on the 11.8 ha study area, a decline of > 75% since peak populations were recorded in 1955. Searchers were less efficient in 1995 than in 1945 1975 for a variety of possible reasons. Among turtles recorded, approximately equal numbers persisted from each of the past five decades, with some individuals surviving > 70 years. A sex ratio strongly favoring males was first recorded in 1975 and continued in 1995, but juveniles and subadults were found in greater proportion in 1995 than in any other survey. Six of nine radio-marked turtles left the bottomland study area and migrated to the adjoining bluffs to hibernate, suggesting more extensive movements and perhaps less stable home ranges than formerly thought. Age structure of trees indicated a gradual change to more shade-tolerant species. Examination of rates of change from survey data suggested that major losses probably resulted from changes in hydrology that exacerbated flooding in 1972, with recovery only beginning in 1995 and perhaps limited both by repeated flood events and successional changes in the forest. Slow recovery from losses may indicate that populations of this species would respond poorly to exploitation.