NESTING ECOLOGY AND HATCHING SUCCESS IN THE TURTLE EMYDOIDEA BLANDINGI

Abstract

Nesting ecology of the Blanding's turtle was studied for 6 yr, from 1976 through 1981 in southeastern Michigan. Beginnings of the nesting seasons varied by 17 days (May 23 to June 9) and lasted from 16-30 (xt = 23) days. Beginnings of nesting seasons were significantly correlated with mean April temperatures but not to mean May temperatures. Nesting activity occurred almost entirely in the evening with average time of nest completion at 2119 h EST. Most females return to the same general nesting areas each year. Nesting areas were usually not adjacent to the female's marsh of residence. Three hypotheses concerning predation of nests were tested. (1) Nests located greater distances from water should have lower predation rates. (2) Nests located in areas where predators can use an essentially linear search pattern should have a higher predation rate. (3) Females that nest early in the nesting season should have lower egg mortality due to predation. None of these hypotheses was supported by our data. Nests were located 2-1115 m (x= 135 m) from the nearest water. Predation accounted for 82% of nest mortality. Most predation (84%) occurred during the first five days after nest completion with 47% occurring within the first 24 h. Percent nest predation ranged from 42% (1978) to 93% (1981). Within the nests that survived predation, an average of 1.20 eggs per nest failed to develop, and 22% of the observed nests produced hatchlings. The average time from egg laying to hatchling emergence was 84 days (mid-August through early October). Forty-five percent of hatchling emergence was synchronous (all hatchlings emerge in one day), and 55% asynchronous (emergence over more than one day). Females mature at a plastron length of from 160-162 mm. There was no relationship between body size of the female and the day of the nesting season when she nested. As few as 23% or as many as 48% of the females in the population may reproduce in a given year, and those that do produce only one clutch of eggs. Clutch size averaged 10 (min.-max. = 3-15) eggs. Data on clutch frequency, nest survivorship and body size distributions for the entire population indicate that recruitment into the adult population may be very low.