SREL Reprint #2512

Nesting ecology and embryo mortality: implications for hatchling success and demography of Blanding's turtles (Emydoidea blandingii)

Justin D. Congdon1, Roy D. Nagle2,1, Owen M. Kinney3, Matthew Osentoski4, Harold W. Avery5,
Richard C. van Loben Sels6, and Donald W. Tinkle7,8

1Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29802 USA
2Juniata College, Huntingdon, Pennsylvania 16652 USA
3Institute of Ecology, University of Georgia, Athens, Georgia 30602 USA
4Department of Biology, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33124 USA
5U.S. Geological Survey, Canyon Crest Field Station, Department of Biology, University of California,
Riverside, California 92521 USA
6Red Mountain High School, 7301 East Brown Road, Mesa, Arizona 85207 USA
7Museum of Zoology, University of Michigan, Ann Arbor, Michigan 48109 USA
8Deceased

Abstract: A 23-year study (1976-98) of Blanding's turtle nesting ecology was conducted concurrently with a mark-recapture study on the University of Michigan's E.S. George Reserve in southeast Michigan. Nesting seasons averaged 28 days duration with the earliest beginning and latest ending on 15 May and 9 July, respectively. Females generally began nesting forays in the evening and completed nests after dark. A total of 451 nests were located, including: 1) intact observed nests associated with a known female (n = 296), 2) intact observed nests not associated with a specific female (n = 16), and 3) unobserved nests found after they were destroyed by predators (n = 139). In the sample of observed nests, 182 were monitored until subsequent destruction by predators, hatchling emergence, or nest inspection for evidence of egg and embryo mortality in late fall. In total, 78% of observed nests were destroyed by surface predators (mainly raccoons), 1% were apparently destroyed by burrowing mammals, and 4% failed entirely due to abiotic and other causes (i. e., soil erosion, flooding, desiccation of eggs, root intrusion into nests). Approximately 10% of the observed nests were partially successful (produced at least one hatchling), and 8% were considered as total success (all eggs produced hatchlings). Adding embryo mortality to nest predation rates reduced embryo survival (Sx age 0) by about 30% (from 0.261 to 0.176). We recalculated the previously published life table (age 0 mortality based on nest predation rates only) that indicated a stable population. Lower embryo survival resulted in a population that would decrease by 50% in 78 years. To compensate for the increased embryo mortality, adult and juvenile survival estimates would have to increase by 1.5 and 2.2%, respectively; these compensatory increases in survival are certainly within the errors of estimates based on mark-recapture data. Because the vast majority of embryo mortality is caused by nest predators, additional embryo mortality in nests surviving predation does not appear to have a major impact on the population dynamics of Blanding's turtles as long as survivorship of older juveniles and adults is not reduced from present levels.

Keywords: Reptilia; Testudines; Emydidae; Emydoidea blandingii; turtle; demography; embryo mortality; nesting; nest predators; reproduction; Michigan; USA

SREL Reprint #2512

Congdon, J. D., R. D. Nagle, O. M. Kinney, M. Osentoski, H. W. Avery, R. C. van Loben Sels, and D. W. Tinkle. 2000. Nesting ecology and embryo mortality: implications for hatchling success and demography of Blanding's turtles (Emydoidea blandingii). Chelonian Conservation and Biology 3:569-579.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).