At the Great Lakes, numbers of the Piping Plover (Charadrius melodus) are gradually increasing, but the population of <100 pairs is still at risk of extinction and remains sensitive to fluctuations in adult survival. Given the central role of adult survival in population recovery, an accurate estimate of this quantity is essential. Using a Barker model and 11 years of mark–resighting data of breeding and nonbreeding Piping Plovers at the Great Lakes (1998–2008), we estimated true adult survival (S), probability of detection of breeding birds (p), probability of detection nonbreeding birds (R), and site fidelity (F). Adults’ survival rate averaged 0.76 but with considerable annual process variation (σ = 0.05) and strong evidence of decline over this period. The probability of detection of breeding birds was near perfect (p = 1.00, 95% CI 0.97–1.00), but probabilities of detection of nonbreeders were substantially lower, although they increased from approximately 0.25 to 0.50 through the study period because of increased effort in observation and reporting. The birds’ fidelity to the area of the Great Lakes in which they were monitored was high ( = 0.91, 95% CI 0.66–0.98), with evidence of an increase through time that we attribute to increased intensity of monitoring. Evidence for a decline in true adult survival over nearly a decade suggests a pressing need for research on the timing and causes of adult mortality in this population.