We estimated variations in breeding parameters and daily survival rates (DSR) of nests of the great egret Ardea alba during 2008-2009 in the Hara Biosphere Reserve, the Persian Gulf. We modelled and compared nesting success using an information-theoretic approach to assess effects of nest site and temporal covariates on DSR. The mean DSR was 0.9896 (95% CI: 0.9931-0.9842) and the overall nest survival was 0.49 (0.35-0.63). Distance to black rat Rattus rattus nest sites was the most important covariate (∑ω_i = 0.96) affecting the survival of great egret nests whereas distance to other great egret and western reef heron Egretta gularis nests was less influential. Neither nest diameter nor nest age effectively explained variation in nesting success. We concluded that black rat predation is the most important factor affecting the breeding performance of great egrets in the Hara Biosphere Reserve, and control measures should be undertaken to reduce the negative effects of this invasive rodent on the heron colonies of mangrove forests in the Persian Gulf.