Play a secondary role in influencing Hg concentrations in egrets and ibis. Disentangling those effects is beyond the scope of this study, but illustrates the complexity of examining different environmental stressors on the physiological condition of birds. Egret HSP70 decreased by 83% across the range of Hg concentrations, suggesting that Hg may have down-regulated these heat shock proteins. Previous research on heat shock protein regulation in relation to both inorganic Hg and MeHg have found that heat shock protein regulation can be either inhibited or induced depending on the chemical form of Hg. Up-regulation of heat shock proteins are associated with protective stress responses to minimize cell protein damage. Methylmercury exposure in birds is associated with oxidative stress in liver, kidney, and brain tissue, and upregulation of heat shock proteins has recently been identified as a potential biological defense mechanism against MeHg toxicity. However, it is unclear what the consequences are for down-regulation of heat shock proteins as we observed with egrets. Presumably, a reduction of heat shock proteins could result in decreased cell function and homeostatic imbalance, given that this is the primary role heat shock proteins when an individual is not in a stressful situation. Opposite response patterns of other stress biomarkers in relation to Hg exposure have been documented in other birds. Herring et al. found that Hg exposure in Forster’s tern chicks depressed FCORT concentrations by up to 81% via the downregulation of the HPA axis. These results suggest that the physiological stress response systems of birds are dynamic and that Hg exposure can negatively influence critical physiological processes. Current Hg exposure Adriamycin levels of egrets and ibises throughout much of the Florida Everglades are low relative to historical reports. However, the fact that for egrets, one of their HSPs was influenced by Hg, demonstrates that the current Hg levels could still influence the physiology of this species. Moreover, Hg hotspots still exist within the Florida Everglades where Hg levels in fish far exceed levels measured anywhere else within the ecosystem, and still pose a risk to wading birds. Ibis heat shock proteins were not influenced by Hg exposure in this study, which was likely a function of Hg exposure levels being approximately 7 times lower than those of egrets. We found that ibis but not egret FCORT levels were influenced by prey biomass levels, and that they declined by 98% across lowto-high range of prey biomass at foraging sites. This is consistent with responses in pre-breeding adult birds, suggesting that this relationship may be consistent across life stages. Similarly, ibis nest success was also more sensitive to changes in prey biomass than that of egrets, demonstrating the importance of prey biomass to ibis. Egret FCORT metabolite concentrations also declined by 79% across the age range of chicks. Other studies of CORT stress levels in chicks have found that concentrations often increase as chicks get older, in preparation for fledging. However, there is some evidence that elevated CORT levels can result in decreased protein deposition in growing feathers, which may lead to poorer feather quality.