Environmental conditions in wetlands facilitate favorable biogeochemical conditions for the conversion of inorganic mercury into methylmercury. For this reason, wetlands are increasingly classified as mercury hotspots, places where biota exhibit elevated mercury concentrations. While it is clear that wetlands play an important role in methylmercury production, factors such as geographic variation in mercury deposition, wetland type, and trophic dynamics can cause variation in mercury dynamics and bioaccumulation in biota occupying wetlands or connected to wetland trophic systems. Here, we use songbirds as bioindicators in a two-pronged approach aimed at evaluating the state of our understanding of mercury bioaccumulation by songbirds in wetland ecosystems. First, we use a case study in southeast Missouri to compare blood mercury concentrations in tree swallows (Tachycineta bicolor) and eastern bluebirds (Sialia sialis) occupying wetland and non-wetland habitats to test the hypothesis that songbirds in wetlands will have higher mercury bioaccumulation than those in non-wetlands. Adult tree swallows in wetlands had significantly higher blood mercury concentrations than those in non-wetlands; however, no difference between ecosystems was detected in eastern bluebirds. Second, we present a review of the current literature on mercury in songbirds in wetland ecosystems across North America. Mercury concentrations in songbirds varied among wetland types and with geographic location, often in an unpredictable manner. Mercury concentrations in songbird blood varied 3–10 fold at locations separated only by ~10 to several hundred kilometers. This magnitude of difference in blood mercury concentrations among wetlands exceeds documented differences between wetland and non-wetland ecosystems. Therefore, we caution against the automatic assumption that songbirds occupying wetlands will have higher mercury bioaccumulation than conspecifics living in other habitats.

湿地的环境条件有利于有利的生物地球化学条件，以将无机汞转化为甲基汞。因此，湿地越来越多地被归类为汞热点，在这些地方生物群群的汞浓度升高。显然，湿地在甲基汞生产中起着重要作用，但诸如汞沉积的地理变化，湿地类型和营养动力学等因素可能会导致汞动态变化以及在占据湿地或与湿地营养系统相连的生物群中的生物蓄积。在这里，我们以两种方式使用鸣禽作为生物指示剂，旨在评估我们对湿地生态系统中鸣禽对汞生物累积的理解状态。第一，Tachycineta bicolor）和东部蓝鸟（Sialia sialis）占据湿地和非湿地栖息地，以检验以下假设：湿地中的鸣禽具有比非湿地中更高的汞生物累积量。湿地的成年树燕子的血汞浓度明显高于非湿地。然而，东部蓝鸟没有发现生态系统之间的差异。其次，我们介绍了有关北美湿地生态系统中鸣禽中汞含量的最新文献。鸣禽中的汞浓度随湿地类型和地理位置的不同而变化，通常是无法预测的。鸣禽血液中的汞浓度在仅相距约10至数百公里的位置变化3-10倍。湿地之间血液汞浓度的这种差异程度超过了湿地和非湿地生态系统之间已记录的差异。因此，我们警告不要自动假设居住在湿地的鸣禽比其他栖息地的同种异体具有更高的汞生物累积量。