Distribution and extent of heavy metal accumulation in Song Sparrows (Melospiza melodia), upper Santa Cruz River watershed, southern Arizona, 2011-12

Riparian ecosystems in arid environments provide critical habitat for breeding, migratory, and wintering birds, yet are often at risk of contamination by heavy metals. Birds and other animals living in contaminated areas are susceptible to adverse health effects as a result of long-term exposure and bioaccumulation of heavy metals. We investigated the distribution and cascading extent of heavy metal accumulation in Song Sparrows (Melospiza melodia) in Arizona’s upper Santa Cruz River watershed. This study had three goals: (1) quantify the degree of heavy metal accumulation in sparrows and determine the distributional patterns among study sites, (2) compare concentrations of metals found in this study to those found in studies performed prior to the 2009 international wastewater treatment plant upgrade, and (3) assess sparrow condition among sites with differing potential sources of contamination exposure.

We examined six study sites that reflected different potential sources of contamination. Hematocrit values, body mass residuals, and leukocyte counts were used to assess sparrow condition. Cadmium, copper, mercury, nickel, and selenium exceeded background concentrations at some sites, but generally were lower than or similar to concentrations found in earlier studies performed prior to the 2009 international wastewater treatment plant upgrade. Concentrations were higher in recaptured birds in 2012 than in 2011 for 7 metals in feathers and 14 metals in blood, suggesting possible bioaccumulation. We found no cascading effects as a result of heavy metal exposure, but did find that heavy metal concentrations were reduced following the 2009 international wastewater treatment plant upgrade.