Blood-lead and ALAD activity levels of Cooper's Hawks (Accipiter cooperii) migrating through the southern Rocky Mountains

Predatory or scavenging raptors can be exposed to lead contamination through the ingestion of hunter-injured or killed game species that contain residual lead bullets, pellets, or fragments thereof, or prey contaminated by lead from other anthropogenic sources. We studied the incidence of lead exposure in Cooper's Hawks (Accipiter cooperii) by sampling southward and northward migrating populations. Cooper's Hawks have been regularly captured for biological data collection at two long-term monitoring and banding stations in north-central New Mexico. We identified blood-lead concentrations, erythrocyte ALAD activity, and hematocrit levels in fall migrating adults and juveniles (N = 45 and 15, respectively), and spring migrating adults (N = 38; no juveniles were captured in spring). Blood-lead concentrations of spring migrating adults ((x) over bar = 0.063 +/- SE 0.011 mug/g) were significantly greater than both fall adults and juveniles (0.032 +/- 0.003 mug/g and 0.028 +/- 0.004 mug/g, respectively). Blood-lead concentrations did not reach levels sufficient to inhibit erythrocyte ALAD activity or depress hematocrit levels. ALAD activity appeared to be age-dependent, however, as activity in fall juveniles (74.9 +/- 2.2 units) was significantly greater than in both fall and spring adults (63.0 +/- 2.9 units and 54.0 +/- 3.1 units, respectively). Hematocrit values indicated no detectable differences between migration season or age. Our findings suggested that Cooper's Hawks were exposed to higher environmental levels of lead in their winter range than they were in the breeding range, though not at concentrations known to cause detrimental health effects.