In 2009 we reported the results of heavy metal contaminant testing on an intact egg and remnant eggshell fragments recovered from the Richmond pair’s two initial failed nesting attempts (see July 16th post). The results documented high concentrations of lead, which prompted the collection of blood samples from the three chicks when they were banded on July 27th. The remains of the 4th unhatched egg of this year’s successful clutch were recovered on August 1st and also sent for testing.

Test results have been reported back to us. In contrast to the eggs from the first two clutches, no lead (or pesticides) was detected in the egg remains from the last clutch. Because the pathway for lead deposition into eggs is through the female parent, this strongly suggests that the female of the pair is not suffering from chronic lead exposure. The bird likely had limited exposure to a lead source and was able to pass the contaminant out of its body by depositing it into the eggs from the first two clutches.

Lead was detected in the blood of both female chicks, but was not detected in the blood of the male chick. Lead concentration in the females was consistent with exposure to a lead source, but was not high enough to produce clinical illness. Generally, lead in the bloodstream is the result of recent exposure, which usually happens through ingestion of contaminated prey. It is likely that both female chicks were fed one or more contaminated birds, whereas the male chick was not. Prior to being penned, the male spent much time away from the nest box area where the females were normally found. In addition, the male was smaller than the two females, and probably less able to compete with them for food items being brought to them by the parents. We can speculate that these characteristics may have prevented his exposure to the contaminated prey item(s).

There are a number of sources that can contribute to lead contamination of falcon prey. Lead can be ingested by potential prey such as pigeons through exposure to contaminated dust while foraging. Contamination of soil and dust dates back to the days of leaded gasoline, and contaminated soil can be exposed through disturbance or construction events. There are also a few local ongoing, small-scale lead release sources in the greater Richmond area as well as an old lead smelter (operated until the 1980's) about 2.5 miles away from the nest site. In addition, lead contamination of falcon prey can occur through ingestion of particulate lead in the form of shotgun pellets or fishing weights, or through wounding by a lead pellet (ex. a dove). The overall test results are consistent with the presence of lead sources within the environment used by the falcons.

Although the falcons are periodically exposed to lead through contaminated prey, at present such exposure does not appear to be frequent enough to result in high cumulative levels of lead that can impact their survivorship. However, high concentrations of lead passed on to eggs can result in failed clutches and ultimately impact the reproductive success of the falcons.

These circumstances highlight the challenges in successfully managing the recovery of this species. We will continue to monitor lead exposure of the pair by testing any future addled eggs that we are able to recover.