POTENTIAL EFFECTS OF ENVIRONMENTAL CONTAMINANTS ON RECOVERY OF THE APLOMADO FALCON IN SOUTH TEXAS

Efforts to reintroduce the aplomado falcon (Falco femoralis) into its former range in the southern part of Texas began in 1977. Not until 19 93, however, were a significant number (26) of fledgling aplomado flac ons released. The first nesting pair of aplomado falcons was reported near the Brownsville Ship Channel during 1995. Because of a long histo ry of pesticide use in the Lower Rio Grande Valley, during 1993-94 we investigated the accumulation of environmental contaminants in plasma of aplomado falcons released at the Laguna Atascosa National Wildlife Refuge. We also assessed the potential contribution of typical prey sp ecies to aplomado falcon contaminant burdens. Organochlorine pesticide s and PCBs were below detection limits (wet wt basis) in plasma; howev er, some organochlorines including 1.75 and 1.41 mu g/g p,p'-DDE, and 0.49 and 1.52 mu g/g total PCBs were detected in addled eggs collected in 1995 and 1996. Mercury also was detected at 1.5 and 4.1 mu g/g dry weight in the addled eggs collected in 1995 and 1996. We detected DDE (range 0.02-0.25 mu g/g) in carcasses of potential prey of the aploma do falcon. Trace metals also were detected in potential prey at levels which are not of concern, except for Hg, which was high in a few mead owlarks. Low levels of DDE and most trace metals in potential prey, in cluding mourning doves (Zenaida macroura) and eastern meadowlarks (Stu rnella magna), are not likely to result in adverse effects on the aplo mado falcon in the Lower Rio Grande Valley. However, elevated Hg resid ues in meadowlarks (in a few cases) and potentially higher DDE levels in other prey species such as the great-tailed grackle. (Quiscalus mex icanus) could result in negative effects on reproduction and survival of some aplomado falcons in south Texas.