Further Assessment of Environmental Contaminants in Avian Prey of the Peregrine Falcon in Big Bend National Park, Texas

A small resident population of peregrine falcons (Falco peregrinus anatum) in the Big Bend region of Texas has suffered reproductive failures since 1990. To continue our assessment of the effects of environmental contaminants on the peregrine falcon, we collected representative avian prey species during 2001 at Mariscal Canyon, Big Bend National Park. The avian carcasses were analyzed for inorganic and organochlorine contaminants. Concentrations of Se and Hg were present at high levels (up to 11 and 2.2 mg/g dry weight, respectively) in some avian prey and could be implicated in reproductive failures of the peregrine falcon in Big Bend National Park. All other inorganic elements were below concentrations known to affect reproduction or to be associated with other deleterious effects in birds. Of all the organochlorines analyzed, only DDE and total PCBs were present above detection limits in all species, although at low concentrations. Our study provides further support to the hypothesis that contaminants in potential avian prey of the peregrine falcon in the Big Bend region are implicated in the productivity failures observed in this species since 1990. RESUMEN—Una población pequeña del halcón peregrino (Falco peregrinus anatum) residente en la región de Big Bend ha tenido fracasos reproductivos desde 1990. Para continuar nuestra evaluación de los efectos de los contaminantes ambientales en el halcón peregrino colectamos especies de aves representativas como presa durante el año 2001 en el cañón de Mariscal, en el Parque Nacional de Big Bend, Los cadáveres de aves se analizaron por contaminantes inorgánicos y organoclorados. Observamos concentraciones de Se y Hg a niveles elevados (hasta 11 y 2.2 mg/g peso seco, respectivamente) en algunas especies presa y podrı́an estar implicados en los fracasos reproductivos del halcón peregrino en el Parque Nacional de Big Bend. Todos los demás elementos inorgánicos se observaron a concentraciones debajo de las que se sabe que afectan la reproducción o que han sido asociadas con otros efectos dañinos en aves. De todos los compuestos organoclorados analizados, solamente DDE y PCBs totales se encontraron por arriba de los lı́mites de detección en todas las especies, pero a bajas concentraciones. Nuestro estudio proporciona apoyo adicional a la hipótesis de que los contaminantes en aves que son presa potencial del halcón peregrino en la región de Big Bend están posiblemente implicados en los fracasos reproductivos observados en la especie desde 1990. The peregrine falcon (Falco peregrinus anatum) was removed from the U. S. Endangered Species List in 1999 (Federal Register, 25 August 1999). Although the species is believed to have recovered significantly throughout most of the United States, a small resident population (around 20 territories) in the Big Bend region of Texas has continued to experience reproductive failures since 1990 (Siegel, 1997; unpublished report). The highest productivity was recorded during 1978 (2.5 young fledged/nesting pair), and the lowest productivity occurred during 1995 (0.14 young fledged/nesting pair) (Siegel, 1997; unpublished report). The number of young fledged/ nesting pair was above a sustainable level only during 4 y within the period 1990 to 2003 (Siegel, 1997; unpublished report). A productivity of 1.25 to 1.5 young fledged/nesting pair is expected to result in a sustainable population with potential for growth (Grier and Barclay, 1988; Wootton and Bell, 1992). Some recruitment of peregrine falcons into Big Bend might be occurring from a nesting population south of the Rio Grande in Maderas del Carmen, Coahuila, Mexico. Low productivity of peregrine falcons during 1993 to 1996 was associated with low rainfall THE SOUTHWESTERN NATURALIST 52(1):54–59 MARCH 2007