Reproductive status of peregrine falcons in Big Bend National Park and the Rio Grande Wild and Scenic River, 1992
Division of Resource Management and Visitor Protection, National Park Service. 1992. Reproductive status of peregrine falcons in Big Bend National Park and the Rio Grande Wild and Scenic River, 1992
This report summarizes the 1992 productivity survey of peregrine falcon (Falco peregrinus anatum) territories in Big Bend National Park and along the Rio Grande Wild and Scenic River. A total of nine peregrine falcons fledged in 1992. Two hatchlings did not survive to fledging. By comparison, 15 fledgings were recorded in 1991 and 9 in 1990. There were 11 confirmed adult peregrine pairs, maintaining as many territories, compared with 12 in 1991 and 10 in 1990. Mountain territories did well, with three productive eyries in the Chisos Mountains. Over several years, considerable movement of eyrie sites within mountain territories has been observed. Remarkably, all three Chisos eyries were located within a 1.5 mile radius. It is unknown if such close proximity could indicate other, unidentified, nesting pairs in the Chisos. The number of known, active territories in the Chisos Mountains has consistently been three since 1986. The reproductive rate this year is 0.82 young per active eyrie. This figure falls below the 1.25 suggested necessary for population maintenance (Enderson, 1985). The last eggshell measured for thickness from Big Bend was collected by Hogan in 1988 and found to be 21% thinner than pre-1947 shells. To establish the relation between eggshell thinning and eyrie success or failure, additional shells should be retrieved and analyzed.
- Type
- Published Report
- Authors
- Division of Resource Management and Visitor Protection, National Park Service
- Date of Issue
- 1992
- Units
- BIBE
- Keywords
- Animal Studies, eggshells, Monitoring, Nests & Nesting, Peregrine Falcon (Falco peregrinus) - Falconidae, Reproduction