The Southeastern American Kestrel (Falco sparverius paulus), a non-migratory subspecies of the widespread American Kestrel, has declined to the point that it is listed as threatened in Florida, the state in which it is most common. We studied the nesting biology of Southeastern American Kestrels in 1999 and 2000 at Eglin Air Force Base, FL, in old-growth longleaf pine savanna, a habitat type historically widely occupied by the kestrels. Most of the nest cavities we observed were in old-growth trees, both living and dead, and were originally excavated by Red-cockaded Woodpeckers (Picoides borealis) and then enlarged by other woodpecker species. Nesting success was 70% in 1999 and 56% in 2000. In 1999, 67% of eggs survived to become fledglings in successful nests, as did 58% in 2000. Nests in live pines and snags were equally successful, and nest success was positively related to cavity height in 1999. Reduced nesting success in 2000 may have been related to severe drought conditions. High nesting concentrations of up to 4 pairs per km² were observed. We suggest that stands of old-growth longleaf pine, with little or no hardwood midstory and a relatively high number of snags, inhabited by Red-cockaded Woodpeckers, may constitute high quality habitat for Southeastern American Kestrels. Therefore, loss of longleaf pine habitat, degradation of remaining longleaf habitat due to fire suppression and removal of old-growth and snags, and the decline of the Red-cockaded Woodpecker, a species on which kestrels may have depended as a source of nest cavities historically, may have contributed to the decline of the Southeastern American Kestrel.