PARENT SESSION
Poster Session # 18: Avian Ecology.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Breeding ecology of Barred Owls on a central Florida cattle ranch.

Bancroft, G. Thomas^*,, McMillian, Mike,

ABSTRACT- We followed the breeding ecology of Barred Owls (Strix varia) on a 10,300-acre cattle ranch in central Florida during 1995 through 1999. Barred Owls nested in palm-oak forest islands spread through a matrix of pastures and isolated wetlands. The number of nesting pairs on this ranch appears to be limited by the number of palm/oak forest patches and the availability of rotten palms for nesting. Twelve to 15 pairs were found on the ranch. From 1 to 6 pairs apparently did not attempt to nest in a given year. Ten clutches were started in 1995, 12 in 1996, 9 in 1997, 8 in 1998 and 9 in 1999. Nesting success averaged 75% over the five years and ranged from 56% to 100%. Success per territory ranged from 42% to 67%. To examine nesting core area selection in Barred Owls, we calculated the habitats found within a 25-h circled centered on the general nesting areas and compared this to habitat components in 50 randomly placed non-overlapping 25-h circles across Buck Island Ranch. Barred Owl core areas had significantly more area of palm and oak forests (8.1 + 1.2 h) than did randomly placed circles (1.9 + 0.6 h; Mann-Whitney U = 48.0, P < 0.001). Hammocks represented 32% of Barred Owl nesting core areas, whereas only 8% of available habitat. Core areas contained significantly less pasture (11.7 + 1.0 h: Mann-Whitney U = 66, P < 0.001) than did randomly placed circles (19.2 + 0.8 h). Maintaining forested islands in this ranching matrix will be critical for maintaining populations of Barred Owls in this area of Florida. These areas are under increasing development pressures as more intensive agriculture, particularly citrus, moves into central Florida.

Key words: nesting success, Owls, habitat selection, ranching