Nest Tree Preference of Ospreys in Northcentral Florida

Abstract

Eighty-four nest trees used by ospreys (Pandion haliaetus) were compared to 80 randomly selected trees on 2 lakes in northcentral Florida to determine whether ospreys exhibited preference for particular tree characteristics. Tests of mean values revealed differences between random and nest trees in surrounding stem density and canopy height. Three components explaining 90% of the variance were derived from principle components analysis of the random trees. Fourteen of 84 nest trees differed from surrounding trees; major differences were in vertical structure and stem density. Lack of large-scale differences between nest and random trees suggests ospreys in northcentral Florida have a fairly wide tolerance for nesting substrates. J. WILDL. MANAGE. 52(1):103-107 A common question in studies of nesting substrates of raptors is why a particular substrate is selected over others. While selected substrates often show differences that are ecologically interpretable (Mosher and White 1976), other comparisons are not simple and may reflect choice for specific attributes not easily detected (Hilden 1965). Alternatively, nesting birds may have a wide tolerance for nesting substrate when certain criteria, such as lateral branches thick enough to support a nest, are met. We examined attributes of nest trees selected by ospreys on 2 lakes in northcentral Florida. The identification of aspects of osprey nesting habitat and substrate in Florida serves several purposes. First, the rapid urbanization of Flor1 Present address: Wisconsin Cooperative Wildlife Research Unit, University of Wisconsin, Madison, WI 53706. This content downloaded from 157.55.39.32 on Mon, 10 Oct 2016 04:17:23 UTC All use subject to http://about.jstor.org/terms 104 NEST TREE PREFERENCE IN OSPREYS * Edwards and Collopy J. Wildl. Manage. 52(1):1988 ida along waterways and lakes makes identification of crucial nesting habitat important. Data from relatively undisturbed locations may serve as baseline information to aid managers evaluating human impacts on ospreys. Second, unlike many coastal populations, osprey at lakes in northcentral Florida typically nest in live trees. Thus, use of live rather than dead trees poses interesting questions regarding use versus availability. Finally, several researchers suggest that raptors exhibit preference for nesting substrates (Matray 1974, Mosher and White 1976, Titus and Mosher 1981, Reynolds et al. 1982, Woffinden and Murphy 1983). Our objectives were to determine whether nest trees used by ospreys differed from surrounding trees. We thank P. Frederick, J. A. Mosher, T. G. O'Brien, H. F. Percival, and an anonymous reviewer for their helpful comments on manuscript drafts. P. Bohall-Wood and H. Dinkler provided assistance in data collection. Partial funding and logistical support were provided by the Florida Cooperative Fish and Wildlife Research Unit and grants from Sigma Xi and The Hawk Mountain Sanctuary Association. We acknowledge T. B. Murphy for his assistance throughout the project. This paper is Contribution 8126 of the Florida Agricultural Experiment Station, Gainesville.