Loggerhead Shrikes (Lanius ludovicianus) are prominent birds of open habitats and are important bioindicators of environmental degradation because they are predatory and closely associated with many agricultural areas. Once relatively common throughout much of North America, the Loggerhead Shrike has been declining in numbers for most of the 20th century and is currently diminishing at about 5% per year (Hess 1910, Graber et al. 1973, Bystrak and Robbins 1977, Geissler and Noon 1981, Morrison 1981, Burnside and Shepherd 1985). It is one of the few species to exhibit significant declines in USFWS Breeding Bird Surveys (BBS) in all continental regions (Robbins et al. 1986, Droege and Sauer 1990, Peterjohn and Sauer 1993). Regions most affected appear to be those with breeding populations of the migratory subspecies (L. L migrans; Bystrak 1983). The Loggerhead Shrike has been included in the National Audubon Society's Blue List since 1972 (Tate 1986): Several factors implicated in this shrike's decline are: (1) poor reproductive success (Strong 1972, Porter et al. 1975, Luukkonen 1987, Gawlik 1988), (2) removal of fencerows and fencelines, a modem agricultural practice that deprives birds of suitable habitat such as hunting substrate, observation perches, and nest sites (Kridelbaugh 1982, 1983; Luukkonen 1987; Novak 1989; Yosef 1994), (3) reduced survival on the winter range in migratory subspecies (Haas and Sloane 1989, Brooks and Temple 1990a), (4) dietary uptake of agricultural pesticides and herbicides by females, resulting in thinning of eggshells (Busbee 1977, Anderson and Duzan 1978, Morrison 1979), (5) inclement weather that reduces reproductive success by destroying nests or reducing the food supplies of parents feeding young (Porter et al. 1975, Craig 1978), (6) disease (Legrand 1986), (7) interspecific competition (Cadman, unpubl. report), and (8) collisions with cars (Robertson 1930, Clark 1970, Bystrak 1983). Scott and Morrison (1990) recently demonstrated that factors other than prey abundance may have prevented shrikes from nesting outside their present range. Brooks and Temple (1990b) found that shrike densities in the upper Midwest do not seem to be limited by availability of suitable breeding habitat, and that habitat changes are not correlated with declines in shrike density. In addition, on the winter range of Loggerhead Shrike, recently Lymn and Temple (1991) found a significant positive correlation between abundance and habitat condition, and a significant negative correlation between shrike numbers and the presence of red imported fire ants (Solenopsis invicta). They suggested that the occurrence of these ants rendered many of the remaining patches of habitat unsuitable because they competed for the same prey. The effects of fire ants on wildlife populations is controversial (Brennan 1991, 1993; Porter et al. 1988; Lymn and Temple 1991; Porter and Savignano 1990; Allen et al. 1993) We hypothesized that if Lymn and Temple's (1991) suggestion is true and these ants have altered the ecosystem to the extent that it is no longer able to support shrike populations, then the effect should be evident on shrikes whose territories were occupied by fire ant colonies. We predicted that shrikes whose breeding territories were heavily infested would have to forage for longer periods of time to catch the minimum sustainable number of prey and their reproductive success might be lower. We tested the hypothesis by surveying 10 shrike breeding territories in our Florida study area containing varying densities of ant colonies, and assumed that all ant colonies are evenly distributed.