This paper presents preliminary ecological data and analysis on three bobcats (two females and one male) that were captured, radio-collared, and tracked using radio-telemetry equipment and triangulation techniques on or adjacent the St. Johns National Wildlife Refuge Beeline Unit. The information presented here comes from data collected as part of the Foundation’s ecological study of free-ranging bobcats in the fragmented landscape of Brevard county, Florida. The purpose of this study is to examine various ecological and biomedical aspects of bobcat populations in fragmented landscapes in order to understand associated dynamics and to suggest habitat conservation guidelines that offset the effects of large-scale habitat fragmentation. The findings presented here are part of a larger study being done by Coryi Foundation Inc. that covers most of Brevard County.

Though the bobcat is not a listed species, there is great potential for its local loss in Brevard County (Mallow, 1999a). With Florida as a whole growing rapidly in terms of population and new development, humans are quickly encroaching upon and eliminating bobcat habitat at an alarming rate. In Brevard County, out of the 203,858 acres of land that exists within the county, 50% is already developed (Mallow, 1999a). Urbanization rations parcels of prime habitat to humans and poor quality habitat to predators in a pattern that is severely fragmented. This patchwork array of poor-quality land may not offer sufficient functionality for the wide-ranging bobcat. Habitat isolation via fragmentation by development could create small isolated populations that could succumb to the deleterious effects of inbreeding. This report is preliminary and discusses the functionality of an existing large block of habitat – the St. Johns National Wildlife Refuge. It was deemed a worthy effort to determine how such lands could play in the future of the bobcat, since it is likely that such places could be all that remains of wild lands in the future, should development trends continue as they are.

For the purpose of habitat selection analysis and home range size estimation, fixes on radio-collared bobcats are located via triangulation with radio-telemetry equipment at distances of less than 500 meters between observer and animal. The difference in bearings at each location is 75 to 105 degrees... and only locations that are temporally independent are used in these analyses. An estimate of density was not calculated due to the small sample size.

Home range sizes were estimated using the 100% minimum convex polygon (MCP) (Mohr 1947) and 95% harmonic means (HM) (Dixon and Chapman 1980) methods. Both methods provide an estimation of home range size, and when their outputs are compared, a degree of internal home range habitat fragmentation. The MCP method is a non-statistical approach that calculates the area formed by the polygon whose boundary scribes the outermost locations. One simply defines a range boundary by connecting the outermost locations of the animal. As such, the home range size estimation does not exclude broad areas of unused space. The harmonic means (HM) method is a statistical estimation that generates a home range boundary on the basis of the clustering of locations and how the boundary ‘hugs’ the spatial density of locations more tightly (Mallow, 1999b). The HM method is more representative of spatial use and excludes unused space. By comparing estimates calculated from the two methods, one can obtain an approximation of the severity of internal fragmentation.

Habitats were indexed according to Florida Land Use Cover Classification Scheme system from May 1993. The classifications used were: upland forests, wetland forests, shrub and brush, range land, agriculture, water, non-forested wetlands, barren land, transportation, communication, utilities, urban and built up, and low density residential.

The habitat selection index for a given cover type was determined as the ratio of the number of observed locations in that type to the number of expected locations in that type. The number of expected locations was calculated as the total number locations multiplied by the percentage of a habitat type that was enclosed within the home range. An index greater than one indicated that a habitat type was preferred. An index of less than one indicated that a habitat type is avoided. An index equal to one indicated that the animal does not care one way or the other about the habitat type - in other words, it randomly selects to use that type. Digitized maps were used in the selection index computation process.

During the period, the MCP home range sizes of the three cats that used the refuge averaged 10.96 and 2.96 square kilometers for the one male and the two females, respectively. HM range sizes averaged 10.49 and 2.27 square kilometers.

Bobcats in the study used the following habitats in the order of descending selection (indices are shown in parenthesis): forested wetlands (2.7), upland forest (2.2), shrub and brush (1.5), low density residential (0.6), non-forested wetlands (0.6), range land (0.5).

Due to the low sample size, the indicated values should not be viewed as indicative of Lynx rufus though the data from the three cats shows a definite preference and avoidance of particular habitat types.

Regarding home range sizes, there was no significant difference between the range size estimates for the MCP and HM methods. That is to say, since the refuge is not fragmented by development, home ranges are not substantially internally fragmented.

Home range sizes are smaller than those reported from other areas in Brevard County (Mallow 1998) and elsewhere in Florida (Mallow 1999b). It is speculated that this is due to the dominance of the non-forested (marsh) communities. Indeed, forested habitats account for a small amount of the total composite, compared to lands east of the flood plain. As a result, bobcats in this matrix may have adapted to smaller home range sizes as a result of conspecific competitive interactions that intimately play in tandem with available resources – limited preferred denning cover (dry ground) and preferred prey.

Bobcats on the refuge show a strong preference for any forested community and avoid the non-forested wetlands, range land, and low density residential (The northern end of the Canaveral Groves subdivision is occasionally used by the male). Shrub and brush were given a mild preference.

These findings suggest that the small home ranges are the result of limited preferred habitat since bobcats appear to spend most of their time in the forested communities. These findings also suggest that, whereas the bobcats of the refuge are able to make use of existing preferred types, despite the limited amount therein, that the flood plain region may not, as a whole, afford a sufficient amount of habitat for population viability. This statement a mere speculation at this point and can only be validated via population viability analysis – a task that will be done by Coryi Foundation.

We have yet to document the movements of dispersing juveniles through the forested links that lace the landscape upon which the refuge is situated. This is because all our animals are adults with well-established and stable home ranges. However, based on these preliminary findings, we feel that juveniles would most likely utilize these forested links as dispersal routes. In time, we are confident we will observe such events.

At this point, we cannot make valid conclusions since we have not yet obtained data in all seasons. We also feel that we have not collared all the cats on the refuge and that it is desirable to increase the sample size. We feel that the number of collared subjects that use the refuge can easily double. Rains from the summer and early fall had destroyed trapping sites on a daily basis. We had to suspend capture activities until the rains had subsided. Now that the area has dried considerably, we will resume trapping.