Masters Theses

Date of Award

8-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Wildlife and Fisheries Science

Major Professor

Michael R. Pelton

Committee Members

Joseph Clark, John Philpot, Frank van Manen

Abstract

I estimated American black bear (Ursus americanus) density, sex and age structure, home ranges, and habitat use from May 1993 to August 1996 on Alligator River National Wildlife Refuge (ARNWR) and the Dare County Range (DCR), an 841-km² area, in northeastern North Carolina.

I captured 218 bears on 330 occasions, and fitted 44 with radio transmitters. The overall sex ratio of captured bears was 3M:1F, and was skewed towards males during all sampling periods. The overall mean and median age of captured bears was 5.15 (± 2.66) and 5.25 (± 2.60) years, respectively. The mean age of female bears (5.90 ± 2.56) was older than males (4.90 ± 2.65) (z = 2.67582, P = 0.00271). I used 3 methods for population estimation: calendar of captures, Lincoln-Petersen, and the Jolly-Seber. The Jolly-Seber technique provided the most precise estimate: 372±57.14 (86 bears/100km²).

A controlled harvest is one method to reduce the number of bears on the refuge. A harvest strategy to increase the probability of harvesting male bears may reduce the chance of overharvest. Food abundance may influence the sex and age structure of harvested bears. Permitting the hunting of bears in and adjacent to the Farming Unit may increase the number of male bears harvested.

I used 1,379 location estimates of 28 bears (16 F, 12 M) for home range and habitat use analyses. I used the 95% convex polygon (CP) and 95% adaptive kernel (AK) methods to estimate seasonal home ranges. Mean fall home ranges did not differ between male and female bears (z = -0.930, P = 0.926). However, the mean spring ranges of male bears were larger than those of females (z = 3.047, P = 0.0023). Home ranges of male bears did not differ among seasons (χ² = 2.501, d.f. = 2, P = 0.286). Using both the CP and AK home range estimators, mean seasonal ranges of female bears differed by season (CP, P = 0.008; AK, P = 0.016), which was primarily a result of small spring ranges. I used a geographic information system (GIS) and land use/land cover (LULC) data, to determine habitat use patterns. By use of compositional analysis, I ranked 8 habitat types at 2 scales: (1) comparing proportion of habitats on the entire study area to the proportion of habitat within each bears' home range (SAHR), and (2) comparing proportion of habitats within each home range to the proportion of locations in each habitat type (HRLOC). Telemetry error did not bias the results of habitat analyses at the SAHR scale (F₇,₁₁₈ = 1.59, P = 0.1439), although it did significantly bias the results at the HRLOC scale (F₇,₁₁₈ = 11.80, P < 0.0001).

Habitat rankings differed between sexes and seasons (P = 0.0001 and P = 0.0001, respectively). At the SAHR scale, females used pine more than any other cover type during spring. Pine and pocosin ranked highest during summer. During fall, there was no difference in the proportional use of bottomland hardwood, pocosin, pine/hardwood, or pine. Atlantic white cedar and low-density vegetation generally were the lowest ranked cover types for females at the SAHR scale. During the spring, males used pine, pocosin, agriculture, and pine/hardwood proportionately at the SAHR scale. Agriculture was used most during the fall by male bears. During the winter, agriculture and pine ranked highest. Overall, marsh, low density vegetation, and Atlantic white cedar were the least used by male bears at the SAHR scale. Differences between cover types were not as pronounced at the HRLOC scale. During spring, pine and bottomland hardwood ranked highest for female bears. During the summer, females used pine, agriculture, pocosin, and bottomland hardwood equally, during the summer. During the fall, female bears did not use any cover types disproportionately. Atlantic white cedar and pine/hardwood were generally the least used LULCs by females at the HRLOC scale. During the spring, male bears used pine, agriculture, and bottomland hardwood more than any other LULC, at the HRLOC scale. During the fall, pine and bottomland hardwood received the greatest use by males. Pine was used disproportionately by male bears, during the winter. Overall, the least used LULCs by male bears at the HRLOC scale were low density vegetation, pine/hardwood, marsh, and Atlantic white cedar.

One should be cautious when interpreting the high ranking of the pine cover type. Stands of tall pocosin with a canopy closure ≥75% was classified as pine. Thus radio locations in tall pocosins classified as pine would inflate the observed use of pine. Large stands of tall pocosin occurred on the refuge. The understory was comprised of mast producing species such as sweet gallberry (Ilex coriacea) and bitter gallberry (I. glabra). An overall assessment of habitat use patterns from this study would indicate habitat diversity of cover types would ensure a continuous supply of food such as soft mast, blackgum fruits, insects, and agricultural crops. Because black bears are high mobile animals and have relatively large home ranges managers should strive to maintain habitat diversity at the landscape scale by developing habitat management goals for a large area (i.e., the entire refuge).

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