Home Ranges of Red-Cockaded Woodpeckers in Coastal South Carolina
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HOME RANGES OF RED-COCKADED WOODPECKERS IN COASTAL SOUTH CAROLINA ROBERTG. HOOPER,• LAWRENCEJ. NILES,2'3 RICHARDF. HARLOW,• AND GENE W. WOOD2 •USDAForest Service, Southeastern Forest Experiment Station, Department of Forestry,Clemson University,Clemson, South Carolina 29631 USA, and •TheBelle W. BaruchForest Science Institute of ClemsonUniversity, Georgetown, South Carolina 29440 USA ABSTR•CT.--Totalobserved ranges of 24 groupsof Red-cockadedWoodpeckers (Picoides borealis)varied from 34 to 225ha and averaged86.9 ha. Groupsdefended portions of these rangesfrom adjacentgroups year-round. Home rangeswere derivedfrom totalobserved rangesby subtractingextraterritorial areas and areasreceiving limited use.The percentage of year-roundhome-range boundaries determined by intergroupconflicts varied from 0% to 54% and averaged23.6%. Year-round home ranges averaged 70.3 ha and variedfrom 30 to 195ha. The portion of year-roundhome rangesused in all samplingperiods varied from 15% to 65% and averaged30.5%. The amountof potentialforaging habitat per groupfor all groupswithin 2,000m of a studygroup's colony, a measureof populationdensity relative to availablehabitat, accountedfor 70% of the variation in size of year-roundhome ranges (P < 0.0001).Various measures of groupsize and habitatquality were weaklyrelated to size of year-roundhome ranges.Measures of group size and populationdensity together ac- countedfor 80% of the variation in size of year-round home ranges. Received14 January 1982, accepted2 March 1982. THE Red-cockadedWoodpecker (Picoides bo- the extensiveareas used by groupsand the fact realis) is dependent upon live southern pines that forestmanagement continually alters home for nestingand roostingcavities (Jackson et al. ranges,a better understandingof home-range 1979) and, to a large extent, for foraging sites requirementsis criticalto the species'manage- (Hooper and Lennartz 1981). The scarcityand ment and survival. The objectiveof this study decline of pines suitable for cavity excavation was to examine relationships between home- are the majorreasons the specieswas classified rangesize, group size, populationdensity, for- as endangered (Federal Register, 13 October aging resources,and habitat quality in order 1970,35, 199: 16047).A scarcityof suitablefor- to test several hypothesesof why year-round aging habitat, however,may alsolimit the oc- home-rangesize varied in coastalSouth Car- currenceof the species.This has been indicat- olina. ed by colonyabandonment where large areas of foraging habitat were clearcutfrom around METHODS colonies. Obviously the home range must en- Studyareas.--Eighteen of 24 homeranges studied compasssome minimal amount of suitable for- were on the Francis Marion National Forest, in South aging habitat. Studies by Baker (1971), Crosby Carolina. The area has at least 400 groups of Red- (1971), Skorupa and McFarlane (1976), Wood cockadedson about 64,000 ha of habitat (Oscar Stew- (1977), Nesbitt et al. (1978), and Sherrill and art pers. comm.). This is one of the largest popula- Case (1980) found that 17 seasonalranges av- tions in existence.Major foragingareas consisted of eraged38.9 ha and varied from 14 to 91 ha. One loblolly(Pinus taeda) and longleaf(P. palustris)pine year-roundrange in south Floridawas 159 ha stands. These stands have been periodically pre- scriptionburned since 1944 and have been under (Patterson and Robertson 1981). Considering even-agemanagement since 1950. Ages of pine stands rangedfrom lessthan 1 to 100 yr. Mixed standsof gum (Nyssa spp.), cypress(Taxodium spp.), oak (Quercusspp.), red maple (Acer rubrum),and other 3 Present address:Georgia Department of Natural specieswere interspersedamong the pine stands. Resources, Game and Fish Division, Route 1, Box Six of 24 home ranges studied were on Hobcaw 547, Fitzgerald, Georgia 31750USA. Barony,3 km east of Georgetown,South Carolina. 675 The Auk 99: 6754582. October 1982 676 HOOPERET t•L. [Auk, Vol. 99 Hobcaw has about 3,000 ha of forest land, 3,000 ha ified into standsof similar speciescomposition, age, of salt marsh, and 1,000 ha of fresh water and brack- and density. Depending on stand size, 3-20 plot cen- ish marshesand abandonedrice fields. Forestvege- ters were locatedsystematically from a random start- tation was similar to that on the Francis Marion Na- ing point. At eachplot center,stems from •3 to <13 tional Forest except that pine stands tended to be cm dbh were recordedby speciesand dbh on a 0.02- older.A detailedanalysis of the vegetationwas made ha plot. Stems•13 cm dbh were sampledwith a 1-m by Barry and Batson(1969). factor wedge prism. Trees in the prism plot were Determinationof ranges.--Year-roundranges of 24 recordedby dbh and species. groups of Red-cockadedswere determined by fol- lowing group membersuniquely marked with col- RESULTS AND DISCUSSION ored plastic leg bands. Red-cockadedgroups were family units consistingof a mated pair, their off- TERRITORIAL BEHAVIOR spring of the year, and, in somegroups, adult male helpers. A group traveled severalkilometers daily The 24 groupsengaged in 146 conflictswith but returnedto its cavitieseach evening. After birds other groups.Intergroup conflicts varied in ob- left their cavitiesin the morning, they were contin- served intensity and duration. Conflicts aver- uouslymonitored for 2-14 h. This was done on 627 aged28.1 min for 87 timed encountersand had days,for a total of 3,080h of monitoringtime. Sam- a range of about 1-200 min. In the overtly less pling intensity was similar in all groupsso that it agonistic conflicts, two groups would forage would not be a variable in determining range size. about 10-100 m apart and were silent or mildly The locationsof groups were recorded at 5-min intervals. On the Francis Marion, l:24,000-scale ae- vocal, as comparedto more intense conflicts. rial photographswere griddedto 15.2 m, with each The more aggressiveconflicts were character- tenth line shown on the photograph.Major (152 x ized by increasedvocalizations, aerial chases, 152 m) grid points were locatedin the forestwhen chaseson the trunks of trees, wing spreading, natural featurescould not be used for accurateplot- and loud pecking (comparedwith normal for- ting of the group's location. On Hobcaw Barony, aging). At different times, breeding males and group locationswere plotted each5 min on forest females,adult helper males, and juveniles were vegetationmaps with a scaleof 1:12,000. seen engaged in these activities during con- On the Francis Marion, movements of six different flicts. Although both male and female Red- groupswere followed from May of one year to May cockadedsdrum, especiallyduring encounters of the next for 3 yr starting in 1976 and ending in 1979. On Hobcaw Barony, six groupswere followed with singlealien birds, they were not observed from September1976 to September1977. The year to do so during intergroupconflicts. In 17 cases, was divided into five samplingperiods based on the two birds from opposinggroups made bodily behaviorof the Red-cockadedand arbitrarydivision. contactby graspingbills or feet and fluttering Theseperiods were nestling(1 May-15 June),post- toward the ground, sometimeslanding there fledging(16 June-15September), fall (16 September- together. Conflicts ended when one of the 31 December)and spring (1 January-30April). Three groups withdrew. of the 24 groupsdid not nest the year we studied Conflicts between groups occurred year- their movements,and thus they did not havea nest- round (Table 1), but only three were seenwhen ling or postfledgingperiod. For thosethree groups, young were in the nest. Only one group had movement was monitored during a comparablepe- riod calledsummer (1 May-15 September).Using ob- no observed intergroup conflict and three servationsfor the nestlingand posffledgingperiods, groupshad only one. In contrast,another group we determineda summer home range for the other engagedin 17 encounterswith adjacentgroups. 21 groups. The mean number of conflictsper group was Total observedrange was determinedby connect- statisticallysimilar among sampling periods. ing outermostpoints at which the group was ob- There appearedto be a reductionin territorial served. Territorial boundaries were determined from encountersin spring,however, when fewer and advances and retreats of respective groups during significantlybriefer conflictswere observed. intergroup conflicts.Extraterritorial areas were por- Typically, a group would not honor its ter- tions of the total observedrange that were across ritorial boundaryif the adjacentgroup was not territorial boundaries. Limited-use areas were por- tions of the total observedrange visited only once aware of its presence. During all periods, by the group. Home range was determinedby sub- groupsleft their territory and traveledinto ad- tracting extraterritorialand limited-use areasfrom jacentones. On theseforays, the residentgroup total observedrange. was sometimes encountered, resulting in re- Measurementof vegetation.--Vegetationwas strat- treat by the trespassinggroup. The longestre- October1982] Red-cockadedWoodpecker Home Ranges 677 TABL•1. Frequencyand durationof conflictsof 23a groupsof Red-cockadedWoodpeckers with adjacent groups. Summer Fall Spring Intergroupconflicts (1 May-15 Sept.) (16 Sept.-31Dec.) (1 Jan.-30Apr.) Number of conflicts Number per groupb 2.3A 2.3A 1.7A Minimum-maximum •6 •6 0-7 Total 54 53 39 Duration of conflicts Mean per conflictc (min) 26.5A 38.8B 16.9C Minimum-maximum (min) 0-123 0-200 0-50 Number conflicts timed 28 32 27 One groupout of 24 had no observedintergroup