Home ranges, habitat selection and mortality of ring-necked pheasants (Phasianus colchicus) in north-central Maryland.
|Abstract:||Between 4 January and 15 May 1988, we captured 16 female and 10 male ring-necked pheasants (Phasianus colchicus) in north-central Maryland at the southern edge of their North American range and fitted them with radiotransmitters. We monitored their movements on an agricultural landscape encompassing 2002 ha from the day of capture until death, transmitter failure or 15 December 1988. Eight of 16 females and seven of 10 males survived to the nesting season. Predation accounted for 61% of the mortality of adult pheasants. Seven males and 12 females, each with [greater than or equal to]30 fixes per analytical time period (winter, nesting, postnesting or maximum), were used in analysis of home and core ranges, seasonal movements and habitat selection and use. Home range sizes did not differ significantly between sexes or among seasons. Pheasants had significantly larger core ranges during the nesting season than during winter or postnesting seasons. Pheasants selected home ranges with a higher proportion of shrublands and wetlands than expected from availability within the study area. A comparison of habitat use within core ranges to that available within home ranges in winter showed that forests were significantly less used than wetlands, croplands, shrublands and developed lands. There were no significant differences in proportional habitat use of home versus core ranges during the nesting season. based on our study, conservation measures should include (1) enhancing preferred nesting cover by compensating landowners for delaying or not mowing hay fields or leaving crop fields fallow and (2) providing suitable dispersed male territory cover (i.e., shrubs or woody cover at crop borders) around existing patches of winter cover (i.e., wetlands and shrublands) and in close proximity to nesting cover.|
Habitat selection (Research)
Home range (Research)
Smith, Scott A.
Stewart, Nancy J.
Gates, J. Edward
|Publication:||Name: The American Midland Naturalist Publisher: University of Notre Dame, Department of Biological Sciences Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Earth sciences Copyright: COPYRIGHT 1999 University of Notre Dame, Department of Biological Sciences ISSN: 0003-0031|
|Issue:||Date: Jan, 1999 Source Volume: 141 Source Issue: 1|
|Geographic:||Geographic Scope: Maryland Geographic Name: Maryland|
The ring-necked pheasant (Phasianus colchicus) population in Maryland began declining in the early 1970s, with an 81% decrease reported from 1975-1984 (Maryland Department of Natural Resources, 1983; Therres, 1989). Declines were noted in other eastern United States pheasant populations during this same time period (Hartman et al., 1984; Droege and Sauer, 1990), with these declines attributed to changing land-use patterns. The Maryland pheasant decline has been attributed to habitat loss through urbanization and changing agricultural practices, particularly an increase in acreage of corn and soybeans and a decrease in hay (Therres, 1989). Home ranges are likely influenced by the spatial arrangement of habitat types in different geographic regions of North America, and range in size from about 35-150 ha (Hanson and Progulske, 1973; Hallett, 1986). Although pheasants appear to preferentially nest in strip cover and hay with residual and shrubby covers less preferred (Carroll et al., 1988; Robertson, 1996), shrubby cover is often the most productive habitat type in terms of successful nests and hatched nests (Robertson, 1996). Predation also takes an increasing toll on nests and adult birds as the quality and/or quantity of pheasant habitats deteriorate (Petersen et al., 1988). The primary objectives of our research were to determine seasonal home and core ranges, movements and habitat use of pheasants in Maryland; and, secondarily, to identify those factors affecting adult survival.
STUDY AREA AND METHODS
The study was conducted on an agricultural landscape in Carroll and Frederick counties in north-central Maryland near the southern edge of pheasant range in eastern North America (Sauer et al., 1997). based on previous population surveys by personnel of the Maryland Department of Natural Resources, this area was identified as important pheasant range as well as having cooperative landowners. It was characterized by low-density residential developments, rolling farmland, upland forests of primarily hardwoods, shrublands and bottomland drainages containing multiflora rose (Rosa multiflora) and willow (Salix spp.). Elevations ranged from 110-245 m.
Based upon the maximum extent of pheasant home ranges, we delineated a 2002 ha study area. We then prepared a habitat map of the study area using aerial photographs; pc Arc/Info, a geographic information system or GIS; and ground-truthing. We grouped habitat types into six main categories: (1) croplands (27.4% of the 2002 ha study area), consisting of row crops (20.7%) and small grains (6.7%); (2) grasslands (41.7%), including alfalfa (2.9%) and mixed hay fields (26.6%), and pastures (12.2%); (3) shrublands (6.2%), containing hedgerows (2.0%), old fields/shrublands ([greater than or equal to]33% shrubby cover, 3.2%) and vineyards/orchards (1.0%); (4) forests (11.7%), consisting of deciduous (10.2%) and mixed woodlands (0.04%), and pine plantations (1.5%); (5) wetlands (4.4%), including emergent (0.9%), scrub/shrub (0.9%) and forested wetlands (2.3%) (Cowardin et al., 1979) and ponds (0.3%); and (6) developed lands (8.6%), encompassing roads, residences, industrial and commercial sites, graveyards and railroad rights-of-way.
We located radiotagged pheasants by triangulation from fixed stations with portable handheld, four-element Yagi antennas. Two or three compass bearings were taken consecutively on one bird from different stations. Time between consecutive fixes was no longer than 2-3 min to reduce location error (Kenward, 1987). Locations of birds that were moving rapidly were not used. The mean degree error was determined to be [+ or -]10 [degrees]. When error polygon size was [greater than or equal to]0.32 ha, the resulting estimated location was deemed unreliable; therefore, those few fixes were excluded from further analyses. The center of the error polygon was considered to be the location of the pheasant.
Radiotagged pheasants were monitored from the day of capture until death, transmitter failure or 15 December 1988. To insure that we included any temporal differences in daily habitat use, monitoring periods covered: (1) morning - 0.5 h before sunrise to the first 20% of the daylight period; (2) midday - the mid 60% of the daylight period; (3) evening - the last 20% of the daylight period to 0.5 h after sunset; and (4) night - 0.5 h after sunset to 0.5 h before sunrise. The study period was divided into three unequal seasons: (1) winter - between the end of the hunting season (31 December 1987) and the initiation of herbaceous growth in the spring (7 March in 1988); (2) nesting - between the initiation of herbaceous growth through egg laying, incubation, hatching and brood rearing to the time when young were eight weeks old and independent (31 July in 1988); and (3) postnesting - between young reaching eight weeks of age (31 July) until the end of the hunting season (31 December). During winter and the nesting season, each pheasant was located 4 x per d approximately 5 x per wk. After the nesting season, fixes were taken 4 x per d every other wk until 15 December.
Home and core ranges, and seasonal movements. - Seasonal home and core ranges and maximum home ranges (Kaufman, 1962) were estimated using minimum convex polygon (home range) (Mohr, 1947) and harmonic mean (core range) (Dixon and Chapman, 1980). Seasonal home and core ranges included fixes for winter, nesting and postnesting periods; maximum home ranges included all fixes accumulated throughout the study period and encompassed major seasonal movements. Core ranges were defined by the harmonic mean isopleth enclosing 65% of the fixes. Areal estimates were computed using a 50 x 50 cell grid with an error polygon length of 0.011 km. Calculation axes, which determined the actual area within the 50 X 50 cell grid, were fine-tuned to the x-y coordinates approaching the outermost fixes for each pheasant. Thirty radio fixes per range provide stable estimates of range size; therefore, ranges derived from [less than]30 fixes were not used in the analysis (Kenward, 1982).
Home and core ranges were tested for differences between sexes and among seasons using analysis of variance (ANOVA) for unequal sample sizes (Sokal and Rohlf, 1969). Before using ANOVA, seasonal data were tested for normality using the Shapiro-Wilk statistic, W (SAS Institute, 1985). If nonnormal, the data were normalized using a [log.sub.10] transformation. Significant results were further analyzed using the Sheffe test (Sokal and Rohlf, 1969). If the data could not be normalized, the Wilcoxon two-sample test (SAS Institute, 1985) was used to test for differences.
Seasonal movements were defined as the distance between the harmonic mean (i.e., center of activity) for each seasonal core range of each pheasant (White and Garrott, 1990). Using the X and Y coordinates of each harmonic mean, the distance (d) between means was calculated as:
d = [[[([X.sub.season1] - [X.sub.season2]).sup.2] + [([Y.sub.season1] - [Y.sub.season2]).sup.2]].sup.1/2]
Differences in seasonal movements between sexes and seasonal periods were examined for the winter-to-nesting period and nesting-to-postnesting period using Wilcoxon two-sample tests (SAS Institute, 1985). Postnesting-to-winter movements were not analyzed due to small sample size (n = 3).
Habitat selection and use. - We determined the proportion of the six study area habitat types within the seasonal home and core ranges and maximum home ranges of each pheasant by overlaying them on the habitat map. Habitat selection and use were based on the log-ratio analysis of compositions or compositional analysis (Aitchison, 1986). This technique overcomes the problem of lack of independence between proportions which sum to one (unit-sum constraint) by converting the n proportions to n - 1 log-ratios, using one proportion as the denominator (Aebischer et al., 1993). Overall departure from random habitat use was tested, considering all habitats simultaneously, using multiple analysis of variance (MANOVA), in particular Wilk's A, applied to the log-ratios. When overall habitat use was nonrandom (P [less than] 0.05), the relative use of each habitat was then compared to all other habitats individually using paired t-tests. We performed compositional analysis following the two-step approach (Aebischer et al., 1993), based on the concept that use of available habitats is the outcome of decisions made at two different levels (Johnson, 1980). First, the animal selects its home range from an arbitrarily defined study area. Second, the animal selects a core range within that home range. Compositional analysis of maximum home ranges did not include pheasants with locations for only one season (n = 4). Postnesting ranges were excluded from compositional analysis due to small sample size (n = 4).
Adult mortality. - When an adult pheasant was found dead we recorded the date, cause of death and whether the area provided cover. Compared to areas without cover, areas with cover had vegetation that was tall and dense enough to enable a pheasant to escape detection by a predator. We noted if the area was the actual mortality site or if there were indications that the bird died elsewhere. Specific causes of death were determined by examining the condition of the pheasant, the transmitter and the surrounding area (Einarsen, 1956; Dumke and Pils, 1973). Deaths occurring within five days of release were considered related to capture and instrumentation (Boag, 1972; Dumke and Pils, 1973). Pheasants found dead along roadsides with large contusions and broken bones, but no obvious sign of predation, were considered vehicle-related. If a transmitter was recovered and the bird was believed to be dead but the cause of death could not be determined, cause of death was classified as unknown. If a transmitter was not recovered and the fate of that individual was unknown, the individual was labeled "censored" (White and Garrott, 1990). Censored individuals were considered lost observations. The dates of all agricultural activities were recorded to assess their potential impact on mortality. Hay fields that were recently mowed were also searched for signs of mortality.
Home and core ranges, and seasonal movements. - Sixteen females and 10 males were captured, radiotagged and released during the 1988 trapping period. Twelve females and seven males, each having [greater than or equal to]30 fixes per analytical time period (winter, nesting, postnesting or maximum), provided 2999 individual radio fixes and served as the basis for home and core range estimations (Table 1). No significant differences in the size of home ranges were detected between sexes or among seasons. However, core ranges were larger during nesting than winter, larger during winter than postnesting and larger during nesting than postnesting (P [less than] 0.05). There was no difference in core range size between the sexes.
No significant differences (P [greater than] 0.05) between sexes were found in winter-to-nesting movements or nesting-to-postnesting movements (Table 2). No significant differences (P [greater than] 0.05) were found when comparing distances moved from the winter-to-nesting period to the nesting-to-postnesting period for either sex or in combination.
Habitat selection and use. - The proportion of habitats within home ranges in winter were significantly different from the proportion of habitats available on the study area (Table 3). There was no detectable difference in use of wetlands and shrublands, but each showed significantly greater use in winter than croplands, developed lands, grasslands and forests (Table 4, [ILLUSTRATION FOR FIGURE 1 OMITTED]). Wetlands and shrublands had the highest ranking of relative use (Table 4). No significant differences in proportional winter habitat use within home ranges were found between the sexes (Table 3). The proportions of habitats in winter core ranges were significantly different from the proportions available within home ranges (Table 3). Forests were used significantly less than wetlands, shrublands, developed lands and grasslands (Table 4). Wetlands, croplands and shrublands were ranked number one, two and three in [TABULAR DATA FOR TABLE 1 OMITTED] [TABULAR DATA FOR TABLE 2 OMITTED] order of relative use (Table 4). No significant differences were found in proportional winter habitat use within core ranges between the sexes (Table 3).
During nesting there was a significant difference in the proportions of habitats within home ranges compared to the proportions available within the study area (Table 3). Shrublands were used significantly more than developed lands, croplands, grasslands and forests; and were ranked number one in relative use (Table 4, [ILLUSTRATION FOR FIGURE 1 OMITTED]). Wetlands were ranked second in relative use, and were used significantly more than forests (Table 4). Proportional habitat use within home ranges was not significantly different between sexes (Table 3). The proportions of habitats within nesting core ranges were not significantly different from the proportions available within home ranges, so no paired t-tests were done (Table 3). No significant differences were found in proportional nesting habitat use within core ranges between the sexes (Table 3).
The proportions of habitats within maximum home ranges were significantly different from the proportions available within the study area (Table 3). There was no detectable difference in use of the highest ranking habitats, shrublands and wetlands; but each showed significantly greater use than croplands, developed lands, grasslands and forests (Table 4, [ILLUSTRATION FOR FIGURE 1 OMITTED]). Proportional habitat use within home ranges was not significantly different between sexes (Table 3).
Adult mortality. - Of 16 females fitted with radiotransmitters, eight survived to the nesting season. Seven of 10 radiotagged males survived to the nesting season. Four out of 26 radiotagged pheasants survived to the end of the study period, 15 December 1988: two males and two females. The transmitters of two males and two females malfunctioned and their status could not be confirmed. Predation accounted for 11 (61%) deaths, with foxes (Vulpes vulpes, Urocyon cinereoargenteus) responsible for 5 (28%) and raptors, including great-horned owls (Bubo virginianus), accountable for 6 (33%). Deaths from fox predation [TABULAR DATA FOR TABLE 3 OMITTED] [TABULAR DATA FOR TABLE 4 OMITTED] occurred in shrublands (5), while those from raptors occurred in shrublands (4), croplands (1) and forests (1). Vehicles caused 2 (11%) deaths, capture and instrumentation caused 3 (17%) and 2 (11%) were due to unknown factors. Deaths attributed to capture and instrumentation also showed signs of fox predation. Significantly more birds died of predation than from all other mortality factors ([[Chi].sup.2] = 9.131, df = 2, P [less than] 0.05, n = 16). Significantly more pheasants were killed within vegetation tall and dense enough to conceal a bird than in more open cover (Mann-Whitney U = -2.010, P [less than] 0.05, n = 11). Kills occurring in tall dense cover were generally attributed to fox; deaths attributed to raptors tended to occur in short or sparse cover. No radiotagged birds were lost to mowing in 1988.
Both sexes had larger home ranges during the nesting season than during the winter season, and females had larger nesting home ranges than males. However, high variability in size of home ranges coupled with small sample sizes resulted in differences being statistically insignificant. Average seasonal and maximum home ranges tended to be somewhat larger than those reported elsewhere; however, the range of values overlapped considerably (Kuck et al., 1970; Hanson and Progulske, 1973; Whiteside and Guthery, 1983; Hallett, 1986; Penrod et al., 1986). Seasonal home ranges reported for some geographic regions were even larger than those estimated for Maryland. In Missouri, Hallett (1986) reported a home range of 63.7 ha in winter compared with 49.7 ha for Maryland. In Iowa, winter home ranges of hens on two study areas were also larger, 76 and 96 ha (Perkins et al., 1997). Differences in home range sizes between geographic regions could be due to a variety of factors, including differences in weather, land use/cover, population densities and even methodology. During our study, range sizes could have been affected by below normal snowfall in winter, sparse rainfall in June and extremely hot weather in June, July and August.
Core ranges paralleled the seasonal size differences observed for home ranges in Maryland. While no significant differences in size were found among seasonal home ranges, core ranges were significantly larger during nesting compared with winter or postnesting seasons. The lack of significant differences in core range sizes between the sexes during winter was not surprising as both were confined to the same small patches of wetlands and shrublands. However, during the nesting season, males were restricted behaviorally to a specific territory, albeit larger than the winter core range; whereas females, in some cases, had more than one nest site due to renests and thus had more than one nesting core range.
Spring movements from wintering areas to breeding territories and nest sites and fall movements back to the wintering area were of the same magnitude reported in other regions (Mallette and Bechtel, 1959; Gates and Hale, 1974; Dumke and Pils, 1979; Whiteside and Guthery, 1983; Hill and Ridley, 1987; Gatti et al., 1989). In spring, females often move farther than males, and first-time breeding females and males move farther than older established birds (Gates and Hale, 1974; Penrod et al., 1986; Hill and Ridley, 1987).
Location of woody and brushy cover has been identified as the critical factor influencing the spatial and temporal distribution of winter pheasant populations (Gates and Hale, 1974; Warner and David, 1982; Whiteside and Guthery, 1983; Penrod et al., 1986; Gatti et al., 1989; Leptich, 1992). In Maryland, emergent and scrub/shrub wetlands and old fields/shrublands provided roosting and thermal cover, and hedgerows and wooded stream corridors provided travel lanes and escape cover while feeding. Feeding occurred primarily in fields of waste grain adjacent to wetlands and shrublands, specifically corn stubble fields. Although the proportion of croplands within core ranges was not significantly different from the proportion available within home ranges, croplands were ranked number two in relative habitat use in winter. Two of the highest ranking habitats in order of relative use, wetlands and shrublands, are also important winter habitats throughout pheasant range (Gates and Hale, 1974; Warner and David, 1982; Whiteside and Guthery, 1983; Penrod et al., 1986; Gatti et al., 1989; Leptich, 1992). However, Perkins et al. (1997) reported that winter home ranges in Iowa were located in areas with more grass habitats than the surrounding landscape. In Maryland, the proportion of grasslands within home ranges was significantly less than wetlands and shrublands when compared with that within the study area. Grasslands ranked near last in relative habitat use. In Idaho, pheasants avoided grasslands and agricultural cover types in winter (Leptich, 1992). Although we had expected high use of forests during severe winter weather (Warner and David, 1982; Robertson et al., 1993a; Robertson, 1996), it was used significantly less than wetlands and shrublands and ranked last in relative habitat use.
During the nesting season, females select habitats such as hay fields, pastures, small grain fields, unmowed roadsides, retired croplands and wetlands (Hanson and Progulske, 1973; Olsen, 1977; Whiteside and Guthery, 1983; Boyd and Richmond, 1984; Hallett, 1986; Penrod et al., 1986). However, nest density and success in these habitat types vary widely (Robertson, 1996). In Great Britain, territorial male densities are higher along shrubby woodland edges bordering cultivated land as opposed to grassland (Olsen, 1977; Ridley and Hill, 1987; Robertson et al., 1993b; Robertson, 1996). Females then establish breeding ranges close to male territories (Hill and Ridley, 1987). A high proportion of the spatial variation in spring pheasant abundance in Great Britain is explained by the availability of shrublands bordering farmland (Robertson et al., 1993b). Shrubby cover also tends to be most productive in terms of successful nests and hatched nests, although the proportion of nests found in it are small (Robertson, 1996). based on the proportion of habitat types within the Maryland study area versus pheasant home ranges, shrublands were more highly ranked in relative habitat use than wetlands during the nesting season. Wetlands were used more often during winter.
Although females included grasslands for nesting in Maryland, the proportion of grasslands within nesting home ranges compared to that on the study area was significantly less than shrublands and wetlands. Its ranking in relative habitat use was low. Because grasslands were the most abundant habitat type, they were probably not limiting for the current population size on the Maryland study area (Carroll et al., 1988). Active selection of other critical habitat types more limited in occurrence may have taken precedence. Furthermore, early and frequent mowing may have limited the value of hay fields, the main grassland type on our study area, to pheasants (Boyd and Richmond, 1984; Warner and Etter, 1989). Alfalfa hay fields were cut up to 6 x during the growing season, and mixed and alfalfa hay fields were cut early in the nesting season, limiting their availability for use as nesting cover.
Predation of adults in Maryland was the major mortality factor, accounting for 61% of losses. Average annual predation is estimated to range from 38-65%, placing Maryland toward the high end (Gates, 1971; Dumke and Pils, 1973; Penrod et al., 1986). Avoidance of predators may have limited the use of both grasslands and forests. Regardless of habitat type, cover height and density were associated with mortality due to predation, with tall dense vegetation cover having significantly more predated individuals than short or sparse cover. This seeming paradox may be related to foxes entering thick concealing cover to consume their prey after killing it elsewhere; or, using open areas next to the edge of tall dense cover for hunting (Samuel and Nelson, 1982). Mowing is considered the main cause of mortality in good pheasant range (Wagner, 1965). No radiotagged birds were lost to mowing in 1988; however, based on a pilot study done in 1987, we noted several female mortalities associated with mowing.
Conservation measures for pheasants in Maryland should focus on both female nesting cover and male territory cover. Preferred nesting cover can be enhanced by compensating landowners for delaying or not mowing hay fields or leaving crop fields fallow. Suitable dispersed male territory cover (i.e., shrubs or woody cover at crop borders) should be provided around existing patches of winter cover (i.e., wetlands and shrublands) and in close proximity to nesting cover. Because wetlands and shrublands appear to be limiting, making up only about 10% of the study area, and were actively selected, landowners should be encouraged whenever possible to maintain or enhance these habitat types.
Acknowledgments. - We thank the employees of the Maryland Department of Natural Resources for their assistance, particularly E. B. Davis, D. G. Long, R. L. Shank, S. L. Bittner, P.S. Jayne, M. L. Mause, J. L. Sandt, J. C. Shugars, J. A. Straw, Jr., D. A. Rasberry and T. A. Palmer. Thanks also go to the staff at Indian Springs Wildlife Management Area and the members of Mayberry Game Protective Association for logistical support. Numerous landowners gave us access to their properties, including the Chillicothes, Irelands, McDaniels, Mowbrays, Myers, Harbaughs, Kuglers, Matthewses, Williamses, Barnhardts, Carbaughs, Haltermans and Strites. J.P. Carroll, D. F. Brinker and D.C. Jacobs helped with data analysis. G. L. Brewer, L. V. Diller, K. B. Fuller, M.P. Guilfoyle, R. P. Morgan, II and F. C. Rohwer commented on the manuscript. Computer time was provided by the Maryland Sea Grant College Program, University of Maryland, College Park. Funding was provided by the Maryland Department of Natural Resources, Forest, Wildlife and Heritage Service. This is Contribution No. 3098-AL, University of Maryland Center for Environmental Science.
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