MANAGEMENT OF FIELDS FOR NOCTURNAL USE BY WINTERING AMERICAN WOODCOCK.
Techniques for management of nocturnal habitat of wintering woodcock are poorly known. We studied the relative attractiveness of several management techniques for wintering woodcock in Georgia. During the first winter (1995-96), we compared the use by woodcock of burned, mowed, burned and mowed, and untreated (control) sites in an old-field. No differences in use by woodcock were observed among the treatments, but one burn treatment strip had considerably more use than all other strips. During the second winter (1996-97), we compared the use by woodcock of fields under 5 management practices (no treatment, harvested crop, seed-tree cut, Arsenal [R] treatment and/or burned, or grazed or mowed). Arsenal [R] sprayed and/or burned stands were used more often than harvested crops. We suggest that the use of manipulative practices, which maintain areas in an early successional state are reasonable management practices to attract and benefit wintering woodcock.
Key words: American woodcock, behavior, courtship, field use, prescribed burns, Scolopax minor.
American woodcock (Scolopax minor) winter in the southern United States (1) where they use many different habitat types (2-7). During the evening crepuscular period, woodcock will often move from their diurnal locations to new locations up to 1.5 km away (5, 8-10). A variety of different cover types are used at night including forests, pastures, fallow/oldfields, agricultural fields, and clearcuts (1-4 years post cut) (2, 11). Reasons for these movements include feeding (12-14), roosting (9), predator avoidance (15), and conducting courtship activities (11,16).
Two structural features appear common among the different nocturnal field types frequently used by woodcock: light ground cover and moderate to dense overhead cover. Woodcock in Louisiana used fields with a herbaceous or brushy canopy at 0.5-1.0 m (2). Lightly to moderately grazed pastures in Louisiana were used by woodcock at night whereas heavily grazed pastures were not used (2). In Texas, woodcock used fields with low foliage density at 0.0-0.25 m, and greater foliage density at 0.26-0.75 m above the ground (17). Woodcock wintering in Georgia most frequently used fields at night with greater foliage volume at 0.8-2.0 m in height and a relatively high percentage of bare soil (10). Woodcock were observed in the furrows of deep-tilled soybean fields in North Carolina (9, 14), but neither wheat nor cornfields were used there. In the lower coastal plain of Georgia, few woodcock were observed using croplands or pastures at night (8). Theoretically, light ground cover allows woodcock to move and forage easily, and overhead cover provides protection from predators (10, 17).
Numerous treatments or natural events such as prescribed burning, mowing/grazing, harvesting of crops, wild fire, hurricanes or tornadoes help maintain areas in an early successional state, but information on treatment methods selected by woodcock is limited (11). The removal of dense vegetation through prescribed burning has been suggested (2, 18). In Alabama, woodcock selected more recently winter-burned stands than those stands burned [greater than] 2 years earlier (18). Woodcock in the Coastal Plain of North Carolina used burned strips more often than control areas (9).
Low survival on the wintering grounds may have contributed to the long-term and range-wide population decline of woodcock (19, 20). Habitat quality may be a contributing factor to the low winter survival rates and population decline (1). Therefore, there is a need to develop habitat management techniques for wintering grounds (11, 21). Further, the application of management techniques must be considered in the context of multiple spatial scales (10). Woodcock use of fields at night may be influenced by several factors: the distance to diurnal habitat, field size, vegetation characteristics, and/or availability of preferred habitats (8, 10).
Our objectives were twofold. First, we wanted to compare woodcock nocturnal use of treatment strips within an oldfield. Second, we wanted to make similar comparisons in forest openings in which the vegetation in the entire opening was manipulated by various methods. Our goal is to develop wintering woodcock management guidelines for interested land managers.
The study was divided into two parts: the experimental surveys (1995-96) and the forest management surveys (1996-97). During both parts of the study, we used evening crepuscular flight surveys (2, 10) as an index to the number of woodcock using treated field strips and forest openings. At the beginning of each survey, an observer was positioned randomly in a strip or field (see below). Surveys were conducted for 30 minutes beginning 10 minutes after sunset. All birds seen or heard performing a nasal peent within the observer's designated field or strip were recorded. If more than one observer was used in a field, observers compared notes at the end of each survey to avoid double-counting woodcock. Surveys were not conducted within 3 days of a full moon, during heavy rain, during winds [greater than] 15 km/hr, or at temperatures [less than]2 C (10). The response variable was the mean number of woodcock detected per observer hour.
We selected a 62.8 ha oldfield adjacent to a bottomland hardwood swamp in Oconee County, Georgia (10). Two plots, each with 4 strips that were 60 x 100 m, were established within the field. Both plots were equidistant from diurnal cover. Within each plot, one of three treatment types (burn, mow, mow and burn) or a control (no treatment) was randomly assigned to each strip. We mowed 4 strips on 26 January 1995, and burned 4 strips on 25 February and 12 March 1995. All strips were oriented perpendicular to the Oconee River (uphill to downhill) and were separated from the adjacent strip by a 20 m wide buffer strip, which aided observers in differentiating treatment strip use.
Four crepuscular flight surveys were performed in each of the eight strips. Each strip was considered an experimental unit; therefore, the number of woodcock observed per individual strip was averaged rather than considered an independent observation. This eliminated the possibility of pseudoreplication and reduced the inherent variation in nightly visits to fields by woodcock for reasons beyond our control, e.g., weather, moon phase (2, 10). We tested for differences in plot use and strip types frequented by woodcock using a nested design where Woodcock observed = mean number of woodcock observed per hour, Strip-type (Plot) = the effect on woodcock use by the th level of the treatment variable [(.sub.i] = burn, mow, burn and mow, control), Strip-type (Plot) [[blank].sub.i(j)]= the effect on woodcock use by the th treatment type within the th plot [(.sub.i] = 2 plots within the field). An alpha level of 0.05 and Tukey's Range Test were used (22).
Forest Management Surveys
We examined 24 sites in the Oconee National Forest and neighboring private lands in Oconee, Greene and Morgan Counties, Georgia. Each site was categorized into 1 of 5 treatment types: no treatment (oldfield), harvested crop, seed-tree cut, Arsenal[R] (Imazapyr) application and/or burned within last 2 years, or grazed or mowed within last year. Visual observations suggested areas treated with Arsenal[R] herbicide showed similar vegetative structure as fire treated areas; therefore, these treatment categories were combined. The same was true for areas grazed or mowed. We located and surveyed unequal numbers of treatment fields because new fields became available during the study period. Each treatment field was considered an experimental unit and nightly observations were averaged within each treatment field.
We investigated whether treatment type explained variation in field use by woodcock using a completely randomized design where Woodcock observed = mean number of woodcock observed per observer hour, and Treatment = the effect on woodcock use by the ith level of the treatment variable [(.sub.i] = control, cropland, seed tree cut, harvested Crop, Arsenal[R] sprayed and/or burned, grazed or mowed). Tukey's test at [alpha] = 0.05 was used to assess which treatments were significantly different (22).
We conducted 32 crepuscular flight surveys, 8 per strip-type, between 11 December 1995 and 31 January 1996. We found that 62% of the variation in numbers of woodcock surveyed was explained by plot and treatment type ([F.sub.7, 31] = 5.52, P = 0.001). Treatment nested within plot ([F.sub.4, 31] = 5.69, P = 0.002) was significant, but treatment type alone was not ([F.sub.3, 31] = 0.93, P = 0.50). We observed many more woodcock in one of the burned strips than in all other strips (Table 1).
Forest Management Surveys
We conducted 44 surveys between 11 December 1996 and 17 February 1997. We found that 24% of the variation in numbers of woodcock surveyed was explained by treatment type ([F.sub.4, 43] = 3.05, P = 0.02). Woodcock used Arsenal[R] treated and/or burned stands (4.7 [+ or -] 0.63) significantly more often than were harvested crops (0.6 [+ or -] 1.19); no other comparisons differed significantly (Table II).
Woodcock have a relatively low survival rate during the winter (20, 23-25). Because most mortality on the wintering grounds is due to predation (25), a primary objective of management in this region should be to create and manage habitats that are both attractive to woodcock and provide security from predators. Previous studies have documented the types of fields and vegetation structure within those fields that are attractive to woodcock at night, and developed hypotheses regarding the manner by which these structures provide security from predators (2, 10, 17).
Although some woodcock remain in forested habitat at night (10), most move to a variety of field types (1, 2, 11). Because crepuscular movements on wintering grounds are usually much shorter than 1.5 km (10), the probability of encountering different field types during a winter depends upon the number of fields available in the wintering area. Assuming that there is a positive relationship between survival and habitat quality (26), woodcock using optimal diurnal cover located near optimal nocturnal field cover may experience higher survival, higher reproductive success, or lower predation rates than woodcock using areas of either optimal diurnal or nocturnal cover. To produce beneficial woodcock habitat, managers should provide both high quality diurnal and nocturnal habitat in close proximity.
We agree that vegetation structure influences the attractiveness of nocturnal habitat (1). We believe that the best means of attaining an adequate combination of bare ground and ground cover, and a moderate to dense shrub/mid-story is through the proper use of prescribed fire and/or Arsenal[R] Herbicide (18). Both methods are widely used and well researched, and the latter is relatively inexpensive (27, 28). When used properly, these methods should achieve the goal of creating an open ground layer while leaving sufficient shrub/mid-story standing vegetation to protect woodcock from predators.
Support was provided by The Ruffed Grouse Society, USGS-Patuxent Wildlife Research Center, Warnell School of Forest Resources, Wildlife Resources Division of the Georgia Department of Natural Resources, and the U.S. Fish and Wildlife Service Division of Migratory Bird Management. We thank John T. Seginak, Dorothy Wolf Welch, and many other volunteers that assisted with this project.
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Mean number and standard error of American woodcock observed per observer hour by strip-type and plot number, Oconee County, Georgia, 1995-96. Stirp-type Plot number Mean Standard error Burn 1 7.50 0.957 Burn 2 2.50 0.500 Mow 1 2.50 0.500 Mow 2 4.00 1.154 Burn and mow 1 2.00 0.000 Burn and mow 2 3.50 1.500 Control 1 1.00 0.577 Control 2 2.50 0.500 Table II. Means, standard errors, and test groupings of the number of American woodcock seen per observer hour, Oconee, Greene and Morgan Counties, Georgia, 1996-97. Treatments with the same letters are not different. (P [greater than] 0.05). Treatment n Mean Standard error Turkey's fields grouping Harvested 3 0.60 1.187 A crop Control 4 2.00 1.327 AB Grazed/ 4 4.00 1.000 AB mowed Seed tree 6 2.70 0.840 AB Burned/ 7 4.72 0.626 B Arsenal [R]
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|Author:||Welch, James R.; Krementz, David G.; Berdeen, James B.|
|Publication:||Georgia Journal of Science|
|Date:||Jun 22, 2001|
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