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Effects of prescribed fire on winter assemblages of birds in ponderosa pine forests of northern Arizona.

Although most studies of avian ecology occur during the breeding season, winter is important to population ecology of birds. survival in winter can affect populations, because birds that survive winter may reproduce the following breeding season (Fretwell, 1972; Kreisel and Stein, 1999). habitat required for breeding might not be the same as habitat that provides food and shelter from harsh conditions in winter (Fretwell, 1972; Grubb, 1975, 1977; Connor, 1979; Graber and Graber, 1983; Morrison et al., 1986). Food generally is limited in winter; as insects are less abundant and many plants are dormant during this time. As a result, food is distributed patchily and birds become opportunistic in their foraging ecology (Beal, 1911; Otvos, 1965; Willson, 1971; Crockett and Hansley, 1978; Brawn et al., 1982; Morrison et al., 1986; Szaro et al., 1990).

For many forests, including ponderosa pine (Pinus ponderosa) forests in northern Arizona, fire was a natural disturbance of the system until fire-suppression efforts began in the early 20th century. Frequent, low-intensity fires were part of the ecology and evolutionary history of ponderosa pine forests (cooper, 1960; Covington and Moore, 1994; Swetnam and Baisan, 1996; Moir et al., 1997). Managers are attempting alternative forest-management strategies that include using prescribed burns in an effort to return fire to the landscape. As such, it will be important to understand effects of these treatments on birds wintering in areas where managers are using this tool.

A few studies have examined effects of wildfire on wintering birds in coniferous forests (Blake, 1982; Kreisel and Stein, 1999; Bock and Block, 2005; Covert-Bratland et al., 2006). Prescribed fire could have different effects on wintering birds than wildfire, yet only one study has examined effects of prescribed fire on wintering birds in a coniferous forest (King et al., 1998). Therefore, we compared assemblages of wintering birds in ponderosa pine forests recently treated by prescribed fire with untreated controls to determine whether prescribed fire affects composition and abundances of species during the first few winters following prescribed treatments.

Materials and Methods--Study Area--We located study sites in the Coconino and Kaibab national forests in northern Arizona, as part of the Birds and Burns Network. Ponderosa pine was the dominant overstory species on both study sites, with Gambel oak (Quercus gambelii) contributing to the canopy on study units in Coconino National Forest. Pinyon pine (Pinus edulis), one-seed juniper (Juniperus monosperma), and alligator juniper (J. deppeana) occurred on control units in Kaibab National Forest, but contributed little to the canopy. Alligator juniper was on both units in Coconino National Forest. Open patches of grassland on both sites were dominated by bunchgrasses, including Arizona fescue (Festuca arizonica) and blue gramma (Bouteloua gracilis). Topography on the study site in Coconino National Forest varied from flat to steep hills, with elevations of 2,070-2,160 m. The study site in Kaibab National Forest was flat, with elevations of 2,100-2,300 m.

Each study site in the forests had a burned treatment unit paired with control unit(s) of similar structure (Table 1). We chose treatment units in consultation with district fire managers on each forest. We then placed control units in representative areas with similar structure within 1 km of the treatment unit where no management (e.g., thinning or prescribed burn) was planned. It was not possible to randomize location of each treatment unit; however, we made efforts to ensure all sampling occurred at randomly placed stations within units. We used a systematic random-sampling design for placement of point-count stations. We randomized placement of the first point, assigning remaining points using a Geographical Information System algorithm (Dickson, 2006).

Personnel of the United States Forest Service administered prescribed fires during autumn 2003 on the treatment unit in Coconino National Forest and on the treatment unit in Kaibab National Forest during autumn 2003 and spring 2004 (Table 2). Fire prescriptions were characterized as broadcast burns with expected behaviors of fire to be low-to-moderate intensity (Dickson, 2006). Fires were heterogeneous in nature, ranging from areas not burned to areas with burns severe enough to kill trees. We measured maximum height of char on bole, percentage of circumference of bole that was charred at the base, and percentage of needles scorched, because these are measures of fire that fire managers can incorporate into fire prescriptions. Average ([+ or -] SE) maximum height of char on bole for burn units was 1.2 m [+ or -] 0.04. Average percentage circumference of bole that was charred at the base was 65.0 [+ or -] 0.81 and average percentage of needles scorched was 6.6 [+ or -] 0.39. Measurements for individual burn units are included in Table 2. Nevertheless, these values represent low-severity fire that had little post-treatment effect on structure of the forest.

Field Methods--We conducted point counts in winter (Reynolds et al., 1980) at 170 point-count stations in northern Arizona during the first 2 winters following treatments. The study site in Coconino National Forest had 40 point-count stations each in burn and control units. The study site in Kaibab National Forest had 40 point-count stations in the burn unit and 50 point-count stations between two control units. each station was ca. 300 m apart and [greater than or equal to] 200 m from edges of units. At each station, we recorded number of individuals and distance to each individual for all birds observed during a 5-min survey period. Point counts began [less than or equal to] 30 min of sunrise and concluded within 5 h. We did not count in windy (i.e., >28 km/h) or wet (more than a light snow) conditions. We visited all stations eight times (4/season) between mid-October and mid-March, 2004-2006, with a single observer per visit.

We assigned all species detected within 100 m of a point-count station to one of four foraging groups (foraging group must include >1 species). We also recorded incidental observations (i.e., observed in a unit but not within 100 m of any point-count station). Foraging groups included seed-eating, bark-foraging/ sapsucking, gleaning insectivores, and generalists (see Table 3 for species-specific assignments to groups).

Statistical Analyses--We used a similarity index and a test of rank order of abundance to describe patterns in assemblages of wintering birds. We used an uncorrected index of abundance because we were examining patterns of abundance and not proposing actual estimates of abundance. We investigated similarity in assemblages of wintering birds between treatments (pooling across years) and years (pooling across treatments) using the Sorenson similarity index, C = 2j/(a + b); where j = number of species common to both treatment units or years, a = total number of species detected in burn units or year 1, and b = total number of species detected in control units or year 2 (Magurran, 1988). The similarity index equals a number between 0 and 1, with higher values representing greater similarity.

We used rank order of abundance to represent structure of assemblages for each year and treatment. We ranked species in order of abundance, based on number of individual detections. We calculated Spearman's rank-order correlation coefficient (Spearman's p; Conover, 1999) using SPSS 15.0 for Windows (SPSS, inc., Chicago, Illinois). A higher value of spearman's p represents a higher correlation in rank order of species between treatments and years. For example, Spearman's p = 1.00 will have species ranked in the same order for each treatment or year.

Results--We detected 39 species of birds during winters of 2004-2006 (Table 3). Nine species comprised 81% of observations. In descending order, these were dark-eyed junco (Junco hyemalis), pygmy nuthatch (Sitta pygmaea), western bluebird (Sialia mexicana), white-breasted nuthatch (Sitta carolinensis), mountain chickadee (Poecile gambeli), ruby-crowned kinglet (Regulus calendula), Steller's jay (Cyanocitta stelleri), hairy woodpecker (Picoides villosus), and brown creeper (Certhia americana). All of these species, except for ruby-crowned kinglet, are year-round residents of ponderosa pine forests in northern Arizona.

Assemblages were similar in composition and structure among years and between treatments. Using the Sorenson similarity index (C)to examine all non-incidental species detected during point counts, similarity between treatments and years was C = 0.85. We detected similar patterns when examining individual foraging groups. Seed-eating birds had C = 1.00 between treatments and C = 0.80 among years. Gleaning insectivores had C = 0.95 between treatments and C = 0.89 among years. Bark-foraging/sapsucking birds had C = 0.89 for both treatment and year. Generalists had C = 0.85 between years, however, C = 0.66 between treatments because we detected two species, pinyon jay (Gymnorhinus cyanocephalus) and American crow (Corvus brachyrhynchos), in control units only.

We also examined how rank order of abundance of species in each treatment differed among years for all non-incidental species. in burn units, Spearman's p = 0.69 (P < 0.01). Spearman's p = 0.70 (P < 0.01) in control units. Because there was no yearly difference, we combined years for a Spearman's p = 0.83 (P < 0.01) correlation between treatments. individual foraging groups differed among years in each treatment. Seed-eating birds had Spearman's p = 0.50 (P = 0.67) among years in burn units and Spearman's p = 1.00 in control units. This group had Spearman's p = 0.50 (P = 0.67) between treatments for both years combined. Generalists had Spearman's p = 1.00 in burn units and control units among years, and Spearman's p = 0.63 (P = 0.37) between treatments. Gleaning insectivores had Spearman's p = 0.47 (P = 0.17) in burn units, Spearman's p = 0.28 (P = 0.43) in control units, yet Spearman's p = 0.91 (P < 0.01) between treatments. Bark-foraging/sapsucking birds had Spearman's p = 0.95 (P < 0.01) in the burn units, Spearman's p = 0.96 (P < 0.01) in the control units, and Spearman's p = 0.92 (P < 0.01) between treatments.

We also compared composition and structure of assemblages of birds between burn units to determine whether intensity of fire had an effect. The Sorenson similarity index was C = 0.78 between burn units and Spearman's p = 0.79 (P < 0.01). order of abundance for individual foraging groups in each burn unit were all correlated (bark-foraging/sapsucking--Spearman's p = 0.97 (P < 0.01); gleaning insectivore--Spearman's p = 0.76 (P = 0.03); generalist--Spearman's p = 1.00) except seed-eating, which had Spearman's p = 0.50 (P = 0.67).

Discussion--Assemblages of birds in northern Arizona were similar in composition and structure among treatments and years during the first 2 winters following low-intensity prescribed fire. Differences in assemblages of wintering birds might depend on type of fire, i.e., whether wildfire (high-intensity) or prescribed fire (low-to-moderate intensity). Blake (1982) compared assemblages of wintering birds in areas burned by wildfire and unburned areas in northern Arizona. in his study, hairy woodpeckers were more common in burned areas. our results were the same although our prescribed fires were lower intensity than many wildfires. Blake (1982) also reported that species that search crevices in bark for insects, such as nuthatches, were more common in unburned sites in winter; however, nuthatches had similar abundances in burned and unburned areas in our study. This pattern could be the result of low-intensity prescribed fire not altering structure of forest stands as much as high-intensity wildfire.

Number of species detected in undisturbed sites in ponderosa pine forests during winter varies between studies. our study and Bock and Block (2005) detected a similar number of species wintering in unburned areas (31 and 26, respectively). However, Haldeman et al. (1973) recorded only 18 species wintering in undisturbed sites in ponderosa pine forests of northern Arizona. Pygmy nuthatch was the most common species reported by Haldeman et al. (1973) and the second-most common species behind dark-eyed juncos in our study. However, common species were generally the same for each study, including mountain chickadee, pygmy and white-breasted nuthatch, dark-eyed junco, western bluebird, hairy woodpecker, northern flicker, and Steller's jay.

Of 39 species we detected, 25 were common between treatment and years (Table 3). However, some species were only present in 1 year or treatment. For example, violet-green swallows (Tachycineta thalassina) had returned from migration before counts ended the first year. We had 13 species only detected in one treatment (five in control, eight in burn). These species were represented mostly by raptors (three), owls (three), and corvids (three). Of these, only pinyon jays were detected more than twice (Table 3). Therefore, less-abundant species may be present in only one treatment, producing diversity while maintaining composition and structure of assemblages. As such, creating a mosaic of burned and unburned areas will enhance species diversity in ponderosa pine forests.

Although there was some variability among foraging groups, assemblages of birds were similar between unburned areas and areas treated with prescribed fire, between each burn unit, and among years during winters initially following prescribed fire. Therefore, managers that use low-severity prescribed fires in ponderosa pine forests of northern Arizona might not be altering structure of the forest enough to impact assemblages of wintering birds during the first few years following prescribed fire.

We thank V. Saab, B. Dickson, S. Vojta, N. Gwinn, C. Breece, N. Breece, S. Hurteau, K. Bratland, S. Stollery, P. Beier, P. Fule, T. Sisk, D. Huebner, and the wildlife lab group in the Northern Arizona University School of Forestry for assistance and constructive advice in different aspects of this project.

Submitted 14 December 2007. Accepted 14 May 2009. Associate Editor was Michael S. Husak.


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United States Forest Service Rocky Mountain Research Station, 2500 South Pine Knoll Drive, Flagstaff, AZ 86001 Present address of TLP: Department of Wildlife and Fisheries Sciences, Texas A&M University, 210 Nagle Hall, College Station, TX 77843-2258

* Correspondent:
TABLE 1--Description of study units in the Birds and Burns Network
of the Coconino and Kaibab national forests, Arizona, including
treatment (burn and control), area (ha), number of trees surveyed,
average ([+ or -]SE) diameter at breast height (cm), and average
([+ or -]SE) height of tree (m).

                        Kaibab National Forest

                             Diameter at          Height of
                            breast height           tree

Treatment   Area    n       x [+ or -] SE       x [+ or -] SE

Burn        369    758    33.7 [+ or -] 0.5   13.7 [+ or -] 0.2
Control     487    872    33.3 [+ or -] 0.4   11.3 [+ or -] 0.1

                        Coconino National Forest

                             Diameter at          Height of
                            breast height           tree

Treatment   Area    n       x [+ or -] SE       x [+ or -] SE

Burn        405    1940   23.1 [+ or -] 0.2   12.7 [+ or -] 0.1
Control     404    1567   24.5 [+ or -] 0.3   10.9 [+ or -] 0.1

TABLE 2--Measurements of fire activity from prescribed fires on each
burn unit and burn units combined on the Coconino and Kaibab national
forests, Arizona.

National                         Maximum height of
forest         Dates burned       char on bole (m)

  Kaibab     27 October 2003     2.6 [+ or -] 0.11
              6 November 2003
             25 March 2004
  Coconino   15 September 2003   0.7 [+ or -] 0.02
             18 September 2003
             19 September 2003
  Combined          --           1.2 [+ or -] 0.04

National                           Percentage of
forest         Dates burned       needles scorched

  Kaibab     27 October 2003     17.6 [+ or -] 1.05
              6 November 2003
             25 March 2004
  Coconino   15 September 2003   2.3 [+ or -] 0.29
             18 September 2003
             19 September 2003
  Combined          --           6.6 [+ or -] 0.39

National                           Percentage of
forest         Dates burned         bole charred

  Kaibab     27 October 2003     85.8 [+ or -] 1.01
              6 November 2003
             25 March 2004
  Coconino   15 September 2003   56.9 [+ or -] 1.00
             18 September 2003
             19 September 2003
  Combined          --           65.0 [+ or -] 0.81

TABLE 3--Species detected during point counts from mid-October to
mid-March 2004--2006, including incidental species (i) only
detected beyond 100-m radius of point-count stations. Species,
scientific name, foraging group, number of detections, percentage
of total detections, year(s) detected, and treatment(s) detected
are listed. Incidental species and those that are the only
representative of their foraging group were not assigned to
foraging groups analyzed in rank order of abundance.

      Common name                 Taxon              Foraging group

Bald eagle                Haliaeetus
                            leucocephalus                  --
Northern goshawk          Accipiter gentiles               --
Red-tailed hawk           Buteo jamaicensis                --
Swainson's hawk           Buteo swainsoni                  --
Wild turkey               Meleagris gallopavo              --
Mourning dove             Zenaida macroura                 --
long-eared owl            Asio otus                        --
Great horned owl          Bubo virginianus                 --
Northern pygmy-owl        Glaucidium gnoma                 --
Northern flicker          Colaptes auratus        Bark-foraging/
Williamson's sapsucker    Sphyrapicus             Bark-foraging/
                            thyroideus              sapsucking
Red-naped sapsucker       Sphyrapicus nuchalis    Bark-foraging/
Downy woodpecker          Picoides pubescens      Bark-foraging/
Hairy woodpecker          Picoides villosus       Bark-foraging/
Three-toed woodpecker     Picoides tridactylus    Bark-foraging/
Steller's jay             Cyanocitta stelleri     Generalist
Clark's nutcracker        Nucifraga columbiana             --
Pinyon jay                Gymnorhinus
                            cyanocephalus         Generalist
American crow             Corvus brachyrhynchos   Generalist
Common raven              Corvus corax            Generalist
Violet-green swallow      Tachycineta
                            thalassina                     --
Mountain chickadee        Poecile gambeli         Gleaning insectivore
Bushtit                   Psaltriparus minimus    Gleaning insectivore
Brown creeper             Certhia americana       Bark-foraging/
White-breasted nuthatch   Sitta carolinensis      Bark-foraging/
Red-breasted nuthatch     Sitta canadensis        Bark-foraging/
Pygmy nuthatch            Sitta pygmaea           Bark-foraging/
Golden-crowned kinglet    Regulus satrapa         Gleaning insectivore
Ruby-crowned kinglet      Regulus calendula       Gleaning insectivore
Western bluebird          Sialia mexicana         Gleaning insectivore
Mountain bluebird         Sialia currucoides      Gleaning insectivore
Townsend's solitaire      Myadestes townsendi     Gleaning insectivore
American robin            Turdus migratorius      Gleaning insectivore
Yellow-rumped warbler     Dendroica coronata      Gleaning insectivore
Olive warbler             Peucedramus taeniatus   Gleaning insectivore
Dark-eyed junco           Junco hyemalis          Seed-eating
Cassin's finch            Carpodacus cassinii              --
Red crossbill             Loxia curvirostra       Seed-eating
Pine siskin               Carduelis pinus         Seed-eating

                            Number of       of total
                            detections     detections    Year(s)
      Common name         (within 100 m)   (n = 4,639)   detected

Bald eagle                        i              --          Both
Northern goshawk                  i              --           1
Red-tailed hawk                   2             0.04         Both
Swainson's hawk                   i              --           1
Wild turkey                       3             0.06         Both
Mourning dove                     1             0.02          2
long-eared owl                    1             0.02          2
Great horned owl                  1             0.02          1
Northern pygmy-owl                1             0.02          1
Northern flicker                 62             1.34        Both
Williamson's sapsucker           11             0.24        Both
Red-naped sapsucker               7             0.15        Both
Downy woodpecker                  2             0.04          1
Hairy woodpecker                160             3.45        Both
Three-toed woodpecker             9             0.19        Both
Steller's jay                   176             3.79        Both
Clark's nutcracker                i              --           2
Pinyon jay                       28             0.60        Both
American crow                     2             0.04        Both
Common raven                     50             1.08        Both
Violet-green swallow              8             0.17          1
Mountain chickadee              405             8.73        Both
Bushtit                          78             1.68        Both
Brown creeper                   133             2.87        Both
White-breasted nuthatch         406             8.75        Both
Red-breasted nuthatch             2             0.04          2
Pygmy nuthatch                  678            14.62        Both
Golden-crowned kinglet           34             0.73        Both
Ruby-crowned kinglet            220             4.74        Both
Western bluebird                508            10.95        Both
Mountain bluebird                 1             0.02          1
Townsend's solitaire             10             0.22        Both
American robin                   84             1.81          1
Yellow-rumped warbler            32             0.69        Both
Olive warbler                    16             0.34        Both
Dark-eyed junco               1,065            22.96        Both
Cassin's finch                    i             --          Both
Red crossbill                    38             0.82        Both
Pine siskin                      32             0.69        Both

      Common name           detected

Bald eagle                Control only

Northern goshawk          Burn only
Red-tailed hawk           Both
Swainson's hawk           Burn only
Wild turkey               Both
Mourning dove             Burn only
long-eared owl            Control only
Great horned owl          Burn only
Northern pygmy-owl        Burn only
Northern flicker          Both
Williamson's sapsucker    Both
Red-naped sapsucker       Both
Downy woodpecker          Burn only
Hairy woodpecker          Both
Three-toed woodpecker     Both
Steller's jay             Both
Clark's nutcracker        Burn only
Pinyon jay                Control only
American crow             Control only
Common raven              Both
Violet-green swallow      Both
Mountain chickadee        Both
Bushtit                   Both
Brown creeper             Both
White-breasted nuthatch   Both
Red-breasted nuthatch     Burn only
Pygmy nuthatch            Both
Golden-crowned kinglet    Both
Ruby-crowned kinglet      Both
Western bluebird          Both
Mountain bluebird         Control only
Townsend's solitaire      Both
American robin            Both
Yellow-rumped warbler     Both
Olive warbler             Both
Dark-eyed junco           Both
Cassin's finch            Both
Red crossbill             Both
Pine siskin               Both
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Author:Pope, Theresa L.; Block, William M.
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1U8AZ
Date:Mar 1, 2010
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