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									                                                                 Long-term bird community patterns at Phoenix’s Desert Botanical Garden
                                                                                                                                                                                                                                                                                  William M. Cook
                                                                                                                                                                                                                                                                     Arizona State University, Tempe, AZ 85287

                                                                                                                                                                                           Deviation in richness from annual mean
                                                                                                                                                                                                                                                                                                                                                                                                                                Figure 8 (left).
                                  Introduction and Methods                                                                                                                                                                               12
                                                                                                                                                                                                                                                                                                                                                                                                                                The Maxwell Desert
                                                                                                                                                                                                                                         10                                                                                                                                                                                     Wildflower Trail,
 Human activities can sometimes transform habitats in ways that provide new and beneficial
                                                                                                                                                                                                                                          8                                                                                                                                                                                     opened in 2000.
 habitats for wild species. Here I document the changes in bird species diversity and
 frequency of observation over the period 1987-2004 at the Desert Botanical Garden (DBG),                                                                                                                                                 6
 located within the heart of the Phoenix metropolitan area. The area surrounding the DBG is                                                                                                                                               4
 mostly native xeric Sonoran Desert vegetation (Figure 1). The core Garden, which dates                                                                                                                                                   2                                                                                                                                                                                     Figure 9 (right).
 from the late 1930s, exhibits desert vegetation but is lush and heavily irrigated (Figure 2).                                                                                                                                            0                                                                                                                                                                                     Small water features
 During the study period several major habitat exhibits have been added to the Garden,
                                                                                                                                                                                                                                         -2                                                                                                                                                                                     have steadily been
 including a pond and cottonwood grove and a large wildflower garden, plus numerous small
                                                                                                                                                                                                                                         -4                                                                                                                                                                                     added to the DBG
 water features. The objective of this study was to document any changes in the DBG bird
                                                                                                                                                                                                                                                                                                                                                                                                                                since the early
 fauna over time, and to determine if these changes were correlated with construction                                                                                                                                                    -6
 projects or changes in Garden management.                                                                                                                                                                                               -8
                                                                                                                                                                                                                                                               0          4        8      12       16      20     24
 At DBG, weekly bird walks were conducted throughout the 1987-2004 interval, recording                                                                                                                                                                                Interval (represents half a calendar month)                                           1.0                                                                           Mallard
 species presence or absence. Observers made the same circuit of DBG each Monday                                                                                                                                                                                                                                                                                               A                                                          American kestrel
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      B                                                                      0.8
                                                                                                                                                                                   Figure 5 (above). Seasonal variation in species richness per weekly sample,                                                                                                                                                                            Phainopepla

                                                                                                                                                                                                                                                                                                                                     Frequency of observation
 (except when new exhibits were added), beginning at 7:00 am May-Sept. and 8:00 am Oct.-                                                                                                                                                                                                                                                                    0.8
                                                                                                                                                                                                                                                                                                                                                                                                                                          Great-tailed grackle

 April. Records represent the pooled observations of a core group of long-term participants.                                                                                       2000-2004.
                                                                                                                                                                                   Figure 6 (right). Examples of species’ variation in frequency of abundance                                                                                                                                                                                                                                                                                0.6
 881 weekly observations were made, forming a nearly complete run except for 1987-88
                                                                                                                                                                                   throughout the year. A) Species present year-round but with significant intra-                                                                                           0.6
 (irregular, 69 combined obs.), 1992 (Oct.-Dec. missing), and when Dec. 25 fell on Monday.
                                                                                                                                                                                   annual variation. B) Through migrants. C) Winter residents. D) Summer                                                                                                                                                                                                                                                                                     0.4
                                                                                                                                                                                   residents.                                                                                                                                                               0.4
                                                                                                                                                                                   Figure 7 (below). Examples of species that colonized the Garden during the
Table 1. Species observed at DBG, arranged into temporal categories.                                                                                                               study or greatly increased in frequency of observation.                                                                                                                  0.2                                                                            Rufous hummingbird
                                                                                                                                                                                                                                                                                                                                                                                                                                           "Western" flycatcher
                                                                                                                                                                                                                                                                                                                                                                                                                                           Wilson's warbler
                                                                                                              Figure 10 (below).                                                                                                                                                                                                                                                                                                           Green-tailed towhee
Species category           N    Examples                                                                      Gambel’s quail is a                                                                                                                                                                                                                           0.0                                                                            Brewer's sparrow                                                                                  0.0
                                                                                                                                                                                                                                                               1.0       Lesser goldfinch
Year-round resident        27   Cactus wren, verdin                                                           commonly encountered                                                                                                                                       Ringed turtle dove
                                                                                                                                                                                                                                                                                                                                                                           0   1   2   3   4   5    6   7   8       9    10 11 12 13                              0       1       2       3       4       5   6    7   8   9   10 11 12 13
                                                                                                                                                                                                                                                                         Ladder-backed woodpecker

                                                                                                                                                                                                                                    Frequency of observation
Year-round visitor         24   Orange-crowned warbler, kestrel                                               Sonoran Desert resident.                                                                                                                                   Northern cardinal                                                                                                         Month                                                                                                      Month
                                                                                                                                                                                                                                                               0.8       Brown-crested flycatcher
                                                                                                                                                                                                                                                                                                                                                                     1.0                                                               Cooper's hawk                                                                                         1.0
Winter resident            4    Yellow-rumped warbler, ruby-crowned kinglet                                                                                                                                                                                                                                                                                                                                                            Costa's hummingbird                D
                                                                                                                                                                                                                                                                                                                                                                               C                                                       Ruby-crowned kinglet

                                                                                                                                                                                                                                                                                                                                          Frequency of observation
Summer resident            6    White-winged dove, black-chinned hummingbird                                                                                                                                                                                   0.6                                                                                                   0.8
                                                                                                                                                                                                                                                                                                                                                                                                                                       Yellow-rumped warbler
                                                                                                                                                                                                                                                                                                                                                                                                                                       White-crowned sparrow                                                                                 0.8
Winter visitor             9    Rock wren, Lincoln's sparrow
Summer visitor             3    Turkey vulture, cliff swallow                                                                                                                                                                                                                                                                                                        0.6                                                                                                                                                                     0.6
Regular migrant            18   Wilson's warbler, rufous hummingbird
                                                                                                                                                                                                                                                                                                                                                                     0.4                                                                                                                                                                     0.4
Occasional migrant         3    Plumbeous vireo, Lucy's warbler                                                                                                                                                                                                0.2
Rare migrant / visitor     72   Long-eared owl, western meadowlark                                                                                                                                                                                                                                                                                                   0.2                                                                White-winged dove
                                                                                                                                                                                                                                                                                                                                                                                                                                        Brown-crested flycatcher
                                                                                                                                                                                                                                                                                                                                                                                                                                        Ash-throated flycatcher
Observed outside walks      9   Mountain chickadee, painted redstart                                                                                                                                                                                                                                                                                                                                                                    Turkey vulture
                                                                                                                                                                                                                                                                                                                                                                     0.0                                                                Black-chinned hummingbird                                                                            0.0
                                                                                                                                                                                                                                                                   1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
Total species observed    175                                                                                                                                                                                                                                                                                                                                              0   1   2   3   4   5   6    7   8   9       10 11 12 13                                   0       1       2       3       4   5    6   7   8   9   10 11 12 13
                                                                                                                                                                                                                                                                                                                                                                                                   Month                                                                                                      Month

                                                                                                                                                                                                                                                                                                                                                                                                                          Summary of Results and Discussion
                                                                 Figure 3 (below). Number of species observed,                                                                  Figure 4 (below). Cumulative number of
                                                                 averaged over all weeks in a given year.                                                                       species observed, beginning in 1987.
                                                                                                                                                                                                                                                                                                                                                                Between 1987 and 2004 observed bird richness increased significantly (Figure 3), and the total number of species
                                                                                                                                                                                                                                                                                                                                                                observed grew steadily without apparent asymptote (Figure 4). 175 species, grouped by temporal guild, were
                                                                                                                                Species observed through indicated year

                                                                 34                                                                                                       180
                                                                                                                                                                                                                                                                                                                                                                observed at least once (Table 1). There was a strong seasonal pattern, with species richness highest during the
                                                                                                                                                                          160                                                                                                                                                                                   two migration seasons and lowest during the winter (Figure 5). Many species often displayed striking seasonal
                                      Average species richness

                                                                 30                                                                                                                                                                                                                                                                                             patterns, either residing at DBG for a specific season or were present at all times of year but with differing
                                                                 28                                                                                                                                                                                                                                                                                             frequencies of occurrence (Figure 6). 22 species increased significantly in frequency of observation, and two
                                                                 26                                                                                                       120                                                                                                                                                                                   seasonal residents significantly increased their length of stay (white-winged dove, summer resident; ruby-crowned
                                                                                                                                                                                                                                                                                                                                                                kinglet, winter resident). Several species which were previously absent or rare visitors became permanent
                                                                 24                                                                                                       100                                                                                                                                                                                   residents of the Garden during the course of the study, or increased dramatically in frequency of observation (Figure
                                                                                     Richness = -1288.2 + 0.65184 * Year                                                  80
                                                                                                                                                                                                                                                                                                                                                                7). Overall, species have steadily colonized the Garden and increased in frequency of observation, with no notable
                                                                 20                                                                                                                                                                                                                                                                                             losses of individual species in the process.
                                                                                     Slope < 0, DF = 1, F = 144.11, P < 0.001
                                                                 18                  R-squared = 90.0%
                                                                                                                                                                                                                                                                                                                                                                Several major exhibit construction projects were undertaken during the time considered. In 1987-88 the 1/3 mi. long
                                                                 16                                                                                                       40
                                                                                                                                                                           1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
                                                                                                                                                                                                                                                                                                                                                                “Plants and People of the Sonoran Desert Trail” was built, adding irrigated high and low desert vegetation, and more
                                                                  1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
                                                                                                                                                                                                                                                                                                                                                                importantly a “desert oasis” consisting of a small pond with reeds and aquatic vegetation and ringed by willows and
                                                                                                                                                                                                                                                                                                                                                                cottonwoods. A new larger-capacity irrigation system was added to the central Garden in 1988. Small wildflower
                                                                                                                                                                                                                                                                                                                                                                gardens were added in 1990 and 1991. In 1999-2000 the 1/3 mi. long irrigated “Harriet K. Maxwell Desert
                                                                                                                                                                                                                                                                                                                                                                Wildflower Trail” was built (Figure 8), providing a habitat where annual and perennial wildflowers bloom at most
Figure 1 (above). The periphery                                                            Acknowledgments                                                                                                                                                                                          Figure 2 (above). The central                               times of year. Four additional small fountains or other permanent water sources were added at different times in the
of the Desert Botanical Garden                     I am indebted to many volunteers, members and staff at the Desert Botanical Garden. DBG                                                                                                                                                          Desert Botanical Garden is                                  1990s and 2000s (Figure 9). Current observations suggest that the Wildflower Trail is particularly enticing to seed-
is visually striking non-irrigated                volunteers Joyce Goodman, Charlie Brenner, Lynn Vogel, Judy Flynn, and particularly Tillie Chew                                                                                                                                                   heavily irrigated with many                                 eating sparrows and finches, and to residents of the surrounding desert. The desert oasis also attracts herons,
foothill Sonoran Desert vegetation.               and Andrée Tarby collected most of the records used in this study; indeed it is their dataset. Desert                                                                                                                                             specimen trees and plants, and                              ducks, rails and migrating warblers and icterids, which would otherwise be unlikely to occur in the Garden.
                                                  Botanical Garden staff members Joe McIntyre, Cathy Babcock, Ruthie Carll and Amy Ford have also                                                                                                                                                   thus is relatively lush with a                              Anecdotal information suggests that many species have become easier to observe in the central Garden, in
                                                  provided advice and helped to track down valuable information. I also must thank all the participants                                                                                                                                             complex vegetation structure.                               association with the added water features. I was not able to credibly associate specific colonizations by bird
                                                  in Monday bird walks for their observations.                                                                                                                                                                                                                                                                  species with specific construction projects, but the larger picture suggests that the Garden is becoming a more
                                                                                                                                                                                                                                                                                                                                                                attractive ‘urban desert oasis’ over time.

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