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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 14 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 1990s. 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 0.2 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 0.4 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 0.2 Ash-throated flycatcher 0.0 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 32 160 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 140 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 22 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 60 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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