Vegetation composition influences avian species distributions in the post oak savannah ecoregion of northeast texas.
Early studies of avian community ecology emphasized the role of vegetative complexity in determining avian community composition (e.g., MacArthur & MacArthur 1961; MacArthur et al. 1966; Karr & Roth 1971; Willson 1974; Roth 1976; James & Warner 1982) with
Abstract--Species conservation has become a topic of global concern, and determining which factors influence habitat choice by bird species is a high priority, particularly in fragmented landscapes. This study examines the influence of habitat characteristics on avian communities in the post oak savannah of northeast Texas. Twenty-one sites, representing four different habitat types, were surveyed for this work. Species richness, diversity, evenness, and dominance of bird communities were not significantly different among sites that were dominated by different vegetation types, or between sites with or without roads. However, species' relative abundances were significantly explained by site vegetative composition. This study indicates the importance of multivariate, landscape-level analyses in explaining avian community composition, as opposed to smaller-scale, univariate, local analyses. Management implications are discussed for avian communities in the post oak savannah. both vertical vegetative complexity (MacArthur & MacArthur 1961; Karr & Roth 1971; Willson 1974; Roth 1976) and horizontal complexity or "patchiness" (MacArthur et al. 1962; MacArthur 1964) being of importance. In addition, some studies indicate that plant community composition has a stronger influence on bird diversity than vegetative complexity (Lovejoy 1974; Tomoff 1974; Power 1975; Wiens & Rotenberry 1981; Rotenberry 1985). While these microhabitat variables are important, the influence of habitat characteristics at larger spatial scales (landscape, regional, intercontinental) in determining patterns of avian species diversity have also been examined (Wiens 1986; Monkkonen 1994; McIntyre 1995; Bohning-Gaese 1997; Estrada et al. 1997; Boulinier et al. 2001; Cody 2001; Coppedge et al. 2001; Cushman & McGarigal 2003).
Landscape-level studies of avian ecology have largely focused on the arrangement of patch, corridor, and matrix elements as factors influencing avian community structure, and on the effects of patch size and isolation on species dispersal, colonization, and local extinction (reviewed in Forman 1995). On a landscape scale, rates of avian reproductive success, survival, and between-patch migration are affected by changes in patch size, proximity to other patches, and the amount of "edge" habitat (Rolstad 1991; Lawton 1995; Franklin et at. 2000), although habitat fragmentation has been identified as a primary contributing factor to population decline of many birds (Whitcomb et al. 1981; Ambuel & Temple 1982; 1983; Robbins et al. 1989; Askins et al. 1990; Faaborg et al. 1995). It is, therefore, evident that a variety of factors influence avian richness and abundance and that more detailed work at a variety of spatial scales and from a variety of habitats is needed to more thoroughly understand avian communities.
To better understand the dynamics of avian community composition in relation to environmental variables at different spatial scales, the work discussed herein focuses on the post oak savannah ecoregion of Texas. While ornithological studies have been conducted in this type of habitat (e.g., Blake 2005; Brawn 2006; Grundel & Pavlovic 2007; Au et al 2008), none have focused on Texas post oak savannah, which may exhibit latitudinal differences from studies conducted in more northern states (Davidowitz & Rosenweig 1998). Therefore, the objectives of this work were to, 1) in general, provide information on the types and scale of environmental variables (both natural and anthropogenic) that may influence avian communities and, 2) specifically, detail the composition of avian communities in an area located in the Texas post oak savannah ecoregion. To accomplish this, 1) a representative survey of the avian community in the post oak savannah ecoregion of Texas was carried out, and 2) the relative strengths of environmental factors influencing differences in avian community composition between sites and between habitat types was determined. In addition, taken together, these data will allow for the formulation of management strategies in the post oak savannah ecoregion of Texas.
Study area.--Twenty-one sites were established throughout Camp Maxey, Lamar Co., Texas, a 2,600 ha military training facility, in the post oak savannah ecoregion of northeast Texas. Camp Maxey is situated in an area that has been heavily converted to cropland and rangeland; however, the base itself has not been grazed or farmed since its establishment as a military base in the 1940s (Jog et al. 2008). Grasslands at the base are maintained by prescribed bums, and have largely reverted to their historical species composition (Jog et al. 2008). The military base has a unique heterogeneous vegetative composition that supports a wide array of avian species, many of which are neotropical migrants (Pogue 2005) and it may provide a critical refugia of habitat for avian species that are sensitive to the agricultural practices typical of this ecoregion.
Sites were chosen based on the following criteria: dominant habitat type, proximity to road, proximity to other sites, and level of accessibility (Fig. 1). The number of sites per dominant vegetation alliance (see Determination of site composition section below) were as follows: post oak-black hickory savannah, 12 (sites 3-4, 6-10, 14, 16, 18, & 20-21); little bluestem--indiangrass grassland, 2 (sites 2 & 19) ; shortleaf pine--oak savannah, 5 (sites 1, 5, 13, 15, & 17); and water oak--willow oak riparian forest, 2 (sites 11-12) (Fig.1). Grouping sites by dominant vegetation alliance did not result in an equal number of sites per alliance due to the overall composition and availability of the four alliances at Camp Maxey, with the post oak-black hickory savannah dominating the facility as to be expected in this ecoregion. However, the site selection used more thoroughly represents the mosaic of deciduous forests and mixed grasslands typical of the post oak savannah ecoregion and most sites varied widely in their vegetative composition, with most including more than one of the above vegetation alliances. In addition, to examine the possible effect of anthropogenic influence/habitat fragmentation on avian community structure, 11 sites (sites 1-11) were crossed by one or more active roads with similar levels of traffic flow, while the other 10 sites were not (sites 12-21).
[FIGURE 1 OMITTED]
Sampiing.--Fixed-radius (100 m) point count surveys (Hamel et al. 1996) were performed at each site from 15 October 2008-28 September 2009. Sites were surveyed between 0700 and 1100 hrs, and the order in which they were surveyed was randomized to avoid a time bias. Sites were located using a handheld Garmin GPSMap 76S handheld GPS Unit (Garmin Ltd., Olathe, KS, USA). Each site was surveyed between 7 and 11 times over the course of this study and all point counts were carried out by J. L. Cantrell.
Each point count was 7 min in duration. This time limit was chosen because it allowed the maximum survey time per site, while still allowing all point counts to be completed by 1100 hrs. Each site was divided into distance bands of 0-25, 25-50, and 50-100 m, and birds were assigned to a distance band according to their distance from the point count center. In spring and summer (peak vocalization times), a separate data sheet was used to record the two-dimensional location of each bird within the plot by species, in order to decrease the likelihood of counting a single bird more than once. Songs and calls were verified using Stokes Field Guide to Bird Songs: Eastern Region audio CD's (1997) and a portable CD player immediately following the completion of any point count in which songs or calls were used for identification purposes.
Determination of site composition.-ln September 2009, J. L. Cantrell walked through each site and made notes of the vegetation alliances present, their approximate sizes, and relative locations within the plot. One meter resolution aerial photos of Lamar County were obtained from the Texas Natural Resource Information System (TNRIS), and field notes and the geo-referenced aerial photo were then used to create site composition polygons using ArcG1S 9.2 (ESRI, Redlands, CA, USA). The polygons were manually delineated over the aerial photo. In total there were six polygon classes: one for each of the four possible vegetation alliances, one for disturbed areas, and one for open water. The "Disturbed" category included roads and grassy roadside areas. Data extracted from these polygons were used to determine the percent composition of each habitat type per site.
Statistical analyses.-Four measures of avian community structure (diversity, dominance, evenness, and richness) were computed for each site using a matrix of species' relative abundances per site. These measures were calculated using PC-ORD version 5.0 (MjM Software, Gleneden Beach, Oregon, U.S.A.). Each site's values were grouped into one of four categories depending on the dominant vegetation alliance of that site (post oak/hickory; pine/oak; riparian; or grassland). Single-factor analyses of variance (ANOVAs) were then conducted on the four groups to test the relationship between dominant vegetation all lances and species community composition. In addition, since the ANOVAs may be too course to detect fine-scale patterns in the data by forcing sites into four categories, multiple regression analyses were also conducted to explain variation in the data set by using the relative amounts of each vegetation type and disturbance present at each site.
A redundancy analysis (RDA) of two correlation matrices was conducted on: 1) the species' relative abundances by site matrix, and 2) a habitat percent composition by site matrix. Species' relative abundances per site were used in this analysis to compensate for differences in sampling efforts between sites. Two bi-plots were generated from the RDA output, showing general trends in the ordination of species and sites along two canonical axes. A Monte Carlo permutation test (9999 permutations) was performed to determine the significance of the RDA results. The RDA and Monte Carlo tests were conducted using Canoco version 4.53 (Biometris--Plant Research International, Wageningen, The Netherlands).
Avian community composition.--A total of 1,265 individuals of 73 species was recorded in 198 surveys conducted from October 2008-September 2009 (Table 1). The Tufted Titmouse (Baelophus bicolor) was detected at every site and was the most abundant species (15.02% of total). Other abundant species (> 5% of total) that were found at all sites included the Northern Cardinal (Cardinalis cardinalis, 8.93%), Blue Jay (('yanocitta cristata, 8.22%), American Crow (Corvus brachyrhynchos, 6.01%), Red-bellied Woodpecker (Melanerpes carolinus, 5.61%), Carolina Wren (Thtyothorus ludovicianus, 5.38%), and Carolina Chickadee (Poecile carolinensis, 5.30%). The Downy Woodpecker (Picoides pubescens, 5.85%) and Northern Flicker (Colaptes. auratus, 4.11%) were also abundant, but were absent from one and two sites, respectively. No other species accounted for > 2.5% of total relative abundance. Species observed exhibited a wide range of residency patterns with 32 of the 73 species observed being permanent residents, while the remainder were migrants (Table 1). Eighteen species were observed only once during the study period, of which 9 were neotropical migrants (either breeding residents or passage migrants), 5 were winter residents, and 4 were potential year-round residents. (Table 1).
Table 1. Number of sites occupied (Sites), total number of individuals (Total), and % of total relative abundances (% RA) for each bird species observed from October 2008 - September 2009 at Camp Maxey, Lamar Co., Texas. Species of conservation concern are indicated by * (U.S. Fish and Wildlife Service. 2008). Species are classified by seasonal residency as breeding residents (BR), winter residents (WR), year-round (YR). or during migration only (DM0). Common Name Scientific Name Code Sites Total % RA American [Crow.sup.BR] Corvus AMCR 21 76 6.01 brachyrhynchos American Spinus tristis AMGO 12 13 1.03 [Goldfinch.sup.WR] American Falco sparverius AMKE 1 1 0.08 [Kestrel.sup.YR] American Setophaga AMRE 1 1 0.08 [Redstart.sup.BR] ruticilla American [Robin.sup.YR] Turdus AMRO 2 2 0.16 migratorius Barred [Owl.sup.YR] Strix varia BADO 1 1 0.08 Black-and-white Mniotilta varia BAWW 11 15 1.19 [Warbler.sup.BR] Blue [Jay.sup.YR] Cyanocitta BLJA 21 104 8.22 cristaia Blue-gray Polioptila BGGN 10 12 0.95 [Gnatcatcher.sup.BR] caerulea Brown [Creeper.sup.WR] Cerihia BRCR 6 7 0.55 americana Brown [Thrasher.sup.YR] Toxostoma ru fum BRTH 3 3 0.24 Brown-headed Molothrus ater BHCO 10 14 1.11 [Cowbird.sup.YR] Carolina Poecile CACH 21 67 5.30 [Chickadee.sup.YR] carol'mensis Carolina [Wren.sup.YR] Thryothorus CARW 21 68 5.38 ludovicianus Chipping Spizella CHSP 4 6 0.47 [Sparrow.sup.YR] passerina Common Geothlypis COYE 4 6 0.47 [Yellowthroat.sup.BR] trichas [Dickcissel.sup.BR] Spiza americana DICK 2 6 0.47 Downy Picoides DO 20 74 5.85 [Woodpecker.sup.YR] pubescens WO Eastern Sialia sialis EABL 13 31 2.45 [Bluebird.sup.YR] Eastern Tvrannus EAK1 1 1 0.08 [Kingbird.sup.BR] tyrannus Eastern [Phoebe.sup.YR] Sayornis phoebe EAPH 6 7 0.55 Eastern Conlopus virens EWPE 8 18 1.42 [Wood-Pewee.sup.BR] Field [Sparrow.sup.YR] Spizella F1SP 10 17 1.34 pusillci Fish [Crow.sup.YR] Corvus FICR 4 6 0.47 ossifragus Gray [Catbird.sup.BR] Dumetella GRCA 2 2 0.16 carolinensis Great Crested Myiarchus GCFL 1 1 0.08 [Flycatcher.sup.BR] crinitus Hairy Picoides HAWO 2 2 0.16 [Woodpecker.sup.YR] villosus Henslow's Ammodramus HESP 1 1 0.08 [Sparrow.sup.*.WR] henslowill Hermit [Thrush.sup.WR] Catharus HETH 5 6 0.47 guttatus House [Finch.sup.YR] Carpodacus HOFI 1 1 0.08 mexicanus Indigo [Bunting.sup.BR] Passerina cyanea INBU 6 14 1.11 Kentucky Oporomis KFWA 1 1 0.08 [Warbler.sup.*.BR] formosus Lark [Sparrow.sup.YR] Chondestes LASP 1 1 0.08 grammacus Mourning [Dove.sup.YR] Zenaida macroura MODO 10 10 0.79 Northern Col inns NOBO 3 3 0.24 [Bobwhite.sup.YR] virginiunus Northern Cardinalis NOCA 21 113 8.93 [Cardinal.sup.YR] cardinal is Northern Colaptes auratus NOFL 19 52 4.11 [Flicker.sup.BR] Northern Circus cyaneus NOMA 1 1 0.08 [Harrier.sup.WR] Northern Mimus NOMO 3 9 0.71 [Mockingbird.sup.YR] polvglottos Northern Parula americana NOPA 1 1 0.08 [Parula.sup.BR] [Ovenbird.sup.DMO] Seiurus OVEN 1 1 0.08 aurocapiUus Painted Passerina ciris PABU 1 1 0.08 [Bunting.sup.*.BR] Pileated Dryocopus PI 12 21 1.66 [Woodpecker.sup.YR] pileatus WO Pine [Warbler.sup.YR] Dendroica pinus PIWA 4 14 1.11 Prothonotary Proionofaria PROW 4 5 0.4 [Warbler.sup.*.BR] eitrea Purple [Martin.sup.BR] Prague sub is PUMA 4 4 0.32 Red-bellied Melanerpes RBWO 21 71 5.61 [Woodpecker.sup.YR] carolinus Red-breasted Silta canadensis RBNU 1 1 0.08 [Nuthatch.supWR] Red-eyed [Vireo.sup.BR] Vireo olivaceus REVI 3 4 0.32 Red-headed Melanerpes RHWO 2 2 0.16 [Woodpecker.sup.*.YR] ervthrocephalus Red-shouldered Buteo Pineal us RSHA 7 10 0.79 [Hawk.sup.YR] Red-tailed Buteo RTHA 5 9 0.71 [Hawk.sup.YR] jamaicensis Red-winged Agelaius RWBL 1 2 0.16 [Blackbird.sup.YR] phoeniceus Ruby-crowned Regulus RCKI 9 13 1.03 [Kinglet.sup.WR] calendula Ruby-throated Archilochus RTHU 6 7 0.55 [Hummingbird.sup.BR] colubris Savannah Passerculus SAVS 3 4 0.32 [Sparrow.sup.WR] sandwichensis Scissor-tailed Tyrannus STFL 1 1 0.08 [Flycatcher.sup.*.BR] forficatm Sedge [Wren.sup.WR] Cistothorus SEWR 3 3 0.24 platensis Sharp-shinned Accipiter SSHA 1 1 0.08 [Hawk.sup.WR] striatus Slate-colored Junco hycmalis SCJU 2 2 0.16 [Junco.sup.WR] Summer [Tanager.sup.BR] Piranga rubra SUTA 14 24 1.90 Swainson's Catharus SWTH 1 1 0.08 [Thrush.sup.DWO] ustulatus Tufted Baeolophus TUTI 21 190 15.02 [Titmouse.sup.YR] bicolor Turkey [Vulture.sup.YR] Cathartes aura TUVU 3 3 0.24 White-breasted Sitta WBNU 13 30 2.37 [Nuthatch.sup.YR] carolinensis White-eyed Vireo griseus WEVI 10 24 1.90 [Vireo.sup.BR] White-throated Zontrichia WTSP 4 4 0.32 [Sparrow.sup.WR] albicollis Winter [Wren.sup.WR] Troglodytes WIWR 1 1 0.08 troglodytes Yellow-bellied Sphyrapicus YBSA 7 8 0.63 [Sapsueker.sup.WR] varitts Yellow-billed Coccyzus amerii YBCU 11 15 1.19 [Cuckoo.sup.BR] anus Yellow-breasted lcteria virens YBCH 4 6 0.47 [Chat.sup.BR] Yellow-rumped Dendroica YRWA 3 4 0.32 [Warbler.sup.WR] coronata Yellow-throated Dendroica YTWA 3 5 0.40 [Warbler.sup.BR] dominica Total Number of Birds Observed (all species): 1265
A local, univariate approach: ANOVAs and multiple regressions.--After percent vegetation composition of each site was determined and sites were grouped according to dominant vegetation alliance, measures of avian species richness, evenness, diversity, and dominance *were calculated for each site-per-alliance group. ANOVAs revealed that none of the 4 dependent measures were significantly different between vegetation alliances (richness: [F.sub.3,17] = 1.46, P = 0.26; evenness: F3,17 = 1.18, P = 0.35; diversity: [F.sub.3,17] = 0A2, P = 0.74; dominance: [F.sub.3,17] = 0.50, P = 0.69). In addition, no significant differences in species richness, evenness, diversity, and dominance existed between sites classified as "bisected by roads" or "not bisected by roads" (richness: F1,17 = 0.29, P = 0.40; evenness: [F.sub.3,17] = 2.68, P = 0.88; diversity: F1,17 = 0.60, P = 0.55; dominance: [F.sub.3,17] = 1.25, P = 0.72). More fine-scale regression analyses resulted in similar non-significant results for all models tested including full multiple regression models, multiple regression models with the number of independent variables reduced based on stepwise variable selection procedures, and all simple regression models.
A multivariate, landscape approach: Redundancy analysis.--RDA indicated a significant relationship between avian species' relative abundances and environmental variables (Fig. 2). A Monte Carlo permutation test (9999 permutations) calculated significance levels of P = 0.04 for the first canonical axis and P < 0.01 for all axes. The first two RDA axes explained 63.4% of the variation in species' relative abundances and associated environmental variables. With the exception of species strongly associated with the "Riparian" environmental variable, species ordinate along the first axis (RDA 1) according to the presence/absence of a canopy layer (Fig. 2). The positive association of all grassland-dominated sites (1, 5, 13, 15, and 17) with this axis further supports this relationship (Fig. 2). Species that are grassland-obligate or that are less sensitive to disturbance (Hunter et al. 2001) are positively associated with this axis (and thus with "Disturbed" and "Grassland" variables) including several grassland sparrows (e.g. Savannah Sparrow and Field Sparrow) and other common grassland passerines (e.g., Sedge Wren and Eastern Bluebird), scrub dwellers, (e.g., Common Yellowthroat and White-eyed Vireo), anthropogenic opportunists (e.g., Blue Jay and Brown-headed Cowbird), and predators/scavengers, (e.g., Red-tailed Hawk and Turkey Vulture). There is one notable exception to this trend. The Northern Parula (NOPA) is a high canopy feeder, and yet this species is very positively associated with RDA axis 1; however, this may be due to insufficient sampling, as the NOPA was detected only once.
[FIGURE 2 OMITTED]
Species negatively associated with RDA 1 are more strongly associated with the "Pine" and "Oak/Hickory" variables, indicating their general preference for those woodlands. Species negatively associated with RDA 1 include flycatchers (e.g., Eastern Wood-pewee and Blue-gray Gnatcatcher), bark-gleaners (e.g., Brown Creeper and White-breasted Nuthatch), and other common forest passerines (e.g., Summer Tanager, Tufted Titmouse, and American Goldfinch).
The second axis (RDA 2) explains 22.3% of the variation in this dataset, and there are multiple factors influencing response variable distributions along this axis. Canopy species (those associated negatively with RDA axis 1) ordinate along RDA axis 2 according to canopy type with Oak/Hickory species (e.g., White-breasted Nuthatch and Eastern Wood-pewee) associating negatively, and Pine/Oak species (e.g., Pine Warbler, Summer Tanager, and Winter Wren) associating positively. Species positively associated with RDA axis 1 are influenced by the Disturbed, and to a lesser extent, the Water and Riparian variables of RDA axis 2. The Red-shouldered Hawk and Yellow-throated Warbler, common species of bottomland forests, are associated with the Riparian and Water variables.
Effect of natural environmental variables: Vegetation .--Although it is well-known that bird species prefer certain habitat types (MacArthur et al. 1962), a multivariate, landscape-scale analysis of their habitat use can describe their response to variables that are not measurable on a local, univariate scale. A significant redundancy analysis indicated that over 85 % of variation in species' relative abundances was explained by vegetation characteristics, while univariate ANOVAs and regressions were unable to detect differences in eveness, diversity, dominance, or richness. The redundancy analysis indicated that 63.4 % of species abundances could be explained by the presence or absence of canopy cover. Additionally, 22.3 % was further explained by 1) what type of canopy cover was present (oak/hickory vs. pine/oak) for species associated with the presence of canopy cover and 2) how disturbed a site was for those species associated with the absence of canopy cover. This indicates that the maintenance of the mosaic of habitat types present in the post oak savannah ecoregion is beneficial to maintaining species abundances, which is a major component of diversity, richness, dominance, and evenness. However, diversity, dominance, evenness, and richness, themselves, were not significantly associated with dominant vegetation alliance, which may be the result of how the sites were grouped. Even though they were dominated by specific vegetation types, more than one vegetation type may have been present at each site. These analyses, therefore, indicate the importance of multivariate, landscape-level analyses in understanding avian communities, as opposed to univariate, smaller-scale microhabitat-level analyses, (Forman 1995; Rolstad 1991; Lawton 1995; Franklin et al. 2000).
Effect of anthropogenic environmental variables: Roadc.--Previous studies of avian community ecology in both forested (McIntyre 1995) and grassland (Herkert 1991) habitats have shown a relationship between fragmentation and decreased avian diversity in the remaining habitat (Whitcomb et al. 1981; Ambuel & Temple 1982; 1983; Robbins et al. 1989; Askins et al. 1990; Faaborg et al. 1995). The results of this study did not support this trend. There were no significant differences in avian community composition between sites bisected by roads and sites not bisected by roads. However, an important point to consider is that only five of the 21 sites surveyed were comprised of one vegetation alliance. All others were comprised of two-four different habitat types. The post oak savannah is characterized by this heterogeneous landscape of forests and grasslands (Griffith et al. 2004). At Camp Maxey, the edges between forested and grassland areas are usually very abrupt, with little transition between the two habitat types, as is typical in post oak savannah habitat. Therefore, the bird communities examined here may be influenced by these edges to such a degree that they are not significantly influenced by the edge effects associated with roads. Another important consideration is that the most abundant species were encountered in all or nearly all of the sites sampled. These ubiquitous species, coupled with the low detection rates of many other species, may obscure trends of habitat use by the less common birds that are potentially sensitive to road proximity. Finally, it may be that roads do not represent a true barrier to avian community development and maintenance or that at this site, they do not equate to a source of habitat fragmentation. However, the possibility that analysis of avian communities on a different spatial scale might reveal patterns of road sensitivity must also be considered. For instance, sites not bisected by roads may not have been far enough removed from roads to be free of their associated edge effects.
Management implications.--The combination of maintaining biological diversity (e.g., Walker 1992) and the presence of seven species of conservation concern (Farley, 2008), six of which were detected in this study (i.e., Henslow's Sparrow, Kentucky Warbler, Painted Bunting, Prothonotary Warbler, Red-headed Woodpecker, Scissor-tailed Flycatcher) (Table 1), equate to the need for management practices to be continued at Camp Maxey and continued/applied to other sites located within the post oak savannah ecoregion of Texas. The data suggest that avian abundance is influenced by the presence of variable habitat types and that maintenance of varied, natural habitat consistent with the post oak savannah ecoregion is required to maintain high numbers of various species. Of utmost importance is the maintenance of post oak savannah ecosystems via prescribed bums, as this restoration technique has been demonstrated to significantly affect the ecology of avian populations and communities and has key implications regarding avian conservation (Brawn et al. 2001; Hunter et al. 2001; Blake 2005; Brawn 2006; Grundel & Pavlovic 2007; Au et al. 2008). Because specific recommendations regarding the six species of conservation concern cannot be elaborated upon due to low samples sizes, the first step in effectively managing these species will be to better assess their habitat utilization in this habitat. In addition, since Camp Maxey, specifically, supports managed native habitat types in a landscape that is dominated by agriculture and urbanization, seasonal studies comparing trends of avian habitat use between Camp Maxey and surrounding agricultural and urban areas would be useful in evaluating the relative importance of post oak savannah habitat to local bird populations.
We thank Troy Anderson for reading and evaluating an early version of this manuscript. Sergeant Matthew Lamonica and Sergeant Keli Gain of the Texas Army National Guard helped to facilitate this work. Jessica Coleman and Elizabeth Farley provided extensive knowledge of Camp Maxey and avian ecology. Support for this research was provided by the Texas Adjutant General's Department (Interagency Cooperation Agreement TX07-ENV-06, 401-7-2905) and the Department of Biology at the University of Texas at Tyler.
Ambuel, B. & S. A. Temple. 1982. Songbird populations in southern Wisconsin forests: 1954 and 1979. J. Field Omithol., 53:149-158.
Ambuel, B. & S. A. Temple. 1983. Area dependent changes in the bird communities and vegetation of southern Wisconsin forests. Ecology, 64:1057-1068.
Askins, R. A., J. F. Lynch & R. Greenberg. 1990. Population declines in migratory birds in eastern North America. Pages 1-39 in D. M. Power editor. Current Ornithology, Volume 7. Plenum Press, New York.
Au, L., D. E. Andersen & M. Davis. 2008. Patterns in bird community structure related to restoration of Minnesota dry oak savannas and across a prairie oak woodland ecological gradient. Nat. Areas J., 28:330-341.
Bohning-Gaese. K. 1997. Determinants of avian species richness at different spatial scales. J. Biogeogr., 24:49-60.
Blake, J. G. 2005. Effects of prescribed burning on distribution and abundance of birds in .a closed-canopy oak-dominated forest, Missouri, USA. Biol. Conserv., 121:519-531.
Blake. J. G. & J. R. Karr. 1987. Breeding birds of isolated woodlots: area and habitat relationships. Ecology, 68:1724-1734.
Boulinier. T.. J. D. Nichols, J. E. Hines. J. R. Sauer, C. H. Flather & K. H. Pollock. 2001. Forest fragmentation and bird community dynamics: inference at regional scales. Ecology, 82:1159-1169.
Brawn. J. D. 2006. Effects of restoring oak savannas on bird communities and populations. Conserv. Biol., 20:460-469.
Brawn, J. D., S. K. Robinson & F. R. Thompson III. 2001. The role of disturbance in the ecology and conservation of birds. Annu. Rev. Ecol. Syst., 32:251-276.
Cody, M. L. 1985. An introduction to habitat selection in birds. Pages 3-56 in M. L.
Cody, editor. Habitat Selection in Birds. Academic Press, Inc., San Diego. CA.
Cody, M. L. 2001. Bird di % ersity components in Australian Eucalyptus and North American Quercus woodlands. Auk, 118:443-456.
Coppedge, B. R., D. M. Engle, R. E. Masters & M. S. Gregory. 2001. Avian responseto landscape change in fragmented southern great plains grasslands. Ecol. Appl., 11:4759.
Cushman, S. A. & K. McGarigal. 2003. Landscape-level patterns of avian diversity in the Oregon coast range. Ecol. Monogr., 73:259-281.
Davidowitz, G. & M. L. Rosenzweig. 1998. The latitudinal gradient of species diversity among North American grasshoppers (Acrididae) within a single habitat: a test of the spatial heterogeneity hypothesis. J. Biogeogr., 25:553-560.
Estrada, A., R. Coates-Estrada & D. A. Meritt. 1997. Anthropogenic landscape changes and avian diversity at Los Tuxtlas, Mexico. Biodivers. Conserv., 6:19-43.
Faaborg, J., M. Briningham, T. Donovan & J. Blake. 1995. Habitat fragmentation in the temperate zone. Pages 357-375 in D. M. Finch, and T. E. Martin editors. Ecology and Management of Neotropical Migratory Birds: a Synthesis and Review of Critical Issues. Oxford University Press, New York.
Farley. E. A. 2008. Breeding biology of Bachman's Sparrows (Annophila aestivalis) in post oak savannah on Camp Maxey. Lamar County, Texas. Unpublished M.S. thesis, The University of Texas at Tyler, Tyler, TX.
Forman, R. T. T. 1995. Some general principles of landscape and regional ecology. Landsc. Ecol., 10:133-142.
Franklin, A. B., D. R. Anderson, R. J. Guitierrez & K. P. Burnham. 2000. Climate, habitat quality, and fitness in northern spotted owl populations in northwestern California. Ecol. Monogr., 70:539-590.
Griffith, G.E., S. A. Bryce, J. M. Omernik, J. A. Comstock, A. C. Rogers, B. Harrison, S. L. Hatch & D. Bezanson. 2004. Ecoregions of Texas (color poster with map, descriptive text, and photographs). U.S. Geological Survey, Reston, VA.
Grundel, R. & N. B. Pavlovic. 2007. Distinctiveness, use, and value of midwestern oak savannas and woodlands as avian habitats. Auk. 124:969-985.
Hamel, P. B., P. S. Winston, D. J. Twedt, J. R. Woehr, E. Morris, R. B. Hamilton 8c R. J. Cooper. 1996. A Land Manager's Guide to Point Counts of Birds in the Southeast. Gen. Tech. Rep. SO-120. U.S. Department of Agriculture, Forest Service, Southern Research Station, New Orleans, LA. 39 pp.
Herkert, J. R. 1991. Prairie birds of Illinois: population response to two centuries of habitat change. III. Nat. Hist. Surv. Bull., 34:393-399.
Hunter, W. C., D. A. Buehler, R. A. Canterbury, J. L. Confer & P. B. Hamel. 2001. Conservation of disturbance-dependent birds in eastern North America. Wildl. Soc. Bull., 29:440-455.
James, F.C. & N.D. Warner. 1982. Relationships between temperate forest bird communities and vegetation structure. Auk. 98:785-800.
Jog. S., J. L. Coleman, D. W. Pogue, M. G. Williams & L. R. Williams. 2008. Vegetation community identification, ground surveys, accuracy assessment, and correction of land cover classification for Fort Wolters and Camp Maxey. Report to the Texas Adjutant General's Department, Austin. TX.
Karr, J. R. & R. R. Roth. 1971. Vegetation structure and avian diversity in several New World areas. Am. Nat., 105:423-435.
Lawton, J. H. 1995. Population dynamics principles. Pages 147-163 in J. H. Lawton. and R. May editors. Extinction Rates. Oxford University Press, New York.
Lovejoy. T. E. 1974. Bird diversity and abundance in Amazon forest communities. Living Bird, 13:127-191.
MacArthur, R. H. & J. W. MacArthur. 1961 On bird species diversity. Ecology, 2:594598.
MacArthur, R. H., J. W. MacArthur & J. Preer. 1962. On bird species diversity. II.
Prediction of bird census from habitat measurements. Am. Nat., 96:167-174. MacArthur. R. H. 1964. Environmental factors affecting bird species diversity. Am. Nat., 98:387-397.
MacArthur, R. H.. H. Recher & M. Cody. 1966. On the relation between habitat selection and species diversity. Am. Nat., 100:319-332.
McIntyre, N. E. 1995. Effects of forest patch size on avian diversity. Lancisc. Ecol., 10:8599.
Monkkonen, M. 1994. Diversity patterns in Palearctic and Nearctic forest bird assemblages. J. Biogeogr.. 21:183-195.
Pogue, D. W. 2005. Baseline survey of birds at Camp Maxey, Texas Army National Guard Training Site. Report to the Texas Adjutant General's Department, Austin, TX. Power, D. M. 1975. Similarity among avifaunas of the Galapagos Islands. Ecology, 56:616-626.
Ricklefs, R. E. & D. Schluter (eds.). 1993. Species Diversity: Historical and Geographical Aspects. University of Chicago Press, Chicago.
Robbins, C. S., J. R. Sauer, R. S. Greenberg & S. Droege. 1989. Population declines in North American birds that migrate to the tropics. Proc. Nat. Acad. Sci. U.S.A., 86:7658-7662.
Rolstad, J. 1991. Consequences of forest fragmentation for the dynamics of bird populations: conceptual issues and the evidence. Biol. J. Linn. Soc. Lond., 42:149163.
Roth, R. R. 1976. Spatial heterogeneity and bird species diversity. Ecology, 57:773-82. Rotenberry, J. T. 1985. The role of habitat in avian community composition: physiognomy or flori sties? Oecologia, 67:2 1 3-2 17.
Soule, M. E., A. C. Alberts & D. T. Bolger. 1992. The effects of habitat fragmentation on chaparral plants and vertebrates. Oikos, 63:39-47.
Stokes, D. 1997. Stokes Field Guide to Bird Songs: Eastern Region. Hachette Audio, New York, NY.
Stillman, R. A. & A. F. Brown. 1998. Pattern in the distribution of Britain's upland breeding birds. J. Biogeogr., 25:73-82.
Tomoff, C. W. 1974. Avian species diversity in desert scrub. Ecology, 55:396-403. U.S. Fish and Wildlife Service. 2008. Birds of conservation concern. United States Department of Interior, Fish and Wildlife Service, Division or Migratory Bird Management, Arlington, VA. http://www.fws.gov/migratorybirds/.
Walker, B. H. 1992. Biodiversity and ecological redundancy. Conserv. Biol.. 6:18-23. Wiens, J. A. & J. T. Rotenberry. 1981. Habitat associations and community structure of birds in shrubsteppe environments. Ecol. Monogr., 51:21-41.
Wiens, J. A. 1986. Spatial scale and temporal variation in studies of shrubsteppe birds. Pages 154-172 in J. Diamond, and T. J. Case editors. Community Ecology. Harper and Row, New York.
Whitcomb. R. F., C. S. Robbins, J. F. Lynch, B. L. Whitcomb, M. K. Kliemkiewicz & D. Bystrak. 1981. Effects of forest fragmentation on avifauna of the eastern deciduous Forest. Pages 125-205 in R. L. Burgess and D. M. Sharpe editors. Forest Island Dynamics in Man-dominated Landscapes. Springer-Verlag, New York.
Willson. M. F. 1974. Avian community organization and habitat structure. Ecology, 55:1(117-1029.
JSP at: firstname.lastname@example.org
Jamie L. Cantrell(1), Darrell W. Poguel(1)*, Lance R. Williams(1) Jacob C. McCumber(2), and John S. Placyk, Jr.(1)
(1) Department of Biology, University of Texas at Tyler 3900 University Blvd., Tyler, Texas 75799
(2) Texas Adjutant General's Department, JFTX-EVP.O. Box 5218. Austin, Texas 78763 USA