Carl E. Bock's research while affiliated with University of Colorado Boulder and other places
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Publications (87)
Developed waters may improve arid landscapes for birds, but their efficacy requires further study. I counted birds along five 300-m transects originating at point sources of water in a New Mexico grassland, and compared results with those from transects without water. Total birds were nearly three times more abundant on transects with water, but di...
We measured fire damage to 250 riparian trees in 2003–2004, and again in 2012–2013, in a southeastern Arizona grassland burned by wildfires in 2002, 2009, or both. Following a single fire, combined mortality or survival only by ground-level resprout was 64% for desert willow (Chilopsis linearis), 57% for Fremont cottonwood (Populus fremontii), 48%...
Livestock grazing and fire influence the composition of desert grassland communities, including their rodent populations. However, there have been few studies of the interactions between grazing and wildfire in arid grasslands of the southwestern United States. We trapped rodents and measured vegetation on grazed versus ungrazed plots before (2001)...
This chapter describes the impacts of rural exurban development on the abundance and variety of plants and animals in North
American ecosystems. The principles of landscape ecology provide a framework for considering the ways that exurban development
can impact biodiversity. We survey the literature and describe the responses of varying components...
Grass and herb cover, and woody plant densities were measured on 25 native and 25 exotic grassland plots in southeastern Arizona between 1984 and 1990. At least 40 yr previously, the exotic plots had been seeded with two species of lovegrasses (Eragrostis spp.) native to southern Africa. A 1987 wildfire burned 11 native and 11 exotic plots. The fir...
Eragrostis intermedia (Plains lovegrass) is a midheight perennial bunchgrass native to semi-arid grasslands of the southwestern USA, that becomes an abundant and dominant component of these grasslands in areas long protected from livestock grazing. Substantial mortality of plains lovegrass occurred on a large livestock exclosure in southeastern Ari...
En el suroeste de los Estados Unidos los ranchos están siendo transformados en desarrollos habitacionales suburbanos de baja densidad, con impactos potencialmente significativos, pero poco estudiados, sobre la diversidad biológica. Contamos conejos (Sylvilagus audubonii y S. floridanus) en pradera y en sabana de mesquite/encino en el sureste de Ari...
We measured grasshopper densities on 66 shortgrass, mixed grass, tallgrass and hayfield plots on Boulder, Colorado, open space in 1995–1996. Grasshoppers as a group, and most species individually, were more abundant on relatively sparse short and mixed grass plots than on lusher hayfields and tallgrass plots—a result consistent with the hypothesis...
Ranches are being converted to low density exurban housing developments in the southwestern United States, with potentially significant but little studied impacts on biological diversity. We counted lizards in a grassland and mesquite/oak savanna in southeastern Arizona, along 48 transects evenly divided among landscapes that were grazed by livesto...
We live-trapped rodents in 2000–2001 at eight sites on a 3160 ha grassland and mesquite-oak savanna in southeastern Arizona that had been ungrazed since 1968, and on eight paired sites on adjacent cattle ranches. There were 917 captures of 14 species during 5760 trap-nights. Four species of Muridae (Sigmodon fulviventer, Baiomys taylori, Reithrodon...
Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little-studied impacts on biological diversity. We counted birds in grasslands and savannas in southeastern Arizona that were grazed by livestock, embedded in low-density exurban housing developments, or both, or neither....
Livestock grazing may or may not be an exogenous disturbance facilitating the spread of exotic grasses, perhaps depending on the historical importance of native ungulates in a particular grassland. We compared canopy cover of native grasses and two African lovegrasses (Eragrostis spp.) over 22 years in ungrazed versus livestock grazed desert grassl...
Increases of velvet mesquite (Prosopis velutina Woot.) in southwestern grasslands might have been caused by livestock consumption of fuels that once burned with sufficient frequency and intensity to kill the trees. However, attempts to control mesquite with fire usually have failed. We measured fire damage and 5 years of postfire recovery for 225 m...
Species richness and evenness are components of biological diversity that may or may not be correlated with one another and with patterns of species abundance. We compared these attributes among flowering plants, grasshoppers, butterflies, lizards, summer birds, winter birds, and rodents across 48 plots in the grasslands and mesquite-oak savannas o...
Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant impacts on biological diversity. We surveyed butterflies on 48 plots in grasslands, mesquite savannas, and oak savannas in southeastern Arizona that were grazed by livestock, embedded in low-density housing developments, or bo...
Large vertebrates are strong interactors in food webs, yet they were lost from most ecosystems after the dispersal of modern humans from Africa and Eurasia. We call for restoration of missing ecological functions and evolutionary potential of lost North American megafauna using extant conspecifics and related taxa. We refer to this restoration as P...
Housing developments are replacing ranches in the southwestern United States, with potentially significant but little-studied ecological effects. We counted grasshoppers (Orthoptera: Acrididae) and measured vegetative cover for 2 years in a grassland and mesquite/oak savanna in southeastern Arizona, on 48 transects that were grazed by livestock, em...
Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little-studied impacts on biological diversity. We captured rodents on 48 traplines in grasslands, mesquite savannas, and oak savannas in southeastern Arizona that were grazed by livestock, embedded in exurban housing deve...
Housing developments are replacing ranches in the southwestern United States, with potentially significant but little-studied ecological effects. We counted grasshoppers (Orthoptera: Acrididae) and measured vegetative cover for 2 years in a grassland and mesquite/oak savanna in southeastern Arizona, on 48 transects that were grazed by livestock, em...
The Botteri's Sparrow (Aimophila botterii) is a bird of tall grasslands that temporarily disappeared from Arizona following heavy livestock grazing in the 1890s. Its return was noted first in sacaton (Sporobolus wrightii), an uncommon native floodplain tallgrass often > 2 m in height, and subsequently in stands of exotic lovegrasses (Eragrostis spp...
The Botteri's Sparrow (Aimophila botterii) is a bird of tall grasslands that temporarily disappeared from Arizona following heavy livestock grazing in the 1890s. Its return was noted first in sacaton (Sporobolus wrightii), an uncommon native floodplain tallgrass often >2 m in height, and subsequently in stands of exotic lovegrasses (Eragrostis spp....
Despite increasing interest in the ecological effects of urbanization, relatively little is known about its effects in grasslands.
We examined population trends and habitat associations of two predators, the rough-legged hawk (Buteo lagopus) and the red-tailed hawk (B. jamaicensis), in a rapidly urbanizing grassland region at the western edge of th...
There are times when birds reproduce at higher rates in places where they are less abundant, limiting the generally accepted value of bird counts as environmental indicators. But how often, and under what circumstances, does this happen? In 109 published cases involving 67 species across North America and Europe, higher density sites displayed grea...
We observed Mexican Jays (Aphelocoma ultramarina) and Northern Flickers (Colaptes auratus) from June 2000 to March 2001, recording interspecific associations and interactions. Flickers were seen with jays only once in summer, but they were observed together 62 times in winter, in mixed flocks of up to 20 jays and 12 flickers, while jays were alone...
Relatively little is known about the response of grassland rodent populations to urban and suburban edges. We live-trapped rodents for three summers on 65 3.1-ha grassland plots on open space of the city of Boulder, Colorado, and compared capture rates among species according to habitat type, percentage of the 40 ha surrounding each plot that was s...
Landscape alterations resulting from urban expansion are among those factors negatively impacting Great Plains grassland birds. The City and County of Boulder, Colorado, manage one of the largest grassland open-space systems in North America, but it is embedded in an area of rapid urban growth. We compared bird count data from the 1980s and 1990s w...
We measured carbon isotope signatures (delta C-13) from 0-10 cm and 10-20 cm soil depth intervals for grassland soils near Boulder Colorado. These grasslands included tall-, short-,and mixed-grass prairies that were grazed, ungrazed, or hayed. Soils exhibited delta C-13 signatures consistent with observations that current sites are a mis of C-3 and...
We examine the relationships between abundance of grassland nesting songbirds observed in the Boulder Open Space, CO, USA and parameters that described landscape and habitat characteristics, in order to provide information for Boulder Open Space planners and managers. Data sets included bird abundance and plant species composition, collected during...
We measured carbon isotope signatures (δ13C) from 0-10 cm and 10-20 cm soil depth intervals for grassland soils near Boulder, Colorado. These grasslands included tall-, short-, and mixed-grass prairies that were grazed, ungrazed, or hayed. Soils exhibited δ13C signatures consistent with observations that current sites are a mix of C3 and C4 species...
In a grassland–oak savanna in southeastern Arizona, we compared vegetative ground cover and bird populations between a 29-year livestock exclosure and an adjacent cattle ranch that was managed according to the principles of holistic resource management, including short-duration rotational grazing. The study took place in the winter after a 2-year d...
We counted nesting songbirds for three summers on 62 200-meter-diameter plots on City of Boulder, Colorado, Open Space grasslands. Habitats included upland mixed-grass prairie and low-lands with tallgrass prairie and irrigated hayfields. Plots were located either at habitat edges adjacent to suburban developments or at least 200 meters interior to...
We conducted point counts of diurnal raptors on Boulder, Colorado, grasslands for three winters and summers, and compared results to landscape features of the count areas. Four wintering species were scarce on plots that included significant amounts of urban habitat, with a critical landscape threshold at about 5-7% urbanization: Bald Eagle (Haliae...
The tallgrass prairie once was continuous throughout the eastern Great Plains. Now, scattered remnants remain. The distribution of some of the most interesting and socially valuable remnants occur along the base of the Rocky Mountains as relicts from a past era. When the species composition of these Colorado grasslands is compared with that of the...
Changes in Baccharis pteronioides and Haplopappus tenuisectus densities in a southeastern Arizona grassland were related to patterns of livestock grazing, fire, and precipitation. Results suggested that both species increased following two periods of relatively wet winters, and declined during an intervening dry period. Baccharis completely recover...
Grasslands have figured prominently in our North American heritage. Prairies first provided significant barriers to westward expansion, then offered both economic and sociological opportunity, as well as heartache, for settlers. Many artists have gained significant inspiration from the beauty as well as the harshness of these regions and its biota....
Tolerance of particular grasslands to the activities of domestic livestock may depend on their historic association with native grazing animals. Southwestern grama (Bouteloua) grasslands are floristically allied to the North American Central Plains but lie outside the historic range of the plains’ principal ungulate grazer, alics bishop. We compare...
The first birds probably evolved from a line of theropod dinosaurs in the late Jurassic or early Cretaceous. The "trees down" theory proposes that avian ancestors were arboreal, whereas the "ground-up" (cursorial) theory suggests that they were terrestrial, and ran and jumped for prey. We present suggestive evidence from reptilian and avian female...
In a 6-yr study of 70 generally insectivorous bird species in Arizona riparian woodlands, abundances of cavity-nesting species increased on 50 experimental plots compared with 49 control plots, following addition of artificial nest boxes. Open-nesting birds increased in abundance on control plots during the study but avoided experimental plots rela...
After four yr, mean annual adult grasshopper density was >2.2 times higher on plots from which birds were excluded, and where grasshoppers were enclosed by dispersal barriers, than on unmanipulated control plots. Mean nymph density was >3.0 times higher in the same comparison. Grasshoppers were significantly more abundant in bird exclosures with in...
We measured vegetation cover and bird abundances on 25 native and 25 exotic grassland plots in southeastern Arizona between 1984 and 1990. A wildfire in 1987 completely burned 11 native and 11 exotic plots. The fire reduced grass and shrub cover, and increased herb cover, for 2 post-fire years in both grassland types. Numbers of fall birds increase...
Small prescribed fires were replicated on an ungrazed semidesert shrub-grassland in southeastern Arizona. Plant densities and shrub heights were measured and compared to unburned plots in one pre-burn and two post-burn growing seasons. Grass and herb densities were reduced by the fires for 1 year not for 2 years. Densities of the shrub Mimosa were...
The High Plains of North America extends from Canada to northern Mexico. This grassland region is subject to prolonged drought, herbivory, and wildfire. Organisms that are indigenous to the High Plains are adapted to these environmental factors. Periodic droughts occur at inexact, but few year, intervals. The grazing by free ranging bison, the indi...
We measured vegetation cover and grasshopper densities on 50 plots in an ungrazed Arizona grassland between 1984 and 1989. A 1987 wildfire completely burned 22 of the plots, reducing grass cover and increasing bare ground and herb cover for 2 postfire growing seasons. Combined adult and nymph grasshopper densities declined over 60% on burned plots...
Bird species densities were determined for summer and winter on 132 study plots grouped into 25 riparian habitats in or near the Huachuca Mountains of southeastern Arizona. The habitats were defined based on the dominant riparian tree species, the size of the riparian stand, and the type of adjacent upland vegetation. Vegetation characteristics and...
Grasshopper densities were compared between grazed and ungrazed semidesert grassland sites in southeastern Arizona. Bouteloua-dominated perennial grass cover was about 1.5 times greater on the livestock exclosure. Grasshoppers were 3.7 times more abundant on the protected area in the summers of 1983 and 1984, when dominant species were grass-feedin...
The riparian Arizona sycamore is failing to reproduce in certain canyons where mature, seed-producing trees occur. Flash flooding events in some canyons washed out the seedlings and saplings present, but left viable larger trees. A permanent, high water table was essential to propagule survival. -from Authors
Distribution and local abundance of 62 landbird species were measured in winter across an elevational gradient in the Huachuca Mountains of southeastern Arizona. The number of 35-m radius plots and the number of habitats occupied by the species were positively correlated with their average abundances within occupied plots and habitats. Common speci...
This research focused on the behavior of populations of the shrub, Baccharis pteronioides D.C. (Asteraceae: Astereae), that were protected from browsing by domestic cattle. Livestock were removed from the Research Ranch (3160 ha) in 1968. Data on plant density, fire resistance and browsing pressure were collected in 1982 and 1983 from paired plots...
Used Audubon Society Christmas bird counts to compute fine-scale measures of average within-range abundance, and 1) compared these for the narrowly distributed vs. widely distributed endemic forms, and 2) correlated range size and within-range abundance (as measured using nonzero counts only) for both the endemics for all 65 species. -from Authors
the conservation and management practices impinging on the welfare of this species, and to further the A.O.U.'s interest in providing scientific advice and suggestions to managers of threatened and endangered species of birds. SUMMARY
The southern African Eragrostis has been used extensively in revegetating SW US rangelands. In SE Arizona the native grassland community included a significantly greater variety and abundance of indigenous grasses, herbs, shrubs, grasshoppers, rodents and birds. Seeding the exotic species is a less desirable land management alternative than giving...
The fires were largely restricted to surface fuels and forest understory vegetation. Effects upon understory shrubs and deciduous trees were modest. Cool-season (autumn and spring) fires consistently reduced densities of Ribes spp. and stimulated Amorpha canescens, while other shrubs were unaffected. These burns significantly reduced the density of...
Livestock have been excluded from a 3,160-ha range in southeastern Arizona since 1968. Compared to an adjacent continuously grazed area, in 1981-82 a protected upland site supported 45% more grass cover, a comparatively heterogeneous grass community, and 4 times as many shrubs. Grama grasses (Bouteloua spp.) were equally common in and outside the e...
Using Christmas Bird Count data, compared range sizes and within-range abundance of 70 species of apodiform, piciform, and passerine landbirds whose ranges are 75% or more restricted in winter to the contiguous US and S Canada. Geography was a powerful predictor of the species' positions in a 2-dimensional space defined by the axes of range size an...
Analysis, using Audubon Society Christmas bird counts, suggests that a positive correlation between geographical range and local abundance may be an inherent property of most groups of species. The North American winter bird assemblage is dominated by widespread species that have very large total population sizes, and that are relatively abundant l...
This study describes biogeograhic patterns of Amphibia and Reptilia in the State of Illinois, USA, using numerical taxonomic methods. The 102 Illinois counties were characterized by the presence vs. absence of amphibian and reptilian species, and by their vegetation, climate and drainage patterns. The counties then served as Operational Taxonomic U...
Acorn woodpeckers (Melanerpes formicivorus) in southeastern Arizona exhibited two different types of social organization: one of highly cooperative and resident groups
and another of birds that migrated and formed only temporary male-female pairs during reproduction. The occurrence of both
patterns in the same population indicates a high degree of...
Winter distribution and abundance patterns were generated for 65 species of fringillid songbirds, using results of 2,732 Christmas bird counts grouped into 59 latitude-longitude blocks. Similarity coefficients were computed among the blocks, based upon the species occurring in each block and their abundances. Similarity matrices were subjected to c...
(1) Approximately 15 000 ha of mixed coniferous forest in the northern Sierra Nevada of California were burned during the Donner Ridge Fire in 1960. (2) Two areas were compared in the burnt forest that had received different management: one area was planted with Pinus jeffreyi Grev. and Balf. and sprayed with 2,4,5-T for shrub control; the other ar...
We studied the impact of fire on an ungrazed sacaton grassland community at The Research Ranch in southeastern Arizona. Two summer burns were followed through two post-fire growing seasons. A winter burn was studied through one post-fire growing season. Burning reduced the height and extent of sacaton grass (Sporobolus wrightii) itself, and stimula...
This study examines the abundance patterns of some land bird species which winter across the North American Great Plains. Data taken from Audubon Society Christmas bird counts permit the mapping not only of species' distributions but also of their abundance patterns within those limits. Results of the analysis of seventy-seven species suggest that...
Audubon Society Christmas count data indicate that between 1962 and 1971 the North American blue jay population (Cyanocitta cristata) increased about 30%, and that migration of this species declined. The most likely cause was the increase in winter feeding by man. Results of this study suggest that winter food supplies and overwinter survival are (...
Analysis of Audubon Society Christmas-count data (1962-1971) revealed a generally synchronous pattern of winter eruptions between eight species of seed-eating birds whose winter ranges normally include boreal forests. Species and populations occupying montane conifer forests in the West did not fit this pattern as well. Literature analysis revealed...
The distribution, ecology and evolution of the three-toed woodpeckers (Picoides) is given a new explanation resolving certain biogeographical paradoxes. One species, Picoides tridactylus, is circumboreally distributed with spruce (Picea), while the other species, P. arcticus, is a larger bird adapted to and distributed with North American closed bo...
Fire was a common prehistoric disturbance in most southwestern grasslands, oak savannas, and coniferous forests, but not in Sonoran and Mojave desertscrub, or in riparian ecosystems. Prescribed burning should be applied, but under experimental conditions that facili-tate studying its impacts on birds and other components of biodiversity. Fire plays...
Citations
... The Sonoita Plain (696 km 2 ) lies in a predominantly semiarid grassland located in northwestern Santa Cruz County, Arizona, USA (31°32′44ʺN, 110°28′44ʺW). The Sonoita Plain is surrounded by the Santa Rita Mountains to the west, the Huachuca Mountains to the south-east, the Empire Mountains to the north, the Whetstone Mountains to the northeast and the Canelo Hills to the south ( The Sonoita Plain is acknowledged to be a prime example of high plain southwestern grassland [90]. It is largely characterized by desert grassland, plains grassland and desert scrub communities (501 km 2 /72% of study area), with some riparian forest and riparian woodland communities along Cienega Creek in the northern part of the study area (22 km 2 /3% of study area) [91]. ...
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... Even with this large population, no evidence of food and space limitations for the establishment of colonies was found, whereas the population growth continued in exponential tendency (Krebs et al. 1994). The exponential growth tendency of Cattle Egret populations was also observed in other areas of the American Continent (Baillie 1963, Bock and Lepthien 1976, Larson 1982, including insular environments (Arendt 1988, Krebs et al. 1994. But only Bock and Lepthien (1976), in their study on Bubulcus ibis in Florida from 1956 to 1971, calculated the growth rate (r = 0.21) of the population. ...
... We conducted nest monitoring and radio-telemetry tracking of adult and fledgling birds at two sites in the NGP, one in western North Dakota (2015Dakota ( -2018 and the other in northeastern Montana (2016Montana ( -2018. Broadly, we hypothesized that there would be variation in rates and drivers among life-history phases, as there are potential differences in predation pressure, vegetation structural requirements, and sensitivity to climate exposure across these stages (Jones and Bock 2005, Low et al. 2010, McCauley et al. 2017, Zuckerberg et al. 2018. We predicted that, overall, greater within-season precipitation would result in more productive range conditions (Barnett and Facey 2016), and thus higher survival across all stages (Conrey et al. 2016), despite some negative effects of extreme precipitation events (Carver et al. 2017). ...
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... Grazing by domestic animals appears almost always to increase the amount of bare ground and herbaceous and woody dicots while reducing grass cover (c. , J. Bock and C. Bock 1989Bock , 1989 Lewis 1989). ...
... But inter-and intraspecific competition and other ecological interactions, whether direct or indirect, can lead to a mismatch between selection or density and what we understand as a species' optimal habitat (Van Horne 1983, Ginger et al. 2003, Cheeseman et al. 2018, Reif et al. 2018. In these instances, using direct indicators of fitness (i.e., survival) leads to more accurate inferences of habitat quality (Bock andJones 2004, Johnson 2007). ...
... All these features make them useful indicators for habitat degradation and for ecosystem management (e.g. Illich and Haslett, 1994;Baldi and Kisbenedek, 1997;Andersen et al., 2001;Bock et al., 2006;Davidson and Lightfoot, 2007). Grasshoppers have already been the object of biogeographical analysis (e.g. ...
... Biogeography. The distribution of this skipper is centered in the western Great Plains, or High Plains, a vast region subject to prolonged drought, wildfire, and herbivory (Bock et al., 1991). Populations also exist in suitable habitats in the southern Rocky Mountains mainly east of the Continental Divide, and across the northern edge of the Mogollon Rim in north-central Arizona. ...
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... However, if factors influencing nest placement or initiation decisions differ from those affecting nest survival, then management recommendations based on survival alone may be inadequate or even inappropriate. Conditions promoting high nest densities could have greater influence on population-level productivity than conditions associated with individual nest survival [14]. ...
... In the pure patches of the Xaltatempa river, young plants of the previously mentioned arboreal species are found in greater percentages (Table 2). Bock and Bock (1989) pointed out that some species in gallery forests often act as pioneers. This is the case of Platanus wrightii, which despite having a high seedling production, also has a high mortality percentage due to desiccation, together with the loss of renewal during the floods. ...
... Within the Great Plains region, tallgrass prairie ecosystems contain many drought-tolerant grass species (Tucker et al. 2011). Native tallgrass prairies of the US Great Plains were once the dominant ecosystem (Bock and Bock 1998), but anthropogenic encroachment has resulted in a drastic reduction in land area, such that only about 1 % of the original tallgrass prairie remains (Cully et al. 2003). As periods of drought become more recurrent, plants in both natural and agricultural systems will need to adapt to survive. ...
