Brad Bergstrom | Valdosta State University (original) (raw)

Papers by Brad Bergstrom

Journal of Avian Biology, 2008

To assess regression models for lipid and lean body mass in small birds, we recorded live body ma... more To assess regression models for lipid and lean body mass in small birds, we recorded live body mass ±0.1 g, total body electrical conductivity (TOBEC; from “third generation” TOBEC machine EM-SCAN® SA-3000) or E-Value, visual fat score (VisFat), and seven body measurements for 52 migratory passerine birds of 13 species (5–40 g). We determined lipid and lean mass of each bird after petroleum-ether extraction of lipids. We obtained “net”E-Value (NEV) for each scanned bird by subtracting the E-Value of the empty bird-restraining tube, because these showed an inverse temperature dependence (P<0.005). Leave-one-out cross validation was used to assess model selection and construct 95% confidence intervals. Although precision of TOBEC increased with bird size (CV of NEV vs. live mass: r=−0.276, P=0.002) and it explained an increasing proportion of variation in lean mass moving from small- to medium- to large-bird classes of our data, it did no better than head length in single-variable prediction of lean or lipid mass and was included in five of the 14 multivariate models we developed. The best multiple regression to predict lean mass included live weight, VisFat, bill length, tarsus and lnNEV (adjusted R2=99.0%); however, the same model lacking only lnNEV yielded aR2=98.9%. A parallel to the above pair of models, but predicting lipid mass, yielded aR2=90.3% and 90.0%, respectively. Subdividing the data by three size classes and three taxa (American redstart Setophaga ruticilla, ovenbird Seiurus aurocapilla, warblers), best-subset multiple-regression models predicted lean mass with aR2 from 94.7 to 99.6% and lipid mass with aR2 from 85.4 to 98.3%. Best models for the size- and species-groups included VisFat and zero to five body measurements, and most included live weight. lnNEV was included only in the models for ovenbird (lipid), warblers (lipid), all birds (both), and large birds (both). Actual lipid mass of all birds was more highly correlated with multiple-regression-predicted lipid mass (r=0.955) than with visual subcutaneous fat-scoring (r=0.683). These multiple-regression models predicting lipid content using live-bird measurements and visual fat score as independent variables represent more accurate and precise estimates of actual lipid content in small passerines than any previously published. They are particularly accurate for placing birds into percentage body-fat classes.

Effects of habitat, season, and age on winter fat storage by migrant and resident birds in Jamaica

Journal of Field Ornithology

Ecosphere

Large mammalian herbivores (LMH) are known to suppress populations of small mammals in African sa... more Large mammalian herbivores (LMH) are known to suppress populations of small mammals in African savanna ecosystems; whether this suppression is driven by depletion of nutrients and food resources, or of cover, is poorly understood. Cattle management creates scattered, persistent, nutrientenriched areas (glades). Similarly, prescribed fire may enhance forage nutrition of burned patches. Both enriched microhabitats attract wild and domestic LMH and are fertilized by their wastes, but removal of vegetative cover by LMH or fire may negate the benefits of enhanced nutrition to risk-averse small-mammal species or individuals. We used replicated LMH exclusion experiments on red sandy loam and black-cotton clay soils, and a multi-scale burn experiment on black cotton to examine abundance, diversity, and biomass of small mammals across sites varying in vegetation cover and enrichment. Small-mammal species composition varied dramatically among habitats. Species diversity and density on red sands were roughly double that of black cotton soils. Small-mammal densities and diversity were dramatically greater inside LMH exclosures; maximal densities occurred inside fenced, nutrient-rich, tall-grass glades. Small-mammal density was similar between black-cotton burn sites and unburned matrix habitat but was significantly greater on unburned than burned patches within the burn sites. Burned patches contained less grassy cover up to 50 months post-burn, although vegetation differences diminished following significant rains. Mice captured on burned patches traveled farther but were not heavier than mice captured on unburned patches. Small mammals were nearly 20-fold more abundant on totally fenced glades than matrix habitat on both soils and ninefold more abundant on fenced bushland (non-glades) on red sands. Unfenced glades supported intermediate densities in black cotton but lower densities in red sands because of close cropping by LMH. Total small-mammal biomass tended to be greater on red sands (though mean body mass was greater on black cotton for two common species), within exclosures, and on glades. Both the grass rat and pouched mouse reached maximal densities within glade LMH exclosures on both soils. This and the positive association of small-mammal densities with grass height and dead-stem density suggest loss of cover is a primary driver of large-herbivore suppression of certain savanna small mammals.

Bats as Predominant Food Items of Nesting Barred Owls

Southeastern Naturalist

Journal of Mammalogy

For 90 years, the American Society of Mammalogists (ASM) has made science-based challenges to wid... more For 90 years, the American Society of Mammalogists (ASM) has made science-based challenges to widespread lethal control of native mammals, particularly by the United States federal government targeting carnivores in the western states. A consensus is emerging among ecologists that extirpated, depleted, and destabilized populations of large predators are negatively affecting the biodiversity and resilience of ecosystems. This Special Feature developed from a thematic session on predator control at ASM's 2013 annual meeting, and in it we present data and arguments from the perspectives of ecology, wildlife biology and management, social science, ethics, and law and policy showing that nonlethal methods of preventing depredation of livestock by large carnivores may be more effective, more defensible on ecological, legal, and wildlife-policy grounds, and more tolerated by society than lethal methods, and that total mortality rates for a large carnivore may be driven higher than previously assumed by human causes that are often underestimated.

Review of "Handbook of mammals of the south-central states

Journal of Wildlife Management, 1997

Wolf recovery: a response to Mech

The Wildlife Professional, Jun 1, 2014

Southeastern Naturalist, 2008

We characterized the tree community of a mesic hardwood hammock in south-central Georgia as an oa... more We characterized the tree community of a mesic hardwood hammock in south-central Georgia as an oak-pine-hickory forest, with Liquidambar styracifl ua (Sweetgum), Magnolia grandifl ora (Southern Magnolia), and Ilex opaca Ait. (American Holly) as subdominants. We surveyed this forest for colonies of the most northerly distributed epiphytic orchid in the Western Hemisphere, Epidendrum magnoliae (Green Fly Orchid), and recorded the species and trunk diameter of 112 host trees (phorophytes) as well as the height and size of each orchid colony. We calculated a selectivity index (SI) to compare phorophyte frequency with availability, based on a point-transect survey. Green Fly Orchid occurred on 8 species of hardwood trees, but had a strong preference for Southern Magnolia as a host and a moderately strong preference for Quercus virginiana (Live Oak). Host trees were much larger (presumably older) than the average of available trees, and that effect was strongest for the most preferred host. Orchid colonies also occupied signifi cantly greater areas on individual Southern Magnolia than on other phorophytes. It is likely that old-growth Southern Magnolia and Live Oak trees are critical to the viability of this population of Green Fly Orchid, which is rare in inland forests in Georgia. In addition to being the most persistent epiphyte substrates in this environment, their broadleaf evergreen canopies-which would be especially true of Southern Magnolia -may provide the most favorable microclimates in terms of shade, humidity, and frost protection.

Distribution and Diagnosis of Three Species of Chipmunks (Tamias) in the Front Range of Colorado

The Southwestern Naturalist, 1991

Endangered Wolves Fall Prey to Politics

Science, 2011

Handbook of Mammals of the South-Central States

Journal of Mammalogy, 1995

... in the United States of America First printing 03 02 01 00 99 98 97 96 95 94 5 4 3 2 1 Design... more ... in the United States of America First printing 03 02 01 00 99 98 97 96 95 94 5 4 3 2 1 Designer: Bob Nance Typeface: ITC ... Cataloging-in-Publication Data Choate, Jerry R. Handbook of mammals of the south-central states /Jerry R. Choate, J. Knox Jones, Jr., and Clyde Jones, p ...

Journal of Mammalogy, 2004

Adult hispid cotton rats (Sigmodon hispidus) were collected from the field monthly for .2 years f... more Adult hispid cotton rats (Sigmodon hispidus) were collected from the field monthly for .2 years from populations near the northern edge of their range in Virginia and contemporaneously from south-central Georgia. Body measurements and weights were taken at capture, and after dissection embryos, corpora lutea, and placental scars were counted and measured; testes and seminal vesicles were dissected out, measured, and weighed. This allowed comparison of several life-history parameters between the populations and tests of several life-history hypotheses. The breeding season was up to 2 months longer in Georgia than in Virginia, where there was typically a 3-month or longer winter inactive period. Some reproductive activity was observed among Georgia females in all 12 calendar months, whereas pregnancies were never observed in Virginia during November-February. Average litter sizes were significantly higher in Virginia (5.91 6 1.41, up to 13) than in Georgia (5.16 6 1.79, up to 9); this difference may partly result from a higher incidence of embryo resorption and prenatal mortality in the Georgia population, primarily in the cooler 6 months of the year. Virginia rats averaged significantly smaller for both sexes, but this was likely the result of a younger age distribution. Among reproductive males and females, no body-size differences were found between populations except that pregnant females from Virginia averaged significantly longer. Fifty percent and 75% of the random sample of adult females and males, respectively, were reproductively active in Georgia, whereas only 35% and 40% were reproductively active in Virginia. Spermatogenically active males in Virginia had significantly greater relative gonadal mass than their Georgia counterparts. Overwinter survival of parous females was lower in Virginia. Virginia populations, in a more seasonal environment, displayed a more r-selected life history, with greater reproductive allocation, faster growth (except over winter), higher mortality, and less iteroparity.

Would East African savanna rodents inhibit woody encroachment? Evidence from stable isotopes and microhistological analysis of feces

Journal of Mammalogy, 2013

Journal of Mammalogy, 1988

License to Kill: Reforming Federal Wildlife Control to Restore Biodiversity and Ecosystem Function

Conservation Letters, 2014

For more than 100 years, the US government has conducted lethal control of native wildlife, to be... more For more than 100 years, the US government has conducted lethal control of native wildlife, to benefit livestock producers and to enhance game populations, especially in the western states. Since 2000, Wildlife Services (WS), an agency of the US Department of Agriculture, has killed 2 million native mammals, predominantly 20 species of carnivores, beavers, and several species of ground-dwelling squirrels, but also many nontarget species. Many are important species in their native ecosystems (e.g., ecosystem engineers such as prairie dogs and beavers, and apex predators such as gray wolves). Reducing their populations, locally or globally, risks cascading negative consequences including impoverishment of biodiversity, loss of resilience to biotic invasions, destabilization of populations at lower trophic levels, and loss of many ecosystem services that benefit human society directly and indirectly. Lethal predator control is not effective at reducing depredation in the long term. Instead, we recommend that WS and its government partners involved in wildlife conflict management emphasize training livestock producers in methods of nonlethal control, with sparing use of lethal control by methods that are species-specific, and cease all lethal control in federal wilderness areas and for the purpose of enhancing populations of common game species.

An analysis of multiple captures in Permoyscus with a critique on methodology

Canadian Journal of Zoology, 1986

Multiple captures obtained in Sherman traps are reported for Peromyscus maniculatus (66 intraspec... more Multiple captures obtained in Sherman traps are reported for Peromyscus maniculatus (66 intraspecific, 6 interspecific) and P. difficilis (12 intraspecific, 4 interspecific) in Colorado. Multiple capture frequency in P. maniculatus. (3.53%) was higher than in P. difficilis (1.94%), which probably resulted from the greater weights of P. difficilis. Only one case of injury or death was noted in 84 multiple captures. Multiple captures occurred in traps in which the treadles were significantly less sensitive to tripping than traps that captured single mice, which suggested that pairs of mice did not enter the traps simultaneoulsy. Adult mice were disproportionatley sampled in single captures because of the insensitivity of the tripping mechanism. For the same reason, immature mice were disproportionately sampled in multiple captures. These trap-related biases can create spurious age and sex associations within multiple captures. Trap bias should be tested explicitly before attempting to...

Animal Conservation, 2006

REA dismissed the isolation of Z. h. preblei from conspecific populations, particularly Z. h. cam... more REA dismissed the isolation of Z. h. preblei from conspecific populations, particularly Z. h. campestris, as merely 160 km; yet, this 160-km swath of non-habitat separating the