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Residues in common flicker and mountain bluebird eggs one year after a DDT application
Common flicker ( Colaptes auratus ) and mountain bluebird ( Sialia currucoides ) eggs were examined 1 year after DDT application and showed a marked difference. Residue levels in mountain bluebird eggs were approximately 10 times higher than in common flicker eggs (5.29 to 0.58 ppm wet weight). These differences can be explained by disparate dietary habits. The mean level in American kestrel ( Falco sparverius) eggs collected in the spray area at the same time was 6.42 ppm wet weight.
Cooperation and competition: nepotistic tolerance and intrasexual aggression in western bluebird winter groups
Two hypothesized benefits of delayed dispersal are access to resources and prolonged brood care (or??parental nepotism). Resource abundance (mistletoe wealth) is a key factor influencing whether sons stay home in western bluebirds, Sialia mexicana, but nepotism is also observed. Western bluebird sons commonly remain in their family groups throughout the winter, whereas daughters usually disperse before winter. Because pairing often takes place in winter groups, with newly formed pairs settling on exclusive all-purpose territories in spring, selection for sexual competition and nepotism co-occur and may simultaneously influence patterns of aggression within groups. We measured aggression at mealworm feeder stations, finding evidence of (1) intrasexual aggression against unrelated group members by experienced breeders of both sexes and (2) nepotism towards sons and daughters by experienced breeder females but not by experienced breeder males. Females showed much higher levels of aggression towards same-sex immigrants than males did. Experienced breeder males did not evict their sons from the natal territory, but they were 12 times more aggressive towards sons than breeder females were towards daughters. They were also equally aggressive towards sons and immigrant males, suggesting that local breeding competition and the benefits of intrasexual dominance counter the benefits of paternal nepotism towards sons. ?? 2009 The Association for the Study of Animal Behaviour.
Oak mistletoe ( Phoradendron villosum ) is linked to microhabitat availability and avian diversity in Oregon white oak ( Quercus garryana ) woodlands
Mistletoes are parasitic or hemi-parasitic flowering plants that parasitize woody plants around the globe. Important food and cover resources provided by mistletoes have been related to strong patterns of positive association between wildlife diversity and mistletoe density. Mistletoes also create microhabitat features known to be important to wildlife by causing deformations in their host trees. However, links between availability of mistletoe-formed microhabitat and wildlife diversity has not been well studied. We investigated this relationship by quantifying microhabitat features and avian abundance and diversity related to infection by Oak Mistletoe (Phoradendron villosum) in Oregon White Oak (Quercus garryana). Q. garryana woodlands support several avian species of conservation concern, so an understanding of the influence of mistletoe on wildlife habitat is critical. Our results suggest that 1) structural heterogeneity within tree crowns; 2) avian species richness and abundance are positively associated with mistletoe load; and 3) P. villosum fruit, available is an important food for western bluebird (Sialia mexicana) and other wildlife in late autumn and early winter. If a goal of restoration is to maintain habitat for oak-associated bird species, managers should consider the retention of some oaks hosting mistletoe.
Monitoring breeding and migration of neotropical migratory birds at Naval Base Coronado, Remote Training Site, Warner Springs, San Diego County, California, 5-year summary, 2013–17
We operated a bird banding station on the Naval Base Coronado, Remote Training Site, Warner Springs (RTSWS), in northeastern San Diego County, California, during the bird breeding season (spring/summer) from 2013 to 2017 and during migration (fall) from 2013 to 2016. The station was established in spring 2013 as part of the Monitoring Avian Productivity and Survivorship (MAPS) program and continued into the fall for the first 4 years as part of a long-term monitoring program for neotropical migratory birds. We captured 705 individuals of 58 species during the MAPS/breeding season from 2013 to 2017 (12–13 days each year in April through August), 79 percent of which were newly banded during the MAPS season (555), 8 percent of which were recaptures banded in previous years (57), and 13 percent of which we released unbanded (64 hummingbirds and 29 other birds that were released or escaped prior to banding). Sixty individuals were captured more than once within a year during MAPS. Bird capture rate averaged 19 ± 1 captures per 100 net-hours (range 17–20) across 5 years. Annual species richness ranged from 28 (2017) to 42 (2014). The average species richness per day was highest in 2014 (9 ± 3) and lowest in 2016 (6 ± 2). Bushtit ( Psaltriparus minimus ) was the most abundant breeding species captured, followed by Spotted Towhee ( Pipilo maculatus ), Oak Titmouse ( Baeolophus inornatus ), Anna’s Hummingbird ( Calypte anna ), House Wren ( Troglodytes aedon ), Ash-throated Flycatcher ( Myiarchus cinerascens ), California Scrub-jay ( Aphelocoma californica ), Bewick’s Wren ( Thryomanes bewickii ), Acorn Woodpecker ( Melanerpes formicivorus ), California Towhee ( Melozone crissalis ), and Western Bluebird ( Sialia mexicana ). Each of these 11 breeding species accounted for at least 5 percent of captures in any 1 year. Fifty-seven percent of known-sex captures were female and 43 percent were male. Thirty-three percent of known-age captures were juveniles. Peaks in number of birds captured were in the first and last weeks of April, and the greatest number of species was captured in early May.
Exposure pathways and biological receptors: baseline data for the canyon uranium mine, Coconino County, Arizona
Recent restrictions on uranium mining within the Grand Canyon watershed have drawn attention to scientific data gaps in evaluating the possible effects of ore extraction to human populations as well as wildlife communities in the area. Tissue contaminant concentrations, one of the most basic data requirements to determine exposure, are not available for biota from any historical or active uranium mines in the region. The Canyon Uranium Mine is under development, providing a unique opportunity to characterize concentrations of uranium and other trace elements, as well as radiation levels in biota, found in the vicinity of the mine before ore extraction begins. Our study objectives were to identify contaminants of potential concern and critical contaminant exposure pathways for ecological receptors; conduct biological surveys to understand the local food web and refine the list of target species (ecological receptors) for contaminant analysis; and collect target species for contaminant analysis prior to the initiation of active mining. Contaminants of potential concern were identified as arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, thallium, uranium, and zinc for chemical toxicity and uranium and associated radionuclides for radiation. The conceptual exposure model identified ingestion, inhalation, absorption, and dietary transfer (bioaccumulation or bioconcentration) as critical contaminant exposure pathways. The biological survey of plants, invertebrates, amphibians, reptiles, birds, and small mammals is the first to document and provide ecological information on .200 species in and around the mine site; this study also provides critical baseline information about the local food web. Most of the species documented at the mine are common to ponderosa pine Pinus ponderosa and pinyon–juniper Pinus–Juniperus spp. forests in northern Arizona and are not considered to have special conservation status by state or federal agencies; exceptions are the locally endemic Tusayan flameflower Phemeranthus validulus, the long-legged bat Myotis volans, and the Arizona bat Myotis occultus. The most common vertebrate species identified at the mine site included the Mexican spadefoot toad Spea multiplicata, plateau fence lizard Sceloporus tristichus, violetgreen swallow Tachycineta thalassina, pygmy nuthatch Sitta pygmaea, purple martin Progne subis, western bluebird Sialia mexicana, deermouse Peromyscus maniculatus, valley pocket gopher Thomomys bottae, cliff chipmunk Tamias dorsalis, black-tailed jackrabbit Lepus californicus, mule deer Odocoileus hemionus, and elk Cervus canadensis. A limited number of the most common species were collected for contaminant analysis to establish baseline contaminant and radiological concentrations prior to ore extraction. These empirical baseline data will help validate contaminant exposure pathways and potential threats from contaminant exposures to ecological receptors. Resource managers will also be able to use these data to determine the extent to which local species are exposed to chemical and radiation contamination once the mine is operational and producing ore. More broadly, these data could inform resource management decisions on mitigating chemical and radiation exposure of biota at high-grade uranium breccia pipes throughout the Grand Canyon watershed.
Eggshell thickness and egg morphometrics in five songbird species from the Central Valley, California
Avian eggshell thickness is an important life history metric in birds and has broad applications across disciplines ranging from animal behavior to toxicology. Empirical eggshell thickness values for songbirds (Order Passeriformes) are under-represented in the literature due to the difficulty of measuring smaller eggs using traditional methods. We used a Hall-effect thickness gauge to measure eggs of five focal songbird species from California’s Central Valley: House Wren ( Troglodytes aedon ; n = 567), Tree Swallow ( Tachycineta bicolor ; n = 297), Ash-throated Flycatcher ( Myiarchus cinerascens ; n = 21), Western Bluebird ( Sialia mexicana ; n = 13), and Bewick’s Wren ( Thryomanes bewickii ; n = 5). We compared minimum eggshell thickness measurements at the equator and sharp pole, and we related eggshell thickness to other egg morphometrics and adult body mass. Eggshell thickness at the equator was 5.6% thicker in Ash-throated Flycatchers and 3.5% thinner in Tree Swallows compared with eggshell thickness at the sharp pole. Among species, eggshell thickness at the sharp pole was greater in species with larger eggs, whereas, within species, larger eggs were thinner at the sharp pole. Eggshells were 8% and 11% thinner in late incubation eggs (≥75% of total incubation duration) than early incubation (≤10% of total incubation duration) for House Wren and Tree Swallow eggs, respectively. Whenever possible, it is preferable to use empirical eggshell thickness data that are specific to the species and geographic region being studied, and a relatively new method used in this study allows accurate measurement of small eggs without having to compromise the integrity of preserved eggshell specimens.
Recent population trends of the eastern bluebird
North American Breeding Bird Survey data for the period 1966-1987 indicate that Eastern Bluebird (Sialia sialis) populations declined during the 1970s, primarily in association with either severe winters or severe spring storms. In recent years, bluebird populations have increased to levels similar to those observed during the first year (1966) of the survey. Survey results suggest that climate has an important role in affecting short-term population declines in bluebirds.
Artificial cavities enhance breeding bird densities in managed cottonwood forests
The paucity of natural cavities within short-rotation hardwood agroforests restricts occupancy by cavity-nesting birds. However, providing 1.6 artificial nesting cavities (nest boxes)/ha within 3- to 10-year-old managed cottonwood forests in the Mississippi Alluvial Valley increased territory density of cavity-nesting birds. Differences in territory densities between forests with and without nest boxes increased as stands aged. Seven bird species initiated 38 nests in 173 boxes during 1997 and 39 nests in 172 boxes during 1998. Prothonotary warblers (Protonotaria citrea) and eastern bluebirds (Sialia sialis) accounted for 67% of nests; nearly all warbler nests were in 1.8-L, plastic-coated cardboard (paper) boxes, whereas bluebird nests were divided between paper boxes and 3.5-L wooden boxes. Larger-volume (16.5-L) wooden nest boxes were used by eastern screech owls (Otus asio) and great crested flycatchers (Myiarchus crinitus), but this box type often was usurped by honey bees (Apis mellifera). To enhance territory densities of cavity-nesting birds in cottonwood agroforests, we recommend placement of plastic-coated paper nest boxes, at a density of 0.5/ha, after trees are >4 years old but at least 2 years before anticipated timber harvest.
Breeding dispersal of Eastern Bluebirds depends on nesting success but not on removal of old nests: An experimental study
One hypothesis to explain both within-and between-season breeding dispersal is that individuals move in response to degradation in the suitability and/or quality of their nesting sites. This hypothesis was experimentally examined by manipulating the suitability and/or quality of nesting boxes used by Eastern Bluebirds (Sialia sialis) on one study site in upstate South Carolina. From 12 randomly assigned boxes, old nests, parasites, dead nestlings, old food or feces were not removed, as they were from 12 other randomly assigned boxes. There were 24 nesting attempts in cleaned boxes; 26 in not-cleaned boxes. Third brood nesting attempts occurred in only one of the cleaned boxes but in five of the not-cleaned boxes. Only 59% of individuals stayed to breed again within the season in not-cleaned boxes, whereas 72% stayed in cleaned boxes. Equal numbers of both males and females returned to breed in cleaned and not-cleaned boxes during the next breeding season, however. Both within-and between-season breeding dispersal is significantly more likely after unsuccessful nesting attempts than successful nesting attempts. There was no significant effect of cleaning or not cleaning nesting boxes on the chance of nesting attempts or the numbers of nestlings fledged from nesting boxes.
Comparative habitat use in a juniper woodland bird community
We compared vegetation structure used by 14 bird species during the 1998 and 1999 breeding seasons to determine what habitat features best accounted for habitat division and community organization in Utah juniper (Juniperus osteosperma) woodlands of southwestern Wyoming. Habitat use was quantified by measuring 24 habitat variables in 461 bird-centered quadrats, each 0.04 ha in size. Using discriminant function analysis, we differentiated between habitat used by 14 bird species along 3 habitat dimensions: (1) variation in shrub cover, overstory juniper cover, mature tree density, understory height, and decadent tree density; (2) a gradient composed of elevation and forb cover; and (3) variation in grass cover, tree height, seedling/sapling cover, and bare ground/rock cover. Of 14 species considered, 9 exhibited substantial habitat partitioning: Mourning Dove (Zenaida macroura), Bewick's Wren (Thryomanes bewickii), Blue-gray Gnatcatcher (Polioptila caerulea), Mountain Bluebird (Sialia currucoides), Plumbeous Vireo (Vireo plumbeus), Green-tailed Towhee (Pipilo chlorurus), Brewer's Sparrow (Spizella breweri), Dark-eyed Junco (Junco hyemalis), and Cassin's Finch (Carpodacus cassinii). Our results indicate juniper bird communities of southwestern Wyoming are organized along a 3-dimensional habitat gradient composed of woodland maturity, elevation, and juniper recruitment. Because juniper birds partition habitat along successional and altitudinal gradients, indiscriminate woodland clearing as well as continued fire suppression will alter species composition. Restoration efforts should ensure that all successional stages of juniper woodland are present on the landscape.
[Book review] Bluebird, what do you eat? by E.L Beal
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New perspectives on threats to cavity nesting birds
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