Icterus Bullockii Research Articles

Revisiting the Baltimore-Bullock's Oriole hybrid zone reveals changing plumage colour in Bullock's Orioles.

Hybrid zones are dynamic areas where populations of two or more interbreeding species may change through an influx of novel genetic material resulting from hybridization or selection on standing genetic variation. Documenting changes in populations through time, however, is challenging because repeated samples are often missing or because long-term storage can affect trait morphologies, especially colour traits that may fade through time. We document a change in carotenoid-based orange breast feathers of Bullock's Orioles (Icterus bullockii) from the Great Plains hybrid zone, USA. Contemporary Bullock's Orioles are more orange than historic individuals from the same location sampled approximately 60 years ago. Spectrophotometry revealed that contemporary Bullock's Orioles resemble orange colour profiles of Baltimore Orioles (I. galbula), the species with which they hybridize. Fading or changes in diet hypotheses do not appear to explain the shift in colour we report for Bullock's Orioles. We propose that these changes in colour are facilitated through introgression with Baltimore Orioles, and favoured by females that choose brighter, more orange males. Our study highlights the long memory of natural history collections and how they offer new insights to the dynamic roll of hybrid zones in trait evolution between interacting species.

Vertebrate florivory of vascular epiphytes: the case of a bromeliad

The avoidance of vertebrate herbivory is thought to be one of the possible drivers for the evolution of epiphytism. Scarce literature suggests that epiphyte herbivory is mainly related to insect attack on reproductive structures. In a pine-oak forest we observed almost all inflorescences of an epiphytic bromeliad (Tillandsia carlos-hankii) with signs of florivory; the degree of damage suggested that vertebrate herbivores could be involved. To assess the intensity of vertebrate florivory damage we recorded the percentage of damaged individuals in a 500 m2 plots during two flowering seasons. To identify possible vertebrate herbivores, we installed 20 mixed capture stations, 10 photo-traps focused on bromeliads and analyzed stomach contents of captured vertebrates. Florivory was observed on 62% of individuals during the first flowering season and 77% on the second; and average one individual lost 41% of reproductive structures. Vertebrates associated with florivory were a bird, Icterus bullockii (Aves, Passeriformes, Icteridae), a squirrel Sciurus aureogaster (Mammalia, Rodentia, Sciuridae), and mice, Peromyscus gratus, P. levipes and P. aztecus (Mammalia, Rodentia, Cricetidae). Our results suggest that vascular epiphytes are used as opportunistic resources for small vertebrates during seasons when preferred resources are scarce.

Conditions on the Mexican moulting grounds influence feather colour and carotenoids in Bullock's orioles (Icterus bullockii)

Carotenoid‐based plumage coloration plays a critical role for both inter‐ and intrasexual communication. Habitat and diet during molt can have important consequences for the development of the ornamental signals used in these contexts. When molt occurs away from the breeding grounds (e.g., pre‐alternate molt on the wintering grounds, or stopover molt), discerning the influence of habitat and diet can be particularly important, as these effects may result in important carryover effects that influence territory acquisition or mate choice in subsequent seasons. Several species of songbirds in western North America, including the Bullock's oriole (Icterus bullockii), migrate from the breeding grounds to undergo a complete prebasic (post‐breeding) molt at a stopover site in the region affected by the Mexican monsoon climate pattern. This strategy appears to have evolved several times independently in response to the harsh, food‐limited late‐summer conditions in the arid West, which contrast strongly with the high productivity driven by heavy rains that is characteristic of the Mexican monsoon region. Within this region, individuals may be able to optimize plumage coloration by molting in favourable areas characterized by high resource abundance. We used stable isotope analysis (δ13C, δ15N) to ask whether the diet and molt habitat/location of Bullock's orioles influenced their expression of carotenoid‐based plumage coloration as well as plumage carotenoid content and composition. Bullock's orioles with lower feather δ15N values acquired more colorful plumage (orange‐shifted hue) but had feathers with lower total carotenoid concentration, lower zeaxanthin concentration, and marginally lower canthaxanthin and lutein concentration. Examining factors occurring throughout the annual cycle are critical for understanding evolutionary and ecological processes. Here, we demonstrate that conditions experienced during a stopover molt, occurring hundreds to thousands of kilometers from the breeding grounds, influence the production of ornamental plumage coloration, which may carryover to influence inter‐ and intrasexual signaling in subsequent seasons.

Rock wren transport in railroad boxcars

In 1956, and again in 1988, breeding pairs of rock wrens (Salpinctes obsoletus) were observed in Churchill, Manitoba, beyond their previously known breeding extent. It has been suggested that these and other vagrant rock wrens might have been accidentally transported in railroad boxcars. Alternative explanations include: 1) that rock wrens are prone to vagrancy during migration and dispersal, and 2) that the species is expanding its range via hydrographic or human-made corridors. I compiled northern and eastern vagrancy records from May 1898 through November 2015 for rock wrens and four other bird species with similar ranges. I calculated the distance of each sighting to the nearest railway and hydrographic features, compared these distances among species, and identified vagrant clusters. Rock wren vagrants were not significantly different from vagrants of lazuli buntings (Passerina amoena) or Bullock's orioles (Icterus bullockii) in their proximity to railways. Results suggest that vagrancy rates of rock wrens are similar to those of sage thrashers (Oreoscoptes montanus) and green-tailed towhees (Pipilo chlorurus), and vagrancy is likely driven by landscape factors rather than the use of railway corridors or accidental transport in freight cars. Proximity of vagrant rock wrens to lakes, reservoirs, rivers, and streams indicates that these and associated habitat features may act as travel and dispersal corridors.

Moult migration in Bullock’s orioles (Icterus bullockii) confirmed by geolocators and stable isotope analysis

In contrast to the majority of migratory songbirds in North America, which moult on or near their breeding grounds, the Bullock’s oriole (Icterus bullockii) is reported to stop during fall migration to moult en route to the wintering grounds. These birds seem to take advantage of food resources during the Mexican monsoon season in the Southwestern USA and Northwestern Mexico. We studied a population of Bullock’s orioles at the northern limit of their breeding range in Kamloops, British Columbia, Canada, using a combination of light-level geolocators and stable hydrogen isotope analysis. We found evidence that supports the existence of moult migration in this species, with geolocators indicating that all birds appeared to stay in the Mexican monsoon region for moult in an extended stopover period during fall migration. Feathers were isotopically enriched with deuterium compared to predicted breeding isotope values and were significantly more negative than winter-grown claws, confirming that moult occurred somewhere between the breeding and wintering grounds. Stable isotope data were consistent with complete prebasic stopover moult in adults and complete contour feather and variable tail feather moult in first-year orioles. Our results confirm that this northern population of Bullock’s orioles employs a moult migration strategy and highlight the usefulness of combining geolocator and stable isotope studies.

Population response to environmental productivity throughout the annual cycle in a migratory songbird

AbstractEnvironmental factors affect migratory animal populations in every phase of their annual cycle and have significant impacts on breeding success and survival. The Breeding Bird Survey provides a long‐term database for examining population trends in North American birds, allowing us to examine large‐scale environmental factors that influence population abundance. We examined plant productivity as measured by normalized difference vegetation index (NDVI) over a 24‐year period from 1983–2006 in bird conservation regions (BCRs) that overlapped Bullock's oriole (Icterus bullockii) breeding, moult, and wintering ranges to ask whether plant productivity in 1 year influences population abundance in the subsequent breeding season. Bullock's orioles have a moult‐migration strategy, with a stopover moult in the Mexican monsoon region, which necessitates examining each stationary phase of the bird's annual cycle to understand the impacts of environmental factors on population abundance. Our results show increased breeding abundance in three (Great Basin, Coastal California and Shortgrass Prairies) of the six BCRs in which the species breeds following years with high NDVI values. We did not detect a response of breeding abundance to high NDVI values in the previous year in either the moulting region or in their primary over‐wintering area in central Mexico. Our results demonstrate that large‐scale annual variation in primary productivity on the breeding grounds can have an impact on breeding abundance in the following season, but further studies on migratory connectivity and on ecological mechanisms during the non‐breeding seasons are needed to understand why we did not detect an influence of productivity during these periods.

Using Historical DNA to Characterize Hybridization Between Baltimore Orioles (Icterus galbula) and Bullock’s Orioles (I. bullockii)

ABSTRACT. Studies of genetic variation across hybrid zones have demonstrated that the evolutionary dynamics within them are often complicated. Using DNA extracted from toe pads of 701 individuals collected by Sibley and Short (1964) about 50 years ago from across the Icterus bullockii—I. galbula hybrid zone, we calculated mitochondrial cline shape parameters and compared them with plumage-based inferences of the hybrid-zone structure. Genetic and hybrid index score dines, estimated from populations collected along the Platte River in Nebraska, were both concordant (equal widths) and coincident (same center). More generally, the proportion of I. bullockii haplotypes within a sampling locality was strongly and significantly correlated with mean hybrid index scores across Colorado, Kansas, Nebraska, Oklahoma, and South Dakota. The relatively narrow width of the mitochondrial cline (328 km) indicates selection against hybridization, which may be mediated through differences in either molt and migration schedu...

A Seven-Year Comparison of Relative-Abundance and Distance-Sampling Methods

AbstractWe used data from statewide surveys of riparian birds in Utah, 1992–1998, to compare relative-abundance and distance-sampling methods. By generating relative-abundance indices with point-count methods and density with point-transect sampling methods, we examined whether the assumptions underlying each method were met during field surveys for four bird species (Brown-headed Cowbird [Molothrus ater], Bullock's Oriole [Icterus bullockii], Warbling Vireo [Vireo gilvus], and Yellow Warbler [Dendroica petechia]). Point-count methods failed to reasonably meet the fundamental assumption of constant proportionality, with estimated detectability varying 3- to 5-fold despite the use of widely accepted and well-standardized methods. Population trends based on relative abundance were subsequently unstable, often varying in both magnitude and direction with the survey plot radius used (25 m, 50 m, or unlimited distance). Distance-sampling methods appeared to meet critical assumptions, were robust to assumption violations, allowed methodological self-assessment, and were demonstrably efficient in a large-scale, multispecies survey setting. Our data show surveys of birds without estimations of detectability are likely biased because the assumption of constant proportionality is violated to a degree that precludes strict inference and may confound trend analyses.

A SEVEN-YEAR COMPARISON OF RELATIVE-ABUNDANCE AND DISTANCE-SAMPLING METHODS

Abstract We used data from statewide surveys of riparian birds in Utah, 1992–1998, to compare relative-abundance and distance-sampling methods. By generating relative-abundance indices with point-count methods and density with point-transect sampling methods, we examined whether the assumptions underlying each method were met during field surveys for four bird species (Brown-headed Cowbird [Molothrus ater], Bullock's Oriole [Icterus bullockii], Warbling Vireo [Vireo gilvus], and Yellow Warbler [Dendroica petechia]). Point-count methods failed to reasonably meet the fundamental assumption of constant proportionality, with estimated detectability varying 3- to 5-fold despite the use of widely accepted and well-standardized methods. Population trends based on relative abundance were subsequently unstable, often varying in both magnitude and direction with the survey plot radius used (25 m, 50 m, or unlimited distance). Distance-sampling methods appeared to meet critical assumptions, were robust to assumption...

A Survey of the Birds of Death Valley

In 1893, A. K. Fisher, a member of the Death Valley Expedition under Dr. C. Hart Merriam, reported 69 species of birds in the below-sea-level region of Death Valley, California. Not until 1917, however, did Dr. Joseph Grinnell and Joseph Dixon continue the study of the avifauna of Death Valley. Grinnell used the sea level contour as the boundary of his study area and in 1923 published a list of 120 species. He wrote that an analysis of his list (1923:45) shows a constituency by seasonal categories which is much different from that usually obtaining in local lists: the proportion of breeding species to casual visitants, transients and winter visitants is exceedingly small. He pointed out that 25 of the 120 species were casual visitors or vagrants, 45 were regular transients, 31 were winter visitors, and 9 were summer visitors. Of these only one, the Bullock Oriole (Icterus bullockii) was known to breed in the below-sea-level area.

Bullock's and Baltimore Orioles, Icterus bullockii and galbula, in Southwest Georgia

Bullock's and Baltimore Orioles, Icterus bullockii and galbula, in Southwest Georgia