Junco Hyemalis Research Articles

An acute handling challenge mobilizes glucose and free fatty acids in mountain Dark-eyed Juncos (Junco hyemalis oreganus)

Resource mobilization and reallocation is a major endpoint of the physiological response to acute challenges. However, energy metabolites have not been the focus of most field studies. Here, we characterized the glycemic and free fatty acid (FFA) response to an acute-handling challenge in a breeding, free-living, population of Mountain Dark-eyed Juncos ( Junco hyemalis oreganus) in Mono County, CA. Juncos ( n = 12) were trapped in seed-baited potter traps at Tioga Pass Meadow, coinciding with territory establishment and early nesting period. Blood samples were collected at 0, 15, and 30 min post-capture, and analysis showed Juncos mobilized both glucose and FFA in response to an acute handling challenge. Blood glucose levels were significantly higher than baseline at 15 min (42.6% increase) and 30 min post-capture (66.7% increase). FFA levels were also significantly higher than baseline at 15 min (29.2% increase) and 30 min post-capture (22% increase). We also measured morphometrics (e.g., wing chord length, tarsus length, etc.), fat, and mass for each individual to investigate the effects of body size and fat storage on energy mobilization using linear models. We found no significant effects of body size or fat and mass on FFA mobilization. However, body size had a significant effect on glucose mobilization, with larger individuals displaying a higher percent increase in glucose from baseline to 15 min. Additionally, we found an effect of sex on glucose mobilization, with males showing a higher percent increase in glucose from baseline to 15 min. These results suggest that energy mobilization capacity is influenced by body size and male Juncos may increase energy mobilization relative to females during the breeding season.

Digest: Morphological diversity in urban dark-eyed juncos.

Populations living in cities face challenges from these novel environments that are expected to drive evolutionary adaptation. Do separate populations of a species living in different cities show similar adaptations to the selection pressures imposed by urban environments? Diamant and Yeh (2024) address this question by comparing the morphological characteristics of dark-eyed juncos in 3 California cities to non-urban junco morphologies. They find that wing size is consistently smaller in more urbanized environments regardless of the population, but bill size tends to vary between urban populations.

Complex patterns of morphological diversity across multiple populations of an urban bird species.

Urbanization presents a natural evolutionary experiment because selection pressures in cities can be strongly mismatched with those found in species' historic habitats. However, some species have managed to adapt and even thrive in these novel conditions. When a species persists across multiple cities, a fundamental question arises: do we see similar traits evolve in similar novel environments? By testing if and how similar phenotypes emerge across multiple urban populations, we can begin to assess the predictability of population response to anthropogenic change. Here, we examine variation within and across multiple populations of a songbird, the dark-eyed junco (Junco hyemalis). We measured morphological variations in juncos across urban and nonurban populations in Southern California. We investigated whether the variations we observed were due to differences in environmental conditions across cities. Bill shape differed across urban populations; Los Angeles and Santa Barbara juncos had shorter, deeper bills than nonurban juncos, but San Diego juncos did not. On the other hand, wing length decreased with the built environment, regardless of the population. Southern Californian urban juncos exhibit both similarities and differences in morphological traits. Studying multiple urban populations can help us determine the predictability of phenotypic evolutionary responses to novel environments.

SERCA uncoupling may facilitate cold acclimation in dark-eyed juncos (Junco hyemalis) without regulation by sarcolipin or phospholamban.

Homeothermic endotherms defend their body temperature in cold environments using a number of behavioral and physiological mechanisms. Maintaining a stable body temperature primarily requires heat production through shivering (ST) or non-shivering thermogenesis (NST). Although the use of NST is well established in mammalian systems, the mechanisms and extent to which NST is used in birds is poorly understood. In mammals, one well-characterized mechanism of NST is through uncoupling of Ca2+ transport from ATP hydrolysis by sarco/endoplasmic reticulum ATPase (SERCA) in the skeletal muscle, which generates heat and may contribute to Ca2+ signaling for fatigue resistance and mitochondrial biogenesis. Two small proteins-sarcolipin (SLN) and phospholamban (PLN)-are known to regulate SERCA in mammals, but recent work shows inconsistent responses of SLN to cold-acclimation in birds. In this study, we measured SERCA uncoupling in the pectoralis flight muscle of control (18°C) and cold-acclimated (-8°C) dark-eyed juncos (Junco hyemalis) that exhibited suppressed SLN transcription in the cold. We measured SERCA activity and Ca2+ uptake rates for the first time in cold-acclimated birds and found greater SERCA uncoupling in the muscle of juncos in the cold. However, SERCA uncoupling was not related to SLN or PLN transcription or measures of mitochondrial biogenesis. Nonetheless, SERCA uncoupling reduced an individual's risk of hypothermia in the cold. Therefore, while SERCA uncoupling in the cold could be indicative of NST, it does not appear to be mediated by known regulatory proteins in these birds. These results prompt interesting questions about the significance of SLN and PLN in birds and the role of SERCA uncoupling in response to environmental conditions.

Breeding Dark-eyed Junco (Junco hyemalis hyemalis) subspecies in western Massachusetts has not changed over previous 80 years

Breeding Dark-eyed Junco (Junco hyemalis hyemalis) subspecies in western Massachusetts has not changed over previous 80 years

David F. DeSante’s Birds of Cabo San Lucas, Fall 1968: A Historic Account

In preparation for his doctoral studies at Stanford University, the late David F. DeSante spent the fall of 1968 studying migratory landbirds at Cabo San Lucas. Although his hopes to capture numerous vagrant warblers were not met, he amassed an impressive list of distributional records for the Baja California Peninsula at a time when few ornithologists were working there. Among these were peninsular firsts for the Ring-necked Duck (Aythya collaris), Broad-billed Hummingbird (Cynanthus latirostris), Broad-winged Hawk (Buteo platypterus), Bobolink (Dolichonyx oryzivorus), and Painted Bunting (Passerina ciris). Another six species, and one subspecies, were found for the first time in Baja California Sur. Venturing away from the immediate confines of Cabo San Lucas, DeSante established the first peninsular record of the Gray-headed Junco (Junco hyemalis caniceps) and first state records for another five species and one subspecies. Although many of these records have been reported previously, the junior authors believe it is appropriate to synthesize them more completely with current context, in Dave’s honor.

Seasonal efficacy and risks from a sodium nitrite toxic bait for wild pigs.

Wild pigs (Sus scrofa) are an invasive and destructive species throughout many regions of the world. A sodium nitrite (SN) toxic bait is currently used in Australia and being developed for use in the US and other countries to combat the increasing populations of wild pigs. In the US, efforts to modify the Australian SN-toxic bait and baiting strategy have focused on reducing issues with non-target animals accessing the SN-toxic bait spilled outside of bait stations by wild pigs. We tested and compared modifications for efficacy (with wild pigs) and hazards (with non-targets) in north-central Texas, US during summer (July 2021) and winter (March 2023) seasons. During both seasons we found that visitation to the bait sites declined 94-99% after deploying the SN-toxic bait, and we found a total of 106 dead wild pigs, indicating considerable lethality for the local population. Prior to deploying the SN-toxic bait, Global Positioning System (GPS)-collared wild pigs were more likely to cease visiting bait sites during summer when foraging resources were abundant. Farrowing decreased visitation to bait sites during the winter. We observed no dead non-targets during summer; winter results showed an average of 5.2 dead migrating birds per bait site (primarily Dark-eye juncos [Junco hyemalis]) from consuming SN-toxic bait spilled by wild pigs. The presence and winter-foraging behaviors of migrating birds appeared to increase hazards for those species. The current formulation of SN-toxic bait was effective at removing wild pigs during both seasons, however it is clear that different baiting strategies may be required in winter when migrating birds are present. Baiting wild pigs prior to farrowing during the winter, and during drier summers, may further improve efficacy of the bait. Reducing hazards to non-targets could be achieved by refining the SN-toxic bait or modifying bait stations to decrease the potential for spillage, decreasing environmental persistence if spilled, or decreasing attractiveness to migrating birds. © 2024 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Determinants of spring migration departure dates in a New World sparrow: Weather variables reign supreme.

Numerous factors influence the timing of spring migration in birds, yet the relative importance of intrinsic and extrinsic variables on migration initiation remains unclear. To test for interactions among weather, migration distance, parasitism, and physiology in determining spring departure date, we used the Dark-eyed Junco (Junco hyemalis) as a model migratory species known to harbor diverse and common haemosporidian parasites. Prior to spring migration departure from their wintering grounds in Indiana, USA, we quantified the intrinsic variables of fat, body condition (i.e., mass ~ tarsus residuals), physiological stress (i.e., ratio of heterophils to lymphocytes), cellular immunity (i.e., leukocyte composition and total count), migration distance (i.e., distance to the breeding grounds) using stable isotopes of hydrogen from feathers, and haemosporidian parasite intensity. We then attached nanotags to determine the timing of spring migration departure date using the Motus Wildlife Tracking System. We used additive Cox proportional hazard mixed models to test how risk of spring migratory departure was predicted by the combined intrinsic measures, along with meteorological predictors on the evening of departure (i.e., average wind speed and direction, relative humidity, and temperature). Model comparisons found that the best predictor of spring departure date was average nightly wind direction and a principal component combining relative humidity and temperature. Juncos were more likely to depart for spring migration on nights with largely southwestern winds and on warmer and drier evenings (relative to cooler and more humid evenings). Our results indicate that weather conditions at take-off are more critical to departure decisions than the measured physiological and parasitism variables.

Cultural shifts after punctuated environmental stress: a study of song distributions in Dark-eyed Junco and Song Sparrow populations

Cultural shifts after punctuated environmental stress: a study of song distributions in Dark-eyed Junco and Song Sparrow populations

Chronic disturbance induces attenuation of the acute glucocorticoid response in an urban adapter, the dark-eyed junco

Urban birds’ stress response frequently differs in magnitude from non-urban conspecifics. This urban phenotype may reflect response to selection, sorting during colonization of urban environments, developmental plasticity, or phenotypic flexibility in response to urban environments. We investigated whether exposure to one characteristic of an urban environment, chronic disturbance, could induce an attenuated acute glucocorticoid response over a short time in adult non-urban dark-eyed juncos (Junco hyemalis), which, if true, would support the phenotypic flexibility hypothesis. We tested this during the period of spring gonadal recrudescence. We simulated a high-disturbance urban-like environment by exposing non-urban experimental birds to chronic disturbance (30-min psychological stressors 4x/day for 3 weeks); controls were minimally disturbed. We found that chronically disturbed birds had a lower acute corticosterone response after 3 weeks of treatment. Baseline corticosterone was not affected. Chronically disturbed birds had less body fat and lower body condition than controls at the end of the experiment, although on average all birds gained weight over the course of the experiment. Feathers grown during the experiment did not show an effect of the disturbance treatment on feather corticosterone or fault bars, although captive-grown feathers had lower corticosterone and more fault bars than wild-grown feathers. We conclude that adult male juncos have the capacity to attenuate their acute corticosterone response in an environment with high frequency of disturbance, potentially facilitating colonization of urban habitats. Future research may show whether successful urban colonists differ from unsuccessful species in this regard.

Urban birds become less fearful following COVID-19 reopenings.

Following the COVID-19 pandemic, many people around the world stayed home, drastically altering human activity in cities. This exceptional moment provided researchers the opportunity to test how urban animals respond to human disturbance, in some cases testing fundamental questions on the mechanistic impact of urban behaviours on animal behaviour. However, at the end of this 'anthropause', human activity returned to cities. How might each of these strong shifts affect wildlife in the short and long term? We focused on fear response, a trait essential to tolerating urban life. We measured flight initiation distance-at both individual and population levels-for an urban bird before, during and after the anthropause to examine if birds experienced longer-term changes after a year and a half of lowered human presence. Dark-eyed juncos did not change fear levels during the anthropause, but they became drastically less fearful afterwards. These surprising and counterintuitive findings, made possible by following the behaviour of individuals over time, has led to a novel understanding that fear response can be driven by plasticity, yet not habituation-like processes. The pandemic-caused changes in human activity have shown that there is great complexity in how humans modify a behavioural trait fundamental to urban tolerance in animals.

Nestling growth rate and food consumption increases under experimentally prolonged daylength in a New World sparrow

When evaluating avian reproduction, life history theory examines the trade‐offs between parental effort, the number and size of offspring, and the rate of nestling development. The growth rates and body sizes of developing birds vary geographically and can diverge with both latitude and migratory strategy. In terms of offspring size, growth rate can deviate in nestlings of the same or similar species due to the correlated influences of weather events, predation pressure, food availability, number of nestmates and parental provisioning. Furthermore, a longer photoperiod for species nesting at higher latitudes increases the duration over which a nestling can be fed each day, and increased nestling provisioning has been positively correlated with growth rate. Whether the amount of time a bird is fed during development drives this variation in growth rate and morphology is unknown. By removing supplemental environmental stressors (e.g. weather, predation) and standardizing feeding rate and environment, we explored the influence of daily duration of nestling provisioning on dark‐eyed junco Junco hyemalis nestlings. We hand‐reared 65 chicks of a sedentary junco subspecies J. h. carolinensis under both their natural photoperiod and the longer photoperiod of a closely related migratory subspecies J. h. hyemalis and compared growth rate, mass, morphology and the amount of food consumed. Average growth rate, fasted mass, wing length and total daily food consumption were all greater in birds hand‐reared under the longer, more northern photoperiod treatment. These findings suggest that increased daily photoperiod at higher latitudes may allow for greater total food provisioning and thus may play a role in the ability of parents in compressed breeding seasons to produce high quality offspring. This points to a trade‐off between provisioning effort and nestling growth rate in lower latitude (shorter photoperiod) populations and points to an important role of developmental plasticity on growth rate and morphology.

An Eccentric Preformative Molt with Incomplete Replacement of Primary Coverts in a Dark-eyed Junco

Though the Dark-eyed Junco has not been reported to replace any juvenile primaries during its preformative molt, one first-cycle bird captured at Stanford, California, in November 2022 had replaced all its remiges but the three innermost primaries. Thus it followed the eccentric pattern more frequently seen in other sparrows, wrens, and some tyrant flycatchers. This novel pattern may be an adaptation to the urban habitats that the junco has recently colonized.

Physiological impacts of chronic and experimental Plasmodium infection on breeding-condition male songbirds

While Plasmodium parasitism is common in songbirds, its impact on avian reproduction is unclear owing to conflicting reports in the existing literature. Particularly understudied is the impact of phase of infection on variation in host reproductive physiology in wild, breeding-condition birds. However, assessing the full impact of Plasmodium on reproductive success in the wild can be difficult because individuals experiencing severe effects of parasitism may not enter the breeding population and may be less likely to be captured during field studies. To address these factors, we quantified metrics of health and reproductive physiology in wild-caught, breeding-condition male dark-eyed juncos (Junco hyemalis hyemalis) before and after experimental Plasmodium inoculation in a captive setting. Metrics of health and reproductive physiology included activity rate, hematocrit, scaled body mass, testosterone and sperm production. Individuals already infected at capture (i.e., chronically infected) had higher levels of hematocrit than males without chronic infections. Experimentally infected males showed a larger reduction in hematocrit and activity rate as compared to controls. However, chronic infection status did not influence the extent of metric decline. Testosterone production did not vary by treatment and most birds produced sperm following inoculation. Broadly, our results suggest that male juncos exposed to Plasmodium during the breeding season likely experience declines in general health, but Plasmodium infections do not negatively impact reproductive physiology. We conclude that physiological tradeoffs in males may favor maintenance of reproductive function despite infection.

Honorary Lifetime Membership Award: Ellen D. Ketterson.

Honorary Lifetime Membership Award: Ellen D. Ketterson.

Effects of short-term experimental manipulation of captive social environment on uropygial gland microbiome and preen oil volatile composition

IntroductionAvian preen oil, secreted by the uropygial gland, is an important source of volatile compounds that convey information about the sender’s identity and quality, making preen oil useful for the recognition and assessment of potential mates and rivals. Although intrinsic factors such as hormone levels, genetic background, and diet can affect preen oil volatile compound composition, many of these compounds are not the products of the animal’s own metabolic processes, but rather those of odor-producing symbiotic microbes. Social behavior affects the composition of uropygial microbial communities, as physical contact results in microbe sharing. We experimentally manipulated social interactions in captive dark-eyed juncos (Junco hyemalis) to assess the relative influence of social interactions, subspecies, and sex on uropygial gland microbial composition and the resulting preen oil odor profiles.MethodsWe captured 24 birds at Mountain Lake Biological Station in Virginia, USA, including birds from two seasonally sympatric subspecies – one resident, one migratory. We housed them in an outdoor aviary in three phases of social configurations: first in same-sex, same-subspecies flocks, then in male-female pairs, and finally in the original flocks. Using samples taken every four days of the experiment, we characterized their uropygial gland microbiome through 16S rRNA gene sequencing and their preen oil volatile compounds via GC-MS.ResultsWe predicted that if social environment was the primary driver of uropygial gland microbiome composition, and if microbiome composition in turn affected preen oil volatile profiles, then birds housed together would become more similar over time. Our results did not support this hypothesis, instead showing that sex and subspecies were stronger predictors of microbiome composition. We observed changes in volatile compounds after the birds had been housed in pairs, which disappeared after they were moved back into flocks, suggesting that hormonal changes related to breeding condition were the most important factor in these patterns.DiscussionAlthough early life social environment of nestlings and long-term social relationships have been shown to be important in shaping uropygial gland microbial communities, our study suggests that shorter-term changes in social environment do not have a strong effect on uropygial microbiomes and the resulting preen oil volatile compounds.

A New Isospora (Apicomplexa: Eimeriidae) from the Dark-Eyed Junco, Junco hyemalis (L.) (Passeriformes: Passerellidae), in West-Central Arkansas, USA.

Many passeriform birds are excellent hosts of coccidian parasites but little is known of the coccidians infecting members of the family Passerellidae, particularly from the dark-eyed junco, Junco hyemalis (Linnaeus, 1758). Here, we report from morphometric and mensural data a new species of Isospora from J. hyemalis in Arkansas, USA. During November 2020, seven adult J. hyemalis were taken with a mist net from Polk County, Arkansas, USA, and their faecal samples examined for coccidian parasites. Samples were placed in individual vials containing aqueous potassium dichromate. They were examined for coccidia after flotation in Sheather's sugar solution, measured, and photographed. A single J. hyemalis (14%) was found to be passing a new species of Isospora. Oöcysts of Isospora pittmani n. sp. were spheroidal to subspheroidal with a smooth bi-layered wall, measured (L × W) 24.8 × 23.8µm, and had a length/width (L/W) ratio of 1.04; a micropyle and oöcyst residuum was absent but typically one to up to four polar granule(s) was present. Sporocysts are ovoidal to ellipsoidal and measured 15.0 × 10.0µm, L/W 1.5; a flattened Stieda body was present as well as a barely discernible sub-Stieda body but para-Stieda bodies were absent. The sporocyst residuum was composed of various-sized granules dispersed between and across the sporozoites. A spheroidal to ellipsoidal posterior refractile body and spheroidal anterior refractile body occasionally seen, but a nucleus was not observed.Only two previous isosporans have been reported from passerellid birds and the new species can readily be distinguished from them. This is the first coccidian reported from J. hyemalis and, more importantly, the first isosporan known from any member of the family Passerellidae in North America.

Survey of the Intestinal Bacterial Compositions of Three Sympatric Passeriformes Species

Aims: The gut microbiota of avian species, especially wild birds, is studied less than that of mammals. Moreover, due to ethical concerns, a vast majority of microbiota studies have been limited to their feces. In this study, we investigated the microbial composition in the upper intestinal tract of sympatric, heterospecific bird species.
 Study Design: We obtained samples from three wild bird species belonging in the same Order Passeriformes: Cedar Waxwing (Bombycilla cedrorum), American Robin (Turdus migratorius) and Dark-eyed Junco (Junco hyemalis). The samples were obtained from wild birds soon after they died due to physical injury. Microbial diversity was analyzed via high-throughput sequencing of 16S rRNA gene fragments.
 Place and Duration of Study: Indiana University Kokomo campus, Indiana. United States, between October 2019 and December 2020.
 Methodology: Illumina Miseq sequencing of V3-V4 region of the 16S rRNA gene was employed to determine microbial composition. The α and β diversity were determined by Shannon’s diversity index and principal coordinate analysis, respectively. Pair-wise comparison of Bray-Curtis dissimilarity between birds of same species, different species, collection dates and years were analyzed.
 Results: The proteobacterial sequences were predominant in all samples. However, the comparison at the level of bacterial class revealed a significant intraspecies variation in both α and β diversity. Additionally, some microbiota exhibited higher interspecies similarity than intraspecies similarity, despite these birds not sharing the same foraging guilds.
 Conclusion: Our study revealed high variability in the microbial compositions within the upper part of the digestive tract of closely related Passeriform birds in their natural environment.

Microplastic accumulation in the gastrointestinal tracts of nestling and adult migratory birds.

This study examines the abundance and types of microplastic (MP) content in the digestive system of different bird species to help us better understand MP transfer to birds from their environments. The lower GI tracts of six bird species (Tree Swallow (Tachycineta bicolor), Ovenbird (Seiurus aurocapilla), Dark-eyed Junco (Junco hyemalis), Hermit Thrush (Catharus guttatus), Tennessee Warbler (Leiothlypis peregrine), White-throated Sparrow (Zonotrichia albicollis)) were collected for MP analysis. Tree Swallows were collected from nine locations along three drainages in the Milwaukee area and at a remote lake in Wisconsin, USA and consisted of nestlings not yet fledged. The five other bird species were adult migratory bird fatalities from window strikes at the Loyola University Chicago's Lake Shore Campus. Results of plastic analysis showed that the lower GI tracts of all bird species contained different types of MPs (i.e., fibers, fragment, beads). Fiber was the most dominant, followed by fragment and beads. Microplastics were polyethylene, polyethylene terephthalate, nylon, and polyvinyl base materials. There was no statistically significant difference in the site average MP concentration for nestling Tree Swallows or in the species average concentration for adult migratory birds. However, except for Ovenbird, species of adult migratory birds had a species average MP concentration (20.1) that was statistically higher than the site-average MP concentration for Tree Swallow nestlings (5.9). The presence of MPs in the lower GI tracts of unfledged swallows could suggest that MPs had been transferred to the birds from the environment via their diet, such as flying insects-the food source of the birds. Further study should be conducted to investigate the potential transfer of MPs from aquatic insects to birds.

No evidence of repeated song divergence across multiple urban and non-urban populations of dark-eyed juncos (Junco hyemalis) in Southern California.

Urbanization can affect species communication by introducing new selection pressures, such as noise pollution and different environmental transmission properties. These selection pressures can trigger divergence between urban and non-urban populations. Songbirds rely on vocalizations to defend territories and attract mates. Urban songbirds have been shown in some species and some populations to increase the frequencies, reduce the length and change other temporal features of their songs. This study compares songs from four urban and three non-urban populations of dark-eyed juncos (Junco hyemalis) throughout Southern California. We examined song length, trill rate, minimum frequency, maximum frequency, peak frequency and frequency bandwidth. We also compared songs recorded from one urban junco population in San Diego nearly two decades ago with recently collected data in 2018–2020. Over all comparisons, we only found significant differences between UCLA and the 2006/2007 UCSD field seasons in minimum and maximum frequencies. These findings partially support and are partially in contrast to previous urban song studies. As urban areas expand, more opportunities will arise to understand urban song divergence in greater detail.