Neuronal activation in the geomagnetic responsive region Cluster N covaries with nocturnal migratory restlessness in white-throated sparrows (Zonotrichia albicollis).

Cluster N is a region of the visual forebrain of nocturnally migrating songbirds that supports the geomagnetic compass of nocturnal migrants. Cluster N expresses immediate-early genes (ZENK), indicating neuronal activation. This neuronal activity has only been recorded at night during the migratory season. Night-to-night variation in Cluster N activity in relation to migratory behaviour has not been previously examined. We tested whether Cluster N is activated only when birds are motivated to migrate and presumably engage their magnetic compass. We measured immediate-early gene activation in Cluster N of white-throated sparrows (Zonotrichia albicollis) in three conditions: daytime, nighttime migratory restless and nighttime resting. Birds in the nighttime migratory restlessness group had significantly greater numbers of ZENK-labelled cells in Cluster N compared to both the daytime and the nighttime resting groups. Additionally, the degree of migratory restlessness was positively correlated with the number of ZENK-labelled cells in the nighttime migratory restless group. Our study adds to the number of species observed to have neural activation in Cluster N and demonstrates for the first time that immediate early gene activation in Cluster N is correlated with the amount of active migratory behaviour displayed across sampled individuals. We conclude that Cluster N is facultatively regulated by the motivation to migrate, together with nocturnal activity, rather than obligatorily active during the migration season.

Perspectives on environmental heterogeneity and seasonal modulation of stress response in neotropical birds.

Corticosterone (CORT), the main glucocorticoid in birds, regulates physiological and behavioral traits linked to predictable and unpredictable environmental fluctuations (i.e., stressors). Baseline and stress-induced CORT concentrations are known to fluctuate seasonally, linked to life history stages (LHS) such as breeding, molt, and wintering stage. These variations have been relatively well described in North American birds, but poorly addressed in neotropical species. To fill this gap, we explored how baseline and stress-induced CORT variation by LHS was affected by seasonality and environmental heterogeneity (i.e., frequency of unpredictable events such as droughts, flashfloods, etc) within the Neotropics using two approaches. First, we reviewed all currently available data about CORT concentrations for neotropical bird species. Second, we performed an in-depth analysis comparing the CORT responses of the two most common species of the Zonotrichia genus from North and South America (Z. leucophrys and Z. capensis, respectively) and their subspecies to seasonality and environmental heterogeneity. These species have been analyzed with the same methodology, allowing for an in-depth comparison of CORT variations. Despite scant data on neotropical bird species, we observed overlap between molt and breeding, and lower fluctuations of CORT among LHS. These patterns would be considered atypical compared to those described for North temperate species. Further, we found no significant associations between environmental heterogeneity and the stress-responses. In Zonotrichia we observed a positive association between baseline and stress-induced concentrations of CORT and latitude. We also observed differences by LHS. Both baseline and stress-induced CORT concentrations were higher during breeding and lower during molt. In addition, for both species, the overall pattern of seasonal modulation of stress response was heavily influenced by the migration strategy, with long-distance migrants showing significantly higher stress-induced CORT levels. Our results highlight the need for more data collection in the Neotropics. Comparative data would shed further light on the sensitivity of the adrenocortical response to stress under different scenarios of environmental seasonality and unpredictability.

Alternative reproductive strategies in white-throated sparrows are associated with differences in parasite load following experimental infection.

Immune defences often trade off with other life-history components. Within species, optimal allocation to immunity may differ between the sexes or between alternative life-history strategies. White-throated sparrows (Zonotrichia albicollis) are unusual in having two discrete plumage morphs, white-striped and tan-striped. Within each sex, white-striped individuals are more aggressive and provide less parental care than tan-striped individuals. We extended immunocompetence handicap models, which predict sex differences in immunity and parasitism, to hypothesize that infection susceptibility should be greater in white-striped than tan-striped birds. We inoculated birds of both morphs with malarial parasites. Contrary to our prediction, among birds that became infected, parasite loads were higher in tan-striped than white-striped individuals and did not differ between the sexes. Circulating androgen levels did not differ between morphs but were higher in males than females. Our findings are not consistent with androgen-mediated immunosuppression. Instead, morph differences in immunity could reflect social interactions or life-history-related differences in risk of injury, and/or genetic factors. Although plumage and behavioural morphs of white-throated sparrow may differ in disease resistance, these differences do not parallel sex differences that have been reported in animals, and do not appear to be mediated by differences in androgen levels.

Intraspecific variation in exploratory behavior and elevational affinity in a widely distributed songbird.

Populations of the same species can vary substantially in their behavioral and morphometric traits when they are subject to different environmental pressures, which may lead to the development of different adaptive strategies. We quantified variation in exploratory behavior and morphometric traits among two rufous-collared sparrow populations that occur at low and high elevations in central Chile. Moreover, we used census and δ2H values of feather and blood to evaluate migration. We found that individual sparrows inhabiting high elevations were larger and showed more intense exploratory behavior in comparison with those that were captured at lower elevation. Moreover, we observed a steady decline in sparrow abundance during the winter and similar δ2H values for blood collected in the winter and summer at this site, which were significantly lower than blood Î´2H values observed at low elevation. This pattern suggests that individuals do not move long distances during winter, and likely they remain at similar elevations in refuge habitats. As predicted, our results support the existent of different adaptive strategies among populations of the same species, and suggest that the combination of behavioral, morphometric, and stable isotope data is a novel and robust integrative approach to assess differences in adaptation across environmental gradients.

Behavioural response to song and genetic divergence in two subspecies of white-crowned sparrows (Zonotrichia leucophrys).

Divergence in sexual signals may drive reproductive isolation between lineages, but behavioural barriers can weaken in contact zones. Here, we investigate the role of song as a behavioural and genetic barrier in a contact zone between two subspecies of white-crowned sparrows (Zonotrichia leucophrys). We employed a reduced genomic data set to assess population structure and infer the history underlying divergence, gene flow and hybridization. We also measured divergence in song and tested behavioural responses to song using playback experiments within and outside the contact zone. We found that the subspecies form distinct genetic clusters, and demographic inference supported a model of secondary contact. Song phenotype, particularly length of the first note (a whistle), was a significant predictor of genetic subspecies identity and genetic distance along the hybrid zone, suggesting a close link between song and genetic divergence in this system. Individuals from both parental and admixed localities responded significantly more strongly to their own song than to the other subspecies song, supporting song as a behavioural barrier. Putative parental and admixed individuals were not significantly different in their strength of discrimination between own and other songs; however, individuals from admixed localities tended to discriminate less strongly, and this difference in discrimination strength was explained by song dissimilarity as well as genetic distance. Therefore, we find that song acts as a reproductive isolating mechanism that is potentially weakening in a contact zone between the subspecies. Our findings also support the hypothesis that intraspecific song variation can reduce gene flow between populations.

Extreme spring conditions in the Arctic delay spring phenology of long-distance migratory songbirds.

Arctic regions are warming rapidly, with extreme weather events increasing in frequency, duration, and intensity just as in other regions. Many studies have focused on how shifting seasonality in environmental conditions affects vegetation phenology, while far fewer have examined how the breeding phenology of arctic fauna responds. We studied two species of long-distance migratory songbirds, Lapland longspurs, Calcarius lapponicus, and white-crowned sparrows, Zonotrichia leucophrys gambelii, across five consecutive breeding seasons in northern Alaskan tundra. We aimed to understand how spring environmental conditions affected breeding cycle phenology, including the timing of arrival on breeding grounds, territory establishment, and clutch initiation. Spring temperatures, precipitation, and snow-free dates differed significantly among years, with 2013 characterized by unusually late snow cover. In response, we found a significant delay in breeding-cycle phenology for both study species in 2013 relative to other study years: the first bird observed was delayed by 6-10 days, with mean arrival by 3-6 days, territory establishment by 6-13 days, and clutch initiation by 4-10 days. Further, snow cover, temperature, and precipitation during the territory establishment period were important predictors of clutch initiation dates for both species. These findings suggest that Arctic-breeding passerine communities may have the flexibility required to adjust breeding phenology in response to the increasingly extreme and unpredictable environmental conditions-although future generations may encounter conditions that exceed their current range of phenological flexibility.

Social network structure in wintering golden-crowned sparrows is not correlated with kinship.

Stable social organization in a wide variety of organisms has been linked to kinship, which can minimize conflict due to the indirect fitness benefits from cooperating with relatives. In birds, kin selection has been mostly studied in the context of reproduction or in species that are social year round. Many birds however are migratory, and the role of kinship in the winter societies of these species is virtually unexplored. In a previous study, we discovered striking social complexity and stability in a wintering population of migratory golden-crowned sparrows (Zonotrichia atricapilla) - individuals repeatedly form close associations with the same social partners, including across multiple winters. Here, we test the possibility that kinship might be involved in these close and stable social affiliations. We examine the relationship between kinship and social structure for two of the consecutive wintering seasons from the previous study. We found no evidence that social structure was influenced by kinship. Relatedness between most pairs of individuals was at most that of first cousins (and mostly far lower). Genetic networks based on relatedness do not correspond to the social networks, and Mantel tests revealed no relationship between kinship and pairwise interaction frequency. Kinship also failed to predict social structure in more fine-grained analyses, including analyses of each sex separately (in the event that sex-biased migration might limit kin selection to one sex), and separate analyses for each social community. The complex winter societies of golden-crowned sparrows appear to be based on cooperative benefits unrelated to kin selection.

Greater shrub dominance alters breeding habitat and food resources for migratory songbirds in Alaskan arctic tundra.

Climate warming is affecting the Arctic in multiple ways, including via increased dominance of deciduous shrubs. Although many studies have focused on how this vegetation shift is altering nutrient cycling and energy balance, few have explicitly considered effects on tundra fauna, such as the millions of migratory songbirds that breed in northern regions every year. To understand how increasing deciduous shrub dominance may alter breeding songbird habitat, we quantified vegetation and arthropod community characteristics in both graminoid and shrub dominated tundra. We combined measurements of preferred nest site characteristics for Lapland longspurs (Calcarius lapponicus) and Gambel's White-crowned sparrows (Zonotrichia leucophrys gambelii) with modeled predictions for the distribution of plant community types in the Alaskan arctic foothills region for the year 2050. Lapland longspur nests were found in sedge-dominated tussock tundra where shrub height does not exceed 20 cm, whereas White-crowned sparrows nested only under shrubs between 20 cm and 1 m in height, with no preference for shrub species. Shrub canopies had higher canopy-dwelling arthropod availability (i.e. small flies and spiders) but lower ground-dwelling arthropod availability (i.e. large spiders and beetles). Since flies are the birds' preferred prey, increasing shrubs may result in a net enhancement in preferred prey availability. Acknowledging the coarse resolution of existing tundra vegetation models, we predict that by 2050 there will be a northward shift in current White-crowned sparrow habitat range and a 20-60% increase in their preferred habitat extent, while Lapland longspur habitat extent will be equivalently reduced. Our findings can be used to make first approximations of future habitat change for species with similar nesting requirements. However, we contend that as exemplified by this study's findings, existing tundra modeling tools cannot yet simulate the fine-scale habitat characteristics that are critical to accurately predicting future habitat extent for many wildlife species.

Haemoproteus infected birds have increased lifetime reproductive success.

The impact of haematozoan infection on host fitness has received substantial attention since Hamilton and Zuk posited that parasites are important drivers of sexual selection. However, short-term studies testing the assumption that these parasites consistently reduce host fitness in the wild have produced contradictory results. To address this complex issue, we conducted a long-term study examining the relationship between naturally occurring infection with Haemoproteus and Plasmodium, and lifetime reproductive success and survival of Mountain White-crowned Sparrows. Specifically, we tested the hypothesis that birds infected with haematozoan parasites have reduced survival (as determined by overwinter return rates) and reproductive success. Contrary to expectation, there was no relationship between Haemoproteus and Plasmodium infection and reproduction or survival in males, nor was there a relationship between Plasmodium infection and reproduction in females. Interestingly, Haemoproteus-infected females had significantly higher overwinter return rates and these females fledged more than twice as many chicks during their lifetimes as did uninfected females. We discuss the impact of parasitic infections on host fitness in light of these findings and suggest that, in the case of less virulent pathogens, investment in excessive immune defence may decrease lifetime reproduction.

A blurring of life-history lines: Immune function, molt and reproduction in a highly stable environment.

Rufous-collared sparrows (Zonotrichia capensis peruviensis) from valleys in the Atacama Desert of Chile, live in an extremely stable environment, and exhibit overlap in molt and reproduction, with valley-specific differences in the proportion of birds engaged in both. To better understand the mechanistic pathways underlying the timing of life-history transitions, we examined the relationships among baseline and stress-induced levels of corticosterone (CORT), testosterone, and bacteria-killing ability of the blood plasma (BKA), as well as haemosporidian parasite infections and the genetic structure of two groups of sparrows from separate valleys over the course of a year. Birds neither molting nor breeding had the lowest BKA, but there were no differences among the other three categories of molt-reproductive stage. BKA varied over the year, with birds in May/June exhibiting significantly lower levels of BKA than the rest of the year. We also documented differences in the direction of the relationship between CORT and BKA at different times during the year. The direction of these relationships coincides with some trends in molt and reproductive stage, but differs enough to indicate that these birds exhibit individual-level plasticity, or population-level variability, in coordinating hypothalamo-pituitary-adrenal axis activity with life-history stage. We found weak preliminary evidence for genetic differentiation between the two populations, but not enough to indicate genetic isolation. No birds were infected with haemosporidia, which may be indicative of reduced parasite pressure in deserts. The data suggest that these birds may not trade off among different life-history components, but rather are able to invest in multiple life-history components based on their condition.

Changes in plasma concentrations of progesterone, dehydroepiandrosterone and corticosterone in response to acute stress of capture, handling and restraint in two subspecies of white-crowned sparrows.

The aim of this study was to determine circulating patterns of the three major adrenal steroids in blood in response to stress during acute restraint handling in two subspecies of white-crowned sparrow. Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) are long distance migrants that breed at high latitudes and Nuttall's white-crowned sparrows (Zonotrichia leucophrys nuttalli) are residents of coastal California. Column partition chromatography was developed to separate progesterone, dehydroepiandrosterone (DHEA), and corticosterone from a small plasma sample. Each of these steroids has the capability to modulate the stress response through various mechanisms. For example, progesterone is bound to corticosterone binding globulin (CBG) with a higher affinity than corticosterone. If plasma levels of progesterone rise during acute stress, then this could displace corticosterone from CBG and increase the amount of biologically active, free, corticosterone in blood. Dehydroepiandrosterone (DHEA) has been implicated to have many anti-stress properties with the potential to mitigate some of the actions of corticosterone. Results indicate that progesterone levels in both subspecies are elevated in response to acute stress handling. DHEA levels declined in Gambel's but did not change in Nuttall's. Thus DHEA does not follow the same secretory pattern as in mammals. Corticosterone levels were elevated in response to acute stress handling in both subspecies. This study provides new insight into an integrated stress response among three steroids.

Breaking down seasonality: androgen modulation and stress response in a highly stable environment.

Previous studies show that most birds inhabiting temperate regions have well defined life history stages, and they modulate the production of testosterone (T) and corticosterone (CORT) in response to changes in seasonality. In this study we aimed to examine baseline and stress-induced levels of CORT and circulating T in relation with life history stages in the rufous-collared sparrow, Zonotrichia capensis. We carried out this study for a year in a population inhabiting riparian habitats in the Atacama Desert in Chile, one of the most climatically stable and driest places in the world. This environment shows minimal yearly change in average temperature and precipitation is virtually zero. We found individuals breeding, molting and overlapping breeding and molt year round, although most individuals were molting during March and in breeding condition during October. T levels were not related to individual breeding condition, and at population level they were not significantly different across sampling months. Baseline levels of CORT did not vary across the year. Stress-induced levels of CORT were suppressed during March when most of the birds were molting. This phenomenon was also observed in birds not molting during this period suggesting a mechanism other than molt in determining the stress-response suppression. Our results strongly suggest that in this study site, long-term extremely stable conditions could have relaxed the selective pressures over the timing of life history stages which was evidenced by the breeding and molt schedules, its overlap and endocrine profiles.

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.

Continent-wide Shifts in Song Dialects of White-Throated Sparrows.

Hypotheses on regional song variation ("dialects") assume that dialects remain stable within regions, are distinct between regions, and persist within populations over extensive periods [1-3]. Theories to explain dialects focus on mechanisms that promote persistence of regional song variants despite gene flow between regions [4-6], such as juveniles settling in non-natal populations retaining only those songs from their repertoires that match neighbors [7, 8]. It would be considered atypical for a novel song variant to invade and replace the established regional variant. Yet some studies have reported song variants shifting rapidly over time within populations [9-11]. White-throated sparrows, Zonotrichia albicolis, for example, traditionally sing a whistled song terminating in a repeated triplet of notes [12], which was the ubiquitous variant in surveys across Canada in the 1960s [13]. However, doublet-ending songs emerged and replaced triplet-ending songs west of the Rocky Mountains sometime between 1960 and 2000 [11] and appeared just east of the Rockies in the 2000s [14]. From recordings collected over two decades across North America, we show that doublet-ending song has now spread at a continental scale. Using geolocator tracking, we confirm that birds from western Canada, where doublet-ending songs originated, overwinter with birds from central Canada, where the song initially spread. This suggests a potential mechanism for spread through song tutoring on wintering grounds. Where the new song variant has spread, it rose from a rare variant to the sole, regional song type, as predicted by the indirect biased transmission hypothesis [10]. VIDEO ABSTRACT.

Nest-site selection and breeding success of passerines in the world's southernmost forests.

BACKGROUND: Birds can maximize their reproductive success through careful selection of nest-sites. The 'total-foliage' hypothesis predicts that nests concealed in vegetation should have higher survival. We propose an additional hypothesis, the 'predator proximity' hypothesis, which states that nests placed farther from predators would have higher survival. We examined these hypotheses in the world's southernmost forests of Navarino Island, in the Cape Horn Biosphere reserve, Chile (55°S). This island has been free of mammalian ground predators until recently, and forest passerines have been subject to depredation only by diurnal and nocturnal raptors. METHODS: During three breeding seasons (2014-2017), we monitored 104 nests for the five most abundant open-cup forest-dwelling passerines (Elaenia albiceps, Zonotrichia capensis, Phrygilus patagonicus, Turdus falcklandii, and Anairetes parulus). We identified nest predators using camera traps and assessed whether habitat characteristics affected nest-site selection and survival. RESULTS: Nest predation was the main cause of nest failure (71% of failed nests). Milvago chimango was the most common predator, depredating 13 (87%) of the 15 nests where we could identify a predator. By contrast, the recently introduced mammal Neovison vison, the only ground predator, depredated one nest (7%). Species selected nest-sites with more understory cover and taller understory, which according to the total-foliage hypothesis would provide more concealment against both avian and mammal predators. However, these variables negatively influenced nest survival. The apparent disconnect between selecting nest-sites to avoid predation and the actual risk of predation could be due to recent changes in the predator assemblage driven by an increased abundance of native M. chimango associated with urban development, and/or the introduction of exotic mammalian ground predators to this island. These predator assemblage changes could have resulted in an ecological trap. Further research will be needed to assess hypotheses that could explain this mismatch between nest-site selection and nest survival.

Song ontogeny in Nuttall's white-crowned sparrows tutored with individual phrases.

Behavioral ontogeny involves the interaction of innate predispositions and experience. In bird song learning, one approach to exploring this interaction is to examine the songs rehearsed by young birds whose exposure to tutor models has been carefully controlled. Here, I analyzed the rehearsed repertoire in Nuttall's white-crowned sparrows (Zonotrichia leucophrys nuttalli) tutored with individual phrases of conspecific and heterospecific songs. The proportions of phrase types rehearsed indicate that the learning biases evident in crystallized song are manifest early on, suggesting preferential memorization rather than preferential retention during attrition. The proportion of songs beginning with whistles increased during song rehearsal and phrase sequence variability decreased, consistent with the idea that innate syntax specifications guide song rehearsal. Single-phrase tutored birds overproduced phrases to the same extent previously observed in birds tutored with full, normal song but retained fewer phrase types in their crystallized repertoires. This suggests that in this subspecies, acquired syntax information does not affect the number of phrase types memorized and rehearsed but does affect repertoire attrition at the end of the sensorimotor phase. I discuss these results with a focus on the action of innate templates in song development and subspecies differences in this process.

Two new feather mite species of the family Analgidae (Acariformes: Analgoidea) from the Rufous-collared Sparrow Zonotrichia capensis (Müller, 1776 (Passeriformes: Passerellidae).

Two new feather mite species of the family Analgidae are described from the Rufous-collared Sparrow, Zonotrichia capensis (Müller, 1776) (Passeriformes: Passerellidae), from Brazil: Analges ticotico sp. nov. (Analginae) and Strelkoviacarus brasiliensis sp. nov. (Anomalginae). Analges ticotico sp. nov. is characterized by the heteromorphic males having three short and rounded spines on the inner margin of femur III, the anterior margin of adanal shield convex, the hysteronotal shield with the anterior margin sinuous, and the terminal lamella rectangular. Strelkoviacarus brasiliensis sp. nov. is characterized by the anterior ends of the adanal shields being convergent and encompassing the bases of setae ps3 in males, and by the strongly convex median extension of the prodorsal shield and short dorsal setae vi, c2, d2 and e2 in females. These species represent the first records of corresponding feather mite genera in Brazil.

No evidence for a link between forest herbicides and offspring sex ratio in a migratory songbird using high-throughput molecular sexing.

Many species that use or require early-successional forest are of conservation concern, including a number of songbirds that have experienced long-term population declines. In this study, our initial goal was to test whether herbicide application intensity was linked to offspring sex ratio in the White-crowned Sparrow (Zonotrichia leucophrys), a species that requires early-successional forest within forested landscapes. However, a rapid and accurate method using direct PCR to sex a large sample of birds (n > 1000 individuals) was unavailable, so our secondary goal was to develop a new approach for rapidly determine offspring sex. We obtained blood samples from sparrow young during the 2013-2014 breeding seasons in regenerating conifer plantations that were treated with one of four treatments (i.e. light, moderate, and intensive herbicide application, or no-spray control). We then optimized a protocol that used a commercially available, direct PCR kit to amplify sex-specific fragments of the CHD (chromo-helicase-DNA-binding) genes directly from whole blood stored in lysis buffer. Using this approach, we found no evidence that offspring sex ratio was linked to herbicide application intensity or to food availability across herbicide treatments. Our molecular sexing technique was 100% accurate when validated on known-sex adults, and 99.9% of our blood samples amplified successfully after being stored in lysis buffer stored for up to 3 years. The application of direct PCR for sexing birds eliminated the need for DNA extraction and substantially reduced sample processing time, cost, and the opportunity for errors during the extraction step. We conclude that forest herbicide application intensity does not influence sparrow offspring sex ratio in our study system, and that our approach provides a rapid, accurate, and tractable method for sexing birds that can facilitate studies that require processing of a large number of samples.

Uncoupling Basal and Summit Metabolic Rates in White-Throated Sparrows: Digestive Demand Drives Maintenance Costs, but Changes in Muscle Mass Are Not Needed to Improve Thermogenic Capacity.

Avian basal metabolic rate (BMR) and summit metabolic rate (Msum) vary in parallel during cold acclimation and acclimatization, which implies a functional link between these variables. However, evidence suggests that these parameters may reflect different physiological systems acting independently. We tested this hypothesis in white-throated sparrows (Zonotrichia albicollis) acclimated to two temperatures (-8° and 28°C) and two diets (0% and 30% cellulose). We expected to find an uncoupling of Msum and BMR where Msum, a measure of maximal shivering heat production, would reflect muscle and heart mass variation and would respond only to temperature, while BMR would reflect changes in digestive and excretory organs in response to daily food intake, responding to both temperature and diet. We found that the gizzard, liver, kidneys, and intestines responded to treatments through a positive relationship with food intake. BMR was 15% higher in cold-acclimated birds and, as expected, varied with food intake and the mass of digestive and excretory organs. In contrast, although Msum was 19% higher in cold-acclimated birds, only heart mass responded to temperature (+18% in the cold). Pectoral muscles did not change in mass with temperature but were 8.2% lighter on the cellulose diet. Nevertheless, Msum varied positively with the mass of heart and skeletal muscles but only in cold-acclimated birds. Our results therefore suggest that an upregulation of muscle metabolic intensity is required for cold acclimation. This study increases support for the hypothesis that BMR and Msum reflect different physiological systems responding in parallel to constraints associated with cold environments.

Haemoproteus erythrogravidus n. sp. (Haemosporida, Haemoproteidae): Description and molecular characterization of a widespread blood parasite of birds in South America.

The great diversity of birds and ecosystems in the Andean mountains has been understudied in terms of their parasite species. We describe a new Haemoproteus parasite, H. (Parahaemoproteus) erythrogravidus infecting Zonotrichia capensis (Rufous-Collared Sparrow) in South America. The description of this blood parasite species is supported by morphological and molecular data based on a fragment of cytochrome b gene (cyt b) and complete mitochondrial genome sequences. The new species is closely related to H. (Parahaemoproteus) coatneyi, and it can be readily distinguished from the latter parasite due to morphology of its blood stages, particularly 1) the formation of a marked protrusion on envelope of infected erythrocytes by the majority of developing gametocytes, a feature which is unique for this Haemoproteus species and 2) the extremely attenuated width of the growing dumbbell-shaped macro- and microgametocytes. Additionally, Haemoproteus erythrogravidus is shown to be a monophyletic taxon that diverges from Haemoproteus coatneyi at the molecular level. We provide the complete mitochondrial DNA genome for both H. coatneyi and H. erythrogravidus. Molecular and morphological evidences indicate that H. erythrogravidus is present in Ecuador and Colombia, and genetic lineages with 100% of identity for the cyt b gene were reported in Chile, Perú, and Venezuela. Our study also indicates that H. erythrogravidus and H. coatneyi are sympatric sister taxa sharing Z. capensis as a host species across its distribution, which could be the result of sympatric speciation or complex biogeographic processes. Further studies on the distribution and evolutionary history of Z. capensis and its parasites H. erythrogravidus and H. coatneyi insight for our better understanding of the factors and dynamics driving parasite speciation.