Zonotrichia Capensis Research Articles

Homogenisation of birdsong along a natural–urban gradient in Argentina

One of the clearest examples of animal adaptation to urban habitats is the variation in their vocalisations driven by anthropogenic noise. A behavioural process that has received less attention in urban habitats is how anthropogenic barriers influence animal spacing behaviour and communication. I addressed the effects of the distribution of bird territories in urban habitats and the pattern of song differentiation over distance among neighbouring birds. I studied natural and suburban populations of the white-crowned sparrow Zonotrichia capensis in Argentina. This songbird dwells in gardens, but is here less abundant and more regularly spaced than in open woodlands. Neighbouring birds in garden suburbs sang songs that were more similar to each other than neighbouring birds in natural habitats. Song differentiation was greater within natural habitats than within suburbs at distance < 400 m. At larger distances differences among habitats were no longer significant. Neighbour songs were more homogeneous where territories were more regularly spaced, considering all habitats or urban ones only. Selection for individual recognition of neighbours through songs and greater male–male interactions could have enhanced acoustic differentiation in natural habitats. Conversely, weak territorial interactions in suburbs with abundant landmarks may have constrained song output, resulting in song homogenisation. This study points to differences in variability that may be more difficult to detect than differences in acoustic properties per se, and suggests that the effects of urbanisation on animal communication can be underestimated if inter-individual variation is not properly addressed.

Modulation of androgens in southern hemisphere temperate breeding sparrows ( Zonotrichia capensis): An altitudinal comparison

Most work investigating modulation of testosterone (T) levels in birds has focused on northern temperate and Arctic species, and to a lesser degree, tropical species. Studies exploring modulation of T in birds in temperate regions of the Southern Hemisphere are lacking. Here we explore patterns of T secretion across the breeding season in two populations of temperate Zonotrichia capensis in Chile, located only 130 km apart, but separated by 2000 m in elevation. We then compared these T profiles to those of conspecifcs in the tropics and congeners in northern zones. We measured baseline T levels during pre-breeding in lowland Z. c. chilensis, early breeding in highland Z. c. chilensis and mid-breeding in both populations. We also tested for social stimulation of T secretion during mid-breeding in both populations. Lastly, we challenged the hypothalamic-pituitary-gonadal (HPG) axis of the lowland population with gonadotropin-releasing hormone (GnRH) to determine maximum possible T production. We found that the highland population adjusted T secretion across the breeding season like northern species. Neither Z. c. chilensis population modulated T in response to social stimuli, nor the HPG axis of the lowland population was not maximally active during either pre- or mid-breeding. These results suggest that patterns of circulating T in the highland population of Z. c. chilensis in the Southern Hemisphere are similar to congeners in the temperate Northern Hemisphere, but those of the lowland population of Z. c. chilensis are not, and are more similar to conspecifics breeding in the tropics.

The Timing of Life-History Stages Across Latitudes inZonotrichiaSparrows

Abstract. Tropical vertebrates are considered to have greater flexibility in the timing of life-history stages than are temperate-zone vertebrates. Yet the annual cycles of most resident tropical species are poorly understood, making latitudinal comparisons of phenology difficult. We investigated the reproductive seasonality and synchrony of a mid-elevation (∼2100 m), equatorial population of the Rufous-collared Sparrow (Zonotrichia capensis) and compared our data with data from three other populations of Zonotrichia across a range of latitudes and elevations (one equatorial high-elevation population of Z. capensis and two temperate-zone populations of Z. leucophrys, one at high elevation and one at sea level). We predicted that (1) the reproductive synchrony and seasonality of temperate-zone populations should be greater than those of the equatorial populations and (2) the reproductive synchrony and seasonality of populations breeding at high elevations should be greater than those of populations breedin...

Variation in the Song of the Rufous-Collared Sparrow, Zonotrichia capensis, in Northwestern Argentina

Variation in the Song of the Rufous-Collared Sparrow, Zonotrichia capensis, in Northwestern Argentina

Bird community responses to different urban conditions in La Paz, Bolivia

Urbanization alters ecosystems worldwide, but little is known about its effects in the Neotropical region. In the present research we examined the relative influence of different levels of urbanization and of some urban development measures on bird species richness, abundance and composition. We surveyed 104 observation stations at which we collected data on the relative abundance of bird species, and also data on seven environmental variables as measures of urban development and human activity. We registered 57 native bird species. Bird species richness and bird abundance increased with lower urbanization levels. Both variables were positively related to vegetation cover and native vegetation, and negatively to built-up cover, abundance of Rock Pigeon (Columa livia), pedestrian rate and car rate. A canonical correspondence analysis produced a significant model that explained 37% of the total variation in species data. This analysis segregated bird species along two important gradients: urbanization and elevation. The most urbanized areas were dominated by a few synanthropic species tolerant to human disturbance, such as Rufous-Collared Sparrow (Zonotrichia capensis), Eared Dove (Zenaida auriculata) or Chiguanco Thrush (Turdus chiguanco). Areas with lower urbanization levels had more species typically associated with native vegetation, such as Plain-Mantled Tit-Spinetail (Leptasthenura aegitaloides) or D’Orbigny’s Chat-Tyrant (Ochthoeca oenanthoides), among others. Elevation had a significant influence in structuring bird communities, with some species restricted to higher elevations and some to lower elevations. Although changes in elevation had an important influence, urbanization had a stronger effect on structuring bird communities. This study provides valuable information and an important baseline for future studies.

The Avian Pancreatic Islets: A Comparison Across Species

The mammalian pancreas has a remarkable ability to maintain glucose homeostasis, through the production of the blood glucose lowering hormone insulin, and its counter‐regulatory hormone glucagon. The concept of avian diabetes arose in early studies of Minkowski in the late 1800's, which demonstrated that removal of the pancreas in domestic fowl and geese did not result in the development of diabetes. A species that deviates from this is horned owls which develop hyperglycemia and die following pancreas removal. Prior studies have demonstrated that the chicken pancreas contains more glucagon‐producing alpha cells compared to insulin‐producing beta cells. This is reflected in low blood levels of insulin in chickens. We hypothesize that species differences may exist in the expression patterns of pancreatic islet cells in birds allowing some to persist after pancreatectomy, whereas other birds perish as a result of hyperglycemia. In the present study, we employed immunohistochemistry to compare the density of alpha and beta cells in pancreatic tissue across the avian species. Studies were conducted on Mourning dove, Hooded Siskin, Collared Warbling Finch, and House Wren and we found that alpha cells were denser in the avian pancreas relative to beta cells. The study has been extended into other species such as Cinereous Conebill, Rufous Collared Sparrow, Amazilia Hummingbird, and Mountain Parakeet.

A formal investigation of Cultural Selection Theory: acoustic adaptation in bird song

The greatest challenge for Cultural Selection Theory lies is the paucity of evidence for structural mechanisms in cultural systems that are sufficient for adaptation by natural selection. In part, clarification is required with respect to the interaction between cultural systems and their purported selective environments. Edmonds et al. have argued that Cultural Selection Theory requires simple, conclusive, unambiguous case studies in order to meet this challenge. To that end, this paper examines the songs of the Rufous-collared Sparrow, which seem to exhibit cultural adaptations minimizing signal degradation relative to local environments. Specifically, the more forested the habitat, the more the tail end of the song resembles a whistle rather than a trill; yet, variation in song is uncorrelated with genetic variation. This paper explores the mechanisms responsible for these putative acoustic adaptations through a series of computer simulations. The main point of this research is not to test this model, but to demonstrate that models of this type have the resources to meet the in-principle objections that have been raised against Cultural Selection Theory. This research lends much-needed empirical support to Cultural Selection Theory by clarifying the nature of the interaction between culture and environment. It also contributes to evolutionary theory by clarifying the scope and limits of adaptation by natural selection.

Seasonal and social modulation of testosterone in Costa Rican rufous-collared sparrows ( Zonotrichia capensis costaricensis)

Previous work shows that most birds breeding in northern temperate regions adjust production of testosterone in response to stage of the breeding cycle and in some cases following social interactions. In contrast, prior research suggests that tropical breeding birds are less likely to modulate testosterone in response to social interactions (the propensity to increase testosterone in response to social instability is known as the challenge hypothesis). To further test the challenge hypothesis in tropical birds, we investigated whether variation in season affects reproductive condition, aggressive behavior, and social modulation of testosterone in two populations of Costa Rican rufous-collared sparrow, Zonotrichia capensis costaricensis. We conducted our study at three distinct times of year: the dry season (March and May); the veranillo, a hiatus in the rainy season (July); and the late rainy season (November). Significantly more birds were in breeding condition in the dry season than in the rainy season or veranillo. In each time period, we collected baseline testosterone samples and conducted simulated territorial intrusions (STIs). Our study shows that testosterone is modulated with season independent of breeding condition, as testosterone levels were affected by season, breeding condition, and an interaction of the two factors. Males breeding in the dry season had higher plasma testosterone levels than non-breeding males in the dry season and both breeding and non-breeding males in the veranillo and rainy season. Males did not socially modulate testosterone in any season. Aggressive behaviors expressed during STIs did not differ among seasons with the exception that males sang fewer songs during the rainy season.

Is there a trade-off between caring for offspring and territorial aggression in tropical male rufous-collared sparrows (Zonotrichia capensis)?

Sex-specific fitness costs and benefits influence the degree of offspring care provided by birds exhibiting biparental care. As males typically invest less initially into reproduction, they are more likely to trade-off time and energy spent on paternal care for alternative activities such as aggressive territorial defense. Trade-offs between male territorial aggression and male provisioning are well studied in temperate-zone species, but tropical studies are lacking. Tropical passerines may show distinct trade-offs that influence investment in offspring care, given life history differences such as lower fecundity, slower offspring development, and higher adult survival. We studied trade-offs between paternal care and aggression in an equatorial population of rufous-collared sparrows ( Zonotrichia capensis ). We hypothesized that males with high territorial aggression would be poor providers. To test this we conducted provisioning observations and simulated territorial intrusions on males during three nestling periods. No direct trade-offs existed between aggression and paternal provisioning. Males provisioned at a lower rate than females overall and nestling body size was positively related to male provisioning rates, suggesting a time/energy trade-off between male and female care. Males may, therefore, invest most into alternative activities. However, males stand to gain fitness benefits from provisioning offspring at a relatively high rate.

Geographic variation in the repeatability of a personality trait

Animal personalities are interindividual behavioral differences that are consistent across time or contexts. Increasing research is revealing the adaptive significance of personalities, although the mechanisms driving this variation remain largely unknown. A possible source of variation in personality traits is interpopulational differences in the strength of selection acting upon them. The response to selection can be measured indirectly via the behavior’s repeatability, as repeatability generally sets an upper limit to trait heritability. However, no information currently exists on geographic variation in personality repeatability. We therefore quantified repeatability in exploratory behavior, a common personality trait, over multiple trials for 3 populations of rufous-collared sparrow (Zonotrichia capensis), focusing on 3 specific measures (exploration speed, diversity of perches visited, and number of hops). We also asked how differences in repeatability of these 3 measures affect other aspects of exploration, such as the temporal consistency of intercorrelations between the measures. Exploration speed was highly repeatable across all populations, whereas diversity was only repeatable in 2 of 3 populations and hopping behavior not at all. These differences in repeatability lead to temporal variation in the correlation matrices of the 3 exploration measures. Finally, only trial number influenced interindividual variability in exploration, whereas population identity, experimental conditions (i.e., conducting the novel environment assay under laboratory or field conditions), and time since capture all had no effect. Our findings highlight the complexity of using measures of behavioral consistency as a definition of personalities and emphasize the value of quantifying interpopulational patterns of trait repeatability.

Disentangling the Effects of Environment and Life‐History Stage on Corticosterone Modulation in Costa Rican Rufous‐Collared Sparrows, Zonotrichia capensis costaricensis

This study explores the factors that influence modulation of baseline corticosterone levels and the hypothalamo-pituitary-adrenal cortex (HPA) axis response to stress in Costa Rican rufous-collared sparrows (Zonotrichia capensis costaricensis). Individuals in our study population vary in their timing of breeding and molt. Thus, at multiple times of the year, we were able to investigate how the HPA axis changes with life-history stage (breeding, molt) and the interaction of season and life-history stage. Season explained most of the variation in corticosterone data. During the dry season, males had higher baseline corticosterone levels and both females and males had a higher stress response, regardless of breeding or molting condition. Breeding did not significantly affect corticosterone levels in either males or females. There was no direct effect of molt on corticosterone levels in males or in females, but there was a significant interaction between season and molt for male baseline corticosterone levels and HPA axis responsiveness. Baseline corticosterone levels were not correlated with body condition, suggesting that body condition is not an explanatory factor for HPA axis change. Our data indicate that environmental conditions may affect how the HPA axis in birds is modulated during different life-history stages. They also emphasize the importance of studying species with diverse life cycles and seasonality.

Supplementary Testosterone Inhibits Paternal Care in a Tropically Breeding Sparrow, Zonotrichia capensis

In most male birds that exhibit paternal care, elevation in testosterone above the breeding baseline reduces nestling provisioning, which can be detrimental to offspring survival. Mechanisms that may allow some males to avoid this detrimental effect of elevated testosterone include (1) decreased sensitivity to testosterone's effects on behavior and (2) uncoupling of testosterone secretion from territorial challenges (thus reducing the number of transient elevations in testosterone above the breeding baseline). Both of these "cost-avoidance" mechanisms have been documented, but whether selection for these mechanisms is correlated or independent is unknown. We investigated the relationship between elevated testosterone and paternal care in a tropical bird, the rufous-collared sparrow (Zonotrichia capensis). Zonotrichia capensis males exhibit an uncoupling of testosterone secretion from territorial aggression, and this species has a flexible breeding season and a clutch size smaller than those of temperate congeners. We implanted males with testosterone or empty implants and observed paternal behavior 2-3 and 6-7 d posthatch. During both observation periods, 100% of control males fed chicks, whereas 22% and 0% of testosterone-implanted males fed chicks on days 2-3 and 6-7, respectively. Chicks of testosterone-implanted males weighed less than control chicks, but tarsus growth, wing growth, and fledging success did not differ. Thus, we demonstrate a robust negative effect of testosterone on nestling provisioning that may not ultimately affect reproductive success. We suggest that these results relate to extreme flexibility in breeding schedule and the small clutch size in this tropical species. Our data also suggest that selection for the two mechanisms to avoid deleterious effects of elevations in testosterone above the breeding baseline likely occurs independently.

Thermal history can affect the short-term thermal acclimation of basal metabolic rate in the passerine Zonotrichia capensis

The obligatory cost of living for endotherms is measured by basal metabolic rate (BMR), a variable that is known to change after thermal acclimation. However, the relative timing between variation in ambient temperature and BMR is not well understood. In this study, we addressed this problem in the sparrow Zonotrichia capensis, studying whether previous thermal history affects the response of BMR to a new acclimation temperature. We found that after 4 weeks of acclimation either to 30 or 15 °C birds exhibited significant differences in BMR from pre-acclimation levels. Nevertheless, after a re-acclimation to the opposite treatment for six additional weeks, in the group previously acclimated to warm conditions the change in BMR was significantly greater than in the group previously acclimated to cold. We also found differences in the mass of the small intestine between groups but constancy in the mass of liver, kidney and heart masses at the end of the experiments. Our results indicate that the thermal history affects metabolic adjustments and highlights the importance of considering this when evaluating the plasticity of metabolic traits in small birds.

Intraspecific basal metabolic rate varies with trophic level in rufous-collared sparrows

One of the most controversial hypotheses that associate basal metabolic rate (BMR) with food habits and habitat productivity is the food habit hypothesis (FHH). Here we examined the relationship between BMR, diet, and climate among populations of the omnivorous passerine, Zonotrichia capensis (Emberizidae). We used nitrogen stable isotopes to estimate each individual's relative trophic level. To tease apart the effect of climatic variables and diet on BMR, we also used structural equation modeling. After the effect of body mass and climatic variables was taken into account, a significant effect of trophic level as estimated by δ 15N on BMR was found. Our result seems to support the FHH at the intraspecific level, i.e., birds from the lower trophic levels – feeding on seeds and bud – had higher BMR than individuals from higher trophic levels.

MIGRATION-SELECTION BALANCE AND LOCAL ADAPTATION OF MITOCHONDRIAL HAPLOTYPES IN RUFOUS-COLLARED SPARROWS (ZONOTRICHIA CAPENSIS) ALONG AN ELEVATIONAL GRADIENT

Variable selection pressures across heterogeneous landscapes can lead to local adaptation of populations. The extent of local adaptation depends on the interplay between natural selection and gene flow, but the nature of this relationship is complex. Gene flow can constrain local adaptation by eroding differentiation driven by natural selection, or local adaptation can itself constrain gene flow through selection against maladapted immigrants. Here we test for evidence that natural selection constrains gene flow among populations of a widespread passerine bird (Zonotrichia capensis) that are distributed along an elevational gradient in the Peruvian Andes. Using multilocus sequences and microsatellites screened in 142 individuals collected along a series of replicate transects, we found that mitochondrial gene flow was significantly reduced along elevational transects relative to latitudinal control transects. Nuclear gene flow, however, was not similarly reduced. Clines in mitochondrial haplotype frequency were strongly associated with transitions in environmental variables along the elevational transects, but this association was not observed for the nuclear markers. These results suggest that natural selection constrains mitochondrial gene flow along elevational gradients and that the mitonuclear discrepancy may be due to local adaptation of mitochondrial haplotypes.

Diet and habitat aridity affect osmoregulatory physiology: An intraspecific field study along environmental gradients in the Rufous-collared sparrow

The urine field osmolality in Zonotrichia capensis along a latitudinal gradient in rainfall and temperature in Chile was examined. We also investigated latitudinal variation in the renal traits that mediate how these birds cope with dehydration. We used the δ 15N of this species' tissue to investigate whether the reliance on animals and seeds varied among birds and if it had any effect on excretion and renal traits. We found a significant latitudinal variation in urine osmolality, a variable that was correlated with habitat aridity. We also found that the kidney size and proportion of kidney devoted to medullary tissue differed between birds from arid and mesic localities, but not in a lineal fashion with aridity. The increment in the position in the food web, as measured by δ 15N, led to an increment in urine osmolality, without changes in kidney features. Our data suggested that differences in dietary habits in the field could be not extended enough to cause changes in the kidney structure in Rufous-collared sparrows.

Physiological responses in rufous-collared sparrows to thermal acclimation and seasonal acclimatization

A large number of physiological acclimation studies assume that flexibility in a certain trait is both adaptive and functionally important for organisms in their natural environment; however, it is not clear how an organism's capacity for temperature acclimation translates to the seasonal acclimatization that these organisms must accomplish. To elucidate this relationship, we measured BMR and TEWL rates in both field-acclimatized and laboratory-acclimated adult rufous-collared sparrows (Zonotrichia capensis). Measurements in field-acclimatized birds were taken during the winter and summer seasons; in the laboratory-acclimated birds, we took our measurements following 4 weeks at either 15 or 30 degrees C. Although BMR and TEWL rates did not differ between winter and summer in the field-acclimatized birds, laboratory-acclimated birds exposed to 15 degrees C exhibited both a higher BMR and TEWL rate when compared to the birds acclimated to 30 degrees C and the field-acclimatized birds. Because organ masses seem to be similar between field and cold-acclimated birds whereas BMR is higher in cold-acclimated birds, the variability in BMR cannot be explained completely by adjustments in organ masses. Our findings suggest that, although rufous-collared sparrows can exhibit thermal acclimation of physiological traits, sparrows do not use this capacity to cope with minor to moderate fluctuations in environmental conditions. Our data support the hypothesis that physiological flexibility in energetic traits is a common feature of avian metabolism.

Transcriptomic variation and plasticity in rufous‐collared sparrows (Zonotrichia capensis) along an altitudinal gradient

As modern genomic tools are developed for ecologically compelling models, field manipulation experiments will become important for establishing the role of functional genomic variation in physiological acclimation and evolutionary adaptation along environmental clines. High-altitude habitats expose individuals to hypoxic and thermal stress, necessitating physiological acclimation, which may result in evolutionary adaptation. We assayed skeletal muscle transcriptomic profiles of rufous-collared sparrows (Zonotrichia capensis) distributed along an altitudinal gradient on the Pacific slope of the Peruvian Andes. Nearly 200 unique transcripts were differentially expressed between high-altitude [4100 m above sea level (a.s.l.)] and low-altitude (2000 m a.s.l.) populations in their native habitats. Gene ontology and network analyses revealed that these transcripts are primarily involved in oxidative phosphorylation, protein biosynthesis, signal transduction and oxidative stress response pathways. To assess the plasticity in gene expression differences between populations, we performed a 'common garden' experiment in which high- and low-altitude individuals were transferred to a common low-altitude site (approximately 150 m). None of the genes that were differentially expressed between populations at the native altitudes remained significantly different between populations in the common garden. The role of gene expression variation in adaptation and acclimation to environmental stress is largely unexplored in natural populations of birds. These results demonstrate substantial plasticity in the biochemical pathways that underpin cold and hypoxia compensation in Z. capensis, which may mechanistically contribute to enabling the broad altitudinal distribution of the species.

An immunocytochemical study of the endocrine cells in the stomach and duodenum of Zonotrichia capensis subtorquata (Passeriformes, Emberizidae)

The main purpose of this study was to evaluate the regional distribution pattern and relative frequency of some endocrine cells in the three portions of the gastrointestinal tract (GIT)--the proventriculus, gizzard and duodenum- of the rufous-collared sparrow (Zonotrichia capensis subtorquata), by immunohistochemical methods using six types of polyclonal antisera, specific for serotonin (5-HT), somatostatin (D cells), glucagon, motilin, polypeptide YY (PYY) and insulin. In the proventriculus, endocrine cells immunoreactive for all of these markers were observed. The somatostatin-immunoreactive cells were found with greater frequency, with the presence of cytoplasmic processes. In the gizzard, endocrine cells secreting somatostatin, 5-HT and PYY were detected, while those secreting glucagon and insulin were not. In the final part of the gizzard, endocrine cells secreting 5-HT were more frequent, and cells secreting somatostatin and insulin were not detected. All of the cell types studied were observed in the duodenum in different frequencies, except for cells immunoreactive for glucagon and insulin. The somatostatin-positive (D cells) were the most numerous, being more prevalent in the intestinal glands. The other endocrine cells were identified in smaller numbers, some of them located in the intestinal villi and Lieberkuhn glands. The finding of these cell types in the duodenum confirms their preferential location in the final portions of the principal segments of the digestive system and suggests control by feedback of its functions. In conclusion, some interesting distributional patterns of gastrointestinal endocrine cells were found in this species of sparrow.

Trophic niche modulate physiological specialization in digestive and renal traits: A field study of sparrows (Zonotrichia capensis) along a latitudinal gradient

Trophic niche modulate physiological specialization in digestive and renal traits: A field study of sparrows (Zonotrichia capensis) along a latitudinal gradient