Mountain White-crowned Sparrows Research Articles

Across time and space: Hormonal variation across temporal and spatial scales in relation to nesting success.

There is a renewed interest in investigating individual variation in hormone levels in relation to fitness metrics, as hormones act as mediators of life-history trade-offs. Hormone concentrations, however, are labile, responding to both internal and external stimuli, so the relationship between hormones and fitness can be non-consistent. One explanation of this inconsistent relationship is that a single hormone sample may not be representative of individual phenotypes in a free-living species. We addressed this issue by repeatedly sampling a free-living population of mountain white-crowned sparrows, Zonotrichia leucophrys oriantha, for baseline and stress-induced corticosterone (cort) and testosterone (T) across different stages of the breeding season. We measured (co)variation using three different methods, taking into account inter- and intra-individual variances, to determine whether hormone levels and the stress response are repeatable. We documented the temporal (over 3months) and spatial (home-range) variation of individual hormone phenotypes and investigated how these components related to nesting success. At the population level, we found significant repeatability in male stress-induced cort concentrations but no repeatability in male or female baseline cort or male T concentrations. Using a new metric of intra-individual variance focusing on the stress response (profile repeatability), we found a wide range of variance scores, with most individuals showing high variation in their stress response. Similarly, we found a low level of repeatability of the reaction norm intercept and slope for the stress response across different life-history stages. Males with higher concentrations of stress-induced cort had more central home-ranges. Males with higher body condition had larger home-ranges; however, home-range size did not relate to male hormone concentrations or nesting success. We also did not find any significant relationship between variation in hormone levels and nesting success. We recommend that future studies combine both physiological and environmental components to better understand the relationship between hormones and fitness.

The depredation of Mountain White-crowned Sparrow (Zonotrichia leucophrys oriantha) nests by the golden-mantled ground squirrel (Callospermophilus lateralis) and long-tailed weasel (Mustela frenata)

The identities of avian nest predators remain unknown in many systems. The Mountain White-crowned Sparrow (Zonotrichia leucophrys oriantha) is a high-elevation ground-nesting passerine for which only 4 of 15 suspected nest predator species have been confirmed. In this short communication, we confirm 2 previously suspected but unverified nest predators of Z. l. oriantha that were video recorded during the 2016 and 2017 summer breeding seasons. These nest depredation events include a golden-mantled ground squirrel (Callospermophilus lateralis) in 2016 and a long-tailed weasel (Mustela frenata) in 2017. Both predators were recorded removing nestlings.

Determinants of parental care in Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha)

ABSTRACT Extent of parental care, such as food provisioning to offspring, can vary widely between sexes in socially monogamous birds. The determinants of the sex-specific provisioning behaviors remain unclear as they could be associated with individual condition, as well as mate contribution and quality. In a population of Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha), we tested the good parent hypothesis, the reproductive compensation hypothesis, and the differential allocation hypothesis among 29 nesting pairs during the breeding season. Using multivariable linear regression, we examined the relationship of offspring food provisioning rate, a measure of parental care, with each parent's own demographic (sex, age), morphological (tail length, wing chord, tarsus, mass, body fat, and cloacal protuberance), and physiological (hematocrit and infection status) characteristics, as well as crown-white, a reliable status signal in this species. In male birds, feeding rate was positively corre...

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.

Song exposure during juvenile dispersal in Mountain White-crowned Sparrows

ABSTRACT The degree to which local song structure reflects the singer's population of origin is a long-standing and contentious issue. Young songbirds that settle to breed outside their natal song-dialect area may learn to produce nonnatal dialect by hearing and memorizing these songs during juvenile dispersal. We quantified adult singing rates in a population of Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) in the Sierra Nevada in 2 yr, and compared them with the arrival schedule of juveniles not hatched on the study area. Our results show that opportunities for juveniles to learn new (nonnatal) song types become highly limited during the premigratory dispersal phase, because adult singing rates are very low by the time nonlocal juveniles begin to arrive. Thus, if individuals learn nonnatal songs during dispersal, they must do so hearing relatively few repetitions of the unfamiliar dialect.

Natural selection and glucocorticoid physiology

Glucocorticoid hormones are considered potent modulators of trade-offs between reproduction and survival. As such, selection should affect glucocorticoid physiology, although relatively little is known about how selection may act on glucocorticoid profiles. In general, the evolution of physiology is less studied and less well understood than morphological or life history traits. Here, we used a long-term data set from a population of mountain white-crowned sparrows to estimate natural selection on glucocorticoid profiles. Our study suggests that survival selection favours higher hormone concentrations for multiple components of glucocorticoid physiology (both baseline and stress-induced glucocorticoid levels). Fecundity selection varies depending on the component of hypothalamic-pituitary-adrenal physiology; greater reproductive output was associated with higher baseline glucocorticoid levels, but lower stress-induced glucocorticoid levels. Additionally, the selection gradient was greater for glucocorticoids than for a morphological trait (wing length). These results support the hypothesis that stress-induced glucocorticoids increase survival over reproduction within a wild population (the CORT-trade-off hypothesis). Taken together, these results add to our knowledge of how selection operates on physiological traits and also provide an evolutionary and ecological perspective on several key open issues in the field of glucocorticoid physiology.

Distance to a Road is Associated with Reproductive Success and Physiological Stress Response in a Migratory Landbird

Abstract We investigated the impacts of an unpaved road on the distribution, reproduction, and stress physiology of Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) in a high-elevation subalpine ecosystem. We found and monitored 152 sparrow nests over 3 years and captured 123 sparrows over 2 years for standardized stress series experiments. Distance of a nest to the road was associated with reproductive success, and low success near the road was primarily because of high rates of nest desertion. The probability of a nest succeeding rose with increasing distance from road up to 40 m, but nests beyond 40 m experienced lower nest success, possibly because of increased predation. Nests at intermediate distance were approximately twice as likely to succeed (70% survival rate) as those near (36% survival) or far (37% survival) from the road. Stress response of male sparrows subjected to a standardized field stress protocol was elevated within 20 m of the road (38.34 ± 5.76 ng/ml) compared to th...

Are white-crowned sparrow badges reliable signals?

Status badges, such as crown plumage, mediate intraspecific interactions. The reliability of crown morphology as a status badge in male mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) is uncertain. We examined morphological and physiological correlates of the proportion of crown that was white (“crown-white”) in 178 male mountain white-crowned sparrows during the 2008–2009 breeding seasons. Using a paired experimental design, we presented territory-holding males with white-enhanced and white-reduced decoys and recorded aggressive behaviors. To assess physiological constraints on signal bluffing, a subsample of birds was captured and released after manipulating natural crowns to simulate bluffed white-enhanced or white-reduced crowns; corticosterone concentrations were assayed from blood drawn upon recapture and after a restraint-induced stressor. We found a significant positive association between crown-white and a measure of body size—tarsus length—which is an established indicator of resource-holding potential. In the decoy challenge, males responded more aggressively toward white-enhanced than white-reduced decoys. In the hormone experiment, white-enhanced birds had higher baseline corticosterone levels, whereas white-reduced birds had similar concentrations to controls. Furthermore, white-enhanced birds had an attenuated restraint-induced corticosterone response, while white-reduced birds mounted a significantly larger increase in corticosterone than controls. Taken together, these findings indicate that crown-white is a reliable status badge of resource-holding potential in male mountain white-crowned sparrows during the breeding season.

The effects of experimentally elevated traffic noise on nestling white-crowned sparrow stress physiology, immune function, and life-history

Roads have been associated with behavioral and physiological changes in wildlife. In birds, roads decrease reproductive success and biodiversity and increase physiological stress. Although the consequences of roads on individuals and communities have been well described, the mechanisms through which roads affect birds remain largely unexplored. Here, we examine one mechanism through which roads could affect birds: traffic noise. We exposed nestling mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) to experimentally elevated traffic noise for 5 days during the nestling period. Following exposure to traffic noise we measured nestling stress physiology, immune function, body size, condition and survival. Based on prior studies, we expected the traffic noise treatment to result in elevated stress hormones (glucocorticoids), and declines in immune function, body size, condition and survival. Surprisingly, nestlings exposed to traffic noise had lower glucocorticoid levels and improved condition relative to control nests. These results indicate that traffic noise does affect physiology and development in white-crowned sparrows, but not at all as predicted. Therefore, when evaluating the mechanisms through which roads affect avian populations, other factors (e.g. edge effects, pollution and mechanical vibration) may be more important than traffic noise in explaining elevated nestling stress responses in this species.

Proximity to a high traffic road: Glucocorticoid and life history consequences for nestling white-crowned sparrows

Roads have been associated with decreased reproductive success and biodiversity in avian communities and increased physiological stress in adult birds. Alternatively, roads may also increase food availability and reduce predator pressure. Previous studies have focused on adult birds, but nestlings may also be susceptible to the detrimental impacts of roads. We examined the effects of proximity to a road on nestling glucocorticoid activity and growth in the mountain white-crowned sparrow ( Zonotrichia leucophrys oriantha). Additionally, we examined several possible indirect factors that may influence nestling corticosterone (CORT) activity secretion in relation to roads. These indirect effects include parental CORT activity, nest-site characteristics, and parental provisioning. And finally, we assessed possible fitness consequences of roads through measures of fledging success. Nestlings near roads had increased CORT activity, elevated at both baseline and stress-induced levels. Surprisingly, these nestlings were also bigger. Generally, greater corticosterone activity is associated with reduced growth. However, the hypothalamic–pituitary–adrenal axis matures through the nestling period (as nestlings get larger, HPA-activation is greater). Although much of the variance in CORT responses was explained by body size, nestling CORT responses were higher close to roads after controlling for developmental differences. Indirect effects of roads may be mediated through paternal care. Nestling CORT responses were correlated with paternal CORT responses and paternal provisioning increased near roads. Hence, nestlings near roads may be larger due to increased paternal attentiveness. And finally, nest predation was higher for nests close to the road. Roads have apparent costs for white-crowned sparrow nestlings – increased predation, and apparent benefits – increased size. The elevation in CORT activity seems to reflect both increased size (benefit) and elevation due to road proximity (cost). Whether or not roads are good or bad for nestlings remains equivocal. However, it is clear that roads affect nestlings; how or if these effects influence adult survival or reproduction remains to be elucidated.

Immune system activation affects song and territorial defense

Previous studies have demonstrated that bird song is influenced by infection. We investigated how mounting an immune response by mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) affects specific aspects of territorial song and behavior. We used song playback to simulate a territorial intrusion and elicit baseline song and behavioral responses. Individuals were then either injected with a saline control or with a lipopolysaccharide (LPS) solution to induce an acute immune response, and posttreatment territorial song and behaviors in response to playback were recorded 1 day and 7 days later. The immune challenge significantly reduced the number of birds that sang compared with control individuals on Day 1. All birds that sang on Day 1 produced abnormal songs with fewer terminal notes, exhibited elevated alarm behavior, and tended to sing at slower rates. By Day 7, LPS treatment had no effect on the likelihood of singing, and song rates had returned to baseline levels, though songs were still sung with fewer terminal notes. Thus, our study shows that simply mounting an immune response to infection, as opposed to the actual infection per se is sufficient to impact avian song production. This study also suggests that for the most sensitive assessment of immune status, familiarity with an individual’s song and behavior is necessary. Key words: acute phase response, bird song, immune system response, life-history trade-offs, lipopolysaccharide, territorial behavior, white-crowned sparrow, Zonotrichia leucophrys. [Behav Ecol]

Free-Living Male Mountain White-Crowned Sparrows Exhibit Territorial Aggression Without Modulating Total or Free Plasma Testosterone

AbstractAbstractIn some species, expression of territorial aggression is accompanied by a rise in testosterone secretion, but in others aggressive behavior is expressed while testosterone levels remain unchanged. Corticosteroid binding globulin (CBG) binds both corticosterone and testosterone in avian plasma. Thus, increasing corticosterone may result in fluctuations in unbound (“free”) testosterone; this could result in greater biological activity of testosterone without an increase in testosterone secretion. We investigated whether such plasma interactions of testosterone, corticosterone, and CBG might result in alterations of free testosterone in male Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha). We conducted simulated territorial intrusions during incubation and compared total and free testosterone of males captured immediately following a simulated territorial intrusion with that of males captured passively. All experimental males showed aggressive behavior, but apparently did not modulate total or free testosterone relative to controls.

FREE-LIVING MALE MOUNTAIN WHITE-CROWNED SPARROWS EXHIBIT TERRITORIAL AGGRESSION WITHOUT MODULATING TOTAL OR FREE PLASMA TESTOSTERONE

Abstract ABSTRACT In some species, expression of territorial aggression is accompanied by a rise in testosterone secretion, but in others aggressive behavior is expressed while testosterone levels remain unchanged. Corticosteroid binding globulin (CBG) binds both corticosterone and testosterone in avian plasma. Thus, increasing corticosterone may result in fluctuations in unbound (“free”) testosterone; this could result in greater biological activity of testosterone without an increase in testosterone secretion. We investigated whether such plasma interactions of testosterone, corticosterone, and CBG might result in alterations of free testosterone in male Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha). We conducted simulated territorial intrusions during incubation and compared total and free testosterone of males captured immediately following a simulated territorial intrusion with that of males captured passively. All experimental males showed aggressive behavior, but apparently did ...

Parasite-mediated heterozygote advantage in an outbred songbird population

Coevolution with parasites is thought to maintain genetic diversity in host populations. However, while there are sound theoretical reasons to expect heterozygosity and parasite resistance to be related, this pattern has generally been shown only in inbred laboratory and island populations. This leaves doubt as to whether parasite-mediated selection for genetic diversity is in fact a general process. Here we show that haematozoan parasite load is linked to two complementary measures of microsatellite variability in an outbred population of mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) for which we know that parasites reduce fitness. Moreover, each of the genetic measures predicts a subtly different aspect of parasitism. Microsatellite heterozygosity is related to an individual's risk of parasitism, and mean d2 (a broader, more long-term measure of parental relatedness) to the severity of infection among parasitized individuals.

Facultative Altitudinal Movements by Mountain White-Crowned Sparrows (Zonotrichia Leucophrys Oriantha) in the Sierra Nevada

Abstract Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) winter in Mexico and often arrive in the vicinity of their breeding grounds in the Sierra Nevada well before nesting is possible. Arrival at Tioga Pass, California (elevation 3,030 m), usually occurs in early May, but residual winter snow and adverse weather can delay nesting for weeks. We used radiotelemetry to determine whether prebreeding Mountain White-crowned Sparrows engaged in weather-related altitudinal movements during the waiting period between the end of spring migration and onset of breeding during 1995–2001, with a range of residual winter snowpacks. Interannual variation in arrival date and onset of egg laying was 18 and 41 days, respectively. We tracked females for two years and males for all seven years. During spring snowstorms (which occurred in four years), radiomarked individuals moved to lower elevation sites, where they often remained for several days. Departing birds left Tioga Pass by early afternoon and returned early in the morning after storms. More frequent storms during tracking increased the likelihood of facultative altitudinal movements, but heavier residual winter snowpack did not. Warm days increased the likelihood of birds returning to Tioga Pass from low elevation. This study demonstrates that facultative altitudinal movement behavior can be a common feature of spring arrival biology in montane-breeding birds.

"The Mountain White-Crowned Sparrow: Migration and Reproduction at High Altitude" by Martin L. Morton. 2002. [book review

"The Mountain White-Crowned Sparrow: Migration and Reproduction at High Altitude" by Martin L. Morton. 2002. [book review

REPRODUCTIVE EFFORT AND RETURN RATES IN THE MOUNTAIN WHITE-CROWNED SPARROW

Abstract We analyzed return rates of high-altitude-breeding Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) in relation to five components of their previous season's reproductive effort: number of fledglings produced, double brooding, number of nesting attempts (first nests plus renests), total number of eggs laid, and fledging date. No relationship of return rate to reproductive effort occurred except in the case of fledging date. Fledging dates spanned a 2-month period from mid-June to mid-August. Returns of females to the study area held steady no matter when their chicks fledged in the previous breeding season, but male return rates increased significantly when their chicks fledged after 20 July. Coincident with that time frame, they entered molt and often withdrew parental care. We hypothesized that males in this montane environment, where thermoregulatory costs are high, traded off reproductive effort (parental care) with survival (return rates). This fits well with models of life-...

FACULTATIVE ALTITUDINAL MOVEMENTS BY MOUNTAIN WHITE-CROWNED SPARROWS (ZONOTRICHIA LEUCOPHRYS ORIANTHA) IN THE SIERRA NEVADA

Abstract Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) winter in Mexico and often arrive in the vicinity of their breeding grounds in the Sierra Nevada well before nesting is possible. Arrival at Tioga Pass, California (elevation 3,030 m), usually occurs in early May, but residual winter snow and adverse weather can delay nesting for weeks. We used radiotelemetry to determine whether prebreeding Mountain White-crowned Sparrows engaged in weather-related altitudinal movements during the waiting period between the end of spring migration and onset of breeding during 1995–2001, with a range of residual winter snowpacks. Interannual variation in arrival date and onset of egg laying was 18 and 41 days, respectively. We tracked females for two years and males for all seven years. During spring snowstorms (which occurred in four years), radiomarked individuals moved to lower elevation sites, where they often remained for several days. Departing birds left Tioga Pass by early afternoon and ret...

Energetics of Altricial Nestlings in Cold Climates: Insights from the Mountain White-Crowned Sparrow

AbstractWe determined the energy budget of nestling Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) at a 2900-m-high subalpine site by combining growth data with measurements of field metabolic rate (doubly labeled water technique) and resting metabolic rate made on different-aged nestlings. Nestling sparrows grow rapidly (their logistic growth rate constant is 129% of the allometric prediction) and they fledge at 9 days of age weighing 20.6 g (75% of adult mass). Relatively rapid growth in a cool montane environment (mean daytime air temperature = 16.5 ± 1.4°C) is associated with high daily and total nestling energy requirements. During the 9 days between hatching and fledging, each nestling metabolized a total of 443 kJ of energy; a value 25% higher than expected for an open-nesting passerine bird. The relative cost of producing a fledgling White-crowned Sparrow (21.5 kJ per g body mass) exceeds that of the three other open-nesting passerine species that have been measured with doubly labeled water (range 16.5–19.3 kJ g−1). The energy that nestling sparrows accumulated as new tissue (115 kJ) constituted 26% of the total energy metabolized; substantially less than the 37% allocated to activity and thermoregulation combined. Nestling White-crowned Sparrows allocated more energy to activity and thermoregulation than nestlings of most other parent-fed species, but much less than the 50–53% of total metabolizable energy allocated by precocial shorebird chicks.La Energética de Pichones Altriciales en Climas Fríos: Lecciones de Zonotrichia leucophrys orianthaResumen. Determinamos el presupuesto energético de pichones de Zonotrichia leucophrys oriantha en un sitio subalpino a 2900 m de altitud combinando datos de crecimiento y de tasa metabólica en el campo (medida con la técnica de agua doblemente marcada) y tasa metabólica en reposo en pichones de diferentes edades. Los pichones crecen rápidamente (sus tasas de crecimiento logístico son el 129% de las tasas alométricas) y empluman a los 9 días de edad, pesando 20.6 g (75% de su peso adulto). El crecimiento relativamente rápido en un ambiente de montaña fresco (temperatura diaria promedio = 16.5 ± 1.4°C) está asociado con altas exigencias energéticas diarias y totales. Durante los 9 días entre la eclosión y el emplumamiento, cada pichón metabolizó un total de 443 kJ de energía, un valor 25% más alto del esperado para un ave paserina de nido abierto. El costo relativo de producir un volantón de Zonotrichia leucophrys oriantha (21.5 kJ por g de peso corporal) es más alto que el de otras tres especies de paserinos de nido abierto que se han estudiado con la técnica de agua doblemente marcada (rango 16.5 a 19.3 kJ g−1). La energía que los pichones acumularon como tejido nuevo (115 kJ) representó el 26% de su metabolismo total, un valor sustancialmente menor que el 37% asignado a la actividad y a la termorregulación combinadas. Los pichones de Z. leucophrys oriantha asignaron más energía a la actividad y a la termorregulación que los pichones de la mayoría de las demás especies alimentadas por los padres, pero menos que los pichones precoces de aves playeras (50 a 53%).

Effects of temperature on photoperiodically induced reproductive development, circulating plasma luteinizing hormone and thyroid hormones, body mass, fat deposition and molt in mountain white-crowned sparrows, Zonotrichia leucophrys oriantha

The mountain white-crowned sparrow, Zonotrichia leucophrys oriantha, breeds in subalpine meadows throughout many mountainous regions of western North America. Mathematical analysis of 20 years of egg-laying dates at Tioga Pass, California (3030 m elevation) indicated a highly predictable breeding season suggesting that precise environmental cues such as the annual change in day length were important for regulating reproductive function. Additionally, it appeared that there was sufficient yearly variation in the timing of breeding to suggest that other environmental cues may also be important for regulating adjustments in reproductive development and regression. Captive populations of Z. l. oriantha showed strong responses in gonadal development following transfer to longs days (15L 9D) and low temperature (5 °C) slowed down photoperiodically induced gonadal growth and subsequent regression, in both males and females. High temperature of 30 °C tended to accelerate gonadal development and regression whereas gonadal development was intermediate in a group exposed to 20 °C. Prior exposure to these temperature regimes while on short days (9L 15D) had no effect on body mass, fat, or plasma levels of luteinizing hormone (LH) and thyroid hormones. Curiously there was no effect of temperature on photoperiodically induced rises in LH in either sex despite marked effects on gonadal growth. Brood patch development was also enhanced in females exposed to 30 °C. Corticosterone levels measured in a subset of plasma samples from this experiment indicated no effect of temperature suggesting that the retarded gonadal development at 5 °C was not a result of thermal stress. Although there was a robust effect of photostimulation on thyroid hormone levels in blood of both sexes, temperature treatment had no effect on tri-iodothyronine (T3) concentrations. However, plasma levels of thyroxine (T4) were lower initially at 5 °C versus 20 and 30 °C treatments. This may be related to the protracted gonadal cycle at 5 °C versus the truncated gonadal cycle at 30 °C. Molt score, an indication of post-reproductive state and onset of photorefractoriness, was delayed in birds exposed to 5 °C. Body mass, and to a lesser extent fat score, tended to be lowest in birds exposed to 5 °C compared with those at 20 and 30 °C. These results demonstrate that ambient temperature significantly affected photoperiodically induced gonadal development and regression in these birds. The endocrine mechanisms underlying these effects require further study.