Subspecies Of White-crowned Sparrow Research Articles

Behavioral and physiological traits of migrant and resident white-crowned sparrows: a common garden approach.

To accommodate a migratory life history, migrants express a greater number of physiological and behavioral stages per annum than residents and are thus considered to have higher finite state diversity (FSD). To investigate the physiological mechanisms and constraints associated with migration, direct comparison of two subspecies of white-crowned sparrow - migrant, Zonotrichia leucophrys gambelii, and resident, Z. l. nuttalli - were made under common garden conditions of photoperiod and housing, as birds progressed from winter through the vernal life history stages. We tested the hypothesis that migrants (higher FSD) respond differently than residents (lower FSD) to the initial predictive cue, photoperiod, to initiate and integrate the progression of vernal stages of prenuptial molt, migration and development of breeding. If differences in vernal phenology were noted, then the basis for the distinctions was considered genetic. Results indicate that (1) residents had a lower threshold to vernal photoperiod with elevations of plasma androgen, growth and development of reproductive structures preceding those of migrants; (2) only migrants displayed prenuptial molt, preparations for migration and migratory restlessness; and (3) neither baseline nor stress-induced plasma corticosterone differed across subspecies, suggesting energetic demands of the common garden were insufficient to induce a differential adrenocortical response in either subspecies, highlighting the impact of environmental conditions on corticosterone secretion. Thus, in a common garden experiment, Z. l. gambelii responds differently to the initial predictive cue, photoperiod, to initiate and execute the vernal stages of molt, migration and development of breeding in comparison to the shared stage of breeding with Z. l. nuttalli, confirming a genetic basis for the subspecies differences.

Annual Hematocrit Profiles in Two Subspecies of White-Crowned Sparrow: A Migrant and a Resident Comparison.

Hematocrit is an easily measured parameter that can be used to assess changes in oxygen carrying capacity necessitated by fluctuations in metabolic demands. Most hematocrit studies draw conclusions from changes in hematocrit that occur over a small sampling interval without an understanding of the variation that exists across the annual cycle. White-crowned sparrows provide an excellent model system due to the existence of a resident subspecies (Zonotrichia leucophrys nuttalli) that serves as a natural control for a migrant subspecies (Zonotrichia leucophrys gambelii). Comparing these two subspecies allows for the investigation of adaptive physiological changes at each life-history stage (i.e., migration, breeding, molt, etc.) in response to changing metabolic demands. Of particular interest, this subspecies comparison, by both calendar month and life-history stage, allows for the separation of adaptive increases in hematocrit due to migration from the natural seasonal variation in hematocrit. Hematocrit levels for males and females ranged throughout the year between 42%-47% and 40%-47% in the resident and between 45%-58% and 45%-56% in the migrant. In both subspecies, hematocrit levels were elevated during the breeding season compared to the nonbreeding season, and levels were reduced in females during egg laying. When grouped by life-history stage, hematocrit levels were always higher in the migrant compared to the resident. During the months in which migration occurred, hematocrit levels were 10%-12% higher in the migrant compared to the resident subspecies. These data suggest differential regulation of hematocrit between the two subspecies that may be attributed to phenotypic plasticity or genetic differences.

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.

Latitudinal variation of immune defense and sickness behavior in the white-crowned sparrow (Zonotrichia leucophrys)

There is a general trend that parasitism risk declines as latitude increases. Host populations breeding at high latitudes should therefore invest less in costly immune defenses than populations breeding in temperate or tropical zones, although it is unknown if such an effect is mediated by environmental (photoperiodic) or genetic factors or both. Acquired immune function (humoral, cell-mediated) and behavioral sickness responses to lipopolysaccharide (LPS; mimics bacterial infection) were assessed in two subspecies of white-crowned sparrow (Zonotrichia leucophrys) that breed at different latitudes in western North America. Zonotrichia l. gambelii (GWCS) is a high-latitude breeder (47–68°N) while Z. l. pugetensis (PWCS) breeds at temperate latitudes (40–49°N). Captive males of each subspecies were acclimated to (1) a short day (non-breeding) photoperiod (8L:16D), (2) the breeding photoperiod of PWCS (16L:8D), or (3) the breeding photoperiod of GWCS (20L:4D). Photoperiod was manipulated because shorter day lengths may enhance immune function. In support of a genetic effect, humoral responses to diphtheria–tetanus vaccination were significantly higher in PWCS compared to GWCS, regardless of photoperiod. There were no differences in cell-mediated responses to phytohemagglutinin (PHA) between subspecies or among photoperiods. For sickness responses to LPS, a significant interaction between photoperiod and subspecies was found, with long day GWCS producing stronger sickness responses (losing more weight, eating less) than short day GWCS and PWCS on all day lengths. However, these effects were influenced by photoperiodic changes in body condition. In conclusion, we find evidence for genetic control of immune responses across latitude, but no support for environmental (photoperiodic) regulation.

Perception of geographical variation in song by male Puget Sound white-crowned sparrows, Zonotrichia leucophrys pugetensis

The songs of male Puget Sound white-crowned sparrows form about 13 dialects along the Pacific Northwest coast of North America. In his original description of dialects in this subspecies, Baptista (1977, Condor, 79, 356–370) defined dialects by the terminal trill portion of the song because most males at a given location sing the same trill. Complex syllables in the introductory part of the song vary between males at a sample location and occur over a wider geographical range than trills. Baptista also recognized two superdialects or ‘themes’ based on differences in the phrase order within songs. We performed three playback experiments to territorial male white-crowned sparrows using both natural and computer-modified stimuli to test which acoustic features of song these birds attend to. Two of the experiments were conducted in nine dialect areas spanning nearly the entire geographical range of the subspecies. The results of the first such experiment indicate that across dialect areas, males give stronger responses (increased song rate and a shorter approach distance) to natural songs from the local dialect than they do to songs from a neighbouring dialect, a different theme, or another subspecies of white-crowned sparrow. Two experiments using modified stimuli conducted either across nine dialects or in one dialect led to the same conclusion: substitution of the trill from a neighbouring dialect into a song elicited weaker responses relative to the local control than did substitution of a neighbouring dialect's introduction. We conclude that the response of male Puget Sound white-crowned sparrows to playback is influenced most by variation in the song's trill. We found no evidence that the birds recognize ‘superdialects’ as do humans.

Genetic analysis of song dialect populations in Puget Sound white-crowned sparrows

The relationship between cultural variation and biological variation among natural populations has been the subject of both theoretical and empirical study. Zonotrichia leucophrys pugetensis is one of three subspecies of white-crowned sparrow known to form geographical song dialects. We investigated whether these dialects correspond to genetic differences among Z. l. pugetensis populations. We compared allele frequencies at four microsatellite loci in males from 11 sites spanning six dialects over the subspecies’ range in Oregon and Washington. Cluster analysis and genotype assignment tests indicated no tendency for sample sites within dialect areas to be genetically more similar than are sites from different dialect areas. AMOVA tests revealed high within-site variation and low but significant cross-site and cross-dialect-area variation. Finally, genetic distance between sites was not correlated with dialect differences when the effect of geographic distance was controlled statistically. We compare our finding of low genetic differentiation among Z. l. pugetensis dialect populations to results of previous studies on Z. l. nuttalli and Z. l. oriantha. Because genetic structuring appears weaker than cultural (song dialect) structure in this species, we discuss the behavioral mechanisms underlying dialect maintenance in the presence of apparent gene flow. Key words: birdsong, cultural evolution, geographic variation, microsatellites, Zonotrichia leucophrys pugetensis. [Behav Ecol 15:636–646 (2004)]

Effects of Ambient Temperature on Photo-Induced Prolactin Secretion in Three Subspecies of White-Crowned Sparrow,Zonotrichia leucophrys

We tested the effects of naturally relevant ambient temperatures (5, 20, and 30°C) on photoinduced prolactin (PRL) secretion in three subspecies of white-crowned sparrow,Zonotrichia leucophrys.In all three subspecies, transfer from short to long days triggered an increase in plasma PRL typical of an avian seasonal breeder. InZ. l. gambelii,which breeds at high latitudes, temperature does not affect the rate of photoinduced gonadal maturation or luteinizing hormone (LH) secretion. In this subspecies, we found that changes in plasma PRL concentrations were similar in all temperature treatments. InZ. l. pugetensis,which breeds in the Pacific Northwest, high temperatures accelerate gonadal development in females but not males and does not affect LH secretion. In this subspecies, we found that like gonadal growth, photoinduced changes in PRL secretion inZ. l. pugetensisvary with ambient temperature in females but not males. InZ. l. oriantha,which breeds in alpine regions of the West, both males and females respond to temperature cues by modulating gonadal growth but not LH secretion. We found inZ. l. orianthathat ambient temperature affects PRL secretion in both sexes. These results suggest that PRL may be involved in the transduction of ambient temperature cues used to time reproductive development and the termination of seasonal breeding. Alternatively, temperature-mediated differences in plasma PRL may be a result rather than a cause of differences in gonadal development, since sex steroids affect PRL secretion in some species.

Seasonal plasticity of the song control system in wild Nuttall's white-crowned sparrows.

Seasonal plasticity in the morphology of telencephalic nuclei that control song behavior has been reported for diverse species of songbirds. The only published report of a lack of seasonal changes in the song nuclei of a seasonally breeding bird is that of Baker et al. in the Nuttall's subspecies of white-crowned sparrow (Zonotrichia leucophrys nuttalli). In this study, they brought wild birds into the laboratory and exposed them to either "summer" or "winter" photoperiods. Previous studies have shown that exposing wild-caught white-crowned sparrows to long-day photoperiods in the laboratory may not induce circulating concentrations of testosterone (T) as high as those seen in wild breeding birds. Changes in circulating T are primarily responsible for the seasonal morphological changes in the song nuclei. To determine whether there is seasonal plasticity of the song system in this subspecies, we measured circulating T, morphological attributes of the song nuclei, and song behavior in wild Nuttall's white-crowned sparrows during the spring and fall. Testis size and circulating T concentrations were greater in spring than fall birds. The absolute volumes of the song nuclei HVc, RA, and Area X, and their volumes relative to those of either the total telencephalon or three thalamic nonsong nuclei, were significantly greater in the spring than fall sparrows. Song behavior also changed seasonally; fall birds sang shorter songs than did spring birds. These results show that there is seasonal plasticity of the song system in wild Nuttall's white-crowned sparrows. Seasonal plasticity can now be regarded as a common feature of the seasonally breeding songbirds studied thus far.

Geographic Variation in Song of Gambel's White-Crowned Sparrow

AbstractWhite-crowned sparrow (Zonotrichia leucophrys) song varies geographically, often forming local 'dialects' in sedentary and short-distance migratory subspecies. In playback experiments males and females can distinguish this variation. Gambel's white-crowned sparrow (Z. L. gambelii) is a long-distance migrant that breeds across subarctic Canada and Alaska. Previous studies identified a wide degree of song variation within local populations of this subspecies. I compared songs recorded in Alaska and Churchill, Manitoba, and found significant differences in acoustic structure. As in other subspecies, the most prominent differences occurred in the terminal trill portion of the song. In a playback experiment to territorial males at Churchill, males gave equivalent strong responses to both Alaska and local gambelii song, significantly weaker responses to mountain white-crowned sparrow (Z. L. oriantha) song, and the weakest responses to heterospecific song. I describe a model of song recognition in which 'dialect recognition' is a component of species recognition. I conclude that as a consequence of differences in the timing of song learning, the subspecies of white-crowned sparrow may differ in the acoustic features that they attend to in song recognition. The diversity of song types at a local level within gambelii populations may interfere with recognizing song differences between populations.

Seasonal changes in song nuclei and song behavior in Gambel's white-crowned sparrows.

In males of several songbird species, the morphology of forebrain nuclei that control song changes seasonally. The only seasonally breeding songbird in which seasonal changes in the structure of song control nuclei have been reported not to occur is the nonmigratory Nuttall's subspecies of white-crowned sparrow. In the present study, we manipulated photoperiod and plasma testosterone concentrations in captive male white-crowned sparrows of the migratory Gambel's subspecies. Males exposed to photoperiods and plasma testosterone concentrations typical of those experienced by wild breeding males had larger song control nuclei than males held on a winter photoperiod. We also found seasonal changes in stereotype of spectral and temporal parameters of song in wild Gambel's white-crowned sparrows. We hypothesize that seasonal changes in the song control nuclei may correlate with seasonal changes in song stereotypy.

Cultural and Genetic Differentiation of Two Subspecies of White-Crowned Sparrow

Cultural and Genetic Differentiation of Two Subspecies of White-Crowned Sparrow

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Corticosterone affects physiology and behavior both during normal daily processes but also in response to environmental challenges and is known to mediate life history trade-offs. Many studies have investigated patterns of corticosterone production at targeted times of year, while ignoring underlying annual profiles. We aimed to understand the annual regulation of hypothalamic-pituitary-adrenal (HPA) axis function of both migrant (Zonotrichia leucophrys gambelii; n = 926) and resident (Z. l. nutalli; n = 688) subspecies of white-crowned sparrow and how it is influenced by environmental conditions – wind, precipitation, and temperature. We predicted that more dramatic seasonal changes in baseline and stress-induced corticosterone would occur in migrants to precisely time the onset of breeding and cope with environmental extremes on their arctic breeding grounds, while changes in residents would be muted as they experience a more forgiving breeding schedule and comparatively benign environmental conditions in coastal California. During the course of a year, the harshest conditions were experienced the summer breeding grounds for migrants, at which point they had higher corticosterone levels compared to residents. For residents, the winter months coincided with harshest conditions at which point they had higher corticosterone levels than migrants. For both subspecies, corticosterone tended to rise as environmental conditions became colder and windier. We found that the annual maxima in stress-induced corticosterone occurred prior to egg lay for all birds except resident females. Migrants had much higher baseline and acute stress-induced corticosterone during breeding compared to residents; where in a harsher environment the timing of the onset of reproduction is more critical because the breeding season is shorter. Interestingly, molt was the only stage within the annual cycle in which subspecies differences were absent suggesting that a requisite reduction in corticosterone may have to be met for feather growth. These data suggest that modulation of the HPA axis is largely driven by environmental factors, social cues, and their potential interactions with a genetic program.