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Variation in song can play a central role in species and subspecies recognition among birds. The ability of individuals to distinguish between songs of their own versus songs of a different subspecies potentially strengthens local adaptation of subspecific populations. We investigated the degree of vocal divergence and discrimination between two subspecies of Swamp Sparrow (Melospiza georgiana) to examine how variation in song could influence behavioral response. We recorded songs of Southern (M. g. georgiana) and Coastal Plain (M. g. nigrescens) Swamp Sparrow males in Maryland and Delaware, respectively, and analyzed variation in syllable composition, repertoire size, trill rate, and frequency bandwidth. In addition to describing differences in song characteristics, we performed an estimate of local song type diversity that predicted larger population repertoires in M. g. nigrescens. We then broadcast recordings to evaluate male territorial responses to song and found that males reacted more strongly to songs of their own subspecies than to songs of the other subspecies. The extent of song variation and discrimination suggests the possibility of continued divergence. Further tests may determine whether such results can be generalized beyond the populations studied to the subspecies level, and whether females as well as males differentiate between songs from separate subspecies. Key words: geographic variation, Melospiza georgiana, song playbacks, subspecies divergence, Swamp Sparrow, vocalizations. La variacion del canto puede desempenar un papel importante en el reconocimiento de especies o subespecies de aves. La capacidad de distinguir entre canto autoctono y aloctono puede reforzar la adaptacion local de las poblaciones subespecificas. Se investigo el grado de divergencia y discriminacion vocal en dos subespecies de Melospiza georgiana para examinar la influencia de la divergencia vocal sobre el comportamiento de ambas subespecies. Se grabaron cantos de M. g. georgiana y nigrescens en Maryland y Delaware, respectivamente, y se analizo la variacion en la composicion silabica, el tamano del repertorio, la velocidad del canto y el ancho de banda. Ademas de describir las diferencias en las caracteristicas del canto entre las dos subespecies, se hizo un calculo de la diversidad local del canto que predijo un repertorio colectivo mas grande en M. g. nigrescens. Despues se reprodujeron grabaciones para evaluar la respuesta territorial de los machos al canto y se encontro que la reaccion era mayor ante cantos de individuos de la misma subespecie que ante aquellos de la otra subespecie. El grado de variacion y discriminacion entre cantos sugiere la existencia de un proceso de divergencia entre estas dos subespecies. Sin embargo, es necesario realizar mas experimentos para generalizar estos resultados mas alla de las poblaciones estudiadas al nivel de subespecies, y para determinar si las hembras tambien pueden discriminar los cantos de diferentes subespecies.

Tracing movements of migratory birds between breeding and wintering areas is important for both theoretical and conservation purposes. Intrinsic markers such as stable isotopes have received considerable attention because of their usefulness for evaluating migratory connections without the need to mark and recapture individuals. Establishing migratory linkages using stable-isotope markers hinges on knowing which tissues most accurately reflect the isotopic signature of previous feeding locations of interest. Here, we assessed the correspondence among stable-hydrogen isotope ([delta]D) values of feathers, claws, and cellular portions of blood from migrating White-throated Sparrows (Zonotrichia albicollis) to determine if these measures provided concordant estimates of origins. [delta]D values of claws from birds captured during spring and fall migration were positively correlated with 8D values of head feathers grown on the wintering grounds and tail feathers grown on breeding grounds, respectively, indicating that claws contained information on origins of individuals. However, analyses contrasting 8D measurements of base and tip of claws, and head and tail feathers suggest that a significant amount of claw growth occurred during migration resulting in biased estimates of breeding and wintering origins. Thus, for ground-foraging birds like White-throated Sparrows, we caution against using isotope measurements of claws as long-term position indicators. 8D values of blood were correlated with the [delta]D values from the base of claws, which represented the most recent claw growth, but were not correlated with the [delta]D values of claw tips and head feathers. Thus, it appears that the 8D values of blood cells are not useful for estimating wintering latitudes of White-throated Sparrows captured during spring migration. Key words: deuterium, natal origin, stable isotopes, turnover, White-throated Sparrow.

We studied the relationships among weather, reproductive success, and population density over 21 years (1980-2000) in a resident Song Sparrow (Melospiza melodia) population in coastal scrub habitat. Our goals were to test potential relationships between annual variation in weather and reproductive success, to evaluate whether reproductive success is density dependent, and to explore the effects of weather and population density on population dynamics. We analyzed the following components of reproductive success: clutch size, hatching success, fledging success, number of young fledged per successful nest, nestling weight, number of fledglings produced per female, number of broods per female, and probability of nest survival. During the study period, several very wet El Nino-Southern Oscillation (ENSO) events as well as an eight-year period of below-average rainfall occurred. Annual reproductive success and population density showed strong positive relationships to annual rainfall levels. Song Sparrow reproductive success increased with increasing rainfall and peaked at above-average rainfall levels. However, no component of reproductive success was related to an index of variation in the ENSO (i.e. Southern Oscillation Index). The components of reproductive success most strongly associated with rainfall were probability of nest survival and length of the breeding season. Nest predation rates were lower in wetter years. Song Sparrows nested over a longer period in years with higher rainfall and lower summer temperatures, and there was an increase in the number of successful broods per female in wetter, cooler years. Nestling weight was not associated with annual rainfall. Neither clutch size nor the onset of laying was associated with spring temperatures. Warmer summer temperatures were associated with a decrease in number of young fledged per successful nest. We found no evidence for decreased reproductive success in years of higher population density, which suggests that reproductive success was limited primarily by density-independent factors, such as weather. Changes in population density from one year to the next were positively related to rainfall-associated variation in reproductive success and negatively related to population density in the previous year. Rainfall in the previous year explained at least 49% of the annual variation in population density. Thus, population dynamics appeared to be driven both by density-independent and density-dependent factors. Received 29 January 2004, accepted 15 November 2004. Key words: breeding phenology, California coastal scrub, density dependence, density independence, El Nino-Southern Oscillation, Melospiza melodia, nest predation, nest success, population density, population dynamics, rainfall, reproductive success, Song Sparrow, temperature, weather.

Understanding nest survival is critical to bird conservation and to studies of avian life history. Nest survival likely varies with nest age and date, but until recently researchers had only limited tools to efficiently address those sources of variability. Beginning with Mayfield (1961), many researchers have averaged survival rates within time-specific categories (e.g. egg and nestling stages; early and late nesting dates). However, Mayfield's estimator assumes constant survival within categories, and violations of that assumption can lead to biased estimates. We used the logistic-exposure method to examine nest survival as a function of nest age and date in Clay-colored Sparrows (Spizella pallida) and Vesper Sparrows (Pooecetes gramineus) breeding in north-central North Dakota. Daily survival rates increased during egg laying, decreased during incubation to a low shortly after hatch, and then increased during brood rearing in both species. Variation in survival with nest age suggests that traditional categorical averaging using Mayfield's or similar methods would have been inappropriate for this study; similar variation may bias results of other studies. Nest survival also varied with date. For both species, survival was high during the peak of nest initiations in late May and early June and declined throughout the remainder of the nesting season. On the basis of our results, we encourage researchers to consider models of nest survival that involve continuous time-specific explanatory variables (e.g. nest age or date). We also encourage researchers to document nest age as precisely as possible (e.g. by candling eggs) to facilitate age-specific analyses. Models of nest survival that incorporate time-specific information may provide insights that are unavailable from averaged data. Determining time-specific patterns in nest survival may improve our understanding of predator-prey interactions, evolution of avian life histories, and aspects of population dynamics that are critical to bird conservation. Received 11 May 2004, accepted 29 November 2004. Key words: Clay-colored Sparrow, logistic exposure, nest survival, Pooecetes gramineus, Spizella pallida, Vesper Sparrow.

Predators (or parasites) can have both direct and indirect effects on prey (or host) demography. Recent theory suggests that the impact of either effect may be greater if predators and parasites skew the sex ratio of survivors. Brown-headed Cowbirds (Molothrusater) are obligate brood parasites. Many studies have shown that adult cowbirds directly cause host offspring mortalities. Cowbird young may indirectly cause additional mortalities by increasing competition in the nest. The sex ratio of surviving host offspring will be skewed if one sex is a poorer competitor and thus more likely to die. We studied whether and how cowbird parasitism affects host offspring sex ratios in Song Sparrow (Melospiza melodia) nests. The proportion of female sparrows in parasitized nests (0.28 [+ or -] 0.01) was half that in unparasitized nests (0.57 [+ or -] 0.05) at six days post-hatch and at fledging (0.27 [+ or -] 0.06 vs. 0.52 [+ or -] 0.11). Consistent with their being at a competitive disadvantage, female sparrows were smaller and lighter than male sparrows in parasitized mixed-sex (both sexes present) nests. This indirect effect of cowbirds on the sex ratio of surviving host offspring may dramatically affect host demography. We suggest that predator- or parasite-mediated sex ratio biases could be important to the demography of many prey or host species. Key words: brood parasitism; Brown-headed Cowbird; Melospiza melodia; Molothrus ater; nestling competition; predator-prey interactions; sex ratios; sexual size dimorphism; sibling competition; Song Sparrow.

We hypothesized that Neotropical passerines would invest more in costly immune function relative to north-temperate passerines, due to differences in their respective life histories. We further hypothesized that latitudinal variation in immune activity would persist in common-garden conditions. To test these hypotheses, we compared immune function, measured via phytohemagglutinin (PHA)-induced wing-web swelling in both wild House Sparrows (Passer domesticus) and House Sparrows kept under common-garden conditions for 18 months. We found that wild Neotropical sparrows had relatively stable immune responses across the year, whereas wild north-temperate sparrows showed substantial seasonal variation in immune activity, having lower responses than Neotropical birds during the early breeding season and significantly higher responses than Neotropical birds during the late and nonbreeding seasons. Latitudinal differences in immune responses were not related to mass, sex, or body condition, but were influenced by mass change 24 hours after immune challenge. Under common-garden conditions, birds from both populations first decreased (after five months) and then increased (after 18 months) their non-breeding immune responses relative to wild values, indicating condition dependence in the PHA response. Relative differences in the PHA response between the populations, however, were maintained in captivity: after 18 months in common gardens, north-temperate sparrows exhibited stronger nonbreeding immune responses than Neotropical sparrows. Keywords: clutch size; common garden; House Sparrow; immunocompetence; life history; Neotropical; Passer domesticus; passerine; PHA; phytohemagglutinin; trade-offs.

A playback experiment is used to evaluate the success of a stranger male that mimics the song of a local song sparrow in order to infiltrate his territory. The response to the invader male was strongly aggressive as shown by charts that accompany the article.

The songs of swamp sparrows are compared for their ability to attract mates, depending upon the relative innovation of the song syntax. Female birds are shown to be more conservative about song syntax than male birds.

Recorded songs from sparrows are played back to subject neighbour sparrows in order to determine the response to song-type. Foreign songs, matching song type, and a song from the same repertoire are compared for eliciting an aggressive response. Graphs of song type, aggression scores, and song type switching accompany the article.

The Rufous-collared Sparrows in Costa Rica popularly possess individual song repertoires and they do not have the terminal trill. Comparative study with the Argentinian population suggest that songs there are more similar than songs from Costa Rica. The studies from Argentina reveal that the Rufous-collared Sparrows generally have the repertoire of one song per bird.

A study of the song of the Rufous-collared Sparrow to understand the relationship between habitat and song structure showed that longer TRINT can be detected in songs from the open habitat, which contradicts the Acoustic Adaptation Hypothesis. Songs from grasslands also had broader TRBAND and lower TRMIN than songs from forested areas. Lower density of singers in open grasslands and existence of strong winds were found to be the two factors influencing the song structure.

Singing by females in two subspecies of white-crowned sparrows was studied. Female members of Zonotrichia leucophrys nuttalli, a coastal species, sing from autumn to early spring, prior to nest-building, and song is considered to have a territorial function and may also be used to advertise for a mate. In the Z.l. oriantha, a migratory, montane subspecies, female song is limited to early summer when birds return to their summer breeding areas to establish nest sites. Singing is more likely when spring arrives late and competition for nest sites is strongest.

The social stimulus and tutoring of well-developed white-crowned sparrows was studied through direct contact between young birds and adults to show that young birds had a tendency to learn songs that were an easy version of songs of the adult. The song elements and the structure of syllables resembled those of the adults. Aberrant songs were observed in many young birds that were open to extreme aggression from adults. This also significantly hampered song development. Field-raised young sparrows, when compared with laboratory-raised birds, demonstrated improved song quality despite aggression by adult tutors.

Permanency and integrity were predominant in song dialects of socially mixing adult male white-crowned sparrows in Northern California. Studies of post-tutoring periods revealed some changes in the songs which could be attributed to motivation levels. Almost 91% of wild adult white-crowns in the Presidio region adopted the vibrato and complex syllables, while around 94% sung simple syllables. In the Twin Peaks region, 82-91 % adopted complex syllables. The Tioga Pass dialect was observed in birds from the Sierra Nevada, California.

The rufous-collared sparrow song was observed for trill features to reveal that trill features are strongly connected with the type of vegetation in the region. There are longer trill intervals and lower minimum frequencies in the songs in talar woodland as compared to those on the steppe. Acoustic degradation is effected by gradually regulated signals as observed in forests. Random amplitude fluctuation in open fields is the result of poor acoustic quality. Differences in dialect could be interpreted by variations in habitat and immigration.

Male White-crowned Sparrows' responses to song stimuli different from their local dialect were examined by comparing responses to unaltered dialect control songs and to hybrid songs consisting of elements from two adjacent dialects. Results revealed that the dialect of the specimens was the most potent stimulus, while the neighboring dialect was the least potent. When local dialect introductory components replaced those of the adjacent dialect, the evoked response was similar to that obtained by the local dialect. Further substitutions in other parts of the song resulted in reduced responses, suggesting that the acoustic features of the first part of the song encode vocal information controlling male territorial behavior.

In the ascending songs of white-throated sparrows (Zonotrichia albicollis), the first note (Phrase 1) is sung lower than the remaining notes (Phrase 2). The production of this frequency change is more reliably predicted by the frequency ratio (Phrase 2 divided by Phrase 1) than by the frequency difference (Phrase 2 - Phrase 1). To determine whether sparrows use the ratio rather than the difference to identify ascending songs, we transposed a low-frequency song upward in frequency, maintaining a normal frequency difference but altering the frequency ratio, and we transposed a high-frequency song downward in the same way. Territorial males tested in the wild sang more and approached more closely to songs with normal ratios than to songs with altered ratios, even when the frequency difference was identical in both. This is the first evidence that the perception of pitch change by songbirds is related to the frequency ratio independent of the difference.

A laboratory study of male song was done to determine the sexual response of female white-crowned sparrows exposed to a change in the learning model of a song during early ontogeny. The findings showed that the females favored the song dialect heard during the first 50 days of life, suggesting that female reproductive behavior was more spurred by the tutoring dialect of the female's early experience than by their later experience.

The presence of temporal relationships in the song of the white-throated sparrow was determined. The durations of the notes were correlated, likewise the duration of the inter-noteintervals. However, the duration of the notes did not correlate with the inter-note interval durations. Hence, although the notes and intervals may havedistinct tempos, the entire song may not have an overall rhythm. The inter-noterelationships were less defined than those previously reported for the species.

Song sparrows appear to possess the neural mechanisms needed to learn their own species' songs after a limited exposure to tape-recorded models. The extent of exposure did not influence the completeness nor the accuracy of the imitation. The study animals were exposed to the song relatively late in the sensitive phase for learning, hence, the timing of the exposure may have significantly influenced the quality of learning.

A geographically wide-ranging study of morphological and allozyme frequency variation in the rufous-collared sparrow is undertaken in order to test the genetic adaptation hypothesis regarding the evolution of vocal dialects in this species. Results show that there is significant heterogeneity in morphology among dialect populations, and there is also heterogeneity in allozyme frequencies among sites in mountainous habitats. Therefore, the said hypothesis is rejected, and topography and patchiness of habitat are seen as factors in population differentiation, rather than vocal dialects.

Research suggests that very young, hand-reared white-crowned sparrows, Zonotrichia leucophrys nuttalli, recognize song from their own species by acoustic cues, before they reach the age of song acquisition. Tapes containing one song type from white-crowned sparrows and one from another species were played to fledglings and their response recorded. The results showed conspecific song was recognized. It is proposed that the ability to respond selectively to conspecific song is due to an innate mechanism that is the basis for selective vocal learning in young birds.

Estimated the amount of frequency variation that affected individual and species recognition by song in territorial male field sparrows with field playbacks of neighbors' songs lowered in frequency in 6 increments between 324 and 1296 Hz, which is about 11% of the mean midfrequency in field sparrow song. Territorial responses were eliminated when neighbors' songs were lowered by more than about 900 Hz. Thus, there is a fairly narrow range of frequencies within which field sparrow songs can vary while functioning in communication. Ss' responses appear to be constained by the normal range of song frequency variation within the species, but the range of variability within songs of individuals did not influence the degree of frequency shift required to render neighbors' songs unfamiliar.