Chamaea Research Articles

Experimentally broadcast ocean surf and river noise alters birdsong.

Anthropogenic noise and its effects on acoustic communication have received considerable attention in recent decades. Yet, the natural acoustic environment’s influence on communication and its role in shaping acoustic signals remains unclear. We used large-scale playbacks of ocean surf in coastal areas and whitewater river noise in riparian areas to investigate how natural sounds influences song structure in six songbird species. We recorded individuals defending territories in a variety of acoustic conditions across 19 study sites in California and 18 sites in Idaho. Acoustic characteristics across the sites included naturally quiet ‘control’ sites, ‘positive control’ sites that were adjacent to the ocean or a whitewater river and thus were naturally noisy, ‘phantom’ playback sites that were exposed to continuous broadcast of low-frequency ocean surf or whitewater noise, and ‘shifted’ playback sites with continuous broadcast of ocean surf or whitewater noise shifted up in frequency. We predicted that spectral and temporal song structure would generally correlate with background sound amplitude and that signal features would differ across site types based on the spectral profile of the acoustic environment. We found that the ways in which song structure varied with background acoustics were quite variable from species to species. For instance, in Idaho both the frequency bandwidth and duration of lazuli bunting (Passerina amoena) and song sparrow (Melospiza melodia) songs decreased with elevated background noise, but these song features were unrelated to background noise in the warbling vireo (Vireo gilvus), which tended to increase both the minimum and maximum frequency of songs with background noise amplitude. In California, the bandwidth of the trill of white-crowned sparrow (Zonotrichia leucophrys) song decreased with background noise amplitude, matching results of previous studies involving both natural and anthropogenic noise. In contrast, wrentit (Chamaea fasciata) song bandwidth was positively related to the amplitude of background noise. Although responses were quite heterogeneous, song features of all six species varied with amplitude and/or frequency of background noise. Collectively, these results provide strong evidence that natural soundscapes have long influenced vocal behavior. More broadly, the evolved behavioral responses to the long-standing challenges presented by natural sources of noise likely explain the many responses observed for species communicating in difficult signal conditions presented by human-made noise.

Short-Term Response of Vegetation and the Riparian Bird Community to Dam Removal on the Rogue River, Oregon

Both establishment and subsequent removal of dams inevitably alter river systems and may impact aquatic and terrestrial organisms. Despite both stated and implicit restoration goals of dam removal, relatively few studies have examined ecological response. Using a before-after-control-impact framework one year before and two years after, I evaluated the short-term effect of a dam removal on the Rogue River in southwestern Oregon on vegetation, bird community composition, and abundance of eight riparian-associated bird species. No differences were detected for tree and shrub strata cover after dam removal for either treatments or controls. Within the three treatment habitat types (mainstem, slough, wetland), shrub and ground cover declined only in wetland areas, likely as a result of post dam removal vegetation management. Significant changes in relative abundance were found for only one of eight focal bird species. Chamaea fasciata (Wrentit) abundance declined on treatment points following dam removal, possibly a response to the decrease in cover of the shrub and ground vegetative strata in the wetland. Bird community composition did not differ between controls and treatments either before or after dam removal. In combination, the similarities in bird community composition and lack of detectable change in abundance for seven riparian associated species are consistent with the results for vegetative cover, suggesting shrub and tree components of riparian habitat did not change substantially in the two years following dam removal. Results from this study have important management implications for maintaining or restoring riparian vegetation in conjunction with future dam removals.

Habitat suitability through time: using time series and habitat models to understand changes in bird density

Confronted with a rapidly changing world and limited resources for conservation, ecologists are increasingly challenged with predicting the impact of climate and land‐use change on wildlife. A common approach is to use habitat‐suitability models (HSMs) to explain aspects of species' occurrence, such as presence, abundance, and distribution, utilizing physical habitat characteristics. Although HSMs are useful, they are limited because they are typically created using spatial rather than temporal data, which omits temporal dynamics. We explored the value of combining spatial and temporal approaches by comparing HSMs with autoregressive population models. We investigated a 28‐year period of bird community dynamics at a field site in northern California during which time the plant community has been transitioning from scrub to conifer forest. We used the two model frameworks to quantify the contribution of vegetation change, weather, and population processes (autoregressive models only) to variation in density of seven bird species over the first 23 years. Model predictive ability was then tested using the subsequent five years of population density data. HSMs explained 58% to 90% of the deviance in species' density. However, models that included density dependence in addition to vegetation covariates provided a better fit to the data for three of the seven species, Song Sparrow (Melospiza melodia), White‐crowned Sparrow (Zonotrichia leucophrys), and Wrentit (Chamaea fasciata). These three species have more localized dispersal compared to the other four species, suggesting that dispersal tendency may be an important life‐history trait to consider when predicting the impact of climate and land‐use change on population levels. Our results suggest that HSMs can effectively explain and predict variation in species' densities through time, however for species with localized dispersal, it may be especially informative to include population processes.

Influence of Suburban Habitat on A Wintering Bird Community in Coastal Northern California

Abstract. To evaluate factors influencing a suburban bird community in coastal northern California, we examined the abundance, richness, and diversity of wintering birds at 75 locations within the city of Arcata. For each location we used aerial imagery to determine the proportions of vegetation and impervious surfaces within 75 m and the distances to various landscape features. Human activity was measured and used as a covariate in model selection. Total bird abundance, species richness, and diversity declined with the proportion of road surface at a site, while the abundance of non-native species increased with the cover of roads and structures. The proportions of shrub and tree cover at a site predicted total abundance and richness positively. The effect of trees on species diversity was increasingly positive in more urban areas. Several species, such as Steller's Jay (Cyanocitta stelleri), Ruby-crowned Kinglet (Regulus calendula), Wrentit (Chamaea fasciata), Winter Wren (Troglodytes troglodytes), Yell...

Effects of Mist Netting on Reproductive Performance of Wrentits and Song Sparrows in Central Coastal California

Abstract. Mist netting is widely used to monitor the reproductive success of passerines, yet little is known about its effects on bird ecology. Using a 25-year data set from central California, we evaluated the effects of constant-effort mist netting on the reproductive performance of the Wrentit (Chamaea fasciata) and Song Sparrow (Melospiza melodia). We compared nest survival, number of young fledged, and an index of nestling condition (mass corrected for body size) at nests where at least one parent was captured while the nest was active to these variables at nests where neither parent was captured. We also compared these characteristics for nests at varying distances from nets run at different frequencies. Wrentit nestlings from nests closer to less frequently run nets were in poorer condition than those from nests close to more frequently run nets and than those far away from any nets. For the Song Sparrow, daily nest survival was higher where at least one parent was captured while the nest was activ...

Responses in Bird Communities to Wildland Fires in Southern California

There is a growing body of literature covering the responses of bird species to wildland fire events. Our study was unique among these because we investigated the effects of large-scale wildland fires on entire bird communities across multiple vegetation types. We conducted avian point counts during the breeding seasons for two years before and two years after the Cedar and Otay Fires in 2003 in southern California. Our balanced sampling effort took place at two sites, one low-elevation and one high-elevation, each containing replicate stations (burned and unburned) within five vegetation types: chaparral, coastal sage scrub, grassland, oak woodland, and riparian. Although fire caused some degree of change in the vegetation structure at all of our impacted survey points, we found that the post-fire shrub and tree cover was significantly lower in only two of the vegetation types within the low-elevation site, coastal sage scrub and chaparral. We found no significant changes in cover at the high-elevation site. Using univariate and multivariate analyses, we tested whether the fires were associated with a change in bird species diversity, community structure, and the relative abundance of individuals within a species. We found that species diversity changed in only one circumstance: it increased in coastal sage scrub at the low-elevation site. Multivariate analyses revealed significant differences in the post-fire bird community structure in the low-elevation chaparral, low-elevation coastal sage scrub, and the high-elevation grassland communities. Vegetation characteristics altered by fire, such as decreases in shrub and tree cover, influenced the changes we observed in the bird communities. The relative abundance of some species (lazuli bunting [Passerina amoena] and horned lark [Eremophila alpestris]) significantly increased after the fires, while other species declined significantly (Anna’s hummingbird [Calypte anna], wrentit [Chamaea fasciata], and bushtit [Psaltriparus minimus]). We detected mixed results for the spotted towhee (Pipilo maculatus), which increased in burned chaparral and declined in burned coastal sage scrub within the low-elevation site. We suggest that the observed responses of birds to these fires may be attributed to: (1) the availability of nearby unburned refugia, (2) the continued suitability of post-fire vegetation at the study sites, and (3) the generally high mobility of this taxon.

INDEPENDENT EFFECTS OF FOOD AND PREDATOR-MEDIATED PROCESSES ON ANNUAL FECUNDITY IN A SONGBIRD

We investigated the relative importance and interaction of ecological processes affecting annual fecundity in birds by simultaneously manipulating food availability and nest predation risk in a small songbird, the Wrentit (Chamaea fasciata). From 2000 to 2002 we provided supplemental food to individual Wrentit territories, and during 2002 we altered nest predation risk by providing supplemental food to their principal predators, Western Scrub-Jays (Aphelocoma californica). These experiments were conducted during a period of high interannual variation in rainfall, with 2002 being one of the driest years on record. Food-supplemented Wrentits in a normal predation environment produced an average of 0.54 more fledglings per year than control pairs over the three breeding seasons. During the feeding plus predation manipulation experiment, Wrentit food supplementation and lowered nest predation risk each independently increased the probability that a Wrentit pair would fledge young; however, the interaction between food supplementation and altered nest predation risk was not significant. Thus, even in an extreme drought year, both food and nest predation had equal but independent effects on reproductive success and annual fecundity. Combining supplemental food with reduced nest predation did not result in a synergistic increase in annual fecundity, primarily because Wrentits did not produce multiple broods. Our results suggest that whether food and predation have additive or synergistic effects on reproductive success depends on the life history of the species and the environment in which they live.

Population-level history of the wrentit ( Chamaea fasciata): Implications for comparative phylogeography in the California Floristic Province

The phylogeography of a variety of species has been studied within the California Floristic Province; however, few studies have examined genetic variation in bird species across the entire region. This study uses mitochondrial DNA data to investigate the phylogeography of the wrentit ( Chamaea fasciata), a sedentary bird native to scrub and chaparral habitats of this region. Analysis of molecular variance shows geographic structure, and maximum likelihood, Bayesian, and parsimony analyses consistently identify six main clades that are each restricted geographically. Nested clade phylogeographic analyses infer an overall range expansion for the entire cladogram, and a range expansion is also inferred from the mismatch distribution. Thus, our results suggest that the wrentit was isolated into southern refugia during the Pleistocene and has undergone a recent range expansion. Southern refugia and a range expansion were also identified in a previous study of the California thrasher ( Toxostoma redivivum). The wrentit did not show marked divergence between northern and southern California defined by the Transverse Ranges, a pattern seen in a variety of other taxa within this region, including some birds.

Variation in top‐down control of avian reproductive success across a fragmentation gradient

Understanding mechanisms that inhibit population persistence in fragmentation‐sensitive species is a key to conservation and management. It has become clear that species vary in their sensitivity to habitat fragmentation caused by urbanization and other land uses. We studied variation in avian reproductive success in coastal sage scrub habitat across a fragmentation gradient (interior of large habitat blocks (>2300 ha)→edge of large habitat blocks→large habitat fragments (37–80 ha)→small habitat fragments (5–17 ha)) in urban southwestern California. We focused on four species of birds: the shrub‐nesting wrentit (Chamaea fasciata) and California towhee (Pipilo crissalis) and the ground‐nesting spotted towhee (P. maculatus) and rufous‐crowned sparrow (Aimophila ruficeps). Snake abundance was the best predictor of nest failure in the ground‐nesting species, whereas abundance of avian predators (Corvidae, Mimidae) was associated with nest failure of the wrentit and a combination of snake and avian predator abundance was correlated with nest failure of the California towhee. Avian nest predator abundance increased across the fragmentation gradient; by contrast, snake abundance decreased across this gradient. As a result, top‐down control of reproductive success in populations of the spotted towhee and rufous‐crowned sparrow was largely absent in habitat fragments. These two species enjoyed much higher nest success on fragments yet, paradoxically, both species are sensitive to fragmentation whereas the shrub‐nesting species are not. Our findings suggest that another process – perhaps differential survivorship or dispersal – yields reduced abundance of ground‐nesting species in habitat fragments. Studies of top‐down control and trophic cascades in fragmented landscapes should reflect that the strength of top‐down forces across a landscape varies with characteristics of predator and prey and their autecological responses to ecological gradients.

PHYLOGENETIC RELATIONSHIPS OF THE WRENTIT BASED ON MITOCHONDRIAL CYTOCHROME b SEQUENCES

Abstract The phylogenetic relationship of the Wrentit (Chamaea fasciata) to other passerine birds is understood poorly. A variety of taxa have been proposed as closely related to the Wrentit, but in general this species is placed in a monotypic taxon to emphasize its morphological distinctiveness and lack of clear relationship to other groups of birds. We used the mitochondrial cytochrome b gene to infer the relationship of this monotypic genus to other avian groups including representatives of Sylvioidea, Muscicapoidea, and Passeroidea. Results of this study corroborate in part earlier proposals based on DNA-DNA hybridization. Maximum parsimony, maximum likelihood, and Bayesian phylogenetic analyses support the Wrentit, Sylvia, and babblers (Garrulax, Illadopsis, Leiothrix, Pomatorhinus, Stachyris, and Yuhina) as a clade, with the Wrentit sharing a more recent common ancestor with Sylvia than with babblers. A Sylvia and Wrentit association is further supported by similarities in morphology and ecology. I...

The Use of Mist-Net Capture Rates to Monitor Annual Variation in Abundance: A Validation Study

Constant-effort mist-netting has become an increasingly popular tool in long-term monitoring of bird populations. Monitoring programs often assume that variation in the capture rates of adults reflects variation in breeding densities of the sampled population. We test this assumption by comparing annual variation in mist-net capture rates to known variation in breeding densities of four species breeding in coastal scrub habitat at Point Reyes National Seashore, California. For the period 1980 to 1992, breeding densities for each species were assessed using spot-mapping observations of color-banded individuals. These were compared to capture rates calculated from constant-effort mist-netting. Capture rates of adults correlated significantly with breeding density for Spotted Towhees (Pipilo maculatus), Song Sparrows (Melospiza melodia), and Wrentits (Chamaea fasciata), but not for White-crowned Sparrows (Zonotrichia leucophrys). Analysis of covariance confirmed that the relationship of mist-net capture rates to breeding density differed among species. Independent of the effects of breeding density on capture rates, adult capture rates of the four species were higher in years with high rainfall. Among Wrentits and Song Sparrows, approximately 50% or more of adults caught were not occupying territories at the study site; the same bias may exist among other species as well. We conclude that relative changes in breeding density over time can be inferred from variation in mist-net capture rates for some, but not all, species. Additional studies are needed to validate the use of mist nets to assess spatial differences in abundance and to monitor temporal changes in abundance in habitats other than coastal scrub.

Correcting Biased Estimates of Dispersal and Survival Due to Limited Study Area: Theory and an Application Using Wrentits

Accurate estimates of dispersal distributions and survival to breeding are essential for estimating gene flow and population demographics, and for testing the predictions of mechanistic models. We derive a method that corrects for the underestimate of dispersal and survival inherent in studies conducted within a finite area. Each dispersal event is weighted by the inverse of the probability of observing that event, calculated by dividing the observable dispersal events of a given distance by all possible dispersal events of that distance. The method takes into account the shape of the study area and suitability of habitat. The method is applied to a twelve-year field study of natal dispersal in Wrentits (Chamaea fasciata) resulting in an increase in the estimate of mean and median dispersal from observed values of 267 and 248 m to corrected values of 375 and 387 m. The correction method also estimates the number of second year birds recruiting to potential breeding territories on and off the study area. Seventy-five of the 799 locally born fledglings recruited onto the study plot (9.3%). We estimate that an additional 101 birds recruited off the study plot, increasing the estimate of yearling survival to recruitment from 9.3% to 21.9% of young fledged. We used a simulation approach to generate testable predictions that validate the assumptions and results of the method. The method is easy to apply, and is easily extended to incorporate greater realism and detail.

The Relationships of the Wrentit as Indicated by DNA-DNA Hybridization

The of the Wrentit (Chamaea fasciata) have been debated since its discovery in 1845. The titmice (Parus), babblers (Timaliini), Old World warblers (Sylviini), bushtits (Psaltriparus), wrens (Troglodytidae), and mockingbirds (Mimini) have been suggested as its closest relatives. Many authors have placed the Wrentit in a monotypic family, Chamaeidae. DNA-DNA hy- bridization comparisons between the homologous nucleotide sequences of the single-copy DNAs of the Wrentit and other passerines indicate that Chamaea is most closely related to the babblers and the Old World warblers, and that the latter two groups are ecotypes of a single, varied, monophyletic assemblage. The Wrentit is annroximatelv eauidistant from the sylviines and the timaliines, but ecologically it is a babbler. _ The Wrentit (Chamaea fasciata) occurs in chaparral and other dense, brushy, plant for- mations in western Oregon, California, and northwestern Baja California. The question of its affinities to other passerines has been de- bated since the 1850's. Sibley (1970:57-60) reviewed the taxonomic history of the Wrentit and presented electrophoretic comparisons between its egg white proteins and those of many other oscine taxa. He concluded that the total evidence did not offer a clear choice be- tween the sylviine warblers and the timaliine babblers as the closest relatives of Chamaea and that the question of the relationships of the wren-tit remains open and further evidence should be presented before the affinities of the wren-tit are considered to have been proved beyond doubt (p. 60). More recently, Sibley and Ahlquist (1980) concluded that Cha- maea is a babbler. In the present paper we offer additional data showing that the sylviine warblers and timaliine babblers are actually ecotypes of a single varied assemblage and that the Wrentit probably was derived from an Asiatic babbler. METHODS

A Study of Methods of Color Determination

IN THE course of an investigation of correlations of color of wren-tits (Chamaea fasciata) with environmental gradients, the author found it necessary accurately to designate and record the colors in question. Although my investigation was not taxonomically oriented, the description and evaluation of the methods of color determination here presented may be useful in taxonomic studies wherever colors are to be considered. North of San Francisco Bay, California, there are three races of Chamaea fasctata. The darkest birds, ascribable to the race C. f. rufula, exist in the coastal humid belt from San Francisco Bay northward. The lightest birds, of the race C. f. henshawi, occur interiorly from the southern tip of the Vaca Mountains northward and northwestward. In between these two, the appropriately named race C. f. irtermedta is found. The color of the breast and belly regions of these birds shows a gradation from moderate brown through various color steps to a lighter, buffier, pale yellowishbrown. The problem of color definition is evident from the adjectival terms used here to describe these extremes in breast color. The terms moderate brown and pale yellowish-brown have meaning to the author in connection with the birds studied because of experience with them. But how similar would these colors appear in the mind's eye of a reader not having had such experience with these particular birds? It is my contention, in view of the high degree of variation in human color-vision response and experience, that color designation in adjectival terms is not sufficiently reliable to convey to others the color sensations perceived by a worker. Because of this belief, I have gone to some lengths to find objective methods of designating the colors of the birds in question. A very important reference for the description of colorimetry is a book by the Committee on Colorimetry of the Optical Society of America (1953). This work is valuable not only for its excellent treatment of the concepts of color and color vision, but for its extensive bibliography in the fields of color and colorimetry.

Call-Notes and Mannerisms of the Wren-Tit

Call-Notes and Mannerisms of the Wren-Tit

Notes on the osteology of the Paridae, Sitta, and Chamaea

Notes on the osteology of the Paridae, Sitta, and Chamaea