Search

Copyright of Journal of Field Ornithology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Many species have already experienced distributional shifts due to changing environmental conditions, and analyzing past shifts can help us to understand the influence of environmental stressors on a species as well as to analyze the effectiveness of conservation strategies. We aimed to (1) quantify regional habitat associations of the California gnatcatcher (Polioptila californica); (2) describe changes in environmental variables and gnatcatcher distributions through time; (3) identify environmental drivers associated with habitat suitability changes; and (4) relate habitat suitability changes through time to habitat conservation plans. Southern California's Western Riverside County (WRC), an approximately 4,675 km2 conservation planning area. We assessed environmental correlates of distributional shifts of the federally threatened California gnatcatcher (hereafter, gnatcatcher) using partitioned Mahalanobis D2 niche modeling for three time periods: 1980-1997, 1998-2003, and 2004-2012, corresponding to distinct periods in habitat conservation planning. Highly suitable gnatcatcher habitat was consistently warmer and drier and occurred at a lower elevation than less suitable habitat and consistently had more CSS, less agriculture, and less chaparral. However, its relationship to development changed among periods, mainly due to the rapid change in this variable. Likewise, other aspects of highly suitable habitat changed among time periods, which became cooler and higher in elevation. The gnatcatcher lost 11.7% and 40.6% of highly suitable habitat within WRC between 1980-1997 to 1998-2003, and 1998-2003 to 2004-2012, respectively. Unprotected landscapes lost relatively more suitable habitat (-64.3%) than protected landscapes (30.5%). Over the past four decades, suitable habitat loss within WRC, especially between the second and third time periods, was associated with temperature-related factors coupled with landscape development across coastal sage scrub habitat; however, development appears to be driving change more rapidly than climate change. Our study demonstrates the importance of providing protected lands for potential suitable habitat in future scenarios.

Many species have already experienced distributional shifts due to changing environmental conditions, and analyzing past shifts can help us to understand the influence of environmental stressors on a species as well as to analyze the effectiveness of conservation strategies. We aimed to (1) quantify regional habitat associations of the California gnatcatcher (Polioptila californica); (2) describe changes in environmental variables and gnatcatcher distributions through time; (3) identify environmental drivers associated with habitat suitability changes; and (4) relate habitat suitability changes through time to habitat conservation plans. Southern California's Western Riverside County (WRC), an approximately 4,675 km2 conservation planning area. We assessed environmental correlates of distributional shifts of the federally threatened California gnatcatcher (hereafter, gnatcatcher) using partitioned Mahalanobis D2 niche modeling for three time periods: 1980-1997, 1998-2003, and 2004-2012, corresponding to distinct periods in habitat conservation planning. Highly suitable gnatcatcher habitat was consistently warmer and drier and occurred at a lower elevation than less suitable habitat and consistently had more CSS, less agriculture, and less chaparral. However, its relationship to development changed among periods, mainly due to the rapid change in this variable. Likewise, other aspects of highly suitable habitat changed among time periods, which became cooler and higher in elevation. The gnatcatcher lost 11.7% and 40.6% of highly suitable habitat within WRC between 1980-1997 to 1998-2003, and 1998-2003 to 2004-2012, respectively. Unprotected landscapes lost relatively more suitable habitat (-64.3%) than protected landscapes (30.5%). Over the past four decades, suitable habitat loss within WRC, especially between the second and third time periods, was associated with temperature-related factors coupled with landscape development across coastal sage scrub habitat; however, development appears to be driving change more rapidly than climate change. Our study demonstrates the importance of providing protected lands for potential suitable habitat in future scenarios.

We studied the foraging behavior of the federally threatened coastal California Gnatcatcher (Polioptila californica), an obligate insectivore, during the non-breeding season, a period of reduced survivorship for this non-migratory passerine due to seasonal aridity and the onset of cold winter storms. During the seasonal dry period in fall (October–November), California Gnatcatchers preferentially foraged in fall-blooming shrubs such as coyote brush (Baccharis pilularis), and California brickelbush (Brickellia californica). Upon the onset of the wet winter period (December–January), foraging California Gnatcatchers demonstrated a seasonal shift toward drought deciduous shrubs then leafing out, especially coastal sagebrush (Artemisia californica). Our findings suggest that California Gnatcatchers shift their foraging preferences seasonally to track available food resources. Additionally, our findings point to the value of floristic diversity within California Gnatcatcher habitat to provide year-round foraging opportunities for this obligate insectivore.

The article offers information on the current northernmost breeding pair of the california gnatcatcher. Topics include, northernmost pair of the california gnatcatcher previously reported to the U.S. Fish and Wildlife Service (USFWS); surveying of bird habitat during breeding season; and observing bird's nesting status.

One goal of Habitat Conservation Plans is to protect viable populations of animal species. Management actions included in such plans often focus on vegetation restoration to benefit the target animal species. Yet, such restoration activities are often uninformed by fine-scale animal survey data. Using the California Gnatcatcher (Polioptila californica californica'j, we demonstrate how survey data can guide restoration toward the goal of improving gnatcatcher viability by identifying habitat conditions most favorable for gnatcatcher occupancy. We found that gnatcatcher presence and colonization probabilities tripled as the coverage of coastal sagebrush (Artemisia californica) increased from 10% to 40%. Coastal sagebrush was more likely to be present at low elevations, and was most closely associated with soil texture of 5%-20% clay, 40%-70% sand, and 20%-40% silt. Higher gnatcatcher extinction probabilities were associated with closed, dense habitat; optimal conditions were between 30% and 40% openness, creating a slightly closed canopy. Open habitat was associated with southern aspects, shallow slopes, and inland areas. An understanding of the soil types and physical parameters of the environment that affect vegetation, especially the amount of coastal sagebrush needed for high gnatcatcher occupancy and colonization rates, will help to define restoration target conditions. Using multiseason, occupancy-based surveys in conjunction with detailed habitat measurements will allow ornithologists and land managers to design powerful restoration prescriptions, even within narrowly defined ecosystems. [ABSTRACT FROM AUTHOR]

Improving the efficiency of monitoring protocols prescribed by conservation plans can release typically limited funding for other management and conservation activities. We present an approach for optimizing protocols that considers the precision of parameter estimates, costs of implementation, and broader monitoring-program goals. In a case study of the Coastal California Gnatcatcher (Polioptila californica californica), we compared the efficiency of pointcount surveys (with and without playbacks of vocalizations) and area-search surveys (with playbacks) for estimating site occupancy. Conducting an area-search survey of a 2.25 ha plot required an average of 19 min longer than conducting an 18-min point-count survey (15 min of silent observation followed by 3 min of playbacks) at the same location. However, the estimated detection probability (p) during a single visit was lower for point counts (0.41 ± 0.05) than for area searches (0.69 ± 0.05), while both methods generated similar occupancy (T) estimates (0.34 ± 0.06). To obtain the specified level of precision for estimates of occupancy (i.e. with 10% coefficient of variation), the total survey effort (travel time + survey time) was projected to be 35% lower for area searches than for point counts because of differences in detection probability and, thus, in the required numbers of sites and visits per site. For point counts, detection probability increased from 0.35 ± 0.02 to 0.46 ± 0.03 visit-1 after playbacks were broadcast at the end of the count. Free use of playbacks is one of the factors that contributed to the higher detection probability of the areasearch method, but playbacks may introduce a slight positive bias into occupancy estimates. Because there are tradeoffs in switching to area-search methods, the decision to switch protocols demands full consideration of monitoring-program goals and the costs and benefits of each survey approach. [ABSTRACT FROM AUTHOR]

Phylogenetic methods increasingly are brought to bear on questions of subspecies taxonomy, but several recent examples highlight the need for a clear and consistent philosophical approach to how genetic data are used to assess subspecies limits. Such standards are crucial conceptually, whether or not taxonomic decisions affect conservation decisions, as they might in a recent study focused on the California Gnatcatcher ( Polioptila californica), a taxon currently protected under the U.S. Endangered Species Act. It is also crucial that any adopted framework allows each of a full range of alternatives to be either supported or rejected. In this spirit, in addition to recommending best practices, I propose an amendment to the phylogenetic species concept to include a subspecies category. Los métodos filogenéticos influencian cada vez más los cuestionamientos sobre la taxonomía de las subespecies, pero varios ejemplos recientes destacan la necesidad de un abordaje filosófico claro y consistente de cómo los datos genéticos son usados para determinar los límites de las subespecies. Estos estándares son conceptualmente cruciales si las decisiones taxonómicas afectan o no a las decisiones de conservación, como podrían haberlo hecho en un estudio reciente enfocado en Polioptila californica, un taxón actualmente protegido por la Ley de Especies en Peligro de Estados Unidos. También es crucial que el marco adoptado permita que cada una de las alternativas de un rango completo sea apoyada o rechazada. Con este espíritu, además de recomendar buenas prácticas, propongo una adenda al concepto filogenético de especie para incluir una categoría de subespecie. Palabras clave: diagnosticabilidad, monofilia recíproca, Polioptila californica, subespecie, tamaño del efecto [ABSTRACT FROM AUTHOR]

Habitat Conservation Plans (HCPs) are a mechanism used for conserving land and often have an umbrella species associated with them. We conducted occupancy surveys for an umbrella species, the Coastal California Gnatcatcher (Polioptila californica californica), from 2004 to 2009 in San Diego County, California, focusing on preserve lands associated with HCPs. We investigated the effects of habitat quality classification, elevation, distance to coast, and heat load on gnatcatcher occupancy, extinction, and colonization probabilities. Our work focused on these factors throughout the range of this species in San Diego County where, through conservation agreements, a preserve system has been assembled addressing management considerations at a landscape scale. In addition, a large wildfire in 2003 burned 17,044 ha, roughly 1/3 of preserve lands, thus we were able to investigate the recolonization process associated with this event. We found that occupancy increased with habitat quality and over time, but decreased with elevation. Extinction probability was generally constant (∼0.13), but colonization varied greatly, with probabilities being greater in higher quality habitat and at lower elevations. Gnatcatchers were more likely to colonize burned areas adjacent to high and very high quality habitat, sites that should receive priority conservation actions, particularly at lower elevations. Our work suggests that umbrella species, like the California Gnatcatcher, may reflect not just habitat quality, but may also be useful indicators of recovery after an unexpected event such as fire. Although not perfect, the use of multiple umbrella species in HCPs may lead to effective conservation and management of biodiversity hotspots. [ABSTRACT FROM AUTHOR]

An important step in conservation is to identify whether threatened populations are evolutionarily discrete and significant to the species. A prior mitochondrial DNA (mtDNA) phylogeographic study of the California Gnatcatcher (Polioptila californica) revealed no geographic structure and, thus, did not support the subspecies validity of the threatened coastal California Gnatcatcher (P. c. californica). The U.S. Fish and Wildlife Service concluded that mtDNA data alone were insufficient to test subspecies taxonomy. We sequenced eight nuclear loci to search for historically discrete groupings that might have been missed by the mtDNA study (which we confirmed with new ND2 sequences). Phylogenetic analyses of the nuclear loci revealed no historically significant groupings and a low level of divergence (GST = 0.013). Sequence data suggested an older population increase in southern populations, consistent with niche modeling that suggested a northward range expansion following the Last Glacial Maximum (LGM). The signal of population increase was most evident in the mtDNA data, revealing the importance of including loci with short coalescence times. The threatened subspecies inhabits the distinctive Coastal Sage Scrub ecosystem, which might indicate ecological differentiation, but a test of niche divergence was insignificant. The best available genetic, morphological, and ecological data indicate a southward population displacement during the LGM followed by northward range expansion, without the occurrence of significant isolating barriers having led to the existence of evolutionarily discrete subspecies or distinct population segments that would qualify as listable units under the Endangered Species Act. [ABSTRACT FROM AUTHOR]

Habitat Conservation Plans are a widely used strategy to balance development and preservation of species of concern and have been used in southern California, USA, to protect the coastal California gnatcatcher (Polioptila californica). Few data exist on gnatcatcher abundance and distribution, and existing data have problems with issues of closure (i.e., sampling occurs in a short enough time period such that abundance or distribution are not changing), detectability, and proper attention to probability-based sampling schemes. Thus, a habitat model has been relied upon in reserve design. California gnatcatchers are the flagship and umbrella species of many plans and we provide the first estimates that incorporate probabilistic sampling and test predictions from the habitat model. Probability of occurrence was 26% (SÊ =0.06); however, occupancy varied by modeled habitat quality with slopes ,40%, warm, and wet sagebrush habitat having higher occupancy probabilities. Interpreting abundance and occupancy probabilities by vegetation type was complicated by error detected in Geographic Information System vegetation metadata files. The slope (1.08, SÊ =0.66), temperature (0.79, SÊ =0.70), and precipitation (-2.62, SÊ; =1.21) variables associated with habitat models were stronger influences on occupancy than was patch size (0.48, SÊ =0.66). Previous models weight patch size equal to slope and climate. Our work demonstrates that probabilistic sampling can be carried out on a large scale and the results provide better information for managers to make decisions about their reserves. [ABSTRACT FROM AUTHOR]

Ecological ‘niche modeling’ using presence-only locality data and large-scale environmental variables provides a powerful tool for identifying and mapping suitable habitat for species over large spatial extents. We describe a niche modeling approach that identifies a minimum (rather than an optimum) set of basic habitat requirements for a species, based on the assumption that constant environmental relationships in a species' distribution (i.e., variables that maintain a consistent value where the species occurs) are most likely to be associated with limiting factors. Environmental variables that take on a wide range of values where a species occurs are less informative because they do not limit a species' distribution, at least over the range of variation sampled. This approach is operationalized by partitioning Mahalanobis D² (standardized difference between values of a set of environmental variables for any point and mean values for those same variables calculated from all points at which a species was detected) into independent components. The smallest of these components represents the linear combination of variables with minimum variance; increasingly larger components represent larger variances and are increasingly less limiting. We illustrate this approach using the California Gnatcatcher (Polioptila californica Brewster) and provide SAS code to implement it. [ABSTRACT FROM AUTHOR]

Designing reserves that preserve the habitat of many coexisting and threatened species often involves use of conservation surrogates, such as umbrella species. Typically, animals with legal protection are used as umbrella species, and these selections are overwhelmingly vertebrates. The tacit assumption that vertebrates automatically serve as conservation umbrellas for invertebrates rarely has been justified. The California Gnatcatcher ( Polioptila californica, Muscicapidae), is a federally listed and endangered species in the United States and has been used as an umbrella species for the conservation of coastal sage scrub in southern California. Conservation planning efforts for this community follow a general paradigm of using vertebrate-based reserve designs as de facto protection for invertebrate cohabitants. To test the effectiveness of this strategy, I surveyed 50 patches of coastal sage scrub in San Diego County for three species of Lepidoptera: Mormon metalmark ( Apodemia mormo, Riodinidae), Bernardino blue, ( Euphilotes bernardino, Lycaenidae), and Electra buckmoth ( Hemileuca electra, Saturniidae). The presence of the gnatcatcher was a poor indicator of the presence of these insects. Only the largest or most recently separated habitat patches supported all three species of Lepidoptera, but the gnatcatcher was present on nearly every site, regardless of size. Results indicate that vertebrates do not automatically function as umbrella species for invertebrate cohabitants. Reserve designs based on vertebrate umbrella species, which assume invertebrates will be protected, may result in the loss of a large portion of invertebrate diversity. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the seasonal and habitat specific patterns of nest placement in a population of California Gnatcatchers, or Polioptila californica. Discussion on variation in nest placement of open nesting birds; Methods; Results and discussion.

The California Gnatcatcher ( Polioptila californica) has become a flagship species in the dispute over development of southern California's unique coastal sage scrub habitat, a fragile, geographically restricted ecosystem with high endemism. One aspect of the controversy concerns the status of the subspecies of this bird in southern California coastal sage scrub that is currently listed as threatened under the U.S. Endangered Species Act. To investigate the recent population history of this species and the genetic distinctiveness of subspecies and to inform conservation planning, we used direct sequencing of mitochondrial DNA (mtDNA) for 64 individuals from 13 samples taken throughout the species' range. We found that coastal sage scrub populations of California Gnatcatchers are not genetically distinct from populations in Baja California, which are dense and continuously distributed throughout the peninsula. Rather, mtDNA sequences from this species contain the signatures of population growth and support a hypothesis of recent expansion of populations from a southern Baja California refugium northward into the southern coastal regions of California. During this expansion, stochastic events led to a reduction in genetic variation in the newly occupied range. Thus, preservation of coastal sage scrub cannot be linked to maintaining the genetic diversity of northern gnatcatcher populations, despite previous recognition of subspecies. Our study suggests that not all currently recognized subspecies are equivalent to evolutionarily significant units and illustrates the danger of focusing conservation efforts for threatened habitats on a single species. [ABSTRACT FROM AUTHOR]

The California gnatcatcher is a threatened species essentially restricted to coastal sage scrub habitat in southern California. Its distribution and population dynamics have been studied intensely, but little is known about its diet. We identified arthropod fragments in 33 fecal samples of the California gnatcatcher to gain insight into its foraging ecology and diet. Fecal samples were collected from adult males, adult females, fledglings, and nestlings. Leaf- and planthoppers (Homoptera) and spiders (Araneae) predominated numerically in samples. Spider prey was most diverse, with eight families represented. True bugs (Hemiptera) and wasps, bees, and ants (Hymenoptera) were only minor components of the gnatcatcher diet. Gnatcatcher adults selected prey to feed their young that was larger than expected given the distribution of arthropod size available in their environment, and chicks were provisioned with larger prey items and significantly more grasshoppers and crickets (Orthoptera) and spiders than adults consumed themselves. Both adults and young consumed more sessile than active prey. Further studies are needed to determine whether arthropods sampled in coastal sage scrub that are common in fecal samples are good indicators of California gnatcatcher habitat. [ABSTRACT FROM AUTHOR]

Presents information on the habitat characteristics and fitness components of California Gnatcatchers between 1993 to 1995. Information on a study of 41 pairs of gnatcatchers using within-territory vegetation and life history; Reference to the effect grass and forb cover has on the gnatcatchers.