DOCSLIB.ORG

Biology of the California Gnatcatcher: Filling in the Gaps

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Biology of the California Gnatcatcher: Filling in the Gaps WESTERN BIRDS Volume 29, Number 4, 1998 BIOLOGY OF THE CALIFORNIA GNATCATCHER: FILLING IN THE GAPS JOHN T. ROTENBERRY, Natural Reserve System and Department of Biology, Universityof California, Riverside,California 92521 THOMAS A. SCOTT, Departmentof EnvironmentalPolicy, Science,and Manage- ment, Universityof California, Berkeley, California 94720 Interest in the coastal populations of the Black-tailed Gnatcatcher (Polioptila melanura) first diffusedoutside of the ornithologicalcommunity in 1978. Notable for its odd vocalizations, localized distribution, and co- occurrencewith a vegetationthen known as "inland sage scrub"(Thorne 1976), the coastal subspeciesof the Black-tailed Gnatcatcher (P.m. californica)was judgedby environmentalplanners to be sensitivebecause of its small range and vulnerabilityto habitat conversion(M. U. Evans pers. comm.). Therefore, it warranted discussionin reviews of development projectswritten in responseto the CaliforniaEnvironmental Quality Act. Discussionsof the bird's sensitivity,however, rapidly intensified as it became apparentthat the subspeciesinhabited some of the most developablelands of coastal California. Conservationof the subspeciessoon became synony- mous with broader goal of conservingcoastal scrub vegetation,which by 1980 was consideredone of the most rapidly disappearingvegetation types in California(Westman 1981). In the late 1980s, Phillips(1986:xxvi and 75, 1991:25-26) and Atwood (1988) elevatedthe subspecies,with its relatives in Baja California,to the level of a species,the CaliforniaGnatcatcher (P. californica), restrictedin the U.S. to the coastalsage scrub vegetationtype and its variations(Westman 1981, O'Leary 1990, White and Padley 1997). Althoughthe CaliforniaGnatcatcher was originallydescribed as a speciesby William Brewsterin 1881, its reappreciationas such a centurylater almost guaranteed that southern California would experience an endangered- species conflict involving billions of dollars of real-estatedevelopment. Becauseof extensivehabitat loss (due to conversionto urban, suburban,and agriculturaldevelopment; Westman 1981, O'Leary 1990) and associated declinein the species'population (e.g., Atwood 1993), the U.S. Fish and Western Birds 29:237-241, 1998 237 BIOLOGY OF THE CALIFORNIA GNATCATCHER: FILLING IN THE GAPS Wildlife Service listed the California Gnatcatcheras a "threatened"species under the EndangeredSpecies Act (ESA) in March 1993 (USFWS 1993). The USFWS went on to state that the speciesprobably warranted "endan- gered" status but that ongoing conservationplanning ("Natural Communi- ties ConservationPlan"; Calif. Dept. Fish & Game 1993) reduced the level of threat. In anticipationof (and subsequentto) the federal listingof the gnatcatcher under the ESA, local, state and federal agencies,as well as conservationists and developers,began collectinginformation and data to support policy decisionsand permits requiredunder the act. Unlike previousconflicts over endangered birds, which occurred primarily on federal lands and were investigatedby teams of agency and resource-industryscientists [e.g., the Northern Spotted Owl ($trix occidentalis caurina); Murphy and Noon 1992, Guti6rrez et al. 1996), that over the gnatcatcherrepresented a new model of conflictover private land, where scientistswould be contractedfor researchby a bewilderingarray of publicagencies, corporations, and private individuals. Most of this information-gatheringactivity focused on the fine-scale details of gnatcatcherdistribution, particularly the identificationof occupied and unoccupiedhabitat. Ancillary to these distributionalstudies, data were also gathered on local movements,breeding biology (particularlyreproduc- tive success),habitat association,and territory sizes. Much of the informa- tion amassedfor managementand conservationdecisions, however, was recordedonly in unpublishedreports, or even simplyburied in an individual's field notebook. Mechanismsfor objectivereview of the information used in policydecisions did not exist.Although thousands of hours of researcheffort had been expended on the California Gnatcatcher, few peer-reviewed papers describingthis work were published.Administrative functions, such as issuanceof permits, continuedin absenceof publishedinformation, but conservation science suffered. Researchers had few avenues of communica- tion, no one could build off the establishedwork of others, and mechanisms for identifyingreliable data went unused.Thus the need for a symposiumon the biology of the California Gnatcatcher,and perhaps a new manner of looking at endangered-speciesresearch, arose from the chaos createdwhen so many researchersplunged into so many studiesin such a short period. We organized this symposiumfor the purpose of bringing gnatcatcher researcherstogether and lobbyingfor the publicationof the large body of data generated on the species. The California GnatcatcherSymposium, held 15-16 September1995 on the campusof the Universityof California, Riverside, drew 160 participants from academia, biological consulting businesses,and governmentagencies. We asked the participantsto present existing data and analyses and to help us identify the current status of scientificallybased knowledgeon the species.Our hope for the symposium proceedingswas to move as much of this knowledgeas possiblefrom the "gray" literatureinto the peer-reviewed(and more widely accessible)main- stream. The papers containedin this issue of Western Birds represent a major portion of the realizationof that goal. In further support of that goal, we were successfulin making a collectionof previouslyunpublished reports availablethrough the auspicesof the Van Tyne Memorial Library, curatedby 238 BIOLOGY OF THE CALIFORNIA GNATCATCHER: FILLING IN THE GAPS the Wilson Ornithological Society, at the Museum of Zoology at the University of Michigan. Although these reports have not undergonepeer review,they containvaluable data; each is cited in one or more of the papers in this volume as appropriate. At the symposium45 oral and poster papers were presented,represent- ing most aspects of California Gnatcatcherbiology. Although many were explicitly conservation or management oriented, that focus was not a criterion for inclusion on the program. From these 45, 22 appear in this collection;we are aware of at least sevenother presentations,portions or all of which have appeared or are currently in review in other professional journals. Publication of these proceedings would not have been possible without the generous support of Ogden Environmental Services, LSA Associates, the Metropolitan Water District of Southern California, the Riverside County Habitat Conservation Agency, and the University of California. From these papers we can distill several facts about the California Gnatcatcher.For example, at a regionalor landscapescale, the distribution of the speciesappears largely constrained by the distributionof coastalsage scrub vegetation;however, at more local scalesbirds may be found in (and perhaps depend on) additionalvegetation types, dependingon the particular local mosaic. Because individualsand pairs can be found in patches of suitable habitat quite isolated from the nearest population of any conse- quence, the power of dispersal of this nonmigratory species may be substantial.It is quite clear that gnatcatchersin southern California occupy a fragmented landscape and are governed by metapopulation dynamics. Territory sizes are highly variable, increasing significantly as one moves inland from the coast,and in generalare much larger on averagethan those of other passerinesof comparablebody mass. They are persistentnesters, constructingas many ten nests within a breedingseason. However, nests are frequentlyabandoned before eggs are laid, so that the number of clutchesis usuallyless than the number of nests built by a pair. Clutch size is variable, and much of the variation seemsrelated to variationin weather,particularly precipitation.Although California Gnatcatchersserve as frequent hosts to the Brown-headedCowbird (Molothrus ater), they also suffer a high rate of nest predation,which seems to exert the greatestcontrol over reproductive success. Nevertheless,numerous gaps in our knowledge of gnatcatcherbiology remain. For example,we lack certainty about the birds' mating systemand criteria for mate choice; although they appear sociallymonogamous, they also demonstratebehaviors that clearly suggesta potential for extra-pair copulationsfor both sexes.While mating systemsare of academicinterest to behavioral ecologists, they are also relevant to conservation biologists because of the implications they may have for genetic structuring of populationsand effective populationsize. Likewise, although there have been severalinvestigations of gnatcatchergenetics with a goal of elucidating taxonomicrelationships, we are currentlyunaware of any studiesexamining the geneticsof populationsor demes. In addition to providinginformation on effective population size, properly done molecularstudies also assess gene flow, genetictraces of the connectionsamong subpopulationsdistrib- 239 BIOLOGY OF THE CALIFORNIA GNATCATCHER: FILLING IN THE GAPS uted over a fragmentedlandscape. Because gnatcatchers nest persistently, their reproductiveeffort can be high; althoughthere is a rich body of life- history theory that deals with trade-offs among aspects of reproduction, none has been systematicallyapplied to the California Gnatcatcher. And althoughclutch size varies from year to year, it also varies from pair to pair
Load more

Recommended publications
  • 3.4 Biological Resources
    3.4 Biological Resources 3.4 BIOLOGICAL RESOURCES 3.4.1 Introduction This section evaluates the potential for implementation of the Proposed Project to have impacts on biological resources, including sensitive plants, animals, and habitats. The Notice of Preparation (NOP) (Appendix A) identified the potential for impacts associated to candidate, sensitive, or special status species (as defined in Section 3.4.6 below), sensitive natural communities, jurisdictional waters of the United States, wildlife corridors or other significant migratory pathway, and a potential to conflict with local policies and ordinances protecting biological resources. Data used to prepare this section were taken from the Orange County General Plan, the City of Lake Forest General Plan, Lake Forest Municipal Code, field observations, and other sources, referenced within this section, for background information. Full bibliographic references are noted in Section 3.4.12 (References). No comments with respect to biological resources were received during the NOP comment period. The Proposed Project includes a General Plan Amendment (GPA) and zone change for development of Sites 1 to 6 and creation of public facilities overlay on Site 7. 3.4.2 Environmental Setting Regional Characteristics The City of Lake Forest, with a population of approximately 77,700 as of January 2004, is an area of 16.6 square miles located in the heart of South Orange County and Saddleback Valley, between the coastal floodplain and the Santa Ana Mountains (see Figure 2-1, Regional Location). The western portion of the City is near sea level, while the northeastern portion reaches elevations of up to 1,500 feet.
    [Show full text]
  • 2011 California Gnatcatcher Habitat Assessment & Protocol Survey
    2011 CALIFORNIA GNATCATCHER HABITAT ASSESSMENT & PROTOCOL SURVEY OF POTENTIAL HABITAT WITHIN SANTA SUSANA FIELD LABORATORY AREA IV AND THE NORTHERN BUFFER ZONE 2011 California Gnatcatcher Habitat Assessment and Protocol Survey of 2 Potential Habitat Within Santa Susana Field Laboratory Area IV and Northern Buffer Zone 2011 CALIFORNIA GNATCATCHER HABITAT ASSESSMENT & PROTOCOL SURVEY OF POTENTIAL HABITAT WITHIN SANTA SUSANA FIELD LABORATORY AREA IV AND THE NORTHERN BUFFER ZONE prepared for: Envicom Corporation Attn: Travis Cullen 28328 Agoura Road Agoura Hills, CA 91301 (818) 879-4700 ext.233 www.envicomcorporation.com prepared by: Griffith Wildlife Biology John T. Griffith 22670 Hwy M-203 P.O. Box 47 Calumet, Michigan 49913 (906) 337-0782 www.griffithwildlife.com Final Letter Report 6 July 2011 2011 California Gnatcatcher Habitat Assessment and Protocol Survey of iii Potential Habitat Within Santa Susana Field Laboratory Area IV and Northern Buffer Zone EXECUTIVE SUMMARY The Santa Susana Field Laboratory in southeastern Ventura County, California, contains coastal sage scrub habitat of the type preferred by the federally threatened Coastal California gnatcatcher (Polioptila californica ssp. californica). As indicated in Figure 1 of the Biological Opinion for the Santa Susana Field Laboratory Area IV Radiological Survey issued by the United States Fish and Wildlife Service, approximately 151 acres in Area IV and the contiguous undeveloped Northern Buffer Zone (NBZ) to the north and west were identified as potentially suitable habitat for the gnatcatcher. A habitat reconnaissance survey was subsequently conducted in areas initially identified as suitable habitat. During this reconnaissance, direct field observation determined that less than 100 of the 151 acres were suitable gnatcatcher habitat.
    [Show full text]
  • A Maximum Estimate of the California Gnatcatcher's Population Size in the United States
    WESTERN BIRDS Volume 23, Number 1, 1992 A MAXIMUM ESTIMATE OF THE CALIFORNIA GNATCATCHER'S POPULATION SIZE IN THE UNITED STATES JONATHAN L. ATWOOD, Manomet Bird Observatory,P.O. Box 1770, Manomet, Massachusetts 02345 The CaliforniaGnatcatcher, Polioptila californica, was recentlyrecog- nizedas a speciesdistinct from the widespreadBlack-tailed Gnatcatcher, P. melanura, of the southwesterndesert regionsof the United States and Mexico (Atwood 1988, American Ornithologists'Union 1989). Although CaliforniaGnatcatchers are distributedthroughout much of BajaCalifornia, the northernmostsubspecies, P. c. californica, now occursonly in remnant fragmentsof coastalsage scrub habitat from LosAngeles County, Califor- nia, southto El Rosario,Baja California(Atwood 1991). Atwood (1980) speculatedthat the numberof CaliforniaGnatcatchers remainingin the UnitedStates was "no more than 1,000 to 1,500 pairs," from estimatesof 30 pairs in VenturaCounty, 130 pairs in Los Angeles County,50 pairsin San BernardinoCounty, 325 pairsin OrangeCounty, 400 pairsin RiversideCounty, and 400 pairsin San Diego County.These valueswere derivedfrom reportsof variousobservers, limited field work in differentportions of the species'range, and visualestimates of habitat availabilityin differentareas. Despite the preliminarynature of theseresults, the patternof continuinghabitat loss evident at that time indicated"imme- diate concern for the survival"of P. c. californica in the United States (Atwood 1980). Extensive destruction of suitable California Gnatcatcher habitat has con-
    [Show full text]
  • Coastal California Gnatcatcher (Polioptila Californica Californica)
    Coastal California Gnatcatcher (Polioptila californica californica) 5-year Review: Summary and Evaluation Coastal California gnatcatcher (Polioptila californica californica) and habitat. Photo credit Marci Koski and Gjon Hazard (USFWS). U.S. Fish and Wildlife Service Carlsbad Fish and Wildlife Office Carlsbad, California September 29, 2010 2010 Coastal California Gnatcatcher 5-year Review 5-YEAR REVIEW coastal California gnatcatcher (Polioptila californica californica) I. GENERAL INFORMATION Purpose of 5-year Reviews: The U.S. Fish and Wildlife Service (Service) is required by section 4(c)(2) of the Endangered Species Act of 1973, as amended (Act), to conduct a review of each listed species at least once every 5 years. The purpose of a 5-year review is to evaluate the status of the species since it was listed or since the most recent 5-year review. Based on the 5-year review, we recommend whether the species should be removed from the list of endangered and threatened species (delisted), be changed in status from endangered to threatened (downlisted), or be changed in status from threatened to endangered (uplisted). Our original listing of a species as endangered or threatened is based on the existence of threats attributable to one or more of the five threat factors described in section 4(a)(1) of the Act, and we must consider these same five factors in any subsequent consideration of reclassification or delisting of a species. In the 5-year review, we consider the best available scientific and commercial data on the species, and focus on new information available since the species was listed or last reviewed.
    [Show full text]
  • Taxonkill Biolcons2009.Pdf
    This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Biological Conservation 142 (2009) 3201–3206 Contents lists available at ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon Short communication The impact of taxonomic change on conservation: Does it kill, can it save, or is it just irrelevant? W.R. Morrison III a,1, J.L. Lohr a,1, P. Duchen a,1, R. Wilches a,1, D. Trujillo a,1, M. Mair a,1, S.S. Renner b,* a Department of Biology, University of Munich, Großhaderner Str. 2, D-82152 Planegg-Martinsried, Germany b Department of Biology, University of Munich, Menzinger Str. 67, D-80638 Munich, Germany article info abstract Article history: The important question of taxonomy and its impact on conservation efforts was brought to general atten- Received 10 April 2009 tion by Robert May in 1990 with a News and Views article in Nature entitled ‘‘Taxonomy as destiny.” Received in revised form 18 July 2009 Taxonomy, however, has built-in instabilities that result in name changes, raising the question of Accepted 23 July 2009 whether name changes have a consistent impact on conservation efforts.
    [Show full text]
  • Appendix C Smith Basin Improvement Project Biological Assessment
    Smith Basin Improvement Project Appendix C Smith Basin Improvement Project Biological Assessment, Orange County Water District, October 2019 Smith Basin Improvement Project Biological Assessment Prepared By Orange County Water District 18700 Ward Street Fountain Valley, CA 92708 Contact: David McMichael October 2019 Table of Contents Section Page SUMMARY ................................................................................................................. 1 Purpose and Need ....................................................................................................... 1 Project Activities .......................................................................................................... 1 Project Analysis ........................................................................................................... 1 Literature Review ..................................................................................................... 1 Vegetation Community Mapping .............................................................................. 2 Wildlife and Plant Surveys ....................................................................................... 2 PROJECT DESCRIPTION .............................................................................................. 3 Background ................................................................................................................. 3 Smith Basin Setting ....................................................................................................
    [Show full text]
  • The Taxonomy, Distribution, and Status of Coastal California Cactus Wrens
    WESTERN BIRDS Volume 21, Number 3, 1990 THE TAXONOMY, DISTRIBUTION, AND STATUS OF COASTAL CALIFORNIA CACTUS WRENS AMADEO M. REA, San Diego Natural History Museum, P. O Box 1390, San Diego, California 92112 KENNETH L. WEAVER, 1113 SenwoodWay, Fallbrook,California 92028 The southerncoastal sage scrub is a distinctiveplant communityof southernCalifornia (Munz and Keck 1959, Mooney 1977). Beginningvery narrowlyin the Santa Barbararegion, it is bestdeveloped in Ventura,Los Angeles,Orange, and San Diegocounties, and endsin northwesternBaja California,where a differentplant assemblage,the maritimedesert scrub, begins(Thorne 1976). One very prominentfeature of coastalsage scrub is thicketsof cactus,including the CoastalCholla, Opun tia prolifera, and two speciesof prickly-pears,Opuntia littoralis and O. oricola. The coastalsage scrub is the primary habitat of two birds, the California Gnatcatcher, Polioptila californica californica, and the San Diego Cactus Wren, Campylorhynchusbrunneicapillus sandiegensis, that are decliningrap- idlybecause of lossof habitatto urbanization.(For explanationof variations in the spellingof the CactusWren's scientificname, see Appendix 1). This paper hasfour goals.First, we presentthe charactersdistinguishing C. b. sandiegensisas a validsubspecies distinct from adjacentraces of Baja Californiaand the interiorcontinental deserts. The charactersare givenin sufficientdetail that anyone with a specimenin hand shouldbe able to identifyit. Second,we evaluatethe taxonomicstatus of the CactusWrens occupyingVentura, Los Angeles,and Orange counties.In the original description (Rea 1986:119), these were referred to as less typical sandiegensis,and the birdsfrom the San FernandoValley, Los Angeles Co., were called anthonyi (Phillips 1986:120). Third, we analyze the habitatrequirements of C. b. sandiegensis.And finally,we presentcensus data from the last ten years demonstratingthe rapid declineof the San Diego CactusWren due to habitatloss.
    [Show full text]
  • California Gnatcatcher 2018 Survey Protocol
    California Gnatcatcher 2018 Survey Protocol Western Riverside County MSHCP Biological Monitoring Program California Gnatcatcher 2018 Survey Protocol INTRODUCTION The Coastal California Gnatcatcher (Polioptila californica californica; gnatcatcher) is one of 45 bird species covered by the Western Riverside County MSHCP and is designated as threatened at the Federal level. Gnatcatchers are specialists of coastal sage scrub (CSS) habitat, one of the unique plant communities found in coastal and inland southern California and Baja California. This habitat type is characterized by low-growing, drought-deciduous, and semi-woody shrubs, such as California buckwheat (Eriogonum fasciculatum), coast brittle-bush (Encelia californica), California sagebrush (Artemisia californica), black sage (Salvia mellifera), and white sage (S. apiana) (Dudek & Associates 2003). CSS habitat is one of the most endangered habitats in the U.S. In Western Riverside County, suitable CSS habitat for gnatcatchers has declined by 48% since the 1980s (Hulton VanTassel et al. 2017). Significant trends, however, have not been demonstrated for gnatcatcher populations in southern California between 1966 and 2000 (Mock 2004), intensive monitoring is critical due to the rapid decline of this species’ breeding habitat. Gnatcatchers are non-migratory insectivores and are distributed in southern coastal California and Baja California (Atwood and Bontrager 2001). In the Plan Area, they are found in the southwestern region, especially in the Riverside Lowlands and San Jacinto Foothills Bioregions along the Interstate 15/215 corridor from the Santa Ana River to Temecula, and into the Vail Lake/Wilson Valley area (Dudek & Associates 2003). Gnatcatchers primarily use CSS, but they occasionally use desert scrub and Riversidean alluvial fan scrub vegetation communities for breeding (Dudek & Associates 2003).
    [Show full text]
  • Monthly Biological Monitoring Report (Draft) ​
    MONTHLY BIOLOGICAL MONITORING REPORT (DRAFT) ​ FAIRVIEW PARK Mitigation Project Management and Inspection Costa Mesa, California Prepared For: City of Costa Mesa Prepared By: Luma Fowler, Associate Project Manager/Biologist and Barry Nerhus, President/Senior Biologist Endemic Environmental Services, Inc. 596 Victoria St Unit B102 Costa Mesa, CA 92627 P: (714) 393-6249 [email protected] July 2018 ________________________________________________ Executive Summary This report has been prepared by Endemic Environmental Service, Inc. (EES) for the City of Costa Mesa located in Costa Mesa, Orange County, California. This report details the Fairview Park riparian mitigation monitoring according to the contract between EES and City of Costa mesa. It also includes an overview of any activities at the park including vandalism, trash, erosion, plants and wildlife surveys, nesting bird survey, vernal pools and other activities described below. 1. Wetlands Quarterly Biological Reports, grassland and oak woodland Oaks are watered daily at this time. A quarterly report will be submitted in September. 2. On site Project Manager, Implementation of Master Plan and consultation with staff Part of this task includes participation in meetings with the City of Costa Mesa Staff. Fairview Park inspections are conducted multiple times per week where the following are observed: Riparian mitigation monitoring The goal is to detect broad-scale changes in aquatic and riparian ecological conditions by observing selected ecological drivers, stressors, and processes. Specific measurable objectives determine the status and long term trends in selected parameters such as removal of algae, cattail and invasive plants from channels that connect ponds. Vandalism Any act involving property damage, such as graffiti and/or property defacement.
    [Show full text]
  • APPENDIX F Coastal California Gnatcatcher Protocol Survey Report
    APPENDIX F Coastal California Gnatcatcher Protocol Survey Report Coastal California Gnatcatcher Protocol Survey Report San Pasqual Undergrounding Project July 2016 Prepared for: City of Escondido Vista Irrigation District Bureau of Indian Affairs Prepared by: 3570 Carmel Mountain Road, Suite 300 San Diego, California 92130 Atkins Project No.: 10004195 Contents 1.0 Summary .......................................................................................................................................... 3 2.0 Introduction ..................................................................................................................................... 3 2.1 Project Description ............................................................................................................. 3 2.2 Project Location .................................................................................................................. 6 3.0 Existing Conditions ........................................................................................................................... 6 4.0 Background Information .................................................................................................................. 7 4.1 Listing and Regulatory......................................................................................................... 7 4.2 Natural History .................................................................................................................... 7 5.0 Methods ..........................................................................................................................................
    [Show full text]
  • Coastal California Gnatcatcher Survey Report 2018
    Western Riverside County Multiple Species Habitat Conservation Plan Biological Monitoring Program 2018 Coastal California Gnatcatcher Survey and Nest Monitoring Report California Gnatcatcher (Polioptila californica californica) nestlings begging for food in 2018. 16 April 2019 2018 Coastal California Gnatcatcher Survey and Nest Monitoring Report TABLE OF CONTENTS INTRODUCTION ..................................................................................................................... 1 GOALS AND OBJECTIVES ................................................................................................................... 2 METHODS ............................................................................................................................. 2 SURVEY DESIGN ................................................................................................................................ 2 FIELD METHODS ................................................................................................................................ 2 DATA ANALYSIS ................................................................................................................................ 3 TRAINING ........................................................................................................................................... 4 RESULTS .............................................................................................................................. 4 NEST SURVIVAL AND REPRODUCTION ..............................................................................................
    [Show full text]
  • California Gnatcatcher Use of Habitats Other Than Coastal Sage Scrub: Conservation and Management Implications
    CALIFORNIA GNATCATCHER USE OF HABITATS OTHER THAN COASTAL SAGE SCRUB: CONSERVATION AND MANAGEMENT IMPLICATIONS KURT F. CAMPBELL, Campbell BioConsulting, 40950 Via Media, Temecula, California 92591-1722 RICHARD A. ERICKSON, LSA Associates, Inc., One Park Plaza, Suite 500, Irvine, California 92614 WILLIAM E. HAAS, Varanus Biological Services, Inc., 7950 Silverton Ave., Suite 116, San Diego, California 92126 MICHAEL A. PATTEN, Department of Biology, University of California, Riverside, California 92521 That California Gnatcatchers (Polioptila californica) within the United Statesare dependenton coastalsage scrubhabitats is well established(Atwood 1993, USFWS 1991, 1993). Our effort in this paper is to look not at whether these habitatsare necessaryon a large scale, but rather to raise the question of whetherthey are alwayssufficient, at both local and largerscales. Existingliterature on these birds makes little mention of their occurrence outside of coastal sage scrub habitats. Some sourcesspecifically state that the speciesis restrictedto coastalsage scrub (Woods 1949, USFWS 1991). The earliestclear, publishedindication to the contrarywas providedby Unitt (1984): "Elizabeth Copper (pers. comm.) suggeststhat the gnatcatchers leave the sage scrub for more humid habitatsnearby in late summerwhen most sage scrub plants are dry and brown." Throughoutthe species'U.S. range since 1990, we have found numerous instancesof California Gnatcatchersmaking potentially significantuse of habitatsother than coastal sage scrub (hereafter,non-CSS). Many of these instances were noted without systematic study, but we also document systematicuse of non-CSSby closelymonitored birds over severalyears. We neither propose nor anticipate that the species is broadening its general habitat requirements,nor that in Californiathe birds regularlynest indepen- dently of coastal sage scrub. We do believe that such use of non-CSS is frequent,at least in some situations,and potentiallyimportant to the long- term viability of U.S.
    [Show full text]