Proceedings of the Third International Conference on Invasive ...

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<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 3: Ecosystem Effects <strong>of</strong> Invasive SpartinaNON-NATIVE CORDGRASS AND THE CALIFORNIA CLAPPER RAIL:BIOGEOGRAPHICALOVERLAP BETWEEN AN INVASIVE PLANT AND AN ENDANGERED BIRDJ. EVENS 1 ,K.ZAREMBA 2 , AND J. ALBERTSON 31Avocet Research Associates, P.O. Box 839, Point Reyes Station, CA 94956; email: jevens@svn.net2San Francisco Estuary Invasive Spartina Project, 2612-A 8 th St., Berkeley, CA 947102Current address: 971 Village Dr. Bowen Island, BC, V0N 1G0 Canada; katyzaremba@yahoo.ca3 Don Edwards San Francisco Bay National Wildlife Refuge, 9500 Thornton Ave.,Newark, CA 94560-3300The federally endangered California clapper rail (Rallus longirostris obsoletus) is a tidal marshdependentbird whose distribution is restricted entirely to <strong>the</strong> San Francisco Estuary. The nativecordgrass, Spartina foliosa, has long been recognized as a critical component <strong>of</strong> clapper rail habitatwithin <strong>the</strong> estuary. The distribution and abundance <strong>of</strong> <strong>the</strong> clapper rail has been monitoredintermittently since <strong>the</strong> mid-1970s and that effort has increased since <strong>the</strong> early 1990s. Theconcurrent invasion <strong>of</strong> <strong>the</strong> bay’s tidal marshes by non-native Spartina alterniflora and its hybridswith S. foliosa has impacted clapper rail abundance and distribution in some areas <strong>of</strong> <strong>the</strong> estuary. Inthis paper we discuss: (1) habitat affinities and density estimates <strong>of</strong> rail in invaded and non-invadedmarshes; (2) <strong>the</strong> distribution <strong>of</strong> non-native Spartina relative to that <strong>of</strong> <strong>the</strong> clapper rails over <strong>the</strong> last15 years; and, (3) potential impacts <strong>of</strong> changing marsh ecology on rail distribution and abundance inboth <strong>the</strong> near term and <strong>the</strong> long term.Keywords: California clapper rail, Rallus longirostris obsoletus, Spartina, cordgrass, impacts,habitat characteristics, distribution, abundanceCLAPPER RAIL DISTRIBUTION, HABITAT AFFINITIES ANDABUNDANCEFormerly more widespread along California’s outercoast (e.g. Morro Bay, Elkhorn Slough, Tomales Bay), <strong>the</strong>breeding distribution <strong>of</strong> <strong>the</strong> California clapper rail is nowrestricted entirely to <strong>the</strong> San Francisco Estuary (Albertsonand Evens 2000). Within <strong>the</strong> estuary, <strong>the</strong> clapper rail ispatchily distributed through tidally influenced marshes, withpopulation centers fairly evenly dispersed among <strong>the</strong> SouthBay and <strong>the</strong> North Bay (aka “San Pablo Bay”) marshes. TheCentral Bay also hosts significant populations, but, like <strong>the</strong>habitat, <strong>the</strong>se tend to be relatively discrete and locallyclustered (e.g. Arrowhead Marsh, San Bruno Marsh, CorteMadera marshes). In Suisun Bay, distribution is very spotty,densities are apparently low, and occurrence may besporadic, especially in <strong>the</strong> nor<strong>the</strong>rn reaches <strong>of</strong> Suisun Marsh(Collins et al. 1994; Albertson and Evens 2000; Estrella2007). Indeed, no clapper rails were detected in <strong>the</strong> Suisunsystem in 2005 or 2007 (Herzog et al. 2005; Estrella 2007).The most recent population estimates suggest thatapproximately 1500 California clapper rails remain in <strong>the</strong>San Francisco Estuary with approximately one-third <strong>of</strong> <strong>the</strong>population in San Pablo Bay and two-thirds in <strong>the</strong> Centraland South bays, combined (Albertson and Evens 2000;Avocet Research Associates 2004; USFWS unpubl. data).This compares with estimates <strong>of</strong> 4200-6000 rails in <strong>the</strong> mid-1970s (Gill 1979). However <strong>the</strong>se numbers require a caveat:Population estimates <strong>of</strong> clapper rails are fraught withuncertainty, survey coverage is sporadic, and numbers mayvary widely from year-to-year.CALIFORNIA CLAPPER RAIL HABITATCHARACTERISTICS: PRE-INVASIONHabitat availability and <strong>the</strong> characteristics <strong>of</strong> tidalmarshes differ between South, Central, and North Baymarshlands. In general, marshlands in <strong>the</strong> nor<strong>the</strong>rn reachesare more extensive and less modified by human activity thanthose in <strong>the</strong> central and sou<strong>the</strong>rn portions <strong>of</strong> <strong>the</strong> estuary.Additionally, invasion <strong>of</strong> <strong>the</strong> estuary by non-nativeSpartina—confined largely to <strong>the</strong> sou<strong>the</strong>rn half <strong>of</strong> <strong>the</strong>estuary (http://www.spartina.org/maps.htm)—has amplifiedthis disparity.Synoptic surveys <strong>of</strong> North Bay marshes (north <strong>of</strong> PointsSan Pedro and San Pablo) in <strong>the</strong> early 1990s describedhabitat use in <strong>the</strong> nor<strong>the</strong>rn reaches <strong>of</strong> <strong>the</strong> estuary (Evens andCollins 1992; Collins et al. 1994). We assume that <strong>the</strong>seecological parameters most closely resemble habitatpreferences <strong>of</strong> California clapper rail’s prior to <strong>the</strong> extensivemodification <strong>of</strong> <strong>the</strong> estuary that began in <strong>the</strong> mid-1800s(Conomos 1979; Goals Project 1999). Additionally, earlierstudies throughout <strong>the</strong> estuary described distribution,abundance, and habitat affinities <strong>of</strong> obsoletus prior toinvasion by non-native Spartina (Grinnell and Miller 1944;Gill 1979; Avocet Research 1992; Evens and Collins 1992;Collins et al. 1994; Albertson 1995). Generalized habitat- 185 -
Chapter 3: Ecosystem Effects <strong>of</strong> Invasive Spartina<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive Spartinaaffinities <strong>of</strong> clapper rails in non-invaded marshes aresummarized as follows:• Distribution limited to fully tidally, saline to brackishmarshlands and <strong>the</strong>ir foreshores within <strong>the</strong> estuary. Clapperrails do not occur upstream in <strong>the</strong> Sacramento-San JoaquinDelta and fresher portions <strong>of</strong> <strong>the</strong> system.• Well-developed channel and slough systems that extendthrough or into patches <strong>of</strong> tall monocot vegetation.Channels function as important areas for foraging and asmovement corridors.• Monocot vegetation is used for nesting material;nests are built at or about Mean Higher High Water(MHHW), <strong>of</strong>ten at <strong>the</strong> headward reach <strong>of</strong> a tidal channel(ARA 1992). Non-native Spartina extends upward to nearlyMHHW (Collins 2002.)• Habitat patches typically comprise some mature andsome youthful marsh. 1 The highest densities in <strong>the</strong> NorthBay marshes are generally associated with <strong>the</strong> largestcontiguous areas <strong>of</strong> youthful, saline marshland adjoining atleast moderate amounts <strong>of</strong> historical, mature marshland(Evens and Collins 1992; Collins et al. 1994).• Broad marshes on <strong>the</strong> bayshore, or near <strong>the</strong> mouths<strong>of</strong> tidal tributaries are favored; narrow, linear, strip marshessupport much lower densities, but serve as important corridorsbetween habitat patches and as foraging areas.• Densities <strong>of</strong> rails are highest where patches <strong>of</strong> habitatare at least 100 hectares (ha) in size (Collins et al. 1994).• Densities <strong>of</strong> rails tend to increase with channel density(length <strong>of</strong> channel per unit <strong>of</strong> marshland.)• Density is positively correlated (R 2 = 0.74) to arealextent <strong>of</strong> contiguous marshland.• Small parcels <strong>of</strong> marsh along <strong>the</strong> immediate margin<strong>of</strong> a tributary are more likely to support California clapperrails than small parcels that are more isolated.• Refugial vegetation, or even man-made structures(docks, duck blinds, etc.) may provide some protection forrails, particularly during high tides and flood events. Populations<strong>of</strong> mesopredators (raccoons, skunks, feral cats, etc.),and especially <strong>the</strong> non-native red fox (Vulpes vulpes),threaten rail survival; aerial predators also pose a threat.• Boardwalks, fence lines, towers, and stakes may increasepredation pressure by providing perch sites for avianpredators (Barn Owl, Great Horned Owl, Nor<strong>the</strong>rn Harrier, etc.)Numerous protocol-level population surveys have beenconducted in <strong>the</strong> nor<strong>the</strong>rn reaches <strong>of</strong> <strong>the</strong> estuary since <strong>the</strong>early 1980s (e.g. Evens and Page 1987; Collins et al. 1994;ARA 2004; Herzog et al. 2005).At San Pablo Bay sites where rails have been detected,densities typically varied between 0.1 and 2.8 birds perhectare (Collins et al. 1992; ARA 2004; Herzog et al. 2005)with highest densities at sites where youthful marsh hasrecently developed, e.g. Bahia Lagoon with 1.7 to 2.8birds/ha (ARA 2004; Herzog et al. 2005).In large maturemarshes, with well-developed channel systems, but wherenative cordgrass is limited to a narrow fringing edge, densityestimates are more typically on <strong>the</strong> order <strong>of</strong> about 0.5birds/ha but, in <strong>the</strong> largest marshes may range up as high as1.8 birds/ha (e.g Gallinas Creek mouth—ARA 2004; Herzoget al. 2005).NON-NATIVE SPARTINA DISTRIBUTION AND ABUNDANCEAND EXTENT OF OVERLAP WITH RAILSWithin <strong>the</strong> estuary, non-native cordgrass (Spartinaalterniflora and hybrids) is limited primarily to <strong>the</strong>marshlands and tidal flats south <strong>of</strong> Point San Pedro andPoint San Pablo (Hogle 2006). Therefore, <strong>the</strong> San Pablo Bayrail subpopulations exist essentially independent <strong>of</strong> invadedhabitat while <strong>the</strong> Central and South Bay rail subpopulationsoverlap extensively with actively colonizing non-nativecordgrass (Broom 2008).Protocol-level surveys over <strong>the</strong> three years 2005-2007that covered 60 sites and were limited to marshes invaded bynon-native cordgrass found mean baywide densities in <strong>the</strong>range <strong>of</strong> 0.58 rails/ha to 0.68 rails/ha (Broom 2008). Thesevalues are not highly disparate from those reported in <strong>the</strong>nor<strong>the</strong>rn reaches <strong>of</strong> <strong>the</strong> estuary (Collins et al. 1994; ARA2004; Herzog et al. 2005) Ano<strong>the</strong>r study <strong>of</strong> 45 Central andSouth bay sites conducted in 2005-2006 derived an overallmean abundance 0f 0.84 (±0.163) rails/ha and found nostatistically significant differences among categories (0 to>50%) <strong>of</strong> Spartina hybrid cover (Spautz et al. 2006).However, at several locations where Spartina clones haveaggresively invaded <strong>the</strong> foreshore, clapper rail densitiesgreatly exceeded those reported in San Pablo Bay, in <strong>the</strong>Central and South bays prior to <strong>the</strong> invasion by non-nativecordgrass, and <strong>the</strong> mean density reported in <strong>the</strong> twoaforementioned surveys. The most obvious examples:San Bruno Marsh (Colma Creek mouth): 2.4 to 3.8birds/ha (J. Evens, unpublished data., Spautz et al. 2006)Arrowhead Marsh: 3.8 to 4.2 birds/ha (Spautz et al.2006; J. Didonato, EBRPD, pers. comm.).This positive response to youthful, recently established,intertidal marsh vegetation by obsoletus is not unexpected.As North Bay studies in <strong>the</strong> early 1990s reported: “. . .highest densities <strong>of</strong> clapper rails were generally associatedwith <strong>the</strong> largest contiguous areas <strong>of</strong> youthful, salinemarshland adjoining at least moderate areas <strong>of</strong> historical,mature marshland . . .” (Collins et al. 1994). The colonization<strong>of</strong> marsh edge and foreshore by non-native cordgrass isapparently mimicking conditions in “native marshes” thatprograde as ecological conditions change (e.g. depositionalerosionpatterns). However, <strong>the</strong> Central and South Baymarshes invaded by non-native cordgrass differ frommarshlands <strong>of</strong> San Pablo Bay, in that few adjoin largemature marshlands, few support a heterogeneity <strong>of</strong> marshage classes, few exhibit a natural transitional grade from <strong>the</strong>low marsh to <strong>the</strong> high marsh plain, and vegetative cover at<strong>the</strong> marsh/upland ecotone is <strong>of</strong>ten sparse or absent. North- 186 -
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FORWARD & ACKNOWLEDGEMENTSThe <stro
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TABLE OF CONTENTSForward & Acknowle
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Community Spartina Education and St
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included the docum
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CHAPTER ONESpartina Biology
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Chapter 1: Spartina Biology
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CHAPTER THREEEcosystem Effects <str
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