Bay Checkerspot Habitat Analysis and Surveys 2008-2014

YOUNG RANCH SANTA CLARA COUNTY, CALIFORNIA

Prepared For:

YCS Investments 170 Maiden Ln Ste 800 San Francisco, CA 94108

WRA Contact: Geoff Smick [email protected]

Date: December 2014

WRA Project: 17082

2169-G East Francisco Blvd., San Rafael, CA 94702 (415) 454-8868 tel [email protected] www.wra-ca.com

EXECUTIVE SUMMARY

Bay checkerspot butterfly (BCB, editha bayensis), a federal threatened of Edith’s checkerspot (E. editha), is a member of the (brushfoot family) and is a medium-sized butterfly with a wingspan of approximately two inches. Bay checkerspot butterfly is endemic to the San Francisco Bay Area and is currently restricted to San Mateo and Santa Clara Counties with virtually all extant populations occurring on or adjacent to Coyote Ridge, which runs roughly northwest to southeast for approximately 20 miles and begins in the southeastern portion of the City of San Jose. The U.S. Fish and Wildlife Service (USFWS) has identified the following threats to BCB: habitat loss and fragmentation, invasion of exotic/invasive , nitrogen deposition (including NOx and NHx), pesticide application (including drift), illegal collecting, fire, overgrazing, and gopher control (USFWS 2007a). Habitat for BCB exists on shallow, serpentine soils that support larval host plants. Bay checkerspot butterfly only inhabits areas with these constituents. The primary larval host is dwarf plantain (Plantago erecta). Secondary larval host plants, including dense owl’s clover ( densiflora) and purple owl's clover (C. exserta), can be utilized later in the season if the dwarf plantain dries-out early in the growing season.

From 2008 through 2014, WRA, Inc. performed an assessment of BCB habitat and conducted focused butterfly surveys at the approximately 2,150-acre Young Ranch (Site) located in San Jose, Santa Clara County, California. The Site contains predominantly grazed ranching land dominated by a mix of non-native annual grassland and serpentine grasslands with pockets of oak woodland, scrub, seasonal wetlands, and riparian vegetation mixed throughout. This report describes the (1) distribution and extent of BCB larval and adult butterfly habitat on the Site, (2) the observed numbers and distribution of BCB adults on the Site, and (3) historical data and knowledge of BCB distribution and population trends on the Site and the vicinity.

In March 2008, prior to initiating the adult butterfly surveys, BCB habitat was mapped on the Site. Habitat was defined as serpentine bunchgrass grassland with larval host and adult plants. The Site was determined to contain 633 acres of grassland supporting larval host and adult nectar plants. Surveys conducted at the site documented the following number of adults in each year of monitoring:

 2008: 636 BCB adults  2009: 586 BCB adults  2010: 564 BCB adults  2011: 1,205 BCB adults  2012: 726 BCB adults  2013: 1,462 BCB adults  2014: 2,767 BCB adults

The majority of these individuals were mapped in the southeastern portion of the Site which supports the largest and highest quality extent of BCB habitat on the Site.

A significant portion of the Site (approximately 1,517 acres) supports habitats such as non- native annual grassland, scrub, aquatic, and woodland communities and limited areas of serpentine bunchgrass grassland in which no larval host plants or adult nectar sources have been observed. As such, this portion of the Site does not provide the elements necessary to support the normal life functions of BCB. This is particularly true of the north-central portion of the Site. Portions of the remaining 633 acres of the Site have been categorized by WRA as

i prime BCB habitat (473 acres), moderate BCB habitat (78 acres), and potential BCB habitat (78 acres). Potential BCB habitat contains all of the elements required to support the life stages of the BCB, but does not regularly support a BCB population. An additional 4 acres of potentially suitable habitat containing both the larval host and the adult nectar plants were observed as small patches distributed among larger concentrations of non-habitat and were not classified into one of the three habitat groups because they were geographically isolated from known BCB population centers at the site. The serpentine bunchgrass community in the southern portion of the Site supports a large population of BCB. By contrast, the vast majority of the northern portion of the Site does not contain the combination of elements necessary to support BCB life functions and very few BCB adults have been observed in this area.

ii TABLE OF CONTENTS

1.0 INTRODUCTION ...... 1 1.1 Summary ...... 1

2.0 METHODS ...... 2 2.1 Biological Communities ...... 2 2.1.1 Biological Communities ...... 2 2.1.2 Habitats with Potential to Support Bay Checkerspot Butterfly ...... 2 2.2 Bay Checkerspot Butterfly ...... 5 2.2.1 Natural History ...... 5 2.2.2 Literature Review and Previous Studies on Nearby Parcels ...... 5 2.2.3 Adult Butterfly Field Surveys ...... 6 2.2.4 Butterfly Habitat Transects ...... 6

3.0 RESULTS AND DISCUSSION ...... 7 3.1 Biological Communities ...... 7 3.1.1 Observed Biological Communities ...... 8 3.1.2 Habitats with Potential to Support Bay Checkerspot Butterfly ...... 13 3.2 Bay Checkerspot Butterfly ...... 17 3.2.1 Natural History ...... 17 3.2.2 BCB Studies on Nearby Parcels ...... 18 3.2.3 Adult Butterfly Field Surveys ...... 20 3.2.4 Comparative Vegetation Transects ...... 25

4.0 SUMMARY AND CONCLUSIONS ...... 27

5.0 REFERENCES ...... 29

LIST OF FIGURES

Figure 1. Site Location Map ...... 3 Figure 2. Biological Communities within the Site ...... 9 Figure 3. Areas Supporting BCB Larval and Nectar Plants...... 15 Figure 4. Adult BCB per Hectare at Young Ranch, Kirby Canyon (Kirby Slope) Preserve and Silver Creek Preserve ...... 19 Figure 5. Bay Checkerspot Butterfly Observations at Young Ranch ...... 23 Figure 6. Young Ranch Adult BCB Nectaring Occurrences from 2009 to 2013 ...... 25 Figure 7. Young Ranch BCB Habitat Vegetation Comparison 2010 ...... 25 Figure 8. Young Ranch BCB Habitat Vegetation Comparison 2011 ...... 27

iii LIST OF TABLES

Table 1. Biological community acreages on the Site ...... 8 Table 2. Summary of BCB transect survey conditions for Young Ranch: 2008 through 2014 ...21 Table 3. Number of adult BCB observed per transect during surveys at Young Ranch ...... 22 Table 4. Number of adult BCB observed in various habitats at Young Ranch ...... 29

LIST OF APPENDICES

Appendix A - List of Observed Plant and Species Appendix B - Young Ranch Butterfly Transect Routes Appendix C - Map of Observed Bay Checkerspot Butterfly Individuals and Habitats Appendix D - Representative Study Area Photographs

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1.0 INTRODUCTION

From 2008 through 2014, WRA, Inc. (WRA) performed an assessment of Bay checkerspot butterfly (BCB, Euphydryas editha bayensis) habitat and conducted focused butterfly surveys at Young Ranch (Site) located in San Jose, Santa Clara County, California (Figure 1). Young Ranch is an approximately 2,150-acre ranch located along Coyote Ridge, east of Highway 101 and between Silver Creek Valley Road to the north and Metcalf Road to the south. The Site contains predominantly grazed ranching lands dominated by non-native annual grassland and serpentine bunchgrass grasslands, with pockets of oak woodland, scrub, and riparian vegetation scattered in drainages and throughout the site.

This report describes the methods and results of the site assessment and focused surveys which were aimed at documenting (1) the distribution and extent of BCB larval and adult butterfly habitat on the Site, (2) the observed numbers and distribution of BCB adults on the Site, and (3) historical data and knowledge of BCB distribution and population trends on the Site. These studies were designed to capture as much information as possible on BCB habitat suitability and the number and distribution of BCB adults at Young Ranch during the BCB flight seasons from 2008 to 2014. Focused BCB surveys were conducted during a similar time period at nearby localities with known populations of BCB to provide a comparison with the population trends observed at Young Ranch.

1.1 Summary

In March 2008, prior to initiating the adult butterfly surveys, all potential BCB habitat was mapped in the Site. Potential BCB habitat was defined as serpentine bunchgrass grassland containing both the larval host and the adult nectar plants. The Site was determined to contain 633 acres of land supporting both the larval host and the adult nectar plants.

Surveys conducted at the site documented the following number of adults in each year of monitoring:

 2008: 636 BCB adults  2009: 586 BCB adults  2010: 564 BCB adults  2011: 1,205 BCB adults  2012: 726 BCB adults  2013: 1,462 BCB adults  2014: 2,767 BCB adults

The majority of these individuals were mapped in the southeast portion of the property which supports the largest and highest quality extent of BCB habitat on the Site. The Site supports 1,517 acres of non-native annual grassland, scrub, aquatic, and woodland communities and limited areas of serpentine bunchgrass grassland where no larval host plants or adult nectar sources have been observed; these areas were determined to not provide the elements necessary to support the normal life functions of BCB. This is especially true in the north- central portion of Young Ranch where chert rock outcrops and related soils replace the serpentine outcrops and soils found in the western, southern, and eastern portions of the Site. Portions of the remaining 633 acres of the Site have been categorized as prime BCB habitat (473 acres), moderate BCB habitat (78 acres), and potential BCB habitat (78 acres). These habitat categories are defined in section 3.1.2. An additional 4 acres of potentially suitable

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habitat containing both the larval host and the adult nectar plants were observed as small patches distributed among larger concentrations of non-habitat and were not classified into one of the three habitat groups because they were geographically isolated from known BCB population centers at the site.

2.0 METHODS

From 2008 through 2014, the Site was traversed on foot during the BCB flight season (approximately late March through mid-April) to determine (1) plant communities present within the Site, (2) the extent of suitable habitat for BCB within the Site, and (3) the presence and distribution of adult BCB within the Site. All plant and wildlife species encountered during these Site visits were recorded and are summarized in Appendix A.

2.1 Biological Communities

Prior to the initial site visit in 2008, the Soil Survey of Santa Clara Area, California (U.S. Department of Agriculture [USDA] 1958), independent soil surveys of the Site (Treadwell and Rollo 2008), satellite images, and previous geologic and hydrologic surveys were examined to determine whether any unique soil types (e.g., serpentine soils) that could support plant communities with the potential to support BCB were present on the Site. Biological communities present on the Site were classified based on existing plant community descriptions described in the Preliminary Descriptions of the Terrestrial Natural Communities of California (Holland 1986). For the purposes of this report, some of the communities described by Holland were adapted to fit within the vegetation communities described in the Santa Clara Valley Habitat Plan (SCVHP, ICF International 2012).

2.1.1 Biological Communities

Biological communities were identified and mapped in the field during site visits conducted on March 31 and April 1, 2008. These surveys were conducted by WRA biologists Geoff Smick, Spencer Badet, and Rosie Wilson, all of whom are familiar with plant species and biological communities in the area. The entire Site was traversed on foot using 1:610 scale maps with 25- foot topographic contour lines and color NAIP aerial photograph base maps for navigation and for recording field observations. Additional field notes and species lists for each biological community were recorded on waterproof field notebooks. Boundaries of each biological community were established based on plant species composition, density, and diversity. Communities were distinguished by homogeneity of species, soils, slope, and other landscape features. Community boundaries were hand-drawn onto field maps and then digitized using ArcMap Geographic Information System (GIS) software. All observed plants were identified to the taxonomic level necessary to determine rarity using The Jepson Manual, Second Edition (Baldwin et al. 2012).

2.1.2 Habitats with Potential to Support Bay Checkerspot Butterfly

During the initial site assessment, the Site was examined for the presence of physical and biological features essential for BCB life history and survival including stable holes, soil cracks, or rock outcrops that provide suitable shelter for BCB larvae, in addition to the plants that the larvae and adult rely upon for feeding. These essential ecological elements are described in the species’ Recovery Plan (USFWS 1998) and in the designation of BCB Critical Habitat (USFWS 2007b, 2008a). Additional habitat elements considered necessary for the

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survival of the species include areas of open grassland, topography with varied slopes and aspects, and wetlands providing moisture during times of spring drought.

The SCVHP identifies serpentine bunchgrass grassland as the primary habitat for BCB reproduction, growth, and breeding. This habitat supports the primary larval host plant, dwarf plantain (Plantago erecta), and the secondary larval host plants, dense flower owl’s clover () and purple owl's clover (C. exserta), which are required for reproduction, larval feeding, and development. In addition, primary habitat supports species of native wildflowers that adult BCB rely upon for feeding such as California goldfields (Lasthenia californica), jeweled onion (Allium serra), tidy tips (Layia platyglossa), common muilla (Muilla maritima), and lomatium (Lomatium spp.). Rock outcrops and/or soil cracks are also important for providing suitable shelter for BCB larvae during summer . The above-listed plants, rock and soil structure, and varied microtopography are all considered primary constituent elements (PCEs) of BCB habitat as designated in the species’ Critical Habitat listing (USFWS 2007a, 2008a). Areas found to support these PCEs at Young Ranch were mapped as habitat with potential to support BCB. The majority of habitat that supports these PCEs (approximately 633 acres) at Young Ranch is located within serpentine bunchgrass grassland.

2.2 Bay Checkerspot Butterfly

2.2.1 Natural History

To obtain information on BCB natural history, WRA reviewed the USFWS BCB species account (2007b), the SCVHP (ICF International 2012), as well as primary scientific literature. Information regarding the designation of Critical Habitat for BCB was obtained from the USFWS final rule as published in the Federal Register (2008a).

2.2.2 Literature Review and Previous Studies on Nearby Parcels

The potential occurrence of BCB and its habitat on the Site was evaluated by first conducting a literature review and searches of the California Department of Fish and Wildlife (CDFW; formerly the California Department of Fish and Game [CDFG]) California Natural Diversity Database (CNDDB; CDFG 2008). Database searches for known occurrences of BCB focused on the San Jose East, Lick Observatory, Morgan Hill, and Santa Teresa Hills 7.5-minute U.S. Geological Survey quadrangles, each of which contains a portion of the Site. These data were compared with data from the SCVHP and other documents describing the historic and contemporary range and distribution of BCB in the vicinity of the Site.

Additionally, data were reviewed from nearby field sites where WRA conducts annual focused surveys for BCB. These sites included the Silver Creek Preserve to the north of the Site and Kirby Canyon Preserve to the south of the Site (Figure 1). Survey data are presented as the number of BCB adults observed per hectare. These numbers were obtained by dividing the total number of adult BCB observed on all transects by the area surveyed (transect length x width x the five transects). The width of the transects were defined as approximately 10 meters (i.e., 5 meters on either side of the transect). While this attempts to make the data more analogous, there are still several differences between the data collected at these sites. For example, the two sites adjacent to Young Ranch are surveyed by two biologists per transect per regulatory permit requirements, whereas only one biologist walked each transect at Young Ranch. Similarly the transects at Kirby Canyon Preserve are all located in high quality habitat, whereas several transects at both the Silver Creek Preserve and Young Ranch include low quality (and even non-) BCB habitat. Because the BCB counts from Kirby Canyon Preserve do

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not incorporate low quality (and even non-) BCB habitat, the overall BCB density there may appear higher even though the number of BCB observed in areas of high-quality BCB habitat may be similar across all three sites.

2.2.3 Adult Butterfly Field Surveys

WRA conducted field surveys for adult BCB on the Site during the 2008 through 2014 BCB adult flight seasons (approximately late March through mid-April) during periods of weather suitable for butterfly flight. Each year, a total of five surveys were conducted. Two of the five surveys were conducted to cover representative habitats, slopes, and aspects throughout the majority of the Site (Appendix B). Each of these surveys used five meandering transects1, each of which ranged in length from 4.9 to 5.9 miles (mean = 5.5 miles). The other three surveys performed each year focused on areas with the most suitable BCB habitat observed during the initial 2008 habitat mapping. Rather than employing five transects, these surveys employed three transects of similar lengths (4.4, 5.3, and 5.7 miles). These transects were designed to refine assessments of BCB abundance and distribution on the Site and focused on areas with the highest potential to support BCB (i.e., areas documented to support both larval host and adult nectar plants as well as other PCEs).

The survey methodology generally followed that of Pollard (1977). WRA biologists walked the transect routes singly, moving at a deliberate pace while surveying a strip approximately 10 meters-wide (i.e., five meters on either side of the transect line). Five biologists participated in each five-transect survey and three biologists participated in each three-transect survey. All adult BCB observed during the surveys were recorded. In addition, the behavior of observed individuals was also documented (e.g., in-flight, resting, nectaring). If a BCB was observed on a flower, its behavior was recorded as “nectaring.” These observations were assumed to be nectaring events; however, it is difficult to determine whether a butterfly is actually nectaring or simply resting or basking on a flower.

Hand-held GPS units were used to record approximate point locations of all observed adult BCB individuals or groups of individuals. Biologists deviated from pre-determined transect routes opportunistically if adjacent areas appeared to provide suitable habitat and returned to the original transect routes in the most efficient manner possible. Care was taken to avoid re- counting butterflies and to distinguish BCB from the sympatric and morphologically similar (E. chalcedona), the flight season of which averages later than, but overlaps with, that of BCB. Biologists used binoculars to study color patterns on the antennae clubs, a characteristic which reliably separates the two species, to ensure accurate identification. Weather conditions were assessed during each survey, and all wildlife and plant species observed were also recorded.

2.2.4 Butterfly Habitat Transects

In the spring of 2010, 14 permanent vegetation transects were established in the northwestern and southern portions of the Site, in areas that had previously been documented to support BCB larval host and adult nectar plants. Rebar was placed in the ground at the endpoints of

1 “Meandering” transects are commonly used for butterfly surveys (Pollard 1977) and are designed to cover a larger are of habitat than would be covered by traditional straight-line transects. Traditionally, the location of meandering transects is random and different transects are used during each survey. To make the study more repeatable, WRA employed a modified meandering transect method whereby the same meandering transects were employed year after year.

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each 50-meter-long transect and their locations were recorded using a handheld GPS unit so they could be readily located in subsequent years. Each transect contained five 1-square-meter quadrats spaced at 10-meter intervals.

In early April of 2010 and 2011, the vegetation in each quadrat was sampled for plant cover and composition. In addition to estimating general plant cover by species, biologists also estimated the number of dwarf plantain and owl’s clover individuals within each quadrat, the approximate percentage of senescent plantain and owl’s clover, the percentage of bare ground, and the average height of grasses in each quadrat.

Based on data collected during the initial adult BCB surveys at the Site, it was determined that there were differences the usage of potential BCB habitat in the northwestern part of the Site relative to the usage of the prime BCB habitat in the southern portion of the Site. Vegetation transect data from these two parts of the Site were compared to determine whether differences in the vegetation corresponded to the differences in adult BCB usage. The “potential” and “prime” habitat groups were chosen for this analysis because they represent the greatest differences between habitats in which BCB occur (relative to comparisons between potential and moderate habitat or moderate and prime habitat). All quadrats, regardless of transect, were treated as separate samples and were lumped within one dataset. Each quadrat in the dataset was categorized as occurring in either prime or potential BCB habitat. The percent cover of measured plant species was compared between prime and potential BCB habitat levels using the Student’s T-test (Zar 1996). All statistical tests used a significance level of P = 0.05.

3.0 RESULTS AND DISCUSSION

The Site is approximately 2,150 acres in size and is located along Coyote Ridge, the westernmost ridge of the Mt. Hamilton Range. This Site is located east of Highway 101, between Silver Creek Valley Road to the north and Metcalf Road to the south. The Site contains predominantly grazed ranching land dominated by non-native annual grassland (approximately 60 percent of the Site) and native serpentine bunchgrass grassland (30 percent of the Site) with pockets of mixed oak woodland and mixed riparian woodland along drainages and scrub habitats on steep slopes with southern exposures (approximately 10 percent of the Site). Site elevations range from approximately 400 to 1200 feet National Geodetic Vertical Datum (NGVD), and site topography is composed of rolling hills, level floodplains, steep grassy slopes, and rocky outcrops. Soils on the Site are primarily undisturbed, native soils, including many areas underlain and influenced by the presence of serpentine rock, resulting in the typical expression of serpentine soils. The Site occurs within the Coyote Creek watershed and is drained by Silver Creek to the northeast and by Coyote Creek to the south and west. Sources of hydrology on the Site include rainfall, natural hillside seeps, and Silver Creek, which is a perennial stream. The majority of the Site falls within the limits of the most recent designation of BCB Critical Habitat by the USFWS (2008a).

3.1 Biological Communities

Table 1 summarizes the area of each biological community type observed on the Site. Biological communities on the Site include non-native annual grassland, serpentine bunchgrass grassland, scrub, mixed oak woodland, mixed riparian woodland, wetlands, streams, and ponds. Descriptions for each biological community are contained in the following sections; the extent and distribution of these biological communities on the Site is shown in Figure 2. Appendix D

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contains a selection of photographs taken on the Site that show various habitats and land features present on the Site.

Table 1. Biological community acreages on the Site

Percent of Biological Community Acres Total Site

Non-Native Annual Grassland 1,273 59

Serpentine Bunchgrass Grassland 675 31 Scrub 98 5

Mixed Oak Woodland 55 3

Mixed Riparian Woodland 22 1

Wetlands (Seasonal Wetland, 19 <1 Freshwater Marsh)

Waters (Pond, Riverine) 3 <1 Developed (Roads, Water Tank) 5 <1 TOTAL 2,150 100

3.1.1 Observed Biological Communities

Non-Native Annual Grassland

Non-native annual grassland is an community dominated by annual grasses that are not native to California. Grass species found in this community on the Site include Italian ryegrass (Lolium multiflorum), rat-tail fescue (Vulpia myuros), ripgut brome (Bromus diandrus), slender wild oat (Avena barbata), soft brome (Bromus hordeaceus), and Harding grass (Phalaris aquatica). Annual and perennial wildflowers and forbs also occur in this biological community, including yarrow (Achillea millefolium), clover (Trifolium spp.), California poppy (Eschscholzia californica), filaree (Erodium spp.), lupine (Lupinus spp.), black mustard (Brassica nigra), and California buttercup (Ranunculus californicus). Non-native annual grassland is located throughout the Site, but dominates the northwestern and central portions. The Site supports approximately 1,273 acres of non-native annual grassland (approximately 59 percent of the total landcover at the Site).

Serpentine Bunchgrass Grassland

Serpentine bunchgrass grassland includes a mosaic of different grass and forb assemblages discussed in the SCVHP. Although native bunchgrasses are not always dominant in areas mapped as this habitat type on the Site, purple needlegrass (Nassella pulchra) was typically present 10 percent or greater cover, in addition to other native grasses. This habitat classification is consistent with the definition of serpentine bunchgrass grassland included in the SCVHP as well as the purple needlegrass Alliance description in The Manual of California

8 Young Ranch Santa Clara County, California

Figure 2. Biological Communities within the Site Young Ranch Site (2,150 acres)

Biological Communities:

California Non-Native Annual Grassland (1,273 acres)

Serpentine Bunchgrass Grassland (675 acres)

Diablan Sage Scrub (98 acres)

Mixed Oak Woodland (55 acres)

Mixed Riparian Woodland (22 acres)

Seasonal Wetland (18 acres)

Developed (5 acres)

Riverine (2 acres) 0 600 1,200 2,400 Feet Pond (1 acre)

Coastal and Valley Freshwater Marsh (1 acre) Date: October 2014 Map by: Michael Rochelle Aerial: ESRI Imagery

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Vegetation (Sawyer et al. 2009). This habitat type occurs on ultramafic, or serpentine, soils. Serpentine soils generally have lower overall cover of vegetation as well as lower cover of non- native species relative to non-serpentine soils and are generally characterized by low plant growth and productivity (Holland 1986).

Many of the areas mapped as serpentine bunchgrass grassland on the Site support the plants necessary for the growth and reproduction of BCB, including the larval host plants dwarf plantain and owl’s clover, in addition to many nectar plants used by the adults, including California goldfields, jeweled onion, tidy tips, common muilla, and lomatium. Other common species found in serpentine bunchgrass grassland at the Site include Italian ryegrass (Lolium multiflorum), wild oat (Avena spp.), cream cups (Platystemon californica), native dandelion (Agoseris spp.), California poppy (Eschscholzia californica), and clovers (Trifolium spp.).

Plant species found on serpentine rock outcrops within this community include two federal-listed species: Santa Clara Valley dudleya (Dudleya setchellii) and Metcalf Canyon jewel-flower (Streptanthus albidus ssp. albidus). This plant community includes small outcrops of nearly bare serpentine bedrock in addition to serpentine soils supporting small areas of California sagebrush (Artemisia californica) intermixed with bunchgrass grassland supporting BCB larval host and adult nectar pants. Because these areas contained less than 50 percent shrub cover, they were classified as serpentine bunchgrass grassland instead of serpentine scrub.

Scrub

Scrub communities occur on thin, rocky soils, often on south- or west-facing slopes that are drier and hotter than surrounding habitats. Scrub communities are dominated by evergreen woody shrubs, sub-shrubs, and drought-tolerant perennial herbs. Areas mapped as scrub at the Site had over 50 percent cover of shrubs or sub-shrubs. Although scrub understory is often thin or lacking, some annual herbs and perennial grass are adapted to the harsh conditions that support scrub communities. Within the Site, areas mapped as scrub are dominated by California sagebrush (Artemisia californica), black sage (Salvia mellifera), bush monkeyflower (Mimulus aurantiacus), and poison oak (Toxicodendron diversilobum). Other associated species include coyote brush (Baccharis pilularis), chia sage (Salvia columbariae), Hall’s bush mallow (Malacothamnus hallii), naked buckwheat (Eriogonum nudum), and woolly sunflower (Eriophyllum lanatum). A few areas of scrub in the southern portion of the Site were associated with serpentine soils and may qualify as serpentine chaparral; however, this level of habitat mapping detail was outside of the current scope, and all serpentine habitats were lumped in to a single serpentine bunchgrass grassland community. Approximately 98 acres of scrub habitat occur on the Site, which represents approximately five percent of the Site’s total landcover.

Mixed Oak Woodland

Mixed oak woodland on the Site includes habitats that are dominated by oak species or habitats in which oaks are co-dominant. These woodlands occur as closed-canopy stands with a shrubby or sparse understory, especially adjacent to riparian woodlands, and as open savannah with a grassy understory within grassland habitats. Coast live oak (Quercus agrifolia) and valley oak (Q. lobata) occur as dominant and co-dominant species in oak woodlands throughout the Site. Other species in this biological community include California bay (Umbellularia californica), black oak (Q. kelloggii), poison oak, and toyon (Heteromeles arbutifolia). Approximately 55 acres of mixed oak woodland habitat occurs on the Site.

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Mixed Riparian Woodland

Although most drainages on the Site do not have well defined riparian vegetation relative to the surrounding habitat, a few of the larger drainages do support such communities. Silver Creek is an example of a large (i.e., five- to eight-foot-wide) intermittent stream with a well-developed assemblage of uniquely riparian species. Commonly observed canopy species in these drainages include arroyo willow (Salix lasiolepis), California buckeye (Aesculus californica), California bay, and valley oak. Species found in the understory include poison oak, snowberry ( mollis), hedge nettle (Stachys bullata), and wild cucumber (Marah fabaceus). Approximately 22 acres of mixed riparian woodland occur on the Site.

Wetlands

Several wetland community types covering approximately 19 acres are present on the Site: seasonal wetlands, freshwater seeps, and freshwater marshes. Seasonal wetland and freshwater seep communities occur in swales, depressions, or hillside slumps that pond or become saturated during the rainy season for sufficient duration to support vegetation adapted to wetland conditions; these communities are mapped together as seasonal wetlands. Freshwater marshes are wetland habitats that are inundated or saturated for the majority of the year and that are dominated by perennial emergent vegetation.

On the Site, seasonal wetlands generally consist of vegetated drainages and depressions in the landscape. Dominant plant species include iris-leaved rush (Juncus xiphioides), spreading rush (Juncus patens), Italian ryegrass, and sedges (Carex spp.). Seasonal wetland features at the Site are often found in ephemeral drainages where a defined bed and bank dissipate into wider wetland swales. These types of wetlands are also commonly found in shallow depressions at the Site.

Seep wetlands on the Site often occur on hillsides and drain into adjacent stream channels, or are hydrologically isolated. Wetland species including tall flatsedge (Cyperus eragrostis), common spikerush (Eleocharis macrostachya), bog rush (Juncus effusus), spreading rush, and iris-leaved rush are dominant. Where standing water was present in seep wetlands, obligate wetland species were observed, including watercress (Nasturtium officinale) and seep monkeyflower (Mimulus guttatus). Other perennial seeps on the Site are associated with serpentine soils and are considered serpentine seeps. Species found primarily in perennial serpentine seeps include common spikerush and Mt. Hamilton thistle (Cirsium fontinale var. campylon), a rare species with a California Native Plant Society Rare Plant Rank of 1B.2.

Freshwater marshes on the Site occur along the edges of stock ponds, primarily in the southern portion of the Site. These marshes are dominated by cattails (Typha spp.), rushes (Juncus spp.), watercress, and seep monkeyflower. Because this habitat type is typically associated with man-made impoundments of water, it is rarely a naturally occurring community type on the Site.

Streams and Ponds

The distribution and extent of waters (i.e., ephemeral drainages, streams, and ponds) on the Site were mapped based on the presence of an ordinary high water mark (OHWM) and the presence of a defined bed and bank. While most of the drainages on the Site are ephemeral to intermittent (seasonal), Upper Silver Creek retains perennial flow due to the presence of perennial seeps in its headwaters. All of these features exhibit an OHWM and were mapped as

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waters. Man-made stock ponds are numerous on the Site and were also classified as waters. Approximately 3 acres of waters have been identified on the Site, generally restricted to topographical depressions.

Developed

The Young Ranch site contains limited development consisting of the main entrance road in the northwest portion of the Site and a Water District tank. The Site also extends onto Metcalf Road to the south in some locations. These areas have been designated as developed as they do not support biological functions. Five acres of developed areas occur on the Site.

3.1.2 Habitats with Potential to Support Bay Checkerspot Butterfly

Bay checkerspot butterfly require a variety of plant species for growth, reproduction, and general survival. WRA conducted an initial BCB habitat assessment in spring of 2008. During this site assessment, areas supporting adult nectar plants and larval host plants were hand- drawn on field maps containing aerial photographs and topographic contour lines. These hand- drawn polygons were then digitized using ArcMap GIS software. The resulting maps show the distribution of suitable BCB habitat on the Site (Figure 3). The definition of BCB habitat used for this assessment was consistent with that used in the SCVHP and that used by the USFWS. During subsequent focused adult BCB and rare plant surveys on the Site, the extent and distribution of serpentine grassland and BCB habitat was refined as needed.

In general, areas supporting BCB habitat were synonymous with the serpentine bunchgrass grassland habitat; however, there were some exceptions. Areas supporting both larval and adult nectar plants totaled 633 acres and always occurred in the serpentine bunchgrass grassland community. Patches with only larval or only adult nectar plants cannot be utilized by BCB for their entire lifecycle because not all necessary resources are present within a given patch. Therefore, only areas supporting both types of plants were considered areas with potential to support BCB. Some portions of serpentine bunchgrass grassland contained either only larval host plants or only adult nectar plants, or did not contain either. This accounted for approximately 42 of the 675 acres of serpentine bunchgrass grassland mapped at the site.

Much of the southeastern third of the Site (473 acres) supported both BCB larval and nectar plants. These open grasslands support large areas of contiguous, thin, rocky, serpentine soils and significant stands of the primary BCB larval host plant, dwarf plantain. Large numbers of a variety of the adult nectar plants also grow in this area, at times forming dense carpets of native wildflowers. This habitat occurs on hillsides and ridge tops with a variety of aspects, providing warm slopes with southern exposure and cooler, less windy northeastern slopes for refuge during extreme weather conditions. This diversity of hillside aspects also allows for essential larval and nectar species to occur at a variety of phenological stages at any given time during the growing season. This variety is important for BCB survival as the butterfly may use nectar and larval host plants on cooler, moister slopes after those same plants on drier, hotter slopes have senesced, or during unusual weather conditions such as prolonged heat waves or drought.

Additionally, rock outcrops with stable cracks and holes were observed throughout the serpentine bunchgrass grassland habitat; these provide shelter for BCB larvae during summer diapause. Four levels of BCB habitat were identified on the Site (Figure 3). This identification is based on (1) the presence and density of larval host plants, (2) the diversity and density of adult BCB nectar plants, (3) the amount and variability of micro-topographic variation, and (4) the

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number of BCB adults observed during surveys from 2008 through 2014. Potentially suitable BCB habitat had to contain both the larval host plants as well as the adult nectar plants to support the entire BCB lifecycle. Based on these characteristics, the following four levels of BCB habitat were defined and are explained further below: prime, moderate, potential, and non- BCB habitat.

Prime BCB habitat lies at the south end of the Site and includes 473 acres of land that support very dense patches of the primary larval host plant, dwarf plantain, and smaller amounts of the secondary host plants, dense flower owl’s clover and purple owl’s clover. This area also supported the most dense and diverse areas of adult nectar plants. Variation in microtopography is complex and provides a variety of aspects and slopes for the butterflies and their host plants. This area is also where the vast majority of BCB adults were observed during all of the surveys.

Moderate BCB habitat covers 78 acres in the northeast of the Site. This area is composed of a few relatively large patches of habitat that support larval host and nectar plants with additional smaller patches scattered in adjacent areas. Microtopographical variation is also present in good abundance. Bay checkerspot butterfly adults were also observed in this portion of the Site during all survey years; however, they were observed in fewer numbers relative to observations from prime habitat.

Potential BCB habitat covers 78 acres of land in the northwest of the Site. This potential habitat includes low-lying and southwest-facing areas supporting small, isolated populations of dwarf plantain, with only moderate densities and lower diversity of adult nectar plants relative to other areas of the Site. In general, only one or two species of nectar plants were observed in any given patch. Microtopographic variation is less diverse here with the majority of the area facing west or southwest. The larval host and nectar plants appeared to desiccate much earlier throughout this area during the 2008 through 2014 survey years compared to the prime and moderate areas, and therefore did not provide suitable feeding or breeding habitat for BCB. Four BCB were observed in these pockets of habitat, during the 2014 surveys, and one other individual was observed adjacent to this habitat during the 2008 survey. These areas are unlikely to support long-term viable BCB populations under normal climatic conditions due to their slope, aspect, elevation, and plant composition.

An additional 4 acres of potentially suitable habitat patches containing both larval host plants and nectaring plants were observed as small patches distributed in between larger concentrations of non-habitat within the north-central portion of the Site. These areas were not classified into one of the three habitat groups because they were geographically isolated from large blocks of potential, moderate, or prime habitat and. Only a few BCB were ever observed in this area, during the 2013 and 2014 surveys. These areas are unlikely to support long-term viable BCB populations due to their small size, patchy distribution, and geographic isolation from other larger, contiguous habitat areas on the Site.

14 Young Ranch Santa Clara County, Moderate California BCB Habitat (78 acres)

Potential BCB Habitat Figure 3.

(78 acres) Areas Supporting BCB Larval and Nectar Plants

Prime BCB Habitat (473 acres)

(Habitat acreages include patches mapped that support both BCB larval and nectar plants. The remainder of Young Ranch Site the site, 1,533 acres, does not support both BCB larval and nectar plants.) BCB Habitat Quality Units . BCB Larval Host Plants (27 acres)

0 750 1,500 3,000 BCB Adult Nectar Plants (16 acres) Feet

BCB Adult Nectar and Larval Host Plants (633 acres) Date: November 2011 Map by: Michael Rochelle Aerial Photo: ESRI Imagery

Path: L:\Acad 2000 Files\17000\17082\gis\ArcMap\BCB Report\2011\Revert to Old Habitat\Fig3_Habitats.mxd

This page intentionally blank, reverse of Figure 3.

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The majority of the remainder of the Site, approximately 1,517 acres, was determined to be non- BBC habitat as it does not support both the larval host plants and the adult nectar plants required by this species. These areas lack serpentine soils, or soils of similar composition, and are dominated by dense, non-native annual grasses with limited native plant diversity or are dominated by woodland or scrub habitat which is not suitable for BCB.

3.2 Bay Checkerspot Butterfly

3.2.1 Natural History

Bay checkerspot butterfly, a subspecies of Edith’s checkerspot (E. editha), is endemic to the San Francisco Bay Area and is currently restricted to San Mateo and Santa Clara counties. Bay checkerspot butterfly is a member of the Nymphalidae (brushfoot family), and is a medium-sized butterfly with a wingspan of approximately two inches. The forewings have black bands along all the veins on the upper surface, contrasting sharply with bright red, yellow, and white spots.

Habitat for BCB exists on shallow, serpentine soils, or soils with similar characteristics, that support larval host plants. Bay checkerspot butterfly only inhabits areas with these PCEs. The primary larval host plant for BCB is dwarf plantain. The secondary larval host plants, dense flower owl’s clover and purple owl's clover, can be utilized later in the season if the dwarf plantain senesces early. During years with particularly favorable ecological conditions, BCB populations may expand from heavily populated, core areas into secondary areas with smaller, but similar, habitat complexity and host plants. Conversely, BCB populations may contract and even suffer local in years with unfavorable ecological conditions. These characteristics fit the model of a metapopulation, or a “population of populations” that show variable localized and re-colonization over time (Harrison et al. 1988).

Adult BCB emerge in early spring to feed on nectar, mate, and lay eggs during a flight season that generally lasts from four to six weeks between early March and late April. The average life span for adults is approximately ten days. Eggs are typically laid in March and April. Females lay up to five egg masses of between five and 250 eggs each, which they deposit near the base of dwarf plantain, or, less often, on owl's clover. Bay checkerspot butterfly larvae hatch from eggs in about ten days, and grow for two weeks or more while molting, or shedding their skin, three times. Larvae that successfully reach the fourth instar (i.e., the larval stage following the third molt) enter a period of dormancy, or diapause, that lasts through the summer. Diapause occurs under rocks or in soil cracks in the soil and ends with the onset of the next rainy season and the subsequent germination of dwarf plantain. The larvae then emerge from diapause, resume growth, feed, and complete their development (USFWS 2007a).

The USFWS has identified the following threats to BCB: habitat loss and fragmentation, invasion of exotic/invasive plants, nitrogen deposition (including NOx and NHx), pesticide application (including drift), illegal collecting, fire, overgrazing, and gopher control (USFWS 2007a).

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3.2.2 BCB Studies on Nearby Parcels

Once found throughout much of the San Francisco Bay Area, BCB is currently restricted to San Mateo and Santa Clara counties. Virtually all extant populations occur in Santa Clara County on or adjacent to Coyote Ridge, which runs roughly northwest to southeast for approximately 20 miles and begins near the southeastern portion of the City of San Jose.

WRA conducted annual BCB monitoring at the Silver Creek Preserve from 2001 to 2010 and again in 2012 and 2013 and at the Kirby Canyon Preserve from 2002 to 2010 and again in 2013. These sites are located north and south of Young Ranch, respectively. The core populations of these sites are located approximately 2.6 miles north and 3.6 miles southeast, respectively, of the prime BCB habitat identified by WRA at Young Ranch. The number of adult BCB observed at Silver Creek during transect surveys generally increased over the 10-year period, with the highest estimated density of 7 BCB per hectare documented in 2008 (WRA 2010). However, counts in 2009 and 2010 were unusually low, which may potentially be due to poor weather conditions during surveys or the tendency for satellite populations to fluctuate more than core populations. Population counts were not conducted in 2011 at Silver Creek as the regulatory-agency mandated monitoring period ended in 2010. Surveys were repeated in 2013, and were similar to counts conducted in 2008, with an estimated 7 BCB per hectare. Numbers of adult BCB observed at Kirby Canyon since 2001 have been variable, with the highest density recorded in 2003 and the lowest in 2010. Figure 4 shows numbers of BCB observed per hectare at Silver Creek, Kirby Canyon, and Young Ranch from 2001 through 2014 (surveys were not conducted at Silver Creek or Kirby Canyon in 2014).

The causes of variability in the data between years and sites are unclear, and population trends between the two preserves and Young Ranch are not clearly related. Potential explanations may be related to the geographic location of the various sites and the corresponding difference in weather patterns (e.g., fog/cloud cover, wind variation). Additionally, the habitats themselves are different in that the BCB habitat at Silver Creek occurs on narrow east-west running ridges and is much smaller in area than the BCB habitat at Young Ranch or Kirby Canyon, which are part of the main Coyote Ridge ridgeline.

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Figure 4. Adult BCB per Hectare at Young Ranch, Kirby Canyon (Kirby Slope) Preserve and Silver Creek Preserve

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3.2.3 Adult Butterfly Field Surveys

Young Ranch BCB general survey transect data from 2008 through 2014 are summarized in Table 2. Adult BCB counts are summarized in Table 3. Bay checkerspot butterfly were observed on the Site during each of the survey dates in every year, and at least once per year on most transects. Most individuals were found in the southeastern portion of the Site (Transects 3, 4, and 5) where suitable habitat is most abundant (Figure 5, Appendix C). Butterfly counts in 2008 through 2010 were in the range of 600 individuals each year. In 2011, this number increased to 1,205 individuals, an approximately two-fold increase from the previous three years, but returned close to previous levels in 2012 with 726 individuals. In 2013, there was another two-fold increase from the previous year with 1,474 individuals counted. In 2014, there was an additional two-fold increase, with 2,767 individuals counted, the highest number recorded at the Site. Annual BCB larval surveys conducted by the Creekside Center for Earth Observation at Young Ranch and at the United Technologies Corporation (UTC) site to the south of Young Ranch indicate that the population has been in a boom phase since 2011 (J. Quenelle, Creekside Center for Earth Observation, personal communication). These findings generally agree with the data collected by WRA on adult BCB trends at Young Ranch from 2011 to 2014.

Dense aggregates of BCB adults in the prime habitat at the southern part of the Site may be due to a variety of factors such as the preponderance of cooler north- and northeast-facing slopes. These slopes have lower solar insolation and are protected from strong westerly afternoon winds and therefore support larval host and adult nectar plants later into the season (Weiss et. al. 1988). Adult BCB may be congregating in those areas to feed, mate, or lay eggs. These areas also often coincide with topographical depressions that may allow BCB adults to avoid exposure to stronger winds.

Adult BCB Nectar Plant Usage

Results of BCB nectaring observations at Young Ranch over five years from 2009 to 2013 indicate that two plant species, California goldfields and tidy tips, are consistently favored by adult BCB at Young Ranch. Together, these two species accounted for 54 percent of the observed nectaring behavior (California goldfields = 31 percent, tidy tips = 23 percent; Figure 6). After California goldfields and tidy tips, the next most common nectar plants appear to depend upon the year and plant abundance at the time of BCB emergence. Purple onion is the second most visited nectar plant (26 percent); however, nearly all observations are from the 2013 surveys. The same is true for common muilla, the fourth most visited nectar plant, with observations predominantly occurring during the 2011 surveys. The remaining nectaring observations occurred among eight plant species, all of which accounted for less than five percent each.

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Table 2. Summary of BCB transect survey conditions for Young Ranch: 2008 through 2014

Number Start End Starting Year Survey Date of Weather Wind speed (mph) time time temp (°F) transects 1 27-Mar 5 10:00 15:00 Partly cloudy Calm 51

2 31-Mar 3 9:50 15:00 Clear Light wind 55

3 4-Apr 5 9:00 15:00 Partly cloudy Calm 53 2008 4 11-Apr 3 10:00 14:45 Clear Calm 65 5 17-Apr 3 10:00 14:30 Clear Calm 65 1 27-Mar 3 9:30 14:30 Clear Calm 58

2 31-Mar 3 9:30 14:30 Clear Calm 60

3 3-Apr 5 9:00 13:30 Few clouds Light winds becoming moderate 55 2009 4 13-Apr 3 10:00 15:30 Few clouds Moderate winds 54 5 17-Apr 5 10:00 14:00 Clear Light winds becoming moderate 60 1 23-Mar 3 10:00 14:15 Clear Calm 65

2 7-Apr 5 10:15 15:30 Clear Light winds becoming moderate > 60

3 9-Apr 3 10:30 14:55 Clear Calm 55 2010 4 15-Apr 5 10:30 15:00 Clear Light breeze 65 5 22-Apr 3 10:30 14:00 Partly cloudy Light wind 60 1 29-Mar 3 9:35 14:45 Clear Light wind 60

2 31-Mar 5 9:30 14:00 Clear Light wind 68

3 4-Apr 3 9:30 14:00 Clear Light wind 65 2011 4 13-Apr 5 10:10 13:45 Clear Moderate winds 60 5 27-Apr 3 9:30 14:00 Clear Moderate winds 65 1 2-Apr 3 9:50 15:40 Clear Light breeze becoming moderate 56

2 9-Apr 5 10:00 14:55 Partly cloudy Light breeze 59

3 16-Apr 3 10:10 14:40 Clear Light breeze 61 2012 4 20-Apr 5 9:35 14:55 Clear Light breeze 72 5 24-Apr 3 9:45 14:20 Partly cloudy Light wind 68 1 29-Mar 3 10:00 15:15 Clear Calm 62

2 3-Apr 5 9:30 15:15 Clear Light breeze 60

3 5-Apr 3 9:40 14:15 Mostly cloudy Light breeze becoming moderate 62 2013 4 10-Apr 5 10:15 15:05 Clear Moderate winds 66 5 18-Apr 3 8:45 13:00 Clear Light breeze becoming moderate 60 1 21-Mar 3 10:00 15:30 Clear Light breeze becoming moderate 56

2 3-Apr 5 10:00 15:30 Partly cloudy Light wind 60

3 8-Apr 3 11:30 16:45 Clear Light breeze 75 2014 4 11-Apr 3 10:00 15:15 Clear Light breeze 61 5 16-Apr 5 10:30 15:35 Clear Light breeze 63

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Table 3. Number of adult BCB observed per transect during surveys at Young Ranch

Transect Total # BCB/ Year Survey 1 2 3 4 5 Mod 3 Mod 4 Mod 5 survey 1 4 29 8 26 - - - 69 2 - - - - - 174 0 122 296

3 0 1 61 21 24 - - - 107

2008 4 - - - - - 79 6 66 151 5 - - - - - 7 0 6 13 Total 2 5 90 29 50 260 6 194 636 1 - - - - - 40 4 68 112 2 - - - - - 119 0 71 190

3 0 9 95 24 49 - - - 177

2009 4 - - - - - 53 4 38 95 5 0 0 7 3 2 - - - 12 Total 0 9 102 27 51 212 8 177 586 1 - - - - - 20 0 72 92 2 0 8 112 38 31 - - - 189

3 - - - - - 47 0 85 132

2010 4 0 3 50 29 35 - - - 117 5 - - - - - 17 0 17 34

Total 0 11 162 67 66 84 0 174 564

1 - - - - - 74 175 1 250 2 91 75 118 17 0 - - - 301

3 - - - - - 110 275 1 386

2011 4 0 68 49 0 146 - - - 263 5 - - - - - 0 3 2 5 Total 91 143 167 17 146 184 453 4 1205

1 - - - - - 70 5 150 225 2 0 5 119 53 88 - - - 265

3 - - - - - 42 1 64 107

2012 4 0 0 49 2 42 - - - 93 5 - - - - - 31 0 5 36 Total 0 5 168 55 130 143 6 219 726

1 - - - - - 239 19 368 626

2 5 36 337 37 108 - - - 523

3 - - - - - 67 3 85 155

2013 4 3 8 141 4 12 - - - 168

5 - - - - - 1 1 0 2

Total 8 44 478 41 120 307 23 453 1474

1 - - - - - 45 1 37 83

2 0 41 125 37 92 295

3 306 38 597 941

2014 4 482 8 310 800

5 0 21 371 91 165 648

Total 0 62 496 128 257 833 47 944 2767

22 Red = 2008 Observations (636 total) Blue = 2009 Observations (586 total) Yellow = 2010 Observations (564 total) Rose = 2011 Observations (1,205 total) Green = 2012 Observations (726 total) Young Ranch Santa Clara County, Orange = 2013 Observations (1,462 total) California Purple = 2014 Observations (2,767 total)

Figure 5.

Bay Checkerspot Butterfly Observations Observed BCB 16 individuals (2008 - 2014) 1 individual 17 individuals 2 individuals 18 individuals 3 individuals 19 individuals 4 individuals 20 individuals 5 individuals 21 individuals 6 individuals 22 individuals 7 individuals 24 individuals

8 individuals 25 individuals 9 individuals 27 individuals 10 individuals 30 individuals 11 individuals 12 individuals 36 individuals 0 750 1,500 3,000 13 individuals Feet 14 individuals 42 individuals

15 individuals Young Ranch Site Date: May 2014 Map by: Michael Rochelle Aerial: ESRI Imagery

Document Path: L:\Acad 2000 Files\17000\17082\gis\ArcMap\BCB Report\2014\Fig5_BCB Observations.mxd

This page intentionally blank, reverse of Figure 5.

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Figure 6. Young Ranch Adult BCB Nectaring Occurrences from 2009 to 2013

3.2.4 Comparative Vegetation Transects

Results of the 2010 and 2011 vegetation transect studies indicate significant differences in key aspects of BCB habitat quality in the northwestern “potential” habitat compared to the southern “prime” habitat. These differences include (1) adult nectar plant densities, (2) timing of larval host plant senescence, and (3) grass species and height (Figures 7 and 8). Differences in three plant species were notable: California goldfields, common muilla, and dwarf plantain. Average grass heights were also significantly different between habitats. California goldfields, the most commonly visited flower based on five years of BCB nectaring data, was far more abundant in 2010 and 2011 in the prime habitat compared to the potential habitat (7.3 percent compared to 0.1 percent coverage, respectively). Common muilla, the fourth most visited BCB adult nectar plant, was also significantly more abundant in the prime habitat compared to the potential habitat, with 0.3 percent average coverage among samples in the prime habitat and no coverage among samples in the potential habitat.

The timing of senescence of the primary larval host plant, dwarf plantain, was significantly different between the two areas in 2010. The plants in the northern potential habitat senesced earlier than the plants in the southern prime habitat. This trend has been discussed in the literature (Weiss 1988, ICF International 2012) and appears to be related to the altitude and aspect of a given population. Weiss (1988) postulated that lower elevation and south- to west- facing slopes on Coyote Ridge, like those present in the northwest of Young Ranch, receive less rain and more solar radiation than the higher elevation slopes, resulting in earlier senescence of dwarf plantain. The 2011 data does not show the same results, as slightly more dwarf plantain were observed to be senesced by April in the prime habitat than in the potential habitat; however, this difference was not statistically significant. This could be related to the above-average rainfall in 2011 which may have prolonged the lifespan of individual plants.

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Figure 7. Young Ranch BCB Habitat Vegetation Comparison 2010

2010 Young Ranch BCB Habitat Vegetation Comparison

100.00 66.9 68.8 50.9 Northwest Potential Habitat - BCB Absent Two Sample T-Test Significance 43.6 * p < 0.05 South Prime Habitat - BCB Present ** p < 0.01 20.1*** *** p < 0.001 *** 10.00 7.3 8.1 *** 4.3 2.9 ** 2.5

1.00

** 0.4 0.3

0.1

0.1 0.1 0.1 0.10

0.1 0.1 0.1 0.1 Percent Coverage Across All Quadrats All (log Across scale) Coverage Percent

0.0 0.0

0.01

(%)***

clover(%)

Lomatium(%)

Dwarf plantainDwarf

BareGround (%)

Grasses(cm)***

Dwarf plantainDwarf (#)

senescence(%)**

AverageHeight of

Dwarf plantainDwarf (%)

Jeweledonion (%)

Denseowl'sflower

Californiagoldfields

CommonMuilla(%)** Purpleowl's clover (%)

BCB Nectar Plants BCB Larval Host Plants Other Parameters

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Figure 8. Young Ranch BCB Habitat Vegetation Comparison 2011

2011 Young Ranch BCB Habitat Vegetation Comparison

100.00 Northwest Potential Habitat - BCB Absent 45.3 ***45.9 South Prime Habitat - BCB Present 32.8 ** *** 21.9 21.9 24.2 16.3 * Two Sample T-Test Significance 13.9 * p < 0.05 9.7 10.00 ** ** p < 0.01 5.0 *** p < 0.001 3.4

** 1.00 0.8 0.7 0.7 0.6

* 0.2 0.1 0.1

0.10 Percent Coverage Across All Quadrats All (log Across scale) Coverage Percent

0.0 0.0 0.0 0.0

0.01

(%)**

clover(%)

Lomatium(%)

Dwarf plantainDwarf

senescence(%)

Grasses(cm)***

Dwarf plantainDwarf (#)

AverageHeight of

Denseowl'sflower

BareGround (%)***

Californiagoldfields

Jewelledonion* (%)

Dwarf plantainDwarf (%)***

CommonMuilla(%)** Purpleowl's clover (%)

BCB Nectar Plants BCB Larval Host Plants Other Parameters

Due to the semi-random placement of transects in the landscape and the phenology of the species, no tidy tips were observed on any transects. However, incidental observations of this species indicate that it grows in many areas of the prime habitat later in the BCB flight season, but is much less common in the potential habitat in the northwest of the Site.

The average grass heights were also significantly different between the potential and prime habitats in both years, with the prime habitat having lower grass height. An abundance of tall grasses can reduce BCB habitat quality, as non-native, invasive grasses out-compete the native plants on which BCB rely, making it more difficult for BCB adults to locate and feed upon nectar plants. The difference in grass height could be attributable to several factors such as soil depth, soil fertility (e.g., serpentine soils in the north may be more favorable for plant growth relative to serpentine soils in the south), grazing regime, or a combination of these and other factors. The grazing regime may have a major role in these differences, as the ranching lessee tries to focus cattle grazing in the south during the early spring to control weed growth in BCB habitat.

4.0 SUMMARY AND CONCLUSIONS

The initial 2008 habitat assessment and subsequent refinements indicate that the Site supports 633 acres of BCB habitat supporting both BCB larval host and adult nectar plants. These plants are necessary to support reproduction, growth, and feeding of adult and larval BCB. The majority of this habitat (75 percent, approximately 473 of 633 acres) is concentrated in the southeastern third of the Site (“prime” BCB habitat, Figure 3), with additional areas in the

27

eastern portion of the Site (“moderate” BCB habitat comprising approximately 78 acres, Figure 3) and along the northwestern west-facing slopes of the Site (“potential” BCB habitat comprising approximately 78 acres of scattered, isolated patches).

The 473-acre southeastern area is considered prime habitat because it contains the largest and densest contiguous patch of BCB larval host and adult nectar plants and because it supported 91 to 98 percent of BCB adults observed in annual surveys conducted from 2008 to 2014 (Table 4; Appendix C). Whereas a large portion of this prime habitat occurs on a relatively flat hilltop, this prime habitat has a range of varying slopes and aspects. This range of slopes and aspects supports BCB under a variety of climatic conditions, based on the range of relatively dry and normal rainfall years that WRA observed from 2008 through 2014.

The moderate BCB habitat in the eastern part of the Site also supports substantial populations of scattered larval host plants and adult nectar plants, but is much smaller, at about 78 acres. The potential BCB habitat in the northwest portion of the Site (approximately 78 acres across many small, isolated patches) supports dense populations of dwarf plantain, but has less adult nectar plant species diversity and density relative to other serpentine bunchgrass grassland habitat on the Site. Furthermore, this habitat is composed of multiple smaller patches separated by large areas of unsuitable habitat (e.g., non-native annual grassland). These patches are generally restricted to isolated, thin-soiled hilltops and side slopes that also support scattered California sagebrush shrubs. Few BCB were observed in these pockets of habitat, and were only observed in this area during the 2008 and 2013 surveys.

During the 2014 surveys, nearly double the amount of BCB were observed compared to the previous high from 2013. The extremely high abundance of BCB in this year is likely directly correlated to the new observations within the potential habitat, as individuals may have dispersed into or through this habitat from densely occupied habitats of higher quality. Because BCB dispersal events have been previously documented to be on the of 5 to 10 percent of individuals or less (McKechnie et al. 1975; ICF 2012), the greater overall number of individuals present means more dispersing individuals overall. Therefore, dispersing BCB are more likely to be observed during surveys.

Although the number of BCB observed each year from 2008 through 2010 remained relatively constant, the number observed in 2011 and 2013 nearly doubled compared to all other survey years with 1,205 and 1,474 BCB observed, respectively. The number of BCB observed in 2012 returned to levels closer to the 2008 to 2010 counts. The number of BCB observed in 2014 was approximately double that of 2011 and 2013 (four times what was observed from 2008-2010), with 2,767 BCB observed, the highest number counted in the seven years of surveys (Table 4). Other researchers also observed a similar explosion of BCB larvae counted along Coyote Ridge in 2011 and 2013 (J. Quenelle, Creekside Center for Earth Observation, personal communication); it is unclear how results from 2014 compared with other sites. It is likely that the extreme drought conditions experienced in 2014 contributed to the record BCB counts in that year by causing non-native grasses to remain at relatively low cover, thereby reducing competition with native plants which are adapted to the periodic droughts experienced in California. Reduced competition from non-native species is likely to have increased the cover of native larval host and adult nectar plants, thereby improving conditions for BCB. The dramatic increase in 2011 population numbers may be due to two consecutive years with average to above-average rainfall. The timing of the rainfall may also be important, as 2010 and 2011 both had several large rain events throughout the spring, prolonging the longevity of individual larval host and adult nectar plants. Late rain events in 2012 may have allowed host plants to remain later into the spring and more larvae to survive resulting in the large number of adults observed

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in the 2013 season. Although rainfall was low during late 2013 and 2014, a singular large rain event in early February may have allowed host plants to persist later in the year, accounting for the record number of individuals counted during the 2014 flight season. The fluctuation in population counts between survey years demonstrates the importance of conducting long-term studies of BCB populations as normal annual fluctuations are expected, but large spikes (or drops) in population size may be hard to observe without consistent monitoring and suitable baseline data for comparison.

Table 4. Number of adult BCB observed in various habitats at Young Ranch Number of BCB Observed (Percentage of Total Observations) Habitat 2008 2009 2010 2011 2012 2013 2014 603 561 547 1,145 697 1,246 2,508 Prime Habitat (95%) (96%) (98%) (95%) (96%) (85%) (91%) Moderate 30 22 13 60 27 202 224 Habitat (5%) (4%) (2%) (5%) (4%) (14%) (8%) 0 0 0 0 0 0 4 Potential Habitat (0%) (0%) (0%) (0%) (0%) (0%) (0%) 3 3 0 0 2 26 31 Non-Habitat (0%) (0%) (0%) (0%) (0%) (1%) (0%) Total 636 586 560 1,205 726 1,474 2,767

The SCVHP discusses how seemingly good BCB habitat situated on “warm slopes” (generally low elevation and west- or south-facing) tends to dry earlier in the spring during years of low spring rainfall. The following year, those potential habitat patches are presumed to support few to no BCB, whereas during years with ample spring rainfall, these areas frequently do support BCB populations as the population cores expand to inhabit these peripheral areas. WRA incidentally observed a similar trend of early senescence of dwarf plantain during the 2008 and 2009 surveys, and documented the trend through direct surveys by using vegetation transects in the normal rainfall year of 2010. These areas are not expected to be extensively used by BCB due to these geomorphic limitations and would likely not be able to support a viable population of BCB for multiple consecutive years. Despite normal winter/spring rains in the 2010-2011 rainfall year and twice as many BCB observed in 2011 than in previous years, no adult BCB were observed in the potential habitat in the northern part of the Site. It should also be noted that the 2010 and 2011 vegetation transects were conducted during the BCB flight season and no incidental BCB were observed in the north during this fieldwork.

The field studies conducted from 2008 through 2014 indicate that the southern portion of the Young Ranch site supports a large population of BCB. By contrast, the vast majority of the northern portion of the Site does not contain all of the elements necessary to support BCB life functions, and very few BCB adults have been observed in the majority of these areas.

5.0 REFERENCES

Baldwin, B.G., D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken (eds.). 2012. The Jepson Manual: Vascular Plants of California, second edition. University of California Press, Berkeley, California.

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[CDFG] California Department of Fish and Game. 2008. Natural Diversity Database, Wildlife and Habitat Data Analysis Branch. Sacramento.

Harrison S., D. D. Murphy and P. R. Ehrlich. 1988. Distribution of the Bay Checkerspot Butterfly, Euphydryas editha bayensis: Evidence for a Metapopulation Model. The American Naturalist 132: 360-382.

Holland, R. F. 1986. Preliminary Descriptions of the Terrestrial Natural Communities of California. Prepared for the California Department of Fish and Game, Sacramento, California.

[ICF] ICF International. 2012. Final Santa Clara Valley Habitat Plan. August.

McKechnie, S.W., P.R. Ehrlich, and R.R. White. 1975. Population genetics of Euphydryas butterflies. I. Genetic variation and the neutrality hypothesis. Genetics 81: 571-594.

Pollard, E. 1977. A method for assessing changes in the abundance of butterflies. Biol. Conserv. 12:115-134.

Quenelle, J. 2011. Phone conversation with Geoff Smick (WRA) re: BCB larval surveys.

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