Determining Bird Species Composition and Abundance at Hawk Hill following Tree Removal

Transcription

1 Determining Bird Species Composition and Abundance at Hawk Hill following Tree Removal A report to The Golden Gate National Parks Conservancy Prepared by: Mark D. Dettling and Diana L. Humple Point Blue Conservation Science 3820 Cypress Dr. #11 Petaluma, CA Submitted April 24, 2015 Point Blue Conservation Science Contribution #2034

2 INTRODUCTION Hawk Hill, Marin County, California is located within the Golden Gate National Recreation Area. In 2009 a number of non-native trees were proposed to be removed due to cultural and ecological considerations and as mitigation for impacts from road and trail construction in the Marin Headlands. The tree removal was proposed predominantly to help the federally endangered Mission blue butterfly (Icaricia icarioides missionensis), as the trees served as a barrier to their movement throughout the area; the removal also would have cultural and recreational value. These trees were artificially established, and formed a tree layer since the 1970s. Additionally, these non-native trees may have had adverse effects on the native plant and animal communities in this area, resulting in different species assemblages than would have been there historically. For more information, see In 2009, Point Blue Conservation Science (Point Blue, formerly PRBO) conducted avian surveys during the winter and summer, before the removal of the trees, to determine bird species community composition and abundance in order to evaluate potential impacts of the removal (Jennings and Gardali 2009). The trees were subsequently removed in winter , native coastal scrub and coastal prairie plantings began in 2012, and restoration activities continue to date. During the summer of 2014 and winter of , Point Blue again conducted surveys in the same areas to evaluate the change in bird species community composition and abundance. This report summarizes the survey methods employed, results of the surveys done after tree removal, and a comparison of the results before and after tree removal. METHODS Hawk Hill (37º 57 N, 122º 30 W) lies in the southern portion of the Marin Headlands in Marin County, California overlooking the Golden Gate Bridge and San Francisco Bay. The site is located on the ridge top at one of the highest points in the Marin Headlands and is part of the Golden Gate National Recreation Area. Two avian survey plots were established (Figure 1) in 2009, covering approximately seven acres in total. A description of the survey plots can be found in Appendix 1. We employed the area search method, which is well suited to small areas, to survey the site for landbirds. The method measures species composition and abundance of the bird community, and is appropriate for obtaining breeding status of resident birds and detecting secretive birds (Hewish and Loyne 1989, Ralph et al. 1993). While standard area search protocols recommend 20-minute searches per plot (Ralph et al. 1993), we employed non-time constrained surveys during both the before tree removal and after tree removal components of this study. Non-time constrained survey allow a more thorough assessment of the species composition and abundance on the plot and allow for smaller and more irregular plots to be surveyed than are typically appropriate for a time-constrained plot. Biologists surveyed each plot on each visit for as long as they determined necessary to detect all species using the plot. Studies of area search methodologies suggest that increasing the amount of total time spent per plot greatly improves determination of species composition and perhaps abundance (Slater 1994, Dieni and Jones 2002). Additionally, the objective here was to do a simple inventory of the site (both plots combined) and not to make comparisons across plots or to plots at other locations, thus standardization of visit length was

3 not necessary. Biologists conducting field work for this study felt that the duration of each survey was adequate to provide a robust picture of species composition and abundance. Figure 1. Map of Point Blue Conservation Science avian survey plots on Hawk Hill, Golden Gate National Recreation Area. Plot B Plot A Surveys before tree removal were conducted during the winter of (January and February 2009) and the summer of 2009 (May and June), with 6 visits to each plot in each season (Jennings and Gardali 2009). Surveys after tree removal were conducted during the summer of 2014 (May and June) and the winter of (December through February), with 6 visits to each plot in each season (Table 1). We limited our surveys to the breeding and wintering periods because we judged any potential impacts to be most discernible in these seasons versus during the migratory periods. Surveys occurred in the mornings and were always completed within four hours following local sunrise. The entire plots were covered during each visit, varying the order in which the plots were consecutively surveyed, with the observer moving throughout the plot and spending as much time as they determined necessary to detect all species. Surveys were not conducted during periods of inclement weather (e.g., rain, strong wind, heavy fog). Individual birds of all species detected within the plot boundaries were counted and detection type recorded (hierarchically as song, call, or visual). Birds flying directly over the study area but not using the habitat in the plots or foraging for prey in them were not counted but were recorded separately as flyovers. It should be noted that Allen s and Rufous Hummingbirds of the genus Selasphorus are often inseparable in the field and were often recorded as Selasphorus Hummingbirds on our surveys. Notes on behavior were recorded, with particular attention paid to those related to breeding status. Observers with extensive experience identifying birds in the region by sight and sound conducted all surveys. Data from the two area search plots were combined for the results.

4 Table 1. Dates of Point Blue Conservation Science avian survey visits after tree removal and effort (minutes spent in each plot), Visit # Date Effort (min.) Summer Plot A Plot B 1 5/3/ /13/ /20/ /28/ /14/ /29/ Winter 1 12/8/ /8/ /23/ /29/ /3/ /19/ Data forms, metadata, and instructions can be found at The data are stored and maintained by Point Blue through the California Avian Data Center ( Report authors can be contacted with requests for access to data. Summary Statistics The summer and winter seasons were analyzed separately. We calculated an average number of detections per visit for each species across both plots combined. The number of visits (out of six) a species was detected is also reported. We evaluated which species were seen only before or after tree removal, and for the species that were seen at both times, we looked for differences in abundance. Data from the avian surveys done before tree removal can be found in Jennings and Gardali (2009). Each species was categorized according its association with trees and scrub habitat, using our knowledge of each species natural history and species accounts in the Birds of North America (Poole and Gill 2002). Scrub habitat species were those that preferred areas dominated by shrubs and do not associate with trees. Tree associated species were those that preferred trees and generally avoided open, shrubby areas. Species that are equally likely to be found in trees or scrub habitat, or that prefer heterogeneous habitat containing both of those vegetation layers, were put into the mixed habitat category. A few species detected didn t fall into any of the above categories so were given the designation other. Individuals of each species may be found outside of their preferred habitat. For example, a species that during the breeding season exclusively uses scrub habitat may be more of a generalist during the winter and be found in tree habitat. Even though this is a simplification of each

5 species habitat preferences, separating the species this way allows us to look at patterns of groups of species possibly affected by the tree removal. RESULTS Overall Patterns A total of 23 species were detected at Hawk Hill on surveys during the summer of 2014 and the winter of , after tree removal. This was lower than the total number detected in 2009 before tree removal (37 species, Table 2). Of the 40 species detected using these plots throughout the duration of this study, 19 were detected both before and after tree removal, 18 were detected only before tree removal, and 3 were detected only after tree removal (Table 2). Since Allen s and Rufous Hummingbirds are often inseparable in the field, they were recorded as Selasphorus Hummingbirds on our surveys when they could not be identified to species. During the 2009 surveys some of these birds were identified to species (Allen s) and were counted in the species total, but the unidentified Selasphorus Hummingbirds were not added as a separate species in the above tally (as most if not all were likely Allen s Hummingbirds). In , all Selasphorus Hummingbirds were recorded as unidentified Selasphorus Hummingbirds, so they were counted in the species total. Winter Season A total of 15 species were detected on six surveys during the winter of ; this was similar to 16 species detected during the winter of 2009 (Table 3). Species seen on three or more visits in after tree removal include California Quail, Anna s Hummingbird, Black Phoebe, Bewick s Wren, Wrentit, Spotted Towhee, Song Sparrow, and Golden-crowned Sparrow. There is very little overlap when comparing this list to the 2009 list, with Song Sparrow being the only species detected consistently before and after tree removal. The other species seen on three or more visits in 2009 were Common Raven, Pygmy Nuthatch, Pacific Wren, and Ruby-crowned Kinglet. Ten species showed an increase in abundance in winter after tree removal, while 11 species decreased in abundance (Table 3), although in some cases these may not reflect significant patterns. One species showed no difference. Seven species were seen more regularly (on at least three visits compared to fewer than three visits) in the winter after tree removal (California Quail, Anna s Humingbird, Black Phoebe, Bewick s Wren, Wrentit, Spotted Towhee, Golden-crowned Sparrow), while four species were seen less regularly after tree removal (Common Raven, Pygmy Nuthatch, Pacific Wren, Ruby-crowned Kinglet). Breeding Season A total of 17 species were detected on six surveys during the summer of 2014, which was lower than the 31 species detected during the summer of 2009 (Table 4). Species seen on three or more visits (and thus likely breeding at or near the site) in 2014 include California Quail, Anna s Hummingbird, Western Scrub- Jay, Bewick s Wren, Wrentit, Spotted Towhee, Song Sparrow, and Dark-eyed Junco. In 2009 before tree removal, many of these species (California Quail, Anna s Hummingbird, Western Scrub-Jay, Bewick s Wren, Wrentit, Spotted Towhee, Song Sparrow) were also detected during three or more visits, along with several other species (Allen s Humingbird, Common Raven, Barn Swallow, Chestnut-backed Chickadee, Bushtit, Pygmy Nuthatch, American Robin, Orange-crowned Warbler, Wilson s Warbler, Purple Finch).

6 Nine species showed an increase in abundance after tree removal, while 21 species decreased in abundance (Table 4), although in some cases these may not reflect significant patterns. Three species showed no change. One species was seen more regularly (on at least three visits) after tree removal in the summer (Dark-eyed Junco), while 10 species were seen less regularly after tree removal (Allen s Hummingbird, Common Raven, Barn Swallow, Chestnut-backed Chickadee, Bushtit, Pygmy Nuthatch, American Robin, Orange-crowned Warbler, Wilson s Warbler, Purple Finch). Evidence of breeding on the area search plots after tree removal was documented for six species (California Quail, Anna s Hummingbird, Western Scrub-Jay, Wrentit, Spotted Towhee, Dark-eyed Junco). These species were observed as breeding pairs (California Quail, Wrentit, Spotted Towhee, Dark-eyed Junco), displaying (Anna s Hummingbird), carrying material (Wrentit), or with young (California Quail, Western Scrub-Jay). To summarize observed changes in abundance across both seasons, we first limited the species we considered to those that were detected on more than one occasion during the entire study, and then organized them according to habitat association (Tables 5). These species were not seen frequently (see Tables 3 and 4), so their abundance in each season should be considered when assessing the significance of the change. In summary, the species associated with mixed habitat show both increases and decreases, the scrub-reliant species generally show increases, and the tree-reliant species generally show decreases.

7 Table 2. All bird species detected across the summer and winter seasons before (2009) and after ( ) tree removal within the boundaries of the Hawk Hill area search plots, Golden Gate National Recreation Area, by Point Blue Conservation Science. Habitat is the type of vegetation each species most closely associates with; M=mixed habitat, S=scrub, T=trees, O=other. Species are listed in taxonomic order (Clements et al. 2014). Species Scientific Name Before After Habitat California Quail Callipepla californica X X M Band-tailed Pigeon Patagioenas fasciata X X T Vaux's Swift Chaetura vauxi X T White-throated Swift Aeronautes saxatalis X M Anna's Hummingbird Calypte anna X X M Allen's Hummingbird Selasphorus sasin X M Selasphorus Hummingbird Selasphorus sp. X X M Black Phoebe Sayornis nigricans X X M Warbling Vireo Vireo gilvus X T Western Scrub-Jay Aphelocoma californica X X M Common Raven Corvus corax X X T Tree Swallow Tachycineta bicolor X T Violet-green Swallow Tachycineta thalassina X T Barn Swallow Hirundo rustica X O Cliff Swallow Petrochelidon pyrrhonota X O Chestnut-backed Chickadee Poecile rufescens X T Bushtit Psaltriparus minimus X X M Pygmy Nuthatch Sitta pygmaea X T Red-breasted Nuthatch Sitta canadensis X T House Wren Troglodytes aedon X T Pacific Wren Troglodytes pacificus X M Bewick's Wren Thryomanes bewickii X X M Ruby-crowned Kinglet Regulus calendula X X M Wrentit Chamaea fasciata X X S Hermit Thrush Catharus guttatus X X M American Robin Turdus migratorius X X M Orange-crowned Warbler Oreothlypis celata X M Yellow-rumped Warbler Setophaga coronata X T Townsend's Warbler Setophaga townsendi X X T Wilson's Warbler Cardellina pusilla X X M Spotted Towhee Pipilo maculatus X X S Fox Sparrow Passerella iliaca X X M Song Sparrow Melospiza melodia X X M White-crowned Sparrow Zonotrichia leucophrys X X S Golden-crowned Sparrow Zonotrichia atricapilla X M Dark-eyed Junco Junco hyemalis X X M Lazuli Bunting Passerina amoena X M House Finch Haemorhous mexicanus X M Purple Finch Haemorhous purpureus X T Red Crossbill Loxia curvirostra X T Lesser Goldfinch Spinus psaltria X M

8 Table 3. Bird species detected in the winter season before (2009) and after ( ) tree removal within the area search plot boundaries at Hawk Hill, Golden Gate National Recreation Area, by Point Blue Conservation Science. Average=number of detections per visit. # Visits=the total number of visits each species was detected. Species in bold are those detected on three or more visits during a single season. Change=direction of change in average from before to after tree removal; +=increase, - =decrease, 0=no change (these do not necessarily represent statistically-significant changes). Before After Species Scientific Name Average # Visits Average # Visits Change California Quail Callipepla californica Anna's Hummingbird Calypte anna Black Phoebe Sayornis nigricans Western Scrub-Jay Aphelocoma californica Common Raven Corvus corax Chestnut-backed Chickadee Poecile rufescens Pygmy Nuthatch Sitta pygmaea Red-breasted Nuthatch Sitta canadensis House Wren Troglodytes aedon Pacific Wren Troglodytes pacificus Bewick's Wren Thryomanes bewickii Ruby-crowned Kinglet Regulus calendula Wrentit Chamaea fasciata Hermit Thrush Catharus guttatus American Robin Turdus migratorius Yellow-rumped Warbler Setophaga coronata Spotted Towhee Pipilo maculatus Fox Sparrow Passerella iliaca Song Sparrow Melospiza melodia White-crowned Sparrow Zonotrichia leucophrys Golden-crowned Sparrow Zonotrichia atricapilla Dark-eyed Junco Junco hyemalis

9 Table 4. Bird species detected in the summer season before (2009) and after (2014) tree removal within the area search plot boundaries at Hawk Hill, Golden Gate National Recreation Area, by Point Blue Conservation Science. Average=the average number of detections per visit. # Visits=the total number of visits each species was detected. Species in bold are those detected on three or more visits during a single season. Change=direction of change in average from before to after tree removal; +=increase, - =decrease, 0=no change (these do not necessarily represent statistically-significant changes). Rufous and Allen s Hummingbirds are often inseparable in the field, so were recorded as Selasphorus Hummingbirds. Before After Species Scientific Name Average # Visits Average # Visits Change California Quail Callipepla californica Band-tailed Pigeon Patagioenas fasciata Vaux's Swift Chaetura vauxi White-throated Swift Aeronautes saxatalis Anna's Hummingbird Calypte anna Allen's Hummingbird Selasphorus sasin Selasphorus Hummingbird Selasphorus sp Warbling Vireo Vireo gilvus Western Scrub-Jay Aphelocoma californica Common Raven Corvus corax Tree Swallow Tachycineta bicolor Violet-green Swallow Tachycineta thalassina Barn Swallow Hirundo rustica Cliff Swallow Petrochelidon pyrrhonota Chestnut-backed Chickadee Poecile rufescens Bushtit Psaltriparus minimus Pygmy Nuthatch Sitta pygmaea Red-breasted Nuthatch Sitta canadensis Bewick's Wren Thryomanes bewickii Wrentit Chamaea fasciata American Robin Turdus migratorius Orange-crowned Warbler Oreothlypis celata Townsend's Warbler* Setophaga townsendi Wilson's Warbler Cardellina pusilla Spotted Towhee Pipilo maculatus Song Sparrow Melospiza melodia White-crowned Sparrow Zonotrichia leucophrys Dark-eyed Junco Junco hyemalis Lazuli Bunting Passerina amoena House Finch Haemorhous mexicanus Purple Finch Haemorhous purpureus Red Crossbill Loxia curvirostra Lesser Goldfinch Spinus psaltria *although detected during breeding season, were simply late migrants, and do not breed in Marin.

10 Table 5. Change in abundance of bird species with more than a single detection over the entire study period, grouped by habitat association, at Hawk Hill, Golden Gate National Recreation Area, by Point Blue Conservation Science. Species in bold were detected on at least three visits during a single season across both years. Habitat=habitat associations: M=mixed habitat, S=scrub, T=tree, O=other. Change=the direction of the difference between abundance before (2009) and after ( ): +=increase, -=decrease, 0=no change, NA=species not detected. Change Species Scientific Name Habitat Winter Breeding California Quail Callipepla californica M + + Anna's Hummingbird Calypte anna M + + Black Phoebe Sayornis nigricans M + NA Western Scrub-Jay Aphelocoma californica M - - Bushtit Psaltriparus minimus M NA + Pacific Wren Troglodytes pacificus M - NA Bewick's Wren Thryomanes bewickii M + + Ruby-crowned Kinglet Regulus calendula M - NA Hermit Thrush Catharus guttatus M 0 NA American Robin Turdus migratorius M - 0 Orange-crowned Warbler Oreothlypis celata M NA - Wilson's Warbler Cardellina pusilla M NA - Fox Sparrow Passerella iliaca M - NA Song Sparrow Melospiza melodia M - - Golden-crowned Sparrow Zonotrichia atricapilla M + NA Dark-eyed Junco Junco hyemalis M + + Wrentit Chamaea fasciata S + + Spotted Towhee Pipilo maculatus S + - White-crowned Sparrow Zonotrichia leucophrys S + + Purple Finch Haemorhous purpureus T NA - Band-tailed Pigeon Patagioenas fasciata T NA 0 Common Raven Corvus corax T - - Chestnut-backed Chickadee Poecile rufescens T - - Pygmy Nuthatch Sitta pygmaea T - - Red-breasted Nuthatch Sitta canadensis T - - Townsend's Warbler Setophaga townsendi T NA + Barn Swallow Hirundo rustica O NA - *although detected during breeding season, were simply late migrants, and do not breed in Marin.

11 DISCUSSION The removal of non-native trees on Hawk Hill resulted in changes to the avian community composition and abundance. The effect on bird species was variable and was likely related to how reliant each species was upon the trees before their removal, or how closely they associate with scrub or open habitat that was more available after removal. In terms of overall species presence across both seasons combined, fewer species were detected after the tree removal. Of the 18 species detected only before tree removal, ten were a single individual detected on a single visit and therefore their absence does not represent a significant change. The other eight species that were detected only before removal were either associated with trees (Chestnutbacked Chickadee, Pygmy Nuthatch, Red-breasted Nuthatch, Purple Finch) or mixed habitat (Pacific Wren; Orange-crowned Warbler, a ground nester that often associates with tree or willows), with one additional species not associated with our focal habitats (Barn Swallow, nests on human built structures). Allen s Hummingbirds (associated with mixed habitat) were not detected after tree removal, but unidentified Selasphorus Hummingbirds were detected and could have been Allen s Hummingbirds, so the extent to which this species was affected by the tree removal is unclear. Combining both the breeding and winter seasons, we found three species that were detected after tree removal but not before. Only one of these was detected on more than one occasion (Golden-crowned Sparrow, a wintering species that was detected on four visits in winter) and is associated with mixed habitat, often preferring to forage on the ground, and frequently associated with shrubs. Even though the removal of trees created more scrub habitat, we did not detect any new scrub-reliant species. The small size of the site, plus the fact that there was scrub habitat within and surrounding the plots both before and after tree removal, meant that scrub-reliant species were also detected when trees were present. To evaluate the effects of tree removal on species it is also important to consider the abundance of each species. Within the winter season, about half of the species showed an increase and the other half showed a decrease. The species showing an increase were associated with mixed habitat (California Quail, Anna s Hummingbird, Black Phoebe, Bewick s Wren, Golden-crowned Sparrow, Dark-eyed Junco) and scrub (Wrentit, Spotted Towhee, White-crowned Sparrow), while the species showing decreases were associated with mixed habitat (Western Scrub-Jay, Pacific Wren, Ruby-crowned Kinglet) and trees (Common Raven, Pygmy Nuthatch, Red-breasted Nuthatch). Four species (Chestnut-backed Chickadee, Hermit Thrush, Fox Sparrow, Song Sparrow) showed little or no change after the tree removal in winter. An additional three species (House Wren, American Robin, Yellow-rumped Warbler) were only detected once in winter, reflecting a chance encounter and do not represent a real change in abundance. The changes in winter abundance indicate that species using mixed habitat and scrub benefited from the tree removal, while the tree-associated species were negatively affected. The decline in the treeassociated species will be very local since the site is small. In the summer season, the changes in abundance were not as clearly split along habitat associations. Only three species had increases in abundance and all of them were associated with mixed habitat (California Quail, which are fairly scrub-associated for actual nesting; Anna s Hummingbird, which are typically tree associated but will nest in shrubs; and Dark-eyed Junco, which typically nest in open understory beneath trees, but may associate to a lesser degree with non-forested areas too if there is

12 enough habitat structure present [although see below]). Species showing decreases were split among the three habitat associations with three mixed-habitat species (Orange-crowned Warbler, a ground nester that often associates with tree or willows; Song Sparrow, which is typically scrub-associated except for in riparian or marsh habitat; and Wilson s Warbler, which is typically scrub or understory associated), four tree species (Common Raven, Chestnut-backed Chickadee, Pygmy Nuthatch, Purple Finch), and one scrub species (Spotted Towhee). Another seven species showed little or no change and were associated with mixed habitat (Western Scrub-Jay, American Robin, Bewick s Wren), tree (Bandtailed Pigeon; and Townsend s Warbler, a migrant that does not breed in Marin), and scrub (Wrentit, White-crowned Sparrow). The remaining 11 species were only detected on one survey during the entire study, reflecting a chance encounter and do not represent a real change in abundance. Our summer surveys were timed to coincide with the breeding season, so changes in abundance are most likely related to changes in available breeding habitat. We see that the four tree-associated species showing declines (Common Raven, Chestnut-backed Chickadee, Pygmy Nuthatch, Purple Finch) are also species that nest in trees. The loss of preferred nesting habitat is the most likely cause for the decline of these species. The decreases in Song Sparrow and Spotted Towhee abundance may be related to tree removal activities if scrub beneath the trees was damaged and the restoration has not developed enough to become preferred nesting habitat. It is unclear why Dark-eyed Juncos, which showed signs of breeding at the site following tree removal, are showing an increase after tree removal during the breeding season since they typically nest in forested habitat, albeit on the ground, but the remaining decadent habitat structure from some of the extant large shrubs and elderberries may satisfy some of their habitat requirements. Additionally, the pair of juncos detected at the site in 2014 may have been breeding at the site prior to tree removal, as sometimes following major habitat modifications, individual breeding birds will persist at their previous breeding territory even if the habitat structure no longer fits the typical preference of the species; additionally, perhaps instead of an actual increase in abundance, they were simply detected more frequently following tree removal due to ease of visibility without the trees. It will be interesting to see if Dark-eyed Juncos occur here in future years. Although we did pay special attention to breeding activity, the area search method does not necessarily allow confirmation of breeding status. We consider a species that was detected on three or more visits during the summer to represent a likely breeding species, and a species for which breeding activity were directly observed to represent a confirmed breeding species. In addition to direct breeding evidence found for six species after tree removal (California Quail, Anna s Hummingbird, Western Scrub-Jay, Wrentit, Spotted Towhee, Dark-eyed Junco [see Results]; all scrub-reliant or mixed-habitat associated species), two other species (Bewick s Wren and Song Sparrow, both associated with mixed habitat) were also likely breeding on the area search plots for a total of eight species. In comparison, before tree removal we found evidence of breeding for five species (Allen s Hummingbird, Common Raven, Pygmy Nuthatch, Bushtit, Song Sparrow), with another 12 likely breeding (Jennings and Gardali 2009). Seven species were confirmed or likely breeding both before and after tree removal, and these were either scrub-reliant (Wrentit, Spotted Towhee) or associated with mixed habitat (California Quail, Anna s Hummingbird, Western Scrub-Jay, Bewick s Wren, Song Sparrow). No breeding evidence was found after tree removal for the three tree-reliant species confirmed or likely breeding before tree removal (Common Raven, Pygmy Nuthatch, Purple Finch). As expected, tree-reliant species appear to be lost as breeding species at this site, with the scrub-reliant and mixed habitat associated species continuing to breed here.

13 CONCLUSIONS Landbirds at Hawk Hill during the winter and breeding seasons showed a variety of responses to tree removal at the site. If we consider species that had more than a single detection and group them by habitat association, a pattern emerges (Table 5). The species associated with mixed habitat have a combination of increases and decreases in abundance and frequency of occurrence across both seasons. For all of the mixed habitat species detected in both seasons, the direction of change was always the same for both seasons. The scrub-reliant species show an increase overall during both seasons, except for Spotted Towhees during the breeding season, which despite an observed decrease were still relatively abundant and frequently detected following tree removal. The tree-reliant species show a decrease overall during both seasons (except for Townsend s Warbler, a typically tree-associated species that can forage in scrub, and that does not breed in Marin but were just late season passage migrants during the breeding season window). The changes are not necessarily all statistically significant, so we urge caution in interpreting these patterns, but due to the small sample sizes this was not assessed. As would be expected, scrub-reliant species populations typically benefited from this restoration, while tree-reliant species populations decreased following the tree removal at Hawk Hill. Numerous species bred (based on direct observation of breeding activity) or likely bred (based on frequency of occurrence) at Hawk Hill post tree removal. These include species that nest on the ground and in shrubs, as well as three more generalist species (Anna s Hummingbird, Bewick s Wren, Western Scrub-Jay) that may nest either in shrubs or trees, and who held breeding territories at Hawk Hill even with an absence of trees. In the winter the community diversity was nearly the same, but in the summer it was reduced by nearly 50%. It stands to reason that if the heterogeneity of the vegetation of the study plot is reduced, the diversity of the bird community would also be reduced; in fact, forested habitats typically support more breeding bird species than scrub habitats do, especially if the forested habitat has an understory where scrub-associated species can also breed. The coastal scrub and coastal prairie habitat that was planted at Hawk Hill is currently younger and shorter than a lot of the surrounding scrub habitat; therefore, as the scrub habitat restoration continues to develop and mature, we would expect to also see increases in abundance of scrub-associated species during the breeding season. A repeat of monitoring at this site in another five years would likely elucidate such a continued response to restoration. ACKNOWLEDGEMENTS We thank Caroline Christman, Sharon Farrell and Bill Merkle for help with logistics during both phases of this study, Garrett Lee and Karen Carlson for assistance with agreements and invoicing, and Tom Gardali for project oversight. We thank Scott Jennings, who conducted some of the surveys before tree removal (the rest of the surveys were completed by the report authors) and for his work on the previous report. This is Point Blue Conservation Science Contribution #2034.

14 LITERATURE CITED Clements, J.F., T.S. Schulenberg, M.J. Iliff, D. Roberson, T.A. Fredericks, B.L. Sullivan, and C.L. Wood The ebird/clements checklist of birds of the world: Version 6.9. Downloaded from Dieni, J.S., and S.L. Jones A field test of the area search method for measuring breeding bird populations. Journal of Field Ornithology 73: Hewish, M.J., and R.H. Loyne Popularity and effectiveness of four survey methods for monitoring populations of Australian birds. R.A.O.U. Report No. 55. Royal Australasian Ornithologists Union, Moonee Ponds, Australia. Jennings, S., and T. Gardali Assessment of the winter and summer bird communities at Hawk Hill pines. Final report to The Golden Gate National Parks Conservancy and The Golden Gate National Recreation Area. PRBO Contribution #1711. Poole, A. and F. Gill. (Editors) The Birds of North America. Philadelphia & Washington, DC. Academy of Natural Sciences & American Ornithologists Union. Ralph, C.J., G.R. Geupel, P. Pyle, T.E. Martin, and D.F. DeSante Handbook of field methods for monitoring landbirds. USDA Forest Service General Technical Report PSW-144. Albany, CA. Slater, P.J Factors affecting the efficiency of the area search method of censusing birds in open forests and woodlands. Emu 94: 9-16.

15 APPENDIX 1 Hawk Hill (HAHI), Golden Gate National Recreation Area, Marin Headlands, Marin County Project: Hawk Hill Getting there: Take Alexander Ave exit and follow Conzelman Road. 6th parking area on left (first, very soon and close to bridge, is for Kirby Cove; 5 th and 6 th are ~1.75 miles from exit and close to each other) and final one before road goes through one-way tunnel. Can access plots A/B by walking up trail / fire road from parking area; or B by walking through 2 nd to last bunker tunnel along road. Notes: B is northerly, A southerly plot. B is steep on east side (may prefer not to walk that slope but to survey that part of plot from top/bottom); survey from trail that makes up SW boundary, and otherwise go into interior from NW end (around sandy area between tunnels). For A, can survey much from trails that make up most of the borders, but also need to go into interior. Note, map is slightly off from reality as borders along trails should be exactly on the trails not 5m offset from trails. Get boundaries onto your GPS unit and use view map feature (see separate instructions). Hiking boots recommended due to slope; some poison oak. Parks Conservancy prior to surveys to let them know you ll be there and check for conflicts; also check first online to see if any volunteer 8events conflict with your dates. Remember these are non-time-constrained area searches. B A