Breeding Songbird Monitoring at the Seton Powerhouse Restoration (Sàt atqwa7) Site

Transcription

1 Breeding Songbird Monitoring at the Seton Powerhouse Restoration (Sàt atqwa7) Site 2011 Summary Report Prepared by: Kenneth G. Wright Box 2341, Lillooet, BC V0K 1V0

2 Powerhouse (Sàt atqwa7) Breeding Birds December 2011 The Seton Powerhouse Restoration Site was established in 2006 in a joint partnership between the Lillooet Naturalist Society, Cayoose Indian Band, and BC Hydro. In 2010, the St'at'imc name Sàt atqwa7 (meaning "the river") was formally adopted. BC Hydro has provided the bulk of the funding through its Bridge Coastal Restoration Program (BCRP) and Fish and Wildlife Compensation Program (FWCP). Initial objectives were to enhance the site for wildlife values and stewardship, while preserving it as a recreational area for Lillooet residents and visitors. Restoration work has included removal of invasive, non-native plants and replacement with native species, barriers to prevent mechanized vehicle disturbance to riparian vegetation areas, cleanup of past dumping on the site and other anthropological disturbance. All this restoration activity has resulted in great improvement of the condition of existing riparian habitats and the establishment of an upland sagebrush-dominated ecosystem. Large diameter "restoration" snags (approx m high) were installed in the hopes of attracting cavity-nesting birds, bats and other wildlife use. While the recreational use of the site has greatly improved over the last few years, it is not clear to what extent wildlife has benefitted from the restoration treatments. The focus of this report is to summarize patterns of diurnal breeding bird use at the Powerhouse for and contrast those results with three control sites established in the Seton-Fraser drainage. This report is meant to be a descriptive and qualitative summary. A more comprehensive analysis, using statistical procedures will follow after the 2012 field season (Year 5). In general, birds provide a useful gauge on how environmental conditions are changing through time. For instance, the North American Breeding Bird Survey (BBS) and the Christmas Bird Count (CBC) have shown significant distributional changes over the past 50 years. Though these changes are linked to "big picture" environmental fluctuation, such as climate regime, they indicate behavioral and distributional flexibility. On a more regional scale, birds respond to local factors, such as habitat changes caused by various factors, including fire,

3 Powerhouse (Sàt atqwa7) Breeding Birds insect-defoliation, introduced predators (cats, racoons, etc.) and especially direct anthropological disturbance. This last point is of most relevance to the Powerhouse site. Sàt atqwa7 is situated in an interface zone that includes riverine, riparian, conifer-woodland, and other upland habitats. Being low-elevation (200 m) and part of a major north-south axis valley, it is also a critical migration corridor for birds and other wildlife. Because birds are highly mobile vertebrates that are sensitive to local habitat conditions and select high-quality habitat features, it is predicted that there will be a change over time in avian composition and abundance over time. ACKNOWLEDGMENTS I would to extend a special thanks to Jeff O'Kelly for completing bird surveys at ungodly hours and with never a complaint, except for the chronic wind which seems to plague this area during the breeding bird period! Thanks to the numerous seasonal hires for joining us on the surveys. Kim North spearheaded this whole initiative from the beginning and has been very supportive of the bird surveys and all related enhancement activities. I'm grateful to Odin Scholz for preparing the point count maps and generating a very detailed list of terrestrial habitat codes. STUDY AREA & METHODS This study was conducted along the Fraser and Seton rivers, immediately south of Lillooet, British Columbia (51 41' N, ' W; Figure 1). Largely owing to a pronounced "rainshadow effect" produced by orographic deflection from the Coast Range, the climate is semi-arid (mean annual precipitation ~ 33 cm). Summers are hot (often over 35 C) with little precipitation, while winters are cool

4 Powerhouse (Sàt atqwa7) Breeding Birds and wetter with occasional snowfall. Vegetation is typical of the southern interior of British Columbia. The overstory is dominated by Ponderosa Pine and Douglasfir on upland sites, while Black Cottonwood and various willows dominate the riparian ecosystem. Bigbrush Sage grows in the open, unforested habitats and Bluebunch Wheatgrass grows well in the upland understory. See Powerhouse report for a detailed description of the vegetation community. It should be noted that the Powerhouse site occurs along the shores of the Fraser River Basin which acts as a migration corridor for numerous birds taking a north-south oriented journey. Confounding this is the Seton River corridor that funnels birds with a more coastal provenance into the area. The Powerhouse site occurs at this juncture and consequently experiences a greater range of species than similar habitats to the north and south. Three control stations were established nearby (see below) to contrast avian diversity and abundance to the Powerhouse site and help understand changes to specific habitats over time. They were chosen on the basis of habitat similarity to the Powerhouse stations. Point Counts Point counts are one of the most widely used methods for assessing avian diversity and abundance. In short, they are a time-constrained survey of birds at a fixed station where an observer records all birds heard and seen in a standardized fashion. Our surveys consisted of a five minute listening period with birds distinguished during the first three minutes to conform with BBS standards. But unlike the BBS method, our point counts used a more rigorous approach which consisted of recording all detections onto a dataform with distance contours which permit density estimation. Emphasis was placed on species detected within the 75-metre contour. Birds occurring outside of this range were more difficult to gauge directionally and especially proximally, thus these species were excluded from the analysis.

5 Powerhouse (Sàt atqwa7) Breeding Birds A total of six point count stations were established at the Powerhouse site (n=3) and at three geographically separated control sites (n=3; Figure 1). See previous reports for a more detailed description of the point count technique. Encounter Transects Encounter transects consisted of walking on a prescribed 1.7 km route that encompasses the perimeter and much of the critical riparian habitat at the Powerhouse site and shorter routes that accessed the three control sites. Other than the point count stations discussed above, there are no fixed stops on such a transect. Basically the observer(s) walks slowly, carefully listening and watching for all birds and wildlife. Each time a species is encountered (visual or auditory), the observer stops (average 25 stops/survey) and records the species and number of individuals. Additionally, documentation of habitat use, breeding evidence and other salient data are documented. Although this survey is not as rigorous as point counts, it does yield more species and other information.

6 Powerhouse (Sàt atqwa7) Breeding Birds Figure 1. Google Earth depiction of Powerhouse study area. Point count stations indicated as follows: Powerhouse sites: P1, P2, P3; Control sites: RA - Roshard Acres, UB - Upper Bench, LSC - Lower Seton Corridor. Table 1. Summary of point count stations. Station Easting Northing Elevation (m) Powerhouse Powerhouse Powerhouse Roshard Acres Upper Bench Lower Seton Corridor

7 Powerhouse (Sàt atqwa7) Breeding Birds RESULTS breeding evidence: OSPR continues to nest; fledged young SPTO seen on 1jun11 Surveys were conducted between 1 June and 5 July 2011 (Table 1). Encounter transects were performed at the Powerhouse (n = 8) and control sites (n = 7), commencing 1 June at the Powerhouse and 10 June at control sites, respectively. Point counts were initiated on 9 June and completed by 5 July. A total of 42 point counts were conducted spread evenly across the three control sites (n = 21) as well as the three treatment (Powerhouse) sites (n = 21). Breeding bird diversity was considerably higher at the Powerhouse (n = 49 species) that at control sites (n = 29), representing a 40% difference (Figure 1). Species capture by method (encounter transect versus point count) differed between Powerhouse and control sites (Table 2). More birds were documented on encounter transects (45 species vs. 37 species, 18% difference) at the Powerhouse. Control sites showed the converse, with more birds detected on point counts (20% difference). Across all sites, Spotted Towhee was the most frequently detected species (all observations pooled). Table 2. Summary of survey effort at the Powerhouse Restoration and control sites, # Encounter transects # Point count surveys Dates Powerhouse 8 June 1,4,9,14,21,29; July 2,4 Control sites Roshard Acres 7 June 10,16,26,30; July 1,3,5 Upper Bench 7 June 10,16,26,30; July 1,3,5 Lower Seton Corridor 7 June 10,16,26,30; July 1,3, each Powerhouse survey consists of 3 point count stations, only one station per control site for a total of 3.

8 Powerhouse (Sàt atqwa7) Breeding Birds Table 3. Summary of survey effort at the Powerhouse Restoration and control sites, # Encounter transects # Point count surveys Dates Powerhouse 8 8 June 8,13,16,21,27; July 1,4,5 Control sites Roshard Acres 8 8 June 8,12,17,25,28; July 2,3,5 Upper Bench 8 8 June 8,12,19,25,28; July 2,3,5 Lower Seton Corridor 8 8 June 10,12,19,25,28; July 2,3, each Powerhouse survey consists of 3 point count stations, only one station per control site for a total of 3. Table 4. Summary of breeding bird diversity at the Powerhouse Restoration and control sites, Encounter Point counts Combined transects Powerhouse Control* All sites *pooled totals from 3 control sites representing a diversity of habitats Point Count Diversity by site (2011) 0 Powerhouse 1 Powerhouse 2 Powerhouse 3 Roshard Acres Upper Bench Lower Seton Corridor

9 Powerhouse (Sàt atqwa7) Breeding Birds Figure Point Count Diversity 10 Mean Species Powerhouse Control sites

10 Powerhouse (Sàt atqwa7) Breeding Birds Encounter transects yielded additional information on the breeding bird composition of the Powerhouse and control areas. The Powerhouse area produced 43 species (n = 8 surveys), while control sites only had 21 species ((n = 7 surveys), for a greater than two-fold difference (Table 00). XXX compare with difference in diversity on PCs. This difference is unquestionably an artifact of differences in sampling effort--the Powerhouse site encompasses a much larger area and requires a longer walk to reach each point count station, thus more time is required to complete an encounter transect. Therefore these data should not be interpreted as a comparison between sites. Encounter transects at control sites were merely designed to capture species that were not recorded during the point counts. Similar to point counts, the most common species ( > 1 / survey) were Spotted Towhee, American Crow, Chipping Sparrow, Cedar Waxwing and American Robin Encounter Transect Summary Table, Powerhouse Control American Crow American Kestrel American Robin Bald Eagle Bank Swallow Barn Swallow Belted Kingfisher Black-capped Chickadee Brown-headed Cowbird Bullock's Oriole Canada Goose Cedar Waxwing Chipping Sparrow Common Raven Dusky Flycatcher Eastern Kingbird European Starling Evening Grosbeak Gray Catbird Hairy Woodpecker House Finch

11 Powerhouse (Sàt atqwa7) Breeding Birds Killdeer Lazuli Bunting Mallard Merlin Mountain Chickadee Nashville Warbler Northern Flicker Orange-crowned Warbler Osprey Pine Siskin Pygmy Nuthatch Red-breasted Nuthatch Red-eyed Vireo Song Sparrow Spotted Sandpiper Spotted Towhee Veery Warbling Vireo Western Kingbird Western Meadowlark Western Tanager Western Wood-Pewee White-crowned Sparrow Yellow Warbler Yellow-rumped Warbler Total species 43 21

12 Powerhouse (Sàt atqwa7) Breeding Birds DISCUSSION There are differences between the Powerhouse and control sites, both in terms of diversity and species composition. The Powerhouse had a significantly higher diversity of species than control sites (43 versus 21). Species composition was noticeably different with only eleven species common to both areas. Such differences are linked to habitat dissimilarities, especially the greater amount of coniferous woodland on or adjacent to the control sites. RECOMMENDATIONS Continue monitoring Powerhouse and reference sites for breeding bird activity during Complete an analysis of breeding bird activity over a five year period after the 2012 restoration season has been completed. Appendix 1. Summary of surveys at Powerhouse and Control Sites, Evening surveys denoted by an "E". Point Count Encounter Transects Powerhouse Control Powerhouse Control 9-June 10-June 9-June 10-June 14-June 16-June 14-June 16-June 21-June 26-June 21-June 26-June 29-June 30-June 29-June 30-June 2-July 1-July 2-July 1-July 2-July E 3-July 2-July E 3-July 4-July E 5-July E 4-July E 5-July E