Estimating Golden-cheeked Warbler Abundance Within the Balcones Canyonlands Preserve

Transcription

1 Estimating Golden-cheeked Warbler Abundance Within the Balcones Canyonlands Preserve Photo by John Ingram Presented by: William Reiner, City of Austin BCP (speaker) Lisa O Donnell, City of Austin BCP William Simper, Travis County BCP

2 The Balcones Canyonlands Conservation Plan (BCCP) and Balcones Canyonlands Preserve (BCP) First multi-species Habitat Conservation Plan, under Section 10(a) of the Endangered Species Act; a national model USFWS issued 30-year permit in 1996 Provides a streamlined approach to Endangered Species Act compliance Allows take of habitat and requires replacement acres protected within the BCP The Balcones Canyonlands Preserve is the mitigation for that take The BCP is a 30,000-acre system of preserves established to protect and mitigate for habitat loss of 8 endangered species and 27 species of concern in western Travis County

3 BCP Partners Permit Holders: Travis County & City of Austin Through USFWS: Private Landowners with 10(a) permits Managing Partners: The Lower Colorado River Authority Travis Audubon Society The Nature Conservancy of Texas Texas Cave Management Association Wild Basin/St. Edwards University

4 Species covered by the BCCP Endangered Species Golden-cheeked warbler ( driving force of the BCCP) Black-capped Vireo Six karst (cave) invertebrates John Ingram Species of Concern 25 karst species 2 plant species John Ingram

5 Travis County supports some of the best and largest blocks of habitat in the heart of the GCWA s breeding range. Photo by John Ingram

6 The BCCP allows development of over 70% of the GCWA s habitat in Travis County; thus, protection and management of the habitat within the Balcones Canyonlands Preserve is critical.

7 The BCCP allows development of over 70% of the GCWA s habitat in Travis County; thus, protection and management of the habitat within the Balcones Canyonlands Preserve is critical.

8 BCP Management Challenges Small patch size/small populations Habitat fragmentation/edge effects Edge-adapted predators/parasites Reduced hardwood recruitment (white-tailed deer, feral hogs, oak wilt) Invasive, non-native plants Wildfire Access management Public misperceptions of BCP

9 Need for Updated Status Assessment Frequently asked questions from the public: How many GCWAs are there on the Balcones Canyonlands Preserve? How are they doing? Taking it a step further: How viable are the warbler populations over the long-term What are the best management strategies to promote their survival and recovery? Photo by John Ingram

10 GCWA Population Viability & Habitat Suitability Modeling Project 5-year contract with U.S. Forest Service to conduct population viability and habitat suitability modeling for the GCWA within the BCP Preliminary results for Year 1 (2011); Year 2 (2012) data collection completed, currently analyzing data Entering Year 3 field season Variety of field methods Color-banding Nest monitoring Intensive territory mapping Point counts Vegetation data for point counts & nests Photo by Gil Eckrich, Fort Hood

11 How Many GCWAs Are There? Reliable estimates needed to model population viability No quick and easy answer Color banding and mapping individual territories provide the most reliable abundance estimates but are time and labor-intensive Photo by John Ingram Point counts provide a faster and more cost-efficient method. However, such quick and easy estimates should be treated with caution and compared with known populations to ensure their reliability

12 Intensive territory mapping March 15-May 25, visits Color-banding Average >70% adult males banded per plot Nest monitoring, productivity March 15-June 15 Typically 2 people per plot Average >130 hours/100 acres Intensive Monitoring Study Plots

13 USFS Point Counts (Reidy and Thompson 2011) Grid of points with 250-m spacing across BCP Designed to allow rapid assessment of large areas using systematic approach Study design includes comparisons with # territories from intensive monitoring

14 USFS Point Count Methods patches 2 observers (one per point) April 7 May points, single visits 10-minute surveys (time recorded for each detection) Unlimited radius, distance measured directly or with range-finder Estimated detection probability for 2 observers and density using Program Distance 6.0; used general linear models to predict density across most supported landscape variables (edge density, 3 forest types)

15 Landscape variables 100-m radius Edge density Proportion of area classified as: Juniper Mixed Hardwood (live oak + deciduous) 1-km radius Total forest cover Proportion of area classified as: Juniper Mixed Hardwood (live oak + deciduous) Most Supported Model: Proportion of juniper forest within 1 km Proportion of mixed forest within 1 km Proportion of hardwood forest within 1 km Edge density within 100 m

16 Predicted relationships between landscape and density on BCP Reidy and Thompson 2011

17 Predicted relationships between landscape and density on Fort Hood Density (birds/ha) Proportion of mixed forest in 100 m Proportion of juniper forest in 100 m Density (birds/ha) Proportion of forest cover in 1 km Forest edge density (m/ha) Peak and Thompson 2013

18 GCWA density (males/hectare) distribution map Predictive map from Year 1

19 USFS Point Counts (2011): Comparison Results Macrosite Intensive Study Plots Plot Size (acres) BCP # territories (average for ) USFS predicted abundance Ratio of USFS/BCP data Bull Creek Forest Ridge Cypress Creek Canyon Vista North Lake Austin Emma Long Bull Creek Kent Butler Cypress Creek Vista Point Bull Creek 3M/St. Edwards Cypress Creek Lake Perspectives/McGregor North Lake Austin Coldwater South Lake Austin JJ&T Cypress Creek Baker Sanctuary Bull Creek Hamilton Cypress Creek Vireo Ridge North Lake Austin Bike Park Barton Creek Barton Creek West Austin Ullrich WTP South Lake Austin Reicher West Austin Vireo Preserve/Wild Basin Barton Creek Sunset Valley Barton Creek Gus Fruh Total/Average Within a total of 2,676 intensively monitored acres: Intensive territory mapping estimated 183 male GCWAs, point counts predicted 288 male GCWAs (roughly 1.6x (SE = 0.21) the number of male GCWAs within this area)

20 USFS Point Count Results: Preliminary Conclusions from Year 1 Current field methods and analyses using generic, remotely derived landscape measures may be adequate at estimating GCWA density and abundance at high density sites, but are not adequate at low density sites or small, fragmented patches. USFS is currently investigating additional landscape scale metrics to represent patch isolation and fragmentation, such as patch cohesion and shape index, to provide more reliable estimates density and abundance from point counts. As the following slides show, results from other researchers (TSU, TAMU), conducting point counts on the BCP, show similar trends to those from the first year of the USFS study.

21 Abundance Estimates from Point Counts Texas State University (Hunt et al. 2012) Designed to compare model-estimated abundance to spotmapping Grid of 36 points (200-meter spacing) superimposed over 7 BCP intensive study plots

22 TSU Point Count Methods Grid of points superimposed on 7 intensive study plots Multiple observers (one per point) Late March-early April 252 points (36 per plot), 4 visits 5-minute surveys, 100-meter fixed radius (0-20m, m distance bins) Data analyzed using both single-season occupancy models (included parameters for occupancy, probability of detecting species) and binomial mixture models using PRESENCE, version 3.1 (included parameters for abundance, probability of detecting individuals)

23 TSU Point Counts (2009): Comparison Results Macrosite Intensive Study Plots Plot Size (acres) BCP # territories (average for ) TSU predicted abundance Ratio of TSU/BCP data Bull Creek 3M/St. Edwards Bull Creek Kent Butler North Lake Austin Emma Long Bull Creek Forest Ridge South Lake Austin JJ&T South Lake Austin Bohls Barton Creek Barton Creek Total/Average Within a total of 700 monitored acres: Intensive territory mapping estimated 76 male GCWAs; TSU point counts predict 130 male GCWAs (roughly 1.7x (SE = 0.27) the number of male GCWAs within this area)

24 Abundance Estimates from Point Counts Texas A&M University (Morrison et al. 2010, Mathewson et al. 2012) Rangewide study to estimate population size of male GCWAs across the breeding range Study objectives: Conduct point count surveys (>400m spacing) in randomly selected patches of potential GCWA habitat Estimate patch-specific density (assumed constant density across each patch) Project patch-specific density estimates to range-wide abundance Results intended to answer spatially-explicit questions and better understand how GCWAs vary in abundance in different locations. Figure 3-2. Locations of warbler abundance surveys in patches of oak-juniper woodland. Surveys were conducted by Texas A&M Institute of Renewable Natural Resources, March May From Morrison et al

25 Abundance Estimates from Point Counts Texas A&M University (Morrison et al. 2010, Mathewson et al. 2012) Rangewide study to estimate population size of male GCWAs across the breeding range Study objectives: Conduct point count surveys (>400m spacing) in randomly selected patches of potential GCWA habitat Estimate patch-specific density (assumed constant density across each patch) Project patch-specific density estimates to range-wide abundance Results intended to answer spatially-explicit questions and better understand how GCWAs vary in abundance in different locations. Figure 3-2. Locations of warbler abundance surveys in patches of oak-juniper woodland. Surveys were conducted by Texas A&M Institute of Renewable Natural Resources, March May From Morrison et al Large concentration of point counts conducted on the BCP (similar opportunity for comparison with territory mapping data)

26 TAMU Point Count Locations Delineated habitat patches throughout the GCWA s breeding range Habitat patches overlapping BCP and City of Austin s Water Quality Protection Lands (WQPL) shown in green All other patches shown in gray Point count locations on BCP shown in red (point counts also conducted on TNC s Barton Creek Habitat Preserve) No point counts on WQPL Predicted occupancy, density, and abundance estimates provided for habitat patches overlapping BCP and most of those overlapping WQPL

27 TAMU Point Count Methods habitat patches on BCP (18% of 150 patches surveyed rangewide in 2009) Double-observer method Mid-March mid-may 110 point counts on BCP (22% of 495 points surveyed rangewide in 2009), single visits 5-minute surveys, 100-meter fixed radius (0-50m, m distance bins) Estimated observed patch-specific density using point count data; developed predictive model incorporating patch-specific metrics (patch size, landscape composition) to predict densities for each habitat patch

28 TAMU Point Counts (2009): Comparison Results Macrosite Intensive Study Plots Plot Size (acres) BCP # territories (average for ) TAMU predicted abundance Ratio of TAMU/BCP data Bull Creek Canyon Vista Cypress Creek Vista Point Bull Creek 3M/St. Edwards Bull Creek Kent Butler North Lake Austin Emma Long Bull Creek Forest Ridge Bull Creek Hamilton Cypress Creek Baker Sanctuary Bull Creek Canyon Creek Cypress Creek Lake Perspectives/McGregor Cypress Creek Vireo Ridge North Lake Austin Bike Park North Lake Austin Coldwater Barton Creek Barton Creek West Austin Ullrich WTP South Lake Austin Reicher South Lake Austin Bohls South Lake Austin JJ&T West Austin Vireo Preserve/Wild Basin Barton Creek Sunset Valley Barton Creek Gus Fruh Total/Average Within a total of 2,876 intensively monitored acres: Intensive territory mapping estimated 196 male GCWAs; TAMU point counts predict 265 male GCWAs (roughly 1.4x (SE = 0.21) the number of male GCWAs in this area)

29 Average point count /territory ratios with 85% confidence intervals for BCP intensive study plots

30 Point Count GCWA density (# males/ha) estimates from point counts and territory mapping on BCP intensive study plots (dashed line represents 1:1 relationship) Pearson (Spearman) correlation coefficients for GCWA density (#males/ha) estimates from point counts and territory mapping on BCP intensive study plots TSU (2009) 0.73 (0.88) TAMU (2009) 0.56 (0.59) TAMU (2009) TSU (2009) USFS (2011) USFS (2011) 0.76 (0.80) Territory Mapping

31 TAMU Point Counts (2009): Comparison Results for Habitat Patches on BCP Macrosite BCP Tract(s) Overlapping TAMU predicted Ratio of BCP # territories TAMU Habitat Patches abundance TAMU/BCP data North Lake Austin Lucas Pedernales River Hamilton Pool Cypress Creek Toops, Crossings North Lake Austin Emma Long, Green Shores North Lake Austin Emma Bike Park Bull Creek Bull Creek tracts Cypress Creek Macgregor, others North Lake Austin Coldwater, others North Lake Austin Emma Long West Austin Wild Basin North Lake Austin Park West, etc Barton Creek Sunset Valley North Lake Austin Steiner Ranch Barton Creek Barton Creek West Austin Vireo Preserve, Wild Basin South Lake Austin Double J&T North Lake Austin Cortana South Lake Austin Double J&T, Reicher, Bohl's North Lake Austin Cortana, Steiner Ranch Barton Creek Gus Fruh Within a total of 17,182 BCP monitored acres: BCP estimates 962 male GCWAs (enumerations, spot mapping, intensive territory mapping); TAMU point counts predict 1882 male GCWAs (roughly 2x the number of male GCWAs within this area)

32 Water Quality Protection Lands Lands purchased primarily to protect the Barton Springs watershed Different mission from BCP

33 Water Quality Protection Lands Small, fragmented patches of GCWA habitat; low GCWA densities GCWAs monitored using standard FWS protocols March 15-May 15 Minimum 5 visits, 1 hour per 25 acres (20 hours/100 acres)

34 TAMU Point Counts: Comparison Results - WQPL Management Units WQPL Tract(s) Overlapping TAMU Habitat Patches Monitored Acres WQPL # territories TAMU predicted abundance Ratio of TAMU/ WQPL data Slaughter Baker Lower Barton Little Barton, others Onion Onion Onion Onion Lower Bear Hays County Upper Bear J17, Andrewartha, others Total/Average Within a total of 3,430 WQPL monitored acres: WQPL estimates 28 male GCWAs, TAMU predicts 372 male GCWAs (roughly 13x the number of male GCWAs within this area) Note: Table includes only management units for which we have GCWA survey data. Also excluded from the table are any patches <25 ha in size because probability of occupancy (<0.08) was so low to be of little value in calculating overall abundance.

35 RATIO OF TAMU Abundance (predicted) to BCP/WQPL Abundance (enumerated)

36 Conclusions and Recommendations Based on comparisons of abundance estimates from point counts and territory mapping from three different studies using different field and analytical methods, current trend is for point counts to overestimate abundance, particularly at sites with low GCWA densities. Similar comparison studies at Fort Hood (Peak 2011, Peak and Thompson 2013), also found that model-derived estimates from point counts overestimate GCWA abundance. Recommend double-sampling design with true abundance (i.e., color-banded populations) on a subset of the area of interest to validate estimates derived from point counts. Recommend continued refinement of methods, such as inclusion of additional habitat quality and landscape scale metrics, to provide more reliable density and abundance estimates from point counts.

37 Acknowledgments City of Austin Travis County LCRA Travis Audubon Society The Nature Conservancy U.S. Forest Service University of Missouri

38 Thoughts? Suggestions? Questions?