The Western Section of The Wildlife Society and Wildlife Research Institute Western Raptor Symposium February 8-9, 2011 Riverside, California

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1 The Western Section of The Wildlife Society and Wildlife Research Institute Western Raptor Symposium February 8-9, 211 Riverside, California Symposium Sponsors February 9 9:15-9:35 am Session: Raptor Management and Monitoring Population Viability Analysis of Burrowing Owls in the Santa Clara Valley John H. Barclay; Albion Environmental, Inc., 1414 Soquel Ave., No. 25, Santa Cruz, CA, 9562; (831) ; jbarclay@albionenvironmental.com I used count-based population viability analysis (PVA) to inform the burrowing owl (Athene cunicularia) conservation strategy in the Santa Clara Valley HCP/NCCP. Growth rates based on annual counts of adult burrowing owls were negative at the three largest remaining colonies in the Santa Clara Valley at San Jose International Airport (2 years, ), Moffett Field (18 years, ), and Shoreline Park (11 years, ). Large variance yielded imprecise probabilities of persistence. Mean probability of quasi-extinction at San Jose Airport and Moffett was approximately 5% in 5 years. Experimentally increasing the adult owl population, which was 51 adults at the three colonies combined in 29, showed that size alone had little effect on probability of population persistence. Negative growth rates have to be reversed to increase the probability of burrowing owls persisting in the Santa Clara Valley. Experimental manipulation showed that it could take up to 16 years of 3% increase in the annual numbers of adult burrowing owls to reverse negative growth rate and lower the probability of extinction in the Santa Clara Valley. The burrowing owl conservation strategy in the SCV HCP/NCCP is based on reversing negative growth rate and monitoring progress of conservation activities using count-based PVA techniques. The authors and institutions that have provided the following presentations are happy to share their information, data, and opinions. However, these are not, necessarily, peer-reviewed presentations and the potential to take something out of context also exists. In order to avoid that, you are requested to contact the respective lead authors(s) before using specific information contained in any of the following papers. Once you have done that, the proper citation is: '[Author(s). Date. Title.] Presented at the Western Raptor Symposium. Jeffrey L. Lincer and David Bittner (Co-Chairs). Hosted by Wildlife Research Institute and The Wildlife Society, Western Section. Riverside Convention center, Riverside, California, USA. February 8-9, 211

2 Population Viability Analysis of Burrowing Owls in the Santa Clara Valley Using PVA to inform the burrowing owl conservation strategy in the Santa Clara Valley HCP/NCCP (Valley Plan) Jack Barclay Albion Environmental, Inc.

3 How many to conserve? So there are burrowing owls in the future

4 How do we determine how many burrowing owls to conserve? Make a guess Make an analytically informed recommendation to increase the chances of burrowing owls persisting in the Santa Clara Valley

5 Population Viability Analysis (PVA) The use of quantitative methods to predict the likely future status of a population of conservation concern. (Morris and Doak, 22) I used count-based PVA (not a demographic PVA with simulations) to determine what has to happen to increase the chances of burrowing owls persisting in the Santa Clara Valley

6 How does count-based PVA work? Quantifies population growth rate and variance Yields estimates of the probability of persistence of a population or probability that a population will fall below a userdefined quasi-extinction threshold

7 Assumptions The data represent exhaustive counts of individuals in a subset of a population (e.g., adults) in a constant proportion of an area occupied Counts were performed in enough years ( 1) to assess year-to-year variation in population growth rate Annual counts of adults reflect the combined effects of demographic and environmental stochasticity Inter-annual variation is not extreme, i.e., no large crashes or bonanzas Other assumptions about the normal distribution

8 Using PVA for Burrowing Owls in the SCV HCP/NCCP A PVA does not yield a finite answer but it enables a more informed decision about long-term conservation goals A PVA enables evaluation of comparative risk of extinction of different populations I used it to quantify growth rate of the three largest burrowing owl colonies in the SCV and determine what has to happen for owls to persist Recommended using count-based PVA to track the burrowing owl population in the plan area during plan implementation

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11 Shoreline Moffett Field San Jose International Airport

12 Data Sources - annual counts of adult burrowing owls at San Jose Int. Airport, Moffett Federal Airfield, and Shoreline Park San Jose Int. Airport Moffett Field Shoreline Park Three colonies combined

13 Population Parameters Annual population growth λ (lambda) λ = (N t+1 )/N t where N t = number of adult owls in year t Stochastic population growth µ (mu) µ = logλ G (logλ t + logλ t-1 + logλ t logλ 2 + logλ 1 + logλ )/t Variance expressed as σ 2 (sigma squared)

14 Population Size (N) Adult burrowing owls at San Jose Int. Airport Time

15 Population Size (N) Adult burrowing owls at Moffett Time

16 Population Size (N) Adult burrowing owls at Shoreline Time

17 Population Size (N) Population Size (N) Population Size (N) Adult burrowing owls at San Jose Int. Airport Adult burrowing owls at Moffett Time Time Adult burrowing owls at Shoreline Time

18 Population Size (N) 16 Combined counts of adult burrowing owls at SJC, Moffett, and Shoreline, Year

19 Population parameters for burrowing owl colonies at San Jose Int. Airport, Moffett, and Shoreline, Parameter San Jose Int. Airport Moffett Field Shoreline Three colonies combined Mean λ (95% CL) ( ) ( ) ( ) ( ) µ (95% CL) ( ) ( ) ( ) ( ) σ Probability of reaching quasiextinction threshold in 5 yrs.519 ( -.994).526 ( -.995).916 ( ).691 ( -.999) (95% CL) Quasi-extinction threshold 2 adults 2 adults 2 adults 6 adults

20 Probability of reaching extinction threshold Probability of the SJC burrowing owl colony reaching the quasi-extinction threshold (2 owls) Years Mean CDF 95% Confidence Interval

21 Probability of reaching extinction threshold 1.2 Probability of the Moffett burrowing owl colony reaching the quasi-extinction threshold (2 owls) Years Mean CDF 95% Confidence Interval

22 Probability of reaching extinction threshold 1.2 Probability of the Shoreline burrowing owl colony reaching the quasi-extinction threshold (2 owls) Years Mean CDF 95% Confidence Interval

23 Probability of reaching extinction threshold Probability of reaching extinction threshold Probability of reaching extinction threshold Probability of the SJC burrowing owl colony reaching the quasi-extinction threshold (2 owls) Years Mean CDF 95% Confidence Interval Probability of the Moffett burrowing owl colony reaching the quasi-extinction threshold (2 owls) Years Mean CDF 95% Confidence Interval 1.2 Probability of the Shoreline burrowing owl colony reaching the quasi-extinction threshold (2 owls) Years Mean CDF 95% Confidence Interval

24 Probability of reaching extinction threshold Population Size (N) Combined counts of adult burrowing owls at SJC, Moffett, and Shoreline, Year Probability of the combined population of burrowing owls at SJC, Moffett, and Shoreline ( ) reaching the quasiextinction threshold (6 owls) Years Mean CDF 95% Confidence Interval

25 Population Size (N) Example of a Stable Burrowing Owl Colony Adult burrowing owls at Sharpe Depot San Joaquin Co Year

26 Probability of reaching extinction threshold 1.2 Probability of the Sharpe Depot burrowing owl colony reaching the quasi-extinction threshold (2 owls) Years Mean CDF 95% Confidence Interval Mean λ = 1.56 ( ), µ =.58 ( ), σ 2 =.67

27 Probability of reaching extinction threshold 1.2 Probability of the combined population of adult burrowing owls at SJC, Moffett, and Shoreline in 29 (51) increased to 12 (2 x) of reaching the quasi-extinction threshold (6 owls) Years Mean CDF 95% Confidence Interval

28 Probability of reaching extinction threshold 1.2 Probability of the combined population of adult burrowing owls at SJC, Moffett, and Shoreline in 29 (51) increased to 24 (4 x) of reaching the quasi-extinction threshold (6 owls) Years Mean CDF 95% Confidence Interval

29 Population Size (N) Annual adult burrowing owls based on combined counts from SJC, Moffett, and Shoreline artificially increased 3% per year for 16 years to achieve μ > Year

30 Probability of reaching extinction threshold 1.2 Probability of the combined population of burrowing owls from SJC, Moffett, and Shoreline in 29 artificially increased 3% per year for 16 years to achieve μ > of reaching a quasi-extinction threshold of six owls Years Mean CDF 95% Confidence Interval

31 Acknowledgments I thank Ken Schreiber, Program Manager of the Santa Clara Valley HCP/NCCP, for supporting work on the PVA I thank Dan Doak for advice about PVA techniques

32 References Dennis, B., P.L. Munholland, and J.M. Scott Estimation of growth and extinction parameters for endangered species. Ecological Monographs 61: Morris, W., D. Doak, M. Groom, P. Kareiva, H. Fieberg, L. Gerber, P. Murphy, and D. Thomson A practical handbook for population viability analysis. The Nature Conservancy. Morris, W.F. and D.F. Doak. 22. Quantitative conservation biology: theory and practice of population viability analysis. Sinauer Associates, Sunderland, MA.