Presentation on theme: "Effects of Human Disturbance and Predation on American Oystercatchers During the Breeding Season, Cumberland Island, Georgia John Sabine Warnell School."— Presentation transcript:
Effects of Human Disturbance and Predation on American Oystercatchers During the Breeding Season, Cumberland Island, Georgia John Sabine Warnell School of Forest Resources University of Georgia Advisors: Sara H. Schweitzer J. Michael Meyers
Introduction Human disturbance and predation thought to contribute to low reproductive success Little focus on causes of nest failure and chick loss –Davis et al. (2001) ID of 40% predators unknown –George (2001) causes of 47% of failures unknown
Introduction Evidence that traditional methods of identifying nest predators unreliable –ID 57% incorrect (Williams and Wood 2002) Correct information vital for effective management
Objectives Determine nest success Determine depredation percentages and sources Determine disturbance frequency and duration and its effects on nesting success Quantify threshold of tolerance to disturbance
Study Site Cumberland Island National Seashore 28-km barrier island Oceanfront beach Image Courtesy of NASA GA FL
Study Site 42,265 visitors in 2002, plus boaters Disturbance limited to southern half of island Forms of disturbance –pedestrian, vehicles, ATV traffic, boat traffic, and pets Map Courtesy of NPS
Methods Nests located by pedestrian surveys Document nest site Install video monitoring equipment Begin collecting activity budget data
Methods Video Monitoring used for nest failure determination –black and white IR camera placed 2 m from nest –time lapse recorder and 12V battery Battery and recorder placed 15 m from nest VHS tape and battery replaced every 2-3 days Continuous record of nest activity
Methods Activity budget data (Baldassarre et al. 1988) –collected for nesting adults –30 min/bird –recorded instantaneous activity every 15 sec 19 activity categories distance from nest/chick Disturbance to subject recorded simultaneously –type of disturbance –distance to subject (<300 m) Recorded habitat use in 2004 –surf, intertidal, wrack, foredune, dune, marsh
Methods Pass-by Experiment –Pedestrian walk-by 20, 40, and 60 m –Vehicle drive-by at high tide line –ATV drive-by at high tide line –Record distance at which bird flushed from nest ?
Results Banding in 2004 –4 individuals banded –Used decoy method Red BYellow OrangeMetal Black Red JGreen OrangeMetal Light Blue Red SGreen OrangeMetal Orange Red TGreen OrangeMetal Orange LeftRightLeftRight LeftRightLeftRight
Results 2003 –11 nesting pairs –19 nest attempts –4 pairs fledged 6 chicks –Estimated daily survival 0.9732* ( 95% CI = 0.9598 - 0.9866 ) *Used Mayfield program to estimate daily survival to fledging (Hines 1982A)
Results No difference* (P = 0.1892) between years Combined years estimated survival 0.9787 (95% CI = 0.9701 - 0.9873 ) Total of 32 nest attempts –9 attempts successful, fledging 15 chicks *Used CONTRAST program compare survival (Hines 1982B)
Results North End –5 nesting pairs –Daily survival 0.9899 ( 95% CI = 0.9819 - 0.9979 ) –7 of 13 successful South End –6 nesting/5 nesting, 1 non –Daily survival 0.9648 ( 95% CI = 0.9484 - 0.9813 ) –2 of 19 successful Difference (P = 0.0072) between regions
Results Identified 18 0f 20 nest failures during incubation Chicks very difficult to monitor –1 of 8 losses identified Causes of Nest Failure –Predation (14) Raccoon (9) Bobcat (3) Crow (1) Ghost crab (1) –Human (1) –Horse Trampling (1) –Overwash (1) –Abandoned (2) –Unknown (2)
Results North End 2 raccoons 1 ghost crab 1 crow 4 depredation events South End 7 raccoons 3 bobcats 1 human 1 horse 12 depredation events
Results Activity and Disturbance Data –More than 750 hrs of observation Data available... –19 attempts during incubation –11 attempts during brood rearing 19 activity categories reduced to 5
Results Pass-by Experiment No difference between pedestrian treatments Some differences between nests, but no pattern found
Results Pooled Pedestrian pass- by data for each nest Calculated mean of nest means and 95% CI –113 m, upper 95% CI of 137 m –Used this for disturbance determination
Conclusions North End successful, South End not. WHY? –Human disturbance low on North End –North End may be isolated from mammalian predators –High quality foraging habitat nearby
Conclusions Predation primary cause of nest failure Higher on South End. WHY? –Human presence on south end supporting larger population of mammalian predators –Human presence on beach encouraging scavengers to use beach –Nesting habitat closer to mammalian predator habitat
Conclusions Tolerant to disturbance to ~137 m radius Expected differences between pass-by distances –Low sample size, high variation may have contributed to lack of significance ATVs, vehicles and boats appear to have little effect on activity –that doesnt mean theyre not a problem!
Still to Come... –How human disturbance effects activity What Next? –How do we keep a closer watch on chicks? –What happens after fledging? –What factors are involved in reproductive success? How does foraging habitat contribute to reproductive success? Who gets the best nesting and foraging habitat? Why?
References Baldassarre, G., S. L. Paulas, A. Tamisier, and R. D. Titman. 1988. Workshop summary: techniques for timing activity of wintering waterfowl. Pages 181-188 in Waterfowl in Winter (M.W. Weller, Ed.). University of Minnesota Press, Minneapolis, MN. Davis, M. B., T. R. Simons, M. J. Groom, J. L. Weaver, and J. R. Cordes. 2001. The breeding status of the American Oystercatcher on the east coast of North America and breeding success in North Carolina. Waterbirds 24:195-202. George, R. C. 2001. Reproductive ecology of the American Oystercatcher (Haematopus palliatus) in Georgia. Thesis, University of Georgia, Athens, GA. Hines, J. E. 1996A. MAYFIELD software to compute estimates of daily survival rate for nest visitation data. USGS-PWRC. http://www.mbr- pwrc.usgs.gov/software/mayfield.html. Hines, J. E. 1996B. CONTRAST software to compare estimates of survival. USGS- PWRC. http://www.mbr-pwrc.usgs.gov/software/mayfield.html. Williams, G. E., and P. B. Wood. 2002. Are traditional methods of determining nest predators and nest fates reliable? An experiment with wood thrushes (Hylocichla mustelina) using miniature video cameras. Auk 199:1126-1132.
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