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 ‘B’Yellow

Orange Metal

Black

Red ‘J’Green

Orange Metal

Light Blue

Red ‘S’Green

Orange Metal

Orange

Red ‘T’Green

Orange Metal

Orange

Left Right Left Right

Left RightLeft Right

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

• 2004– 10 nesting pairs, 1 non-

nesting pair– 13 nest attempts– 5 pairs fledged 9 chicks– Estimated daily survival

0.9846 (95% CI = 0.9740 -

0.9952)

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

• Multivariate Analysis of Variance (MANOVA)– Predictor variables

• disturbance (pedestrian only!), temperature, tide

– Response variables• 5 activity categories

– locomotion, self-maintenance, reproduction, vigilance, alarm

– Analysis not complete

*Disturbance within 137 m radius *Disturbance within 300 m radius

*Disturbance within 300 m radius*Disturbance within 300 m radius

Results• Pass-by Experiment

• No difference between pedestrian treatments• Some differences between nests, but no pattern found

n Rate of Flush Ave DistancePed 20 11 1.00 111Ped 40 10 0.78 120Ped 60 9 0.78 120Vehicle 9 0.00 0ATV 8 0.13 170

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 doesn’t mean they’re 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.

Questions??

Image courtesy of Ethan Meleg