Effects of human disturbance on waterbirds

The San Francisco Bay supports millions of waterbirds, shorebirds, diving ducks, and

waterfowl

Recreational activities are increasing in Recreational activities are increasing in the Estuarythe Estuary

Potential Disturbance

event

Decreased body

condition

Increased risk of predation

Decreased reproductive

success

Modified from White 2009

Conceptual model of disturbance impacts

Behavioral response (increased vigilance,

fleeing)

No behavioral response ?

Decreased food intake and increased energy

expenditure

Decreased population

Need to assess potential impacts of disturbance on waterbirds

What have other studies found?

•Searched published and unpublished literature

•Reviewed 110 studies

•Restricted analysis to 49 studies on birds that are likely to occur in the Bay Area.

No impact Impact

Perc

ent o

f stu

dies

20

40

60

80

Disturbance impacted birds

Change in behavior most frequently cited effect of human disturbance

•Increasing vigilance

•Calling

•Changing daily activities

• Flushing

57% reported birds flushing as disturbing agent approached

Flush distance varied by species and type of disturbance

Dabbling ducks flushed at 50 m

Sanderlings flushed at 15 m

Flush distance may not be indicative of sensitivity

•Birds in good condition may be more likely to respond to disturbance

•Trade-off between perceived risk of predation and risk of starvation

Factors affecting response to disturbance

Distance from disturbance

Frequency of disturbance

Number of people, dogs, vehicles,

boats

Angle of approach (direct or

tangential)Body condition

Food availability

Season

Flock size

Distance to other suitable foraging or roosting areas

Reaction of conspecifics

Modified from White 2009

Body size

Speed

Immediate versus population level effects

•8 studies assessed impacts to reproduction

•8 studies reported changes in foraging time

•3 reported energetic consequences.

Energetic expenditure

•Increased by 10.5 kcal/day above the normal for every 4 boats/hour of disturbance

•Five boating disturbances per day increased energy expenditure in Canvasbacks

•Need to consume an additional 75 kcal/day to compensate

•Disturbed Mallards lost more body mass than undisturbed birds

•Energy expenditure increased 13% for every 30 minute of alarm flights

•Increased 0.6 kcal/hour for every hour of disturbance

Energetic expenditure

Reproductive Costs

•Increased risk of nest abandonment

•Increased risk of loss due to exposure

•Increased risk of loss due to predator attraction

Management recommendations

•Identify locations and times when birds may be more sensitive to disturbance

•Route trails around sensitive areas

•Establish set-back distances (250 m)

•Seasonal closures

•Enforce leash laws

•Public education and docent programs

Research recommendations1. Determine population level consequences of

disturbance

2. Determine energetic costs of disturbance

3. Determine what areas should have seasonal closures or set-back distances imposed

4. Create individual based models to help predict the impacts of disturbance

Future Plans

• Conduct a before and after study to assess the impacts of the water trail on diving ducks in the bay

• Partner with USGS to identify diving duck hotspots

• Overlay water trail sites with diving duck hotspots

• Work with Bay Area Audubon Chapters to help assess potential impacts

• Develop a docent and educational program