science to inform adaptive management for ravens · science to inform adaptive management for...

Science to Inform Adaptive Management for Ravens

U.S. Geological Survey, Western Ecological Research CenterPartners: Nevada Department of Wildlife, Idaho State University, Oregon State University

Breeding Bird Survey Data

Detected ravens at ~40% of surveys

(BBS; Sauer and Link)

Breeding Bird Survey Data

Detected ravens at ~80% of surveys

Increased number of

observations per detection


Surveys in the late 1960s and early 1970s

• Nearly all areas consisted of <10 ravens/survey

• Highest raven count predictions

• Great Basin (>5)• Northern Rockies (>5)• Southern Rockies/

Colorado Plateu (<5)


Raven Population Growth within Great

Basin BCR

~230% increase

Raven Counts Currently:• Great Basin to >15• Sonoran and Mojave to >10• Coastal CA to >15• Southern Rockies/Colorado

Plateau to >20 No Decreases

Secondary Roads

Primary Roads

2 -tracks

Powerlines

Findings

• 1-km increase in distance to power line decreased selection by 31%

• 100-m increase in distance from edge decreased selections by 20%

• Included non-resident (non-breeding) ravens – selected at larger spatial scales

• Effect of transmission line greatest within 2.2 km (4.5 km corridor)

• Additive effects of energy infrastructure and altered land cover types

Increased land cover edges, non-native vegetation, and patchiness

Odds of raven occurrence

increased 45.8% in areas where

livestock were present

Bill Boarman, USGS, 2003

7341

28

21

16

27 38

0

10

20

30

40

50

60

70

80

Ju

ve

nile

su

rviv

al (%

)

Nest distance to nearest anthropogenic resource (km)

(χ2 = 16.8, P < 0.001)

ANTHROPOGENIC RESOURCES INCREASE

SURVIVAL TO DISPERSAL (CA)

Webb et al. 2004 Condor 106:517-528

13

Raven

Populations

Prey Population

Vital Rate

Habitats

of Prey

Prey Behavior

Anthropogenic

Subsidies (e.g., food sources,

nest substrate)

Anthropogenic Factors Indirectly

Affect Prey

Indirect Effect – Nest Predation

Common Name

Raven

Impact #

Sources

Likely or

Potential

Raven

Impact

USESA (Year

Listed) U.S. States

Desert Tortoise Numerous High T (1980) T (CA, UT); S2 (AZ)

Piping Plover Limited Low E / T* (1985) E (DE, MD, ME, NC, ND, NH, NJ), S2B (MT); T (CO,

FL, GA, KS, MA, NE, NM, VA; CT, SD, TX); SP (AL)

Greater Sage-Grouse Numerous High NL T (WA); S2 (ID); S3 (NV); SC (CO, UT)

Roseate Tern Limited Low E/T^ (1987) Ex (MD); E (MA, ME, NC, NH, NJ, NY, CT); T (FL)

Marbled Murrelet Numerous High T^^ (1992) E (CA); T (OR, WA)

San Clemente Loggerhead Shrike Limited Unknown E (1977) NL

California Condor Limited High E/T*** (1967) E (CA)

Gunnison Sage-Grouse Limited High T (2014) SC (CO); T (UT)

Greater Sandhill Crane Numerous High NL E (WA); T (CA); S3B (ID); SC (CO)

California Least Tern Numerous High E (1970) E (CA, OR)

Western Snowy Plover Numerous High T^^^ (1993) T (OR); SC (CO)

Preliminary Information—Subject to Revision. Not for Citation or Distribution

DRAFT

Common Raven53%American

Badger25%

Bobcat3%

Coyote14%

Long-Tailed Weasel

5%

Ravens are most frequent predator of Sage-Grouse (9 years of video data)

Literature:Coates et al. 2008. JFO 79:421–428. Lockyer et al. 2013. JFWM 4: 242 – 254. Casazza, USGS, unpublished

Sage-Grouse nest survival declines with increased raven numbers

Nests fail in areas of high raven abundance

Coates 2007. Dissertation. Idaho State University.

~0.4 ravens / km 2

Ravens per transectCoates 2007

~0.4 ravens / km 2

Threshold of raven abundance

Coates 2007

~0.9 ravens / km 2

Ravens per transect

Resp. Covariate Estimate lower upper

Ravens predation increases with less shrub cover

95% CI

• 1% decreasein shrub cover increased the odds of ravenpredation by 7.5%

• 20–30%sagebrush cover and >40% total shrub coverCoates et al. 2010. JWM 74:240–248.

Raven raven 0.23 0.11 0.41*

shrub cover -0.08 -0.15 -0.02*

grass 0.17 -0.63 0.41

forb 0.16 -0.40 0.70

understory 0.02 -0.04 0.08

shrub height 0.00 -0.06 0.06

Important Interaction

Indirect Effect – Nest Predation

Population Growth

Example of Science-based Adaptive Management Strategy

Tier 1 –Maintain or improve

habitat conditions that reduce

predation

Tier 2 – Reduce access to

anthropogenic subsidies

(concurrent with Tier 1 actions)

Tier 3 – Lethal raven removal

(concurrent with Tier 1 and 2 actions)

Example of Science-based Adaptive Management Strategy

1. Course-scale site selection for targeted management actions

2. Local-scale surveys at selected sites for density estimates

3. Three-tiered management action approach

4. Conduct post management monitoring

1. Course-scale site selection for targeted management actions

Informing management: Which areas of the state would benefit from raven management actions?

Information Products:

• State-wide map (course-scale) of raven occurrence map

• State-wide map (course-scale) of raven density

• Impact state-wide maps (prey distribution, raven density, and raven occurrence)

Example

Surveyed sites = 15

Surveys = 12,420

Survey with ravens = 3,482

Ravens detected = 5115


1. Course-scale site selection for targeted management actionsExample

Preliminary State-wide Raven Occurrence Map


• Land cover & vegetation– % Sagebrush, herbaceous, grassland, non-

sagebrush shrubland, annual grasses, shrub height, sagebrush height, pinyon-juniper, forested, riparian, NDVI, wet meadow

• Anthropogenic– Impervious (developed), road density,

transmission lines (low, medium, high), cell and radio towers, agriculture, land ownership, county-level livestock density

• Elevation & Topography– Elevation, topographic roughness, topographic

radiation aspect index, heat load index, compound topographic index, topographic position index

• Habitat edges– open vs. shrub habitat, agriculture vs. shrub

habitat, forested & pj vs. shrub, forested & pj vs. open

• Disturbance– Cumulative burned area (wildfire)

• Hydrology– Streams, springs, water bodies, open water




DRAFT

Influential Effects

% Agriculture (1450 m) +

Topographic depressions (3590 m) +

Greenness (3590 m) +

Bare Ground (570 m) +

Distance to Spring +

Road Density (570 m) +

Cum. Burned Area (3590 m) +

Distance to Developed Area +

Road Density% Agriculture

Pro

bab

ility

of

Occ

urr

en

ce



DRAFT

% Agriculture Road Density


DRAFTSage-grouse Nesting Habitat(Coates et al. 2016)

Raven Probability of Occurrence

DRAFT


Preliminary State-wide Impact Map

Informing management: How to prioritize actions among sites? What is rationale for actions? At specific sites, where to start?

Information Product:

Develop standardized raven survey protocol

o User-friendly interface to estimate densities annually across site and state-wide

o User-friendly interface to generate site-specific raven maps and prey potential impact maps

2. Local-scale surveys at selected sites for density estimates

Example

DRAFT

Developing models and user-friendly interface for agencies to estimate density with confidence intervals


2. Local-scale surveys at selected sites for density estimatesExample

Standardized Protocol for Estimating Raven Density

0 5 10 15


Informing management: What evidence of potential impacts exist to assign management action?

Information Products:

• Predation thresholds for management use (inform tiers)

o Raven density effects

o Overlap between ravens and species of concern

• Scientific findings to inform specific actions

o Movement, space use patterns, and demography

Example


DRAFTRecent Population-level analysis:

Sample sizes:

• 14 sites

• ~400 sage-grouse nests

• ~12,000 raven surveys

• 45 site/year nest survival and raven density estimates


Previous Finding:

Effect on sage-grouse nestingin NE Nevada

~0.4 ravens / km 2

Example

Science to Inform Management Actions (Thresholds)


DRAFT

Low raven density

=

increased variation in sage-grouse nest survival

3. Three-tiered management action approachExample



DRAFT




Informing Management Tiers (and site-specific actions)

Based on: 1) empirical density estimate, confidence limit and intersection with effects threshold2) intersection with species of concern maps

~0.4 ravens / km 2

DRAFT


Density Thresholds

Developing model and user-friendly interface for agencies to develop spatially explicit maps for targeting areas for management actions



Specific Areas to Target for Management

DRAFT DRAFT

Local Scale Analysis


Credit: Walter Wehtje

Credit: Walter Wehtje

Breeding Period Non-Breeding Period

GPS Marked Individuals = 10 (objective = 30); Locations = 9,350• Estimate seasonal utilization distributions for breeding and non-breeding seasons• Relate space use to sage-grouse nesting areas and anthropogenic subsidies


Movement and Space Use Information

Informing Management: Are management actions beneficial? Is there variation in their effectiveness? When to stop actions?

• Continue rapid survey assessment• Modify management actions based outcomes

• Adjust plan to accommodate changes in raven numbers and use• Graduate sites out of the plan


4. Conduct post management monitoringExample

Measuring Effectiveness of Actions

Pre-management Post-management

Pre Post

Den

sity

(ra

ven

s /

km 2

)

DRAFT

DRAFT DRAFT


Average raven density:~ 0.39 ravens / km 2

Estimated raven abundance in sage-grouse habitat:~ 40,000

Estimated raven abundance in Nevada:~ 110,000

*Likely low state-wide estimates based on sampling assumptions

Sage-grouse spring habitat

Coates et al. 2016

4. Conduct post management monitoringExample

State-wide Initial Density Estimates and Rate of Change

Next Steps

• Continue to improve state-wide occurrence, density, and impact maps

• Develop user-friendly interface to generate local scale maps and density estimates with survey data

• Incorporate new information on relationships between ravens, habitat and sage-grouse populations

• Incorporate findings using GPS data to inform dispersal, movement patterns, and space use of ravens

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