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Science to Inform Adaptive Management for Ravens
U.S. Geological Survey, Western Ecological Research Center Partners: 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
(BBS; Sauer and Link)
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
William Boarman, USGS 0
2
4
6
8
10
1960 1970 1980 1990 2000 2010
Year
Co
un
t
Raven Numbers
300% Increase, 1966-2007
n = 1,226 P < 0.001
Sauer et al 2007
Sauer et
al. 2004
Unnatural Nest Substrate
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
73 41
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
9
Raven
Populations
Prey Population
Vital Rate
Habitats
of Prey
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 Raven 53% American
Badger 25%
Bobcat 3%
Coyote 14%
Long-Tailed Weasel
5%
Impacts on 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
Threshold of raven abundance
Coates 2007
~0.4 ravens / km 2
Ravens per transect
Resp. Covariate Estimate lower upper
Ravens predation increases with less shrub cover
95% CI
• 1% decrease in shrub cover increased the odds of raven predation by 7.5%
• 20–30% sagebrush cover and >40% total shrub cover Coates 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
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 = ~32 Surveys = >15,000 Survey with ravens = >11,000
Preliminary Information—Subject to Revision. Not for Citation or Distribution
1. Course-scale site selection for targeted management actions Example
Preliminary State-wide Raven Occurrence Map
Preliminary Information—Subject to Revision. Not for Citation or Distribution
• 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
1. Course-scale site selection for targeted management actions Example
Preliminary State-wide Raven Occurrence Map
Elevation Developed
Vegetation (NDVI) % Herbaceous
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT
1. Course-scale site selection for targeted management actions Example
Preliminary State-wide and Great Basin Raven Occurrence Map
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT
1. Course-scale site selection for targeted management actions Example
Preliminary State-wide and Great Basin Raven Occurrence Map
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT
1. Course-scale site selection for targeted management actions Example
Preliminary State-wide and Great Basin Raven Density Map
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT Sage-grouse Nesting Habitat (Coates et al. 2016)
Index: Raven occurrence x density
DRAFT
1. Course-scale site selection for targeted management actions Example
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
2. Local-scale surveys at selected sites for density estimates
Example
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT
Developing models and user-friendly interface for agencies to estimate density with confidence intervals
2. Local-scale surveys at selected sites for density estimates Example
EXAMPLE
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT
~0.53 ravens per km2
2. Local-scale surveys at selected sites for density estimates
Example
Examples of time-series estimates
DRAFT DRAFT
Preliminary Information—Subject to Revision. Not for Citation or Distribution
3. Three-tiered management action approach
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
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT Recent Population-level analysis: Sample sizes: • 14 sites
• ~400 sage-
grouse nests
• ~12,000 raven surveys
• 45 site/year nest survival and raven density estimates
3. Three-tiered management action approach
Previous Finding: Effect on sage-grouse nesting in NE Nevada ~0.4 ravens / km 2
Example
Science to Inform Management Actions (Thresholds)
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT
Low raven density = increased variation in sage-grouse nest survival
3. Three-tiered management action approach Example
Science to Inform Management Actions (Thresholds)
Preliminary Information—Subject to Revision. Not for Citation or Distribution
DRAFT
3. Three-tiered management action approach Example
Science to Inform Management Actions (Thresholds)
EXAMPLE
Preliminary Information—Subject to Revision. Not for Citation or Distribution
Informing Management Tiers (and site-specific actions) Based on: 1) empirical density estimate, confidence limit and intersection with effects threshold 2) intersection with species of concern maps
~0.4 ravens/km 2
DRAFT
3. Three-tiered management action approach Example
Developing model and user-friendly interface for agencies to develop spatially explicit maps for targeting areas for management actions
Preliminary Information—Subject to Revision. Not for Citation or Distribution
3. Three-tiered management action approach Example
Specific Areas to Target for Management
DRAFT DRAFT
Local Scale Analysis
Developing model and user-friendly interface for agencies to develop spatially explicit maps for targeting areas for management actions
Preliminary Information—Subject to Revision. Not for Citation or Distribution
3. Three-tiered management action approach Example
Specific Areas to Target for Management
DRAFT DRAFT
Local Scale Analysis
Preliminary Information—Subject to Revision. Not for Citation or Distribution
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
3. Three-tiered management action approach Example
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 action
Preliminary Information—Subject to Revision. Not for Citation or Distribution
4. Conduct post management monitoring Example
Measuring Effectiveness of Actions
Pre-management Post-management
Pre Post
Den
sity
(ra
ven
s /
km 2
)
DRAFT
DRAFT DRAFT
Preliminary Information—Subject to Revision. Not for Citation or Distribution
4. Conduct post management monitoring Example
Measuring Effectiveness of Actions
Preliminary Information—Subject to Revision. Not for Citation or Distribution
Preliminary Abundance Estimates of Ravens
Number of Ravens in sagebrush cover types across Great Basin ~145,000 Number in Nevada sage-grouse habitat ~40,000 Number across state ~110,000
Sage-grouse spring habitat
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