From a Study Design Assessment for Waterfowl Production Surveys on Tetlin NWR by Jonathan Greenberg (intern) and Joel Reynolds (former Regional Biometrician)

Peter KellerWildlife BiologistTetlin National Wildlife RefugeTok, AK

Friends of Alaska National Wildlife Refuges, 19 October 2010

The Science Behind the Survey: A very short introduction to some behind the scenes design (re-)considerations of a typical Refuge study.

Where is the Refuge?

http://alaska.fws.gov/nwr/images/map.jpg

Background

Survey designed in the 1980’s using maps from the 1950’s

Potential for improvements in design and analysis?

Survey Protocol

Survey 11 clusters of lakes each year fly out and walk around

Identify all waterfowl and broods Age-class all broods

1 – downy ball of fluff (~1-18d) 2 – feathers come in (~19-43d) 3 – fully feathered chick, flightless (~44-

50) Takes 22 person-days per year to complete

Project Goals

Assess Tetlin NWR’s waterfowl brood production survey (initiated 1980’s)

o Use historic data to suggest design improvements

Why Survey?

Provide short-term production data for hunting regulations

Enhance understanding of waterfowl population dynamics

Provide a “red flag” for the effects of climate change on waterfowl environment

Protocol Assessment: Management Objectives

Current Objective: Detect major population changes on the order of

25% with 95% certainty

Issues: Objectives are not detailed enough

Recommendations: Clearly define species and time-scales of interest, type

of change of interest (yr. to yr., trend), and acceptable precision rates

Example: Detecting an average annual decline of 5% over a 5-year period in Wigeon density on Tetlin NWR with significance level of 10% and 80% power

Protocol Assessment: Species of Interest

Current: 12 species are currently

being studied

Issues: Not all species are abundance

enough to support analysis

Recommendations: Limit analysis to AGWT,

AMWI, MALL, BUFF, RNDU, SCAU

(that was easy!)

Species

Average # Broods /

Year

Divers

Bufflehead 14.4

Ring-necked Duck 8

Scaup species 23.6

Canvasback 3.3

Surf Scoter n/a

White-winged Scoter n/a

Goldeneye species n/a

Dabblers

Green-winged Teal 13.4

American Wigeon 16.6

Mallard 12.6

Blue-winged Teal 0.2

Northern Pintail 5.3

Northern Shoveler 3.1

How to choose what/where to study?

Definitions: Target universe – all items we wish to learn about

Recommendation: Define the target universe as all waterbodies within Tetlin NWR

Sample frame – portion of the target universe that we’re actually able to study to make inference about the

target universe

Recommendations: Identify and label all clusters of waterbodies in the sample frame using GIS

(only 700,000 acres to choose from!)

Recommendations: Define constraints: logistical (can we get there? can we survey it in one day?) and waterbody size (e.g. between 0.5 and 5 acres)

Sample unit – the level at which we sample

Measurement: Responses of InterestCurrent:

Species, brood age class, and number of young for each detected brood in each waterbody

Issues: Not all broods are detected Number of young is problematic due to within season

mortality Mortality is related to survey timing

Recommendations:1. Analysis 1: Use broods (instead of young) as the response

variable2. Analysis 2: Develop a mortality model to project # fledged

from # young per age class3. Design 1: Time surveys so the brood age class distribution is

consistent across years for a species4. Design 2: Develop 2 surveys (1 for dabblers, 1 for divers)

Measurement Issues: Mortality

Current: The potential

effects of mortality are not accounted for in the current analysis or survey design

Young (regardless of age class) are counted equally

Measurement Issues: Accounting for Survey Timing/Mortality Issues

Recommendations (Cont.):Analysis 2:Develop a model of within-season mortality to project the number of young observed to the number of fledged young expected

Measurement Issues: Mortality Modeling

Recommendations: Conduct a study on waterfowl mortality in Tetlin NWR Develop a more refined mortality model, fit it to the

historic data, and validate it with local studies on waterfowl mortality

Measurement Issues: Accounting for Survey Timing/Mortality Issues

Recommendations (Cont.) Design 2:

Develop 2 surveys (1 for dabblers, 1 for divers)

Assessment: Covariates (cont.)

Recommendations (Cont.): What other factors are known/expected to influence

brood production? Are any of them available from other sources or ‘easily’ measured?

Cluster-scale factors hunting/gathering; fires; river influences, etc.

Refuge-scale factors precipitation; temperature, etc.

Migratory factors (that are available) flyway weather patterns; food resources, etc.

Survey Recommendations

1. Clearly define management objectives2. List all clusters in the Tetlin NWR3. Determine the accessibility of all clusters, establish size

and logistical constraints, and clearly define the sample frame

4. Calculate the percentage of inaccessible clusters to assess the magnitude of potential bias

5. Develop a protocol for re-measuring waterbodies and water acreage in the target universe every 10-20 years

6. Brainstorm possible biologically related covariates for brood production

7. Examine the relationship between water level and brood production

Survey Recommendations

8. Observe a random sample of clusters in addition to the 11 clusters currently selected in order to develop a calibration between the current sample and the target universe (apply this calibration to the historical data)

9. Approximate brood/young mortality in Tetlin and develop a model to account for it (a graduate project for sure!)

10. Celebrate!

Survey Suggestions

The target universe should be defined as all clusters of waterbodies in Tetlin NWR

The sample frame should be defined as all accessible clusters of waterbodies in Tetlin NWR

Waterfowl production calculations should use number of broods (instead of number of young) because broods are less sensitive to mortality (but then we don’t get any estimate of young produced)

Canvasbacks, Blue-winged Teals, Northern Pintails, and Northern Shovelers do not occur with sufficient frequency or abundance to support summarization or analysis (although we should still document their occurrence in case this changes, as all things do)

The End!

Thank you for this opportunity!