Presentation Title

Employing Digital Still Imaging And Observer Counts To Estimate Bias In Aerial Surveys Of Wintering Sea Ducks

Session Title

The Biological and Physical Factors Driving Marine Bird Population Dynamics in the Salish Sea

Conference Track

Species and Food Webs

Conference Name

Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type of Presentation

Oral

Abstract

To better understand the bias in aerial survey abundance estimation that results from aircraft and observer effects, we conducted a study to estimate availability bias, detection, and misidentification by collecting images and observer counts of wintering sea ducks. We employed a fixed-wing aircraft with two digital still-image cameras and two observers to survey multiple 50m-wide strip-transects. A forward-facing (FF) camera attached to the wing strut captured images of the transect 250-300m ahead of the aircraft, while a point-of-view (POV) camera mounted to the rear window captured images of the transect abeam of the aircraft. Comparing the FF to POV camera counts allowed estimation of availability bias, or aircraft effect (the proportion of birds that flew out of the transect or dove due to the aircraft). Analyses suggested that 5-30% of sea ducks dove or flew off-transect as the aircraft approached: 5% for goldeneye, 20% for long-tailed duck and surf scoter, 25% for white-winged scoter, and 30% for bufflehead. Comparing the POV camera to observer counts allowed estimation of detection (the percentage of birds within the transect that were detected by observers) and misidentification. Estimates of birds detected on transects ranged from 50% to 95%, varying by species and observer, with long-tailed duck detection being slightly higher than other species. Misidentification of surf and white-winged scoters was about 1% and 4-6%, respectively. Our results suggest that, due to a combination of aircraft and observer effects, current survey estimates could be increased by a factor of 1.3 to 2.2 depending on species. We are developing methods for additional studies to address these biases, as well as effects of transect width and aircraft type.

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Language

English

Format

application/pdf

Type

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Employing Digital Still Imaging And Observer Counts To Estimate Bias In Aerial Surveys Of Wintering Sea Ducks

2016SSEC

To better understand the bias in aerial survey abundance estimation that results from aircraft and observer effects, we conducted a study to estimate availability bias, detection, and misidentification by collecting images and observer counts of wintering sea ducks. We employed a fixed-wing aircraft with two digital still-image cameras and two observers to survey multiple 50m-wide strip-transects. A forward-facing (FF) camera attached to the wing strut captured images of the transect 250-300m ahead of the aircraft, while a point-of-view (POV) camera mounted to the rear window captured images of the transect abeam of the aircraft. Comparing the FF to POV camera counts allowed estimation of availability bias, or aircraft effect (the proportion of birds that flew out of the transect or dove due to the aircraft). Analyses suggested that 5-30% of sea ducks dove or flew off-transect as the aircraft approached: 5% for goldeneye, 20% for long-tailed duck and surf scoter, 25% for white-winged scoter, and 30% for bufflehead. Comparing the POV camera to observer counts allowed estimation of detection (the percentage of birds within the transect that were detected by observers) and misidentification. Estimates of birds detected on transects ranged from 50% to 95%, varying by species and observer, with long-tailed duck detection being slightly higher than other species. Misidentification of surf and white-winged scoters was about 1% and 4-6%, respectively. Our results suggest that, due to a combination of aircraft and observer effects, current survey estimates could be increased by a factor of 1.3 to 2.2 depending on species. We are developing methods for additional studies to address these biases, as well as effects of transect width and aircraft type.