BioOne.org will be down briefly for maintenance on 17 December 2024 between 18:00-22:00 Pacific Time US. We apologize for any inconvenience.
How to translate text using browser tools
1 November 2007 A Field Evaluation of Distance Measurement Error in Auditory Avian Point Count Surveys
MATHEW W. ALLDREDGE, THEODORE R. SIMONS, KENNETH H. POLLOCK
Author Affiliations +
Abstract

Detection distance is an important and common auxiliary variable measured during avian point count surveys. Distance data are used to determine the area sampled and to model the detection process using distance sampling theory. In densely forested habitats, visual detections of birds are rare, and most estimates of detection distance are based on auditory cues. Distance sampling theory assumes detection distances are measured accurately, but empirical validation of this assumption for auditory detections is lacking. We used a song playback system to simulate avian point counts with known distances in a forested habitat to determine the error structure of distance estimates based on auditory detections. We conducted field evaluations with 6 experienced observers both before and after distance estimation training. We conducted additional studies to determine the effect of height and speaker orientation (toward or away from observers) on distance estimation error. Distance estimation errors for all evaluations were substantial, although training reduced errors and bias in distance estimates by approximately 15%. Measurement errors showed a nonlinear relationship to distance. Our results suggest observers were not able to differentiate distances beyond 65 m. The height from which we played songs had no effect on distance estimation errors in this habitat. The orientation of the song source did have a large effect on distance estimation errors; observers generally doubled their distance estimates for songs played away from them compared with distance estimates for songs played directly toward them. These findings, which we based on realistic field conditions, suggest measures of uncertainty in distance estimates to auditory detections are substantially higher than assumed by most researchers. This means aural point count estimates of avian abundance based on distance methods deserve careful scrutiny because they are likely biased.

MATHEW W. ALLDREDGE, THEODORE R. SIMONS, and KENNETH H. POLLOCK "A Field Evaluation of Distance Measurement Error in Auditory Avian Point Count Surveys," Journal of Wildlife Management 71(8), 2759-2766, (1 November 2007). https://doi.org/10.2193/2006-161
Published: 1 November 2007
JOURNAL ARTICLE
8 PAGES

This article is only available to subscribers.
It is not available for individual sale.
+ SAVE TO MY LIBRARY

KEYWORDS
abundance
auditory detections
bird surveys
distance estimation
measurement error
point count surveys
RIGHTS & PERMISSIONS
Get copyright permission
Back to Top