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Point counts from clustered populations: Lessons from an experiment with Hawaiian crows

Condor

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Abstract

We designed an experiment to identify factors contributing most to error in counts of Hawaiian Crow or Alala (Corvus hawaiiensis) groups that are detected aurally. Seven observers failed to detect calling Alala on 197 of 361 3-min point counts on four transects extending from cages with captive Alala. A detection curve describing the relation between frequency of flock detection and distance typified the distribution expected in transect or point counts. Failure to detect calling Alala was affected most by distance, observer, and Alala calling frequency. The number of individual Alala calling was not important in detection rate. Estimates of the number of Alala calling (flock size) were biased and imprecise: average difference between number of Alala calling and number heard was 3.24 (.+-. 0.277). Distance, observer, number of Alala calling, and Alala calling frequency all contributed to errors in estimates of group size (P < 0.0001). Multiple regression suggested that number of Alala calling contributed most to errors. These results suggest that well-designed point counts may be used to estimate the number of Alala flocks but cast doubt on attempts to estimate flock size when individuals are counted aurally.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Point counts from clustered populations: Lessons from an experiment with Hawaiian crows
Series title:
Condor
Volume
93
Issue:
3
Year Published:
1991
Language:
English
Contributing office(s):
Patuxent Wildlife Research Center
Description:
676-682
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Condor
First page:
676
Last page:
682
Number of Pages:
7