EVALUATION OF FIELD SAMPLING TECHNIQUES FOR ESTIMATION OF BIRD DAMAGE IN PISTACHIO ORCHARDS

Authors

A. Charles Crabb, Professor, Crop Science Department, Cal Poly State University, San Luis Obispo, California
James J. Marois, Associate Professor, Department of Plant Pathology, University of California, Davis, California
Terrell P. Salmon, Director, Division of Agriculture and Natural Resources - North Region, University of California, Davis, California

Date of this Version

February 1994

Abstract

Pistachio orchards were selected and evaluated for damage caused by either scrub jays (Aphelocoma coerulescens) or American crows (Corvus brachyrhynchos). The distribution of damage caused by each species was evaluated and quantified. The percentage of trees damaged by scrub jays ranged from 58% to 99% and tended to be distributed randomly throughout the. orchard. In orchards with crow damage, the percentage of trees damaged ranged from 18% to 46% and damage tended to be aggregated. Data from orchards were used to evaluate the relative accuracy and precision of various sampling strategies. Randomly distributed bird damage could be sampled with relatively simple strategies such as walking diagonally across the orchard. Aggregated bird damage was most effectively sampled using stratified random sampling. If action thresholds are going to be used to determine when bird control programs should be initiated, an understanding of the distribution of bird damage in a crop must be understood so reasonable sampling techniques can be developed.