Interpreting population estimates of birds following pesticide applications--behavior of male starlings exposed to an organophosphate pesticide

Abstract

We determined activity budgets for 10 pairs of captive male Starlings between 7 May and 18 July 1980. Our objective was to quantify changes in behavior after exposure to an organophosphate (OP) pesticide and to assess the impact of changes in behavior on the interpretation of population estimates of birds following pesticide applications. We observed each pair of males for an hour at 07:30 and 09:30 for four days and classified their behavior into one of four categories: flying, perching, foraging, or singing and displaying. At 06:30 on day 2, one male received a single oral dose of 2.5 mg dicrotophos (3-hydroxy-N, N-dimethyl-cis-crotonamide dimethyl phosphate) per kg of body weight; the other male received an equivalent exposure of corn oil. Changes in the activity budgets of OP-dosed and control males were compared using t-tests. Activity of OP-dosed males was significantly (P _ 0.05) reduced within the 2-4 h following exposure. OP-dosed males spent more time perching (46.1%) than controls and less time flying (-96.6%), foraging (-28.5%), and singing and displaying (-49.5%). The frequency of perching (-75.3%), flying (-83.8%), foraging (-54.1%), and singing and displaying (- 59.2%) was significantly reduced. Activity in OP-dosed males returned to normal by 26-28 h posttreatment. Results suggest that movement and vocalization may be significantly reduced in birds exposed to organophosphate and carbamate pesticides. Conventional censusing techniques and population estimating procedures may, therefore, be inadequate to assess changes in bird populations after pesticide applications because of the difficulty in separating decreases in density due to mortality or emigration from reductions in activity.