PARENT SESSION
PM12 - Population Modeling in Ecological Risk Assessment
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P326) Do agricultural pesticides affect burrowing owls? A matrix modeling approach.

Gervais, Jennifer^*,1,2, Anthony, Robert¹, ¹ Oregon State University, Corvallis, OR, USA² Utah State University, Logan, UT, USA

ABSTRACT- We used matrix population models to assess the potential effects of exposure to agricultural pesticides on a burrowing owl ( Athene cunicularia ) population in the Central Valley of California, USA. Initial model parameter values of survival and reproductive success were estimated from demographic data collected from 1997 to 2001. Exposure scenarios were based on sampling eggs for p,p'DDE residues and radio telemetry sampling of breeding male owls to estimate exposure to carbamate and organophosphorus compounds during foraging activities. Matrix models were used to examine population growth rate, or lambda, over four years and elasticity analyses identified life cycle stages with the greatest influence on population growth rate. Scenarios based on field exposure data led to reductions of population growth rate that were negligible compared to the annual variability in estimates of lambda. The rankng of the importnace of life cycle stages varied annually, with adult survival being most important when populations appeared to be declining, but juvenile survival and reproductive success most important in growing populations. Pesticide exposure is unlikely to be an important factor in the population dynamics of this population of burrowing owls. Elasticity values are context-specific and must be used only as a general guide to identify critical stages for environmental monitoring.

Key words: population risk assessment, matrix modeling, p,p'DDE, burrowing owls