| Patuxent Science Meeting 2006 Poster Abstract |
| | Uncertainty in detection bias: Hidden management costs of index- |
| | based population monitoring |
| | Moore CT, Kendall WL |
| | Managers of wildlife populations commonly rely on simple counts of detected animals in making |
| | decisions regarding conservation, harvest, or control. The main appeal in using such indirect |
| | counts is their low material expense compared to methods that estimate the undetected |
| | population (and therefore the entire population). However, their correct use rests on the rarely- |
| | tested but often-assumed premise that they proportionately reflect population size, that is, that |
| | they constitute a population index. We investigated forest management for the endangered |
| | Red-cockaded Woodpecker (Picoides borealis) and the Wood Thrush (Hylocichla mustelina) at |
| | the Piedmont National Wildlife Refuge in central Georgia (USA). We derived optimal decision |
| | policies for a joint species objective under each of two alternative models of Wood Thrush |
| | population dynamics. We simulated the optimal policies under each model for three scenarios |
| | of bias for observed Wood Thrush densities: (1) unbiasedness, (2) consistent negative bias (i.e., |
| | a valid population index), and (3) habitat-dependent negative bias. Differences in simulation |
| | outcomes between biased and unbiased detection scenarios provided the expected loss in |
| | resource objectives (here, forest habitat and birds) through the basing of decisions on biased |
| | population counts. Under the models and objective function we used, expected losses were as |
| | great as 11%. For applications such as endangered species management, such a degree of |
| | loss may not be trivial and could be far greater under different model assumptions. Our analysis |
| | demonstrates that costs of uncertainty about the relationship between the population and its |
| | observation can be measured in units of the resource, costs which may offset apparent savings |
| | achieved by collecting uncorrected population counts. |
| | Friday, September 22, 2006 |