Comparing a Bioenergetics Model with Feeding Rates of Caged European Starlings

We tested a bioenergetics model integrated within a mortality model that estimates numbers of European starlings (Sturnus vulgaris) poisoned with the avicide, Compound DRC-1339 Concentrate. The bioenergetics model predicted daily metabolic rate. Accuracy and reliability of this variable is critical because other algorithms (e.g., toxicity regressions, feeding behavior) in the mortality model depend on metabolic rate to calculate the amount of DRC-1339 ingested per bird. We tested the bioenergetics model by comparing its estimates of metabolic rate with those generated from measuring feeding rates of caged starlings during a feeding trial conducted outdoors during January 2008. Over the 12-day feeding trial, daily feeding rates of caged starlings indicated that metabolic rates ranged from 157 kJ/bird per day to 305 kJ/bird per day. The bioenergetics model predicted metabolic rates ranging from 208 kJ/bird per day to 274 kJ/bird per day. There was no difference between these 2 independently derived estimates of daily metabolic rate (paired t-test: t ₍₁₁₎ = 1.4, P = 0.18). Using 95% confidence intervals calculated from variation of feeding rates among cages (n = 4, 6 birds/cage), the bioenergetics model's estimates were within 95% confidence intervals on 9 of 12 days and greater than the upper 95% confidence interval on 3 days. Daily estimates of metabolic rate were directly correlated between the bioenergetics model and the feeding-rate model (r ₁₂ = 0.57, P = 0.05). A broad range of temperatures (-17°°C to 14°°C), wind speeds (0––40 km/hr), and percent cloud cover (0––100%) were encountered during the feeding trial. The bioenergetics model's predictions appeared robust to varying meteorological conditions typical of winters in middle latitudes of the interior United States. Compound DRC-1339 Concentrate is used by USDA Wildlife Services to manage chronic infestations of starlings at livestock facilities, which occur mainly during fall and winter. Compared to other methods used for estimating DRC-1339 mortality (e.g., counting birds pre- and posttreatment), bioenergetics modeling should improve the mortality model's overall accuracy and precision.