Avian Conservation and Ecology - Écologie et conservation des oiseaux: Contrasting Effects of Cattle Grazing Intensity on Upland-nesting duck Production at Nest and Field Scales in the Aspen Parkland, Canada

Table 1. Rankings of duck nest density (DEN) models investigating effects of grass type (GT) and grazing co-variates, and year (YEAR). Grazing co-variates include residual cover (RC), residual cover field trend (FTREND), and pasture score (PS). All models contain a co-variate to control for field-specific water conditions (proportion of flooded basins or PBASIN). Models are generalized linear models with a negative binomial error distribution (n = 100 fields). Only models within the 95% confidence interval group of models, i.e., Σw_i = 0.95, are presented (Burnham and Anderson 1998).

Model^† k^‡ ΔAIC_c^§ w_i^|

DEN(PBASIN+RC+PS+YR) 5 0.00 0.465

DEN(PBASIN+RC+PS) 4 0.78 0.315

DEN(PBASIN+RC*FTREND) 5 3.77 0.071

DEN(PBASIN+RC+YR) 4 4.00 0.063

DEN(PBASIN+RC+FTREND+GT+YR) 6 4.63 0.046

^†Models including interaction terms include all main effects.
^‡Number of estimated parameters.
^§The difference in AIC_c scores between the present model and the best model (AIC_c= 107.10).
^|Normalized relative model likelihoods.