Habitat Selection and Breeding Status of Swainson's Warblers in Southern Missouri

Abstract

Habitat selection and productivity are poorly documented for the Swainson's warbler (Limnothlypis swainsonii) throughout its breeding range. In southern Missouri in 1992-93, we quantified and compared habitat structure of occupied and unoccupied canebrakes (Arundinaria gigantea) and monitored nests to determine productivity. Twenty-nine of 100 canebrakes searched in 1992 were occupied by Swainson's warblers. Occupied canebrakes (n = 29) had higher cane density (P = 0.009), lower canopy (P = 0.018) and sub-canopy height (P = 0.008), and less herbaceous ground cover (P = 0.003) than did unoccupied canebrakes (n = 30). In 1993, we compared 16 additional occupied sites with 15 new unoccupied sites. Cane height (P = 0.030), tree diameter at breast height (dbh) (P = 0.006), and percent herbaceous cover (P = 0.001) were higher in occupied than in unoccupied canebrakes, whereas percent leaf litter was lower (P = 0.011). Using the 1992 data, we developed a linear logistic regression model to predict the probability of Swainson's warbler occurrence. Applied to the 1993 data, this model correctly predicted only 3 of 16 occupied and 8 of 15 unoccupied canebrakes. We then pooled the data and developed a new model that correctly predicted 31 of 45 occupied and 35 of 45 unoccupied canebrakes. Clutch size averaged 3.65 eggs/nest (n = 17) and nest production was 2.12 fledglings/nest. We failed to identify consistent distinctions between occupied and unoccupied canebrakes, and reproductive success was within the range reported for this and similar species. Therefore, based upon our results, we found no evidence that suitable habitat limited Swainson's warbler abundance in Missouri.