Figure 1.
Location of feather sample collection sites and the underlying gradient in amount-weighted average δ2H in precipitation.
Shown are locations for 544 calibration samples collected for this study, and the location of 269 samples from previously published sources used as model validation samples. Underlying isoscape based on Bowen et al. [20].
Figure 2.
Relationship between δ2Hf and isoscape predicted δ2Hp.
A) For 542 model calibration samples, B) for Neotropical migrants, C) for short-distance migrants, and D) for resident species. The relationship between δ2Hf and δ2Hp was modeled using a linear modeling approach with lines indicating predictions from our best AICc selected model (see methods). Our best model included a factor for whether the species foraged on the ground or elsewhere; thus, the predictive equations and regression line are shown separately for ground foragers (solid lines) and non-ground foragers (dashed lines).
Table 1.
Parameter estimates for the top linear model examining variation in δ2Hf.
Figure 3.
Regression of observed versus model predicted δ2Hf for 269 samples from previously published sources.
Solid line depicts ordinary least squares fit (observed = −17.38 (3.56 SE)+0.84*predicted (0.03 SE)), and dashed line is 1∶1 correspondence line.
Figure 4.
Frequency distribution of residuals from top model.
For A) ground foraging short-distance migrants, B) non-ground foraging Neotropical migrants, C) ground foraging Neotropical migrants, and D) non-ground foraging short-distance migrants. Residuals are not shown for resident species.
Figure 5.
Boxplot of residuals from the top model for δ2Hf versus the year in which the feather was grown.
Dark solid line represents the median, gray box indicates the range inter-quartile range, whiskers are 1.5 time the inter-quartile range, and dots indicate extreme values. Note: only years with at least ten samples are shown.