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, 7 (4), e35137

Linking Hydrogen (δ2H) Isotopes in Feathers and Precipitation: Sources of Variance and Consequences for Assignment to Isoscapes


Linking Hydrogen (δ2H) Isotopes in Feathers and Precipitation: Sources of Variance and Consequences for Assignment to Isoscapes

Keith A Hobson et al. PLoS One.


Background: Tracking small migrant organisms worldwide has been hampered by technological and recovery limitations and sampling bias inherent in exogenous markers. Naturally occurring stable isotopes of H (δ(2)H) in feathers provide an alternative intrinsic marker of animal origin due to the predictable spatial linkage to underlying hydrologically driven flow of H isotopes into foodwebs. This approach can assess the likelihood that a migrant animal originated from a given location(s) within a continent but requires a robust algorithm linking H isotopes in tissues of interest to an appropriate hydrological isotopic spatio-temporal pattern, such as weighted-annual rainfall. However, a number of factors contribute to or alter expected isotopic patterns in animals. We present results of an extensive investigation into taxonomic and environmental factors influencing feather δ(2)H patterns across North America.

Principal findings: Stable isotope data were measured from 544 feathers from 40 species and 140 known locations. For δ(2)H, the most parsimonious model explaining 83% of the isotopic variance was found with amount-weighted growing-season precipitation δ(2)H, foraging substrate and migratory strategy.

Conclusions/significance: This extensive H isotopic analysis of known-origin feathers of songbirds in North America and elsewhere reconfirmed the strong coupling between tissue δ(2)H and global hydrologic δ(2)H patterns, and accounting for variance associated with foraging substrate and migratory strategy, can be used in conservation and research for the purpose of assigning birds and other species to their approximate origin.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Location of feather sample collection sites and the underlying gradient in amount-weighted average δ 2H 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. .
Figure 2
Figure 2. Relationship between δ 2Hf and isoscape predicted δ 2Hp.
A) For 542 model calibration samples, B) for Neotropical migrants, C) for short-distance migrants, and D) for resident species. The relationship between δ 2Hf and δ 2Hp 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).
Figure 3
Figure 3. Regression of observed versus model predicted δ 2Hf 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
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
Figure 5. Boxplot of residuals from the top model for δ 2Hf 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.

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