Table 1.
Differences between species and times of the year in stable isotope ratios.
| Source | Type III Sum of Squares | df | Mean Square | F | P | η2 |
|---|---|---|---|---|---|---|
| Dependent: δ13C | ||||||
| species | 17.9 | 1 | 17.9 | 9.7 | 0.002 | 0.044 |
| time | 16.6 | 1 | 16.6 | 9.0 | 0.003 | 0.041 |
| species × time | 1226.7 | 1 | 1226.7 | 666.1 | <0.001 | 0.760 |
| Error | 386.7 | 210 | 1.8 | |||
| Total | 1698.9 | 213 | ||||
| Dependent: δ15N | ||||||
| δ13C | 138.2 | 1 | 138.2 | 131.9 | <0.001 | 0.387 |
| species | 303.1 | 1 | 303.1 | 289.4 | <0.001 | 0.581 |
| time | 18.3 | 1 | 18.3 | 17.5 | <0.001 | 0.077 |
| species × time | 3.5 | 1 | 3. 5 | 3.3 | 0.070 | 0.016 |
| Error | 218.9 | 209 | 1.0 | |||
| Total | 1540.3 | 213 | ||||
Carbon and nitrogen stable isotope ratios were measured in feathers of Thin-billed prions and Wilson's storm-petrels (winter vs. summer), tested using GLM. Location (δ13C) was included in the model for nitrogen to account for differences in baseline levels with latitude (e.g. see Fig. 2B).