Geolocator tracking seabird migration and moult reveal large-scale temperature-driven isoscapes in the NE Atlantic

Rationale: By combining precision satellite-tracking with blood sampling it has been possible to use seabirds to validate marine carbon and nitrogen isoscapes, but it is unclear whether a comparable approach using low precision light-level geolocators (GLS) and feather sampling can be similarly effective. Methods: Here we used GLS to identify wintering areas of northern gannets Morus bassanus and sampled winter grown feathers (confirmed from image analysis of non-breeding birds) to test for spatial gradients in δ13C and δ15N in the NE Atlantic. Results: By matching winter-grown feathers with non-breeding location of tracked birds we found latitudinal gradients in δ13C and δ15N in neritic waters. Moreover, isotopic patterns were best explained by sea surface temperature. Similar isotope gradients were found in fish muscle sampled at local ports. Conclusions: Our study reveals the potential of using seabird GLS and feathers to reconstruct large scale isotopic patterns