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

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Rationale By combining precision satellite‐tracking with blood sampling, seabirds can be used 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 δ 13 C and δ 15 N in the NE Atlantic. Results By matching winter‐grown feathers with the non‐breeding location of tracked birds we found latitudinal gradients in δ 13 C and δ 15 N 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.