We are pleased to announce the publication of the paper: Aguilar A, Giménez J, Gómez–Campos E, Cardona L, Borrell A (2014) δ15N Value Does Not Reflect Fasting in Mysticetes. PLoS ONE 9(3): e92288. doi:10.1371/journal.pone.0092288 Abstract: The finding that tissue δ15N values increase with protein catabolism has led researchers to apply this value to gauge nutritive condition in vertebrates. However, its application to marine mammals has in most occasions failed. We investigated the relationship between δ15N values and the fattening/fasting cycle in a model species, the fin whale, a migratory capital breeder that experiences severe seasonal variation in body condition. We analyzed two tissues providing complementary insights: one with isotopic turnover (muscle) and one that keeps a permanent record of variations in isotopic values (baleen plates). In both tissues δ15N values increased with intensive feeding but decreased with fasting, thus contradicting the pattern previously anticipated. The apparent inconsistency during fasting is explained by the fact that a) individuals migrate between different isotopic isoscapes, b) starvation may not trigger significant negative nitrogen balance, and c) excretion drops and elimination of 15N-depleted urine is minimized. Conversely, when intensive feeding is resumed in the northern grounds, protein anabolism and excretion start again, triggering 15N enrichment. It can be concluded that in whales and other mammals that accrue massive depots of lipids as energetic reserves and which have limited access to drinking water, the δ15N value is not affected by fasting and therefore cannot be used as an indicatior of nutritive condition. A PDF copy of the work can be downloaded from: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0092288 Please do not hesitate to contact us for any question regarding our work. Best regards, Joan Gimenez -- *Joan Giménez Verdugo* PhD Student *Estación Biológica de Doñana (CSIC)* *Department of Conservation Biology* Avenida Americo Vespucio s/n 41092 Sevilla www.ebd.csic.es Mail: joan.gimenez@csic.es Phone: +34619176849