Agriculture, fertilizers and life history of a coastal seabird

1. Leakage of fertilizers from farmland has affected levels of nitrogen and phosphorus in many coastal areas, reducing limitation of primary productivity with consequences for timing and magnitude of the annual peak in phytoplankton and zooplankton. Such changes in nutrient availability may have affected temporal patterns of abundance of marine invertebrates and vertebrates that are the main prey of seabirds. 2. We investigated the extent to which changes in the use of fertilizers by farmers affected timing of breeding, clutch size, recruitment and longevity of a coastal seabird, the Arctic tern Sterna paradisaea Pont., in Denmark. 3. Timing of breeding advanced with the increase in use of fertilizers, with an effect as a consequence of a phenotypic response of individuals exposed to different levels of fertilizers. 4. Annual mean clutch size increased with the amount of fertilizer. While individual Arctic terns increased their clutch size with fertilizer level, there was no evidence of individual Arctic terns in different years changing their clutch size in response to changes in fertilizer use. 5. Annual recruitment rate, estimated as the proportion of young that were subsequently recovered as adults, was related to fertilizer use. 6. Mean longevity, estimated as the maximum age of adult individuals, decreased in response to fertilizer use. 7. These findings provide evidence of fertilizer use in agriculture having significant indirect effects on timing of reproduction, clutch size, recruitment and longevity of a seabird.