The feeding and breeding ecology of Arctic terns (Sterna paradisaea)

Bridal gifts were displayed in a variety of systems in the animal kingdoms and play an important role during the courtship display, for the choice of the mate. In this study, extensive video analyses of behavioural records across all breeding season stages and novel application of simultaneous triple stable isotope analyses to avian research were combined to detect the important parameters of the feeding and breeding ecology of the Arctic tern (Sterna paradisaea). The aim of this study was to describe the prey composition of bridal gifts during mating and incubation stages, and the diet spectrum and feed composition of chick provisioning in my study year, and (2) assessing whether females distinguish by acceptance and subsequent courtship behaviors between different types of bridal gifts, also entailing exploratory analyses whether preferred types of bridal gifts are linked to better chick condition when occurring at a higher proportion in chick diet. The findings were, that the most attractive species as bridal gifts were syngnathid pipefish, but this gift type did not score the highest subsequent courtship displays. The prey category that had the highest absolute number in acceptance by female was the goby. Other species that were often accepted by females in absolute numbers were smelt, clupeids and Crangon crangon. The highest scores of courtship displays were reached with smelt and goby as bridal gifts, which also reached high numbers and proportions in the acceptance of the female. Crangon crangon, Clupeidae and smelt were the most important species for chick feeding. The prey items that were fed to the chicks were significantly smaller than those that were imported to the colony, but subsequently eventually ingested by the parents. Goby, smelt and Clupeidae had the shortest times between delivery to the chick ingestion. I detected higher d15N values for the chicks of all location and years, compared to the adults of all location and years indicate that the chicks were fed with prey of higher trophic levels. Trip;e stable isotope analyses also unravelled higher d34S values for adults compared to the chicks, showing that adults fed on a higher proportion of pelagic prey items, and fed a higher proportion of benthic prey to their chicks. The significant negative correlation between wing/weight-ratio and smelt contribution to chick diet and the significant correlation with contribution of other shrimp than Crangon, showed that chicks which were fed with a higher amount of smelt and these shrimps, were in better conditions, whereas chicks having a higher C. maenas contribution in their diet were in poorer condition. Different acceptance of different prey species show that female Arctic terns distinguished between different types rather than sizes of bridal gifts, and that such courtship gifts may contain information on mate quality of the advertising male. A positive correlation between female courtship behavior initiated by different bridal gift types, and the contribution of these prey types to chick condition, however, indicated that female Arctic terns may judge bridal gifts according to suitability for their own satiation, providing indication of male mate quality, rather than of his future feed choices during parenting. Further research on banded adult Arctic terns is needed to highlight the nutritional content of distinctive bridal gift types and its effects on female acceptance and mate choice, and to assess whether high quality males in bridal gift provisioning are also good chick providers.