Post-fledging body mass increase in Common Terns Sterna hirundo: influence of age, sex and year

• Published in: Ibis (London, England) England), 2008, Vol.150 (1), p.50-58
• Main Authors: SCHAUROTH, CARMEN, BECKER, PETER H
• Format: Article
• Language: English
• Subjects: Age differences; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Aves; Banter See; Biological and medical sciences; fledging age; Fundamental and applied biological sciences. Psychology; Gender differences; Ornithology; post-fledging mass growth; post-fledging survival; Size; Vertebrata; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0019-1019; 1474-919X
• DOI: 10.1111/j.1474-919X.2007.00735.x

We studied the inter-year and inter-sex variation of the post-fledging body mass development of Common Terns Sterna hirundo in 2000 and 2001 at the Banter See colony, northern Germany. Here, post-fledglings can be identified and weighed remotely and automatically by a transponder system that makes use of automated balances installed at the colony. Individuals were sexed with PCR amplification methods. After fledging, young generally continued to increase their mass. However, in 2000, the young did not significantly increase their mass during the post-fledging period. In 2001, conditions were more favourable and body mass increased continuously. Further, in 2001, male post-fledglings were significantly heavier than female post-fledglings. Once having left the colony area (on average 18-23 days after fledging in 2000, and 14-16 days after fledging in 2001), post-fledgling body mass had still not reached adult body mass. The longer a juvenile stayed at the colony, the higher was its final body mass, which if acting as a threshold level may control departure time. Neither brood size nor hatching order affected post-fledging mass or period. In the unfavourable year 2000, when many individuals were found dead after fledging, fledging age but not fledging mass was found to be a predictor of post-fledging survival before departure: individuals fledging when older had a lower survival probability. Our results stress the importance of the post-fledging period for body mass increase and survival prior to departure. The variation in post-fledging mass growth between years and between the sexes is discussed with respect to parental effort and a possible selective provisioning of sons over daughters.