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Titre :	Productivity of the Black-legged Kittiwake Rissa tridactyla required to maintain numbers (2017)
Auteurs :	J. C. Coulson, Auteur
Type de document :	Article
Dans :	Bird Study (64(1) janvier 2, 2017)
Article en page(s) :	84-89
Résumé :	Capsule: To maintain the breeding numbers in Britain, Black-legged Kittiwakes Rissa tridactyla need to produce a mean of 0.8–1.5 fledged young per year.Aims: To obtain a new estimate for the number of young Kittiwakes fledged per pair required to maintain breeding numbers in Britain in the period 1985–2015 based on field data.Methods: The annual values of productivity in the River Tyne area of northeast England are compared with the long-term increases in numbers of breeding pairs in that area. Regressions between the annual productivity and the corresponding change in breeding numbers at 12 sites in Britain are used for the periods 1985–2000 and 15 sites for 2000–15.Results: A long series of records of the annual productivity of Kittiwakes, where breeding pairs increased progressively over 61 years, showed that an annual productivity of 1.5 young fledged per pair was an extremely rare event. Over the periods 1985–2000 and 2000–15 regressions of the change in breeding numbers against mean annual productivity for 15 sites indicated that about 0.8 fledglings per pair were needed to maintain breeding numbers and this value remained unchanged over the 30 years, suggesting that adult mortality rates had not changed over this period of time.Conclusion: The decline of Kittiwakes in Britain has occurred because fewer than 0.8 chicks per pair have been fledged at many sites in recent years. The mortality rate of adult Kittiwakes breeding in Britain 1985–2015 does not indicate an increase over time and so is unlikely to have been a major contributor to the decline in breeding numbers.
En ligne :	http://dx.doi.org/10.1080/00063657.2016.1274286

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