Growth and demography of a re‐introduced population of White‐tailed Eagles Haliaeetus albicilla

• Published in: Ibis
• Main Authors: EVANS, RICHARD J., WILSON, JEREMY D., AMAR, ARJUN, DOUSE, ANDREW, MACLENNAN, ALISON, RATCLIFFE, NORMAN, WHITFIELD, D. PHILIP
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2009
• Subjects: Norway; Haliaeetus albicilla
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.2009.00908.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.2009.00908.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.2009.00908.x

White‐tailed Eagles Haliaeetus albicilla became extinct in Britain in 1918 following prolonged persecution. Intensive conservation efforts since the 1970s have included the re‐introduction of the species to Britain through two phases of release of Norwegian fledglings in western Scotland in 1975–85 and 1993–98. Population growth and breeding success have been monitored closely to the present day, aided by the use of patagial tags to individually mark most released birds as well as a high proportion of wild‐bred nestlings. This study reviews the growth and demography of this re‐introduced population, and makes comparisons with other European populations. For the first time, we compare the demographic rates of released and wild‐bred birds in the Scottish population. Breeding success in the Scottish population has increased over time as the average age and experience of individuals in the population have increased, and success tends to be higher where one or both adults are wild‐bred. Current levels of breeding success remain low compared with some other populations in Europe, but similar to those in Norway where weather conditions and food availability are likely to be most similar. Survival rates in Scotland are similar to those recorded elsewhere, but survival rates of released birds are lower than those of wild‐bred birds, especially during the first 3 years of life. Despite the effect of lower survival rates of released birds in limiting overall population growth rate, the recent rate of growth of the Scottish population remains high relative to other recovering populations across Europe. Differences in demographic rates of wild‐bred and released birds suggest that in future re‐introduction programmes, steps to maximize the success and output of the earliest breeding attempts would help ensure the most rapid shift to a population composed largely of wild‐bred birds, which should then have a higher rate of increase.