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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Age-specific production of young and lifetime reproductive success of Sparrowhawks in Vendsyssel, northern Denmark
Auteurs :	Jan Tottrup Nielsen, Auteur
Type de document :	Article
Dans :	Dansk Ornitologisk Forenings Tidsskrift (99(4) 2005)
Article en page(s) :	209-217
Langues:	Anglais
Résumé :	Data were collected during 1977-1997 in a 2417 km(2) study area in Vendsyssel (see Nielsen 2004 and 2005 for details). The females were identified, and their age determined, on basis of shed feathers, and the length of primary #5 was used as an index of body size. Females the feathers of which were no longer found were supposed to have died. Clutch initiation (date of first egg) was calculated from nestling age at ringing, and clutch size was estimated as the number of surviving and dead young, plus any unhatched eggs (whole or broken) found. Throughout, reproduction is given in terms of fledged young.With females grouped as 'adult' (2 years old or more) and 1-year old, adult females laid in 96.7% of 1099 cases (female-seasons), 1-year olds in 85.4% of 268 cases. The adults produced 4.87 +/- 0.66 SD eggs per clutch (n=712) and 3,18 1,94 fledglings per laid clutch (n=1036) (4.00 per successful brood). 1-year old females produced 3.94 +/- 0.82 eggs per clutch (n=149) and 1.95 +/- 1.85 fledglings per laid clutch (n=224) (3.14 per successful brood). In addition to the larger clutches, the proportion of failed breeding attempts was lower in adults (20%) than in 1-year old females (38%). Pairs where both mates were adult produced more fledglings than pairs where one or both mates were 1 year old.The age-specific reproduction of females is shown in Fig. 1, where an increase is apparent until the age of 4-6 years, most marked between age I and age 2; after the age of 6-7 years, a decreasing performance is suggested.The lifetime reproductive success (LRS) of 232 females is shown in Fig. 2. Almost one quarter (52) of these females failed to produce any young, while the rest fledged between 1 and 40 young; 19% of the females produced 50% of the young. Life span was an important determinant of LRS (Fig. 3). In total, the females produced 1518 fledglings (6.54 per female, 8.43 per productive female). The age at which a female starts breeding appears to be relatively unimportant for her LRS, provided that she survives for some years (Table 5-6), but postponing breeding significantly increases the risk of never producing any offspring, considering the relatively high mortality rate of Sparrowhawks. A clear relationship between female body size and longevity, and LRS, appears from Fig. 4.

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