Age at first breeding and fitness in goshawk <i>Accipiter gentilis</i>

Krüger, Oliver

doi:10.1111/j.1365-2656.2005.00920.x

Cited by 90 publications

(135 citation statements)

References 51 publications

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“…On the other hand, we also obtained support for the hypothesis of differential selection of goshawk phenotypes: those birds best able to catch pigeons when young tended to live longest (see figure 2b). Empirical data support the finding that differential recruitment and/or mortality patterns play a role in goshawks; recruitment age is known to vary in this species (review: Rutz et al in press), and mortality rates are comparatively high and decrease steeply with age (Bijlsma 1993;Kenward et al 1999;Krü ger 2005). We were unable to test the effort hypothesis (Forslund & Pärt 1995), because we lacked direct measures of individual hunting skills (e.g.…”

Section: Discussionmentioning

confidence: 91%

“…The method is routinely used in goshawk population studies (for further methodological details, see Kü hnapfel & Brune 1995;Rust & Kechele 1996;Bijlsma 1997), including those that are concerned with age-related trends in breeding performance (e.g. Nielsen & Drachmann 2003;Risch et al 2004;Krü ger 2005).…”

Section: Methodsmentioning

confidence: 99%

“…Male hawks are responsible for providing their females and, later in the season, their young with food (reviews: Glutz von Blotzheim et al 1971;Cramp & Simmons 1980). Goshawks hunt agile avian prey (review: Rutz et al in press), and we hypothesized that young males may lack skills for efficient foraging, which would explain their poor breeding performance (see Krü ger 2005). The feral pigeon Columba livia is the principal avian prey of most European goshawk populations (Rutz et al in press), and, according to recent independent studies, the use of pigeons may significantly enhance fitness in this raptor (Krü ger & Stefener 1996;C.…”

Section: Introductionmentioning

confidence: 99%

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Age-dependent diet choice in an avian top predator

2005

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Age-dependent breeding performance is arguably one of the best-documented phenomena in ornithology. The existence of age-related trends has major implications for life-history theory, but the proximate reasons for these patterns remain poorly understood. It has been proposed that poor breeding performance of young individuals might reflect lack of foraging skills. We investigated this possibility in a medium-sized, powerful raptor-the northern goshawk Accipiter gentilis. Male goshawks are responsible for providing their females and their offspring with food. We hypothesized that young males may generally show poor breeding performance or even delay breeding, because they lack the experience to hunt efficiently-especially, their principal avian prey, the feral pigeon Columba livia. Our study exploited a rare 'natural experiment', the expansion phase of an urban population, where intraspecific interference was negligible and many young males bred successfully. This enabled us to examine the improvement of foraging skills in a larger sample of young individuals, and in more controlled conditions than usually possible. Using data from individually identified male breeders, we show that, consistent with our hypothesis, the proportion of pigeons in the diet increased significantly with male age, for at least the first three years of life. Other studies have shown a parallel increase in productivity, and a positive effect of a pigeon-rich diet on brood size and nestling condition, stressing the potential fitness relevance of this prey species for goshawks. Our results suggest a causal link between patterns of age-dependence in foraging ecology and reproductive performance. Furthermore, our study is, to our knowledge, the first demonstration that prey choice of breeders, which might reflect individual hunting skills, is age-dependent in a raptor.

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Section: Discussionmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Age-dependent diet choice in an avian top predator

2005

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“…Although density-dependent effects have been recorded in many populations (for example, Jorgenson et al 1997;Bennetts et al 2000;Kruger 2005;Stewart et al 2005), effects in the red deer population of the North Block of the Isle of Rum, Scotland are particularly well characterized thanks to long-term monitoring of life histories. Previous work has shown that age at primiparity, birth date and inter-birth interval increased with population density, while female fecundity and calf over-winter survival declined (Clutton-Brock et al 1982;Kruuk et al 1999a;Clutton-Brock & Coulson 2002).…”

Section: Introductionmentioning

confidence: 99%

Individual differences, density dependence and offspring birth traits in a population of red deer

et al. 2008

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Variation between individuals is an essential component of natural selection and evolutionary change, but it is only recently that the consequences of persistent differences between individuals on population dynamics have been considered. In particular, few authors have addressed whether interactions exist between individual quality and environmental variation. In part, this is due to the difficulties of collecting sufficient data, but also the challenge of defining individual quality. Using a long-established study population of red deer, Cervus elaphus, inhabiting the North Block of the Isle of Rum, and three quality measures, this paper investigates how differences in maternal quality affect variation in birth body mass and date, as population density varies, and how this differs depending on the sex of the offspring and the maternal quality measure used. Significant interactions between maternal quality, measured as a hind's total contribution to population growth, and population density are reported for birth mass, but only for male calves. Analyses using dominance or age at primiparity to define maternal quality showed no significant interactions with population density, highlighting the difficulties of defining a consistent measure of individual quality.

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“…In this increasing population, a possible explanation of deferred breeding may be related to the increase in density (Donázar et al 2005, Carrete et al 2006a, that could affect age at maturity (Krüger 2004).…”

mentioning

confidence: 99%