Seasonal distribution and timing of migration of Cormorants<i>Phalacrocorax carbo sinensis</i>breeding in Denmark

Bregnballe, Thomas; Frederiksen, Morten; Gregersen, J.

doi:10.1080/00063659709461062

Cited by 41 publications

(32 citation statements)

References 2 publications

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“…We therefore feel it most likely that the male-biased sex ratio is caused by a higher male immature survival. Wintering areas of male and female great cormorants overlap widely throughout Europe but, on average, males winter further north, closer to the breeding areas (van Eerden & Munsterman 1995;Bregnballe et al 1997). Conceivably, males, which are, on average, ca.…”

Section: Discussionmentioning

confidence: 99%

“…First reproduction can a¡ect ¢tness in subsequent years through e¡ects on both survival and future reproduction (Viallefont et al 1995), and there should be evolutionary pressure to minimize the net ¢tness costs by choosing a suitable place and time to breed for the ¢rst time. Several hypotheses have been proposed to explain the choice of where to join the breeding population: the conspeci¢c-attraction hypothesis (Stamps 1988;Reed & Dobson 1993) states that pre-breeders use the presence of breeders of the same species as a cue in breeding-habitat selection, and thus that dense populations or large colonies attract many new breeders; the conspeci¢c-reproductive-success hypothesis (Boulinier & Lemel 1996;Boulinier & Danchin 1997) states that pre-breeders prospect in several breeding patches and preferentially settle in those where reproductive success is high, normally in the subsequent breeding season (Danchin et al 1998;Brown et al 2000).…”

Section: Introductionmentioning

confidence: 99%

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Conspecific reproductive success affects age of recruitment in a great cormorant, Phalacrocorax carbo sinensis , colony

Frederiksen

Bregnballe²

2001

Proc. R. Soc. Lond. B

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Few studies have addressed the proximate factors a¡ecting the age at which individuals of long-lived bird species are recruited into the breeding population. We use capture^recapture analysis of resightings of 16 birth cohorts of colour-ringed great cormorants, Phalacrocorax carbo sinensis, in a Danish colony to assess the evidence for two hypotheses: conspeci¢c attraction (earlier recruitment when the colony is large) and conspeci¢c reproductive success (earlier recruitment following years of high breeding success). For both males and females, conspeci¢c reproductive success was the most important covariate explaining the interannual variation in age of recruitment; colony size was also important for females. These covariates explained nearly 60% of the year-to-year variation for both sexes. The age of recruitment increased for cohorts born after 1990, and this increase was correlated with a decline in breeding success in the colony; we interpret this as an indirect and delayed density-dependent e¡ect. Females were recruited earlier than males (mean age of recruitment for cohorts born before 1990: 2.98 years versus 3.53 years); the most plausible reason for this is a skewed sex ratio in favour of males in the adult population. Recruitment of males may thus, to some extent, be constrained by the availability of females. This study provides the ¢rst evidence that conspeci¢c reproductive success can a¡ect the age at which individual birds start to breed.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Conspecific reproductive success affects age of recruitment in a great cormorant, Phalacrocorax carbo sinensis , colony

Frederiksen

Bregnballe²

2001

Proc. R. Soc. Lond. B

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“…The area from which recoveries were included was restricted to Denmark, south Sweden and northeast Germany (for definitions of borders see Bregnballe & Rasmussen 2000). This region constitutes the main post-breeding area for Danish cormorants (Bregnballe et al 1997a, Bregnballe & Rasmussen 2000. It is also the area in Europe, together with The Netherlands and Germany/Switzerland, which has the highest pro-portion of individuals recovered drowned (Bregnballe 1999).…”

Section: Methodsmentioning

confidence: 99%

“…There are at least three different explanations for this difference. First, the number of bird-days spent in regions where pound net fishing is widespread is higher for first-year birds than for older birds during the peak pound net fishing season (Bregnballe et al 1997a, Bregnballe 1999, Bregnballe & Rasmussen 2000. However, we estimate that the difference in distribution and timing of migration cannot explain more than 5-10% of the age-related difference in the risk of drowning.…”

Section: Risk In Relation To Agementioning

confidence: 99%

Net-entrapment of great cormorants Phalacrocorax carbo sinensis in relation to individual age and population size

Bregnballe

Frederiksen

2006

Wildlife Biology

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Population control of great cormorants Phalacrocorax carbo sinensis has been suggested as a tool to mitigate fish losses by cormorants foraging in pound nets, gill nets and fykes. The objective of our study was to quantify the difference between first-year birds and older birds in the risk of drowning in fishing gear, and to explore the influence of population size on the proportion of individuals drowning. An index of the proportion of first-year birds and older birds that drowned was obtained for cormorants ringed in the Danish Vorsø colony using resightings of colour-ringed individuals and ring recoveries of individuals found dead. First-year birds were approximately 10 times more likely to drown than older birds. We used ring recoveries of cormorants ringed in Denmark and found dead in Denmark, North Germany and South Sweden (i.e. in the main postbreeding area) to reveal changes over a 25-year period in the proportion drowned among those recovered. Among first-year birds the proportion drowned declined from 66% in 1978-1984 to 24% in 2000-2002, and among older birds the proportion declined from 46% in 1978-1984 to 26% in 1999-2002 . During 1978-2000, breeding numbers in Denmark increased from 1,400 to 42,500 nests, and the proportion of cormorants drowned among those recovered was significantly negatively correlated with population size. This suggests that the proportion of the population foraging in nets declined as the population increased. The damage caused by cormorants foraging in pound nets is, therefore, unlikely to decrease in proportion to reductions in population size reached through population control.

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“…-The establishment of winter sites: This phase takes place between December and January and the population steadily decreases. A decrease in recorded population in December is probably due to migrations to warmer areas in the southern Europe (Bregnballe et al, 1997). It is generally confirmed in January when the population is well-established in wintering sites.…”

Section: > Movements During the Wintermentioning

confidence: 58%

Development of great cormorant population (Phalacrocorax carbo sinensis) in North-East France – synthesis of long term monitoring (1997–2008)

Collas

Burgun

2011

Knowl. Managt. Aquatic Ecosyst.

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Seasonal distribution and timing of migration of CormorantsPhalacrocorax carbo sinensisbreeding in Denmark

Cited by 41 publications

References 2 publications

Conspecific reproductive success affects age of recruitment in a great cormorant, Phalacrocorax carbo sinensis , colony

Conspecific reproductive success affects age of recruitment in a great cormorant, Phalacrocorax carbo sinensis , colony

Net-entrapment of great cormorants Phalacrocorax carbo sinensis in relation to individual age and population size

Development of great cormorant population (Phalacrocorax carbo sinensis) in North-East France – synthesis of long term monitoring (1997–2008)

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