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| 2. |
- Simmons, RE
(författare)
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Why don't all siblicidal eagles lay insurance eggs? The egg quality hypothesis
- 1997
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Ingår i: BEHAVIORAL ECOLOGY. - : OXFORD UNIV PRESS INC. - 1045-2249. ; 8:5, s. 544-550
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Several species of birds lay second eggs that are eliminated by the siblicidal behavior of the first-hatched chick. A widely accepted explanation for the occurrence of these second eggs is insurance against complete nest failure, However, if insurance is
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| 3. |
- Smith, Henrik G., et al.
(författare)
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Intrasexual competition among polygynously mated female starlings (Sturnus vulgaris)
- 1994
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Ingår i: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 5, s. 57-63
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Tidskriftsartikel (refereegranskat)abstract
- In southern Sweden, the starling (Sturnus vulgaris) has a variable mating system with some males mating monogamously and others attracting several females. Mating status affected the reproductive success of females: monogamous and primary females laid larger clutches and fledged more and heavier young than secondary females. This pattern was explained by female competition for male help, with the male primarily helping the offspring of highest value (i.e., the oldest brood). However, when the nesting attempt of the primary female failed, the success of the secondary female increased to the same level as that for primary and monogamous females. The success of the secondary female in terms of fledging success and fledgling size was higher when the secondary female hatched her eggs soon after the primary female. This was due to the fact that a male divided his effort between his broods when the age difference between broods was small
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| 4. |
- Berndtson, Eva, et al.
(författare)
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Campylobacter incidence on a chicken farm and the spread of Campylobacter during the slaughter process
- 1996
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 32:1-2, s. 35-47
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Tidskriftsartikel (refereegranskat)abstract
- To get a better understanding of the epidemiology of Campylobacter, a chicken farm was studied for 16 weeks with samplings in each flock weekly from input until the flock became colonized with Campylobacter or slaughtered. Samples were taken from fresh droppings and from drinkers during the rearing period, as well as from the environment in empty houses. The spread of Campylobacter during the slaughter process was also surveyed. No Campylobacter was found in samples from newly-hatched ol one-week-old chickens or their drinkers. All Hocks but one were colonized at two to five weeks of age. All Campylobacter isolates belonged to the same sero- and biotype; C. jejuni Penner 2. The spread of Campylobacter in the flock was rapid and usually all samples were positive once colonization had been proven. C. jejuni was isolated from flies in ante-rooms as well as from air in chicken units ill houses with positive chicken flocks. Samples were taken at slaughter when some of the Campylobacter positive Hocks from the farm were slaughtered. Campylobacter were isolated from all sampled equipment along the processing line, from the chicken transport crates to the chillers, as well as from the air.
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| 5. |
- Bruun, Måns, et al.
(författare)
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Polygynous male starlings allocate parental effort according to relative hatching date
- 1997
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 54, s. 73-79
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Tidskriftsartikel (refereegranskat)abstract
- In many polygynous bird species, males allocate most of their parental effort to their primary females’ broods. There are several hypotheses that may explain this: the relative reproductive value of the brood, the energetic demand of the brood, the genetic quality of the female and the certainty of fatherhood may all be higher for the primary females’ broods. Since these parameters may covary in nature, experiments are necessary to determine their importance. Bigynous male European starlings,Sturnus vulgarispredominantly incubated the eggs and fed the nestlings of their primary females. In an experiment we altered the order in which the clutches hatched by exchanging the primary and secondary females’ eggs before hatching. Even though experimental males mostly incubated their primary females’ clutches, they predominantly fed the nestlings of the secondary female. Experimental males fed secondary females’ nestlings significantly more than control males did. In fact, experimental males invested in their secondary females’ broods to the same extent as control males invested in their primary females’ broods. This result demonstrates that males use relative brood age to decide how to allocate their parental effort between their broods which has important implications for the evolution of the starling mating system.
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| 6. |
- Larsson, Kjell, et al.
(författare)
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Intraspecific nest parasitism and adoption of young in the barnacle goose : effects on survival and reproductive performance
- 1995
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Ingår i: Animal Behaviour. - : Elsevier. - 0003-3472 .- 1095-8282. ; 50:5, s. 1349-1360
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Tidskriftsartikel (refereegranskat)abstract
- DNA fingerprinting was used to determine the proportion of extra-pair young in a population of barnacle geese, Branta leticopsis, breeding in the Baltic area, Sweden. Of 137 analysed fledged young 17% were found to be extra-pair young. One or more extra-pair young were found in 27% of the 63 analysed families. The proportion of extra-pair young differed between years. No case of extra-pair fertilization was detected. All extra-pair young at fledgling originated either from intraspecific nest parasitism or from adoptions of foreign hatched young. Broods with extra-pair young at fledgling were significantly larger than broods without extra-pair young. However, the number of within-pair young did not differ significantly in broods with and without extra-pair young. Body mass, survival or subsequent reproductive performance did not differ between parents with and without extra-pair fledged young. Post-fledgling survival and age at first breeding were not significantly different between the three analysed classes of fledged young, i.e., within-pair young in families without extra-pair young, within-pair young in families with at least one extra-pair young, and extra-pair young. It is concluded that possible costs or benefits associated with caring for extra-pair fledged young are small or absent in this population.
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| 7. |
- Larsson, Kjell, et al.
(författare)
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Continuing growth of the Baltic barnacle goose population : Number of individuals and reproductive success in different colonies
- 1997
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Ingår i: Research on arctic geese. - : Norsk Polarinstitutt. - 8276661548 ; , s. 213-219
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Konferensbidrag (refereegranskat)abstract
- The Baltic barnacle goose population increased rapidly after 1971, when the first breeding attempt was observed off the eastern coast of Gotland, Sweden. In 1997, about 3,990 pairs bred along the Baltic coast in Sweden, western Estonia and southern Finland. The majority of these pairs, about 3,490 pairs, were found breeding in colonies along the eastern coasts of Gotland and Oland, Sweden. The total population size at the end of July in 1997 was estimated to be approximately 17,000 individuals. The production of fledged young per breeding pair was negatively related to the size of colonies, although the production varied greatly among different colonies. In 1997, the largest Baltic colony hosted more than 50% of the total number of breeding pairs but produced less than 15% of the total number of fledged young. This finding points out the need to consider different colonies as separate demographic units when studying regulation processes in populations of colonially breeding geese. In the future, we find it most probable that the Baltic population will continue to increase and that new colonies will be established. We also expect that the number of Baltic barnacle geese eventually will be limited by the availability of predator-safe grazing grounds with short, protein rich grass which families with newly hatched goslings are dependent on.
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| 8. |
- Smith, Henrik G.
(författare)
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Seasonal Decline in Clutch Size of the Marsh Tit (Parus palustris) in Relation to Date-Specific Survival of Offspring
- 1993
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Ingår i: Auk. - : Oxford University Press (OUP). - 0004-8038. ; 110, s. 889-899
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Tidskriftsartikel (refereegranskat)abstract
- This paper documents and evaluates seasonal trends in reproductive performance in the Marsh Tit (Parus palustris) in southern Sweden. Clutch size decreased for nests started later in the season. This pattern held true both for second-year and older females when analyzed separately. Individual females adjusted clutch size in relation to the relative time of season they produced a clutch a particular year. The seasonal decline in clutch size was also evident for clutches produced in the same territory at different parts of the season in different years. Females breeding for several years demonstrated a high consistency in relative laying date and clutch size. The same was not true for males or for territories. The length of the incubation period normally decreased with season. Nestling mass and survival did not show any systematic seasonal trend. Nest predation was probably more prevalent late in the season. Fledglings that hatched later had poorer survival until autumn. This effect was evident for males, but not for females. Hatching date did not influence fledglings' survival to the next breeding season, but sample sizes were small. I suggest that the Marsh Tit adjusts clutch size to the survival probability of nestlings, this being affected by the probability of nest predation and by fledgling survival. Hence, late-laying females are not prepared to accept as large reproductive costs as early laying females.
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| 9. |
- Forsell, Johan, et al.
(författare)
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Role of the pineal organ in the photoregulated hatching of the Atlantic halibut
- 1997
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Ingår i: International Journal of Developmental Biology. - 0214-6282. ; 41:4, s. 591-595
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Tidskriftsartikel (refereegranskat)abstract
- The timing of hatching in the Atlantic halibut (Hippoglossus hippoglossus) has been suggested to be regulated by environmental light conditions. However, the photosensory organ that perceives the triggering light has not been identified. In the present study, we investigated the morphogenesis of the pineal organ and the neurochemical differentiation of photoreceptors in the pineal organ and the retina of the Atlantic halibut during embryonic development. Immunocytochemical techniques were used for detection of integral protein components of the phototransduction process: opsins, arrestin (S-antigen) and α-transducin. We also studied the expression of serotonin (5-HT), a precursor of the neurohormone melatonin known to be synthesized by pineal photoreceptors. In the pineal anlage, opsin immunoreactive (ir) cells appear at 11 days post-fertilization (pf), arrestin, α-transducin and serotonin ir cells appear at 14 days pf; hatching took place 15 days pf. The retina contained no immunoreactive cells in embryos or in newly hatched larva. During this period, the pineal anlage is morphologically discernible only as a wedge-shaped region in the diencephalic roof, where elongated cells are aligned with their long axes converging toward a centrally located presumptive pineal lumen. The results show that the pineal photoreceptors contain serotonin and molecules involved in the phototransduction cascade before hatching. We suggest that the pineal organ has the capacity to perceive and mediate photic information before hatching in halibut embryos, and may thereby influence the timing of hatching.
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| 10. |
- Larsson, Kjell, et al.
(författare)
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Population dynamics of the barnacle goose Branta leucopsis in the Baltic area : density-dependent effects on reproduction
- 1994
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Ingår i: Journal of Animal Ecology. - : British Ecological Society. - 0021-8790 .- 1365-2656. ; 63:4, s. 954-962
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Tidskriftsartikel (refereegranskat)abstract
- 1. The three largest breeding colonies of barnacle geese Branta leucopsis in the Baltic area were studied from their natural establishments in 1971, 1982 and 1987, respectively, to 1993. The number of breeding pairs increased from one pair in 1971 to 1550, 225 and 150 pairs in the largest, second largest, and third largest colonies, respectively, in 1993. 2. Data on clutch size and number of hatched and fledged young were collected from the beginning or the middle of the 1980s. In the largest colony most data on reproductive success were obtained from observations of individually marked geese. 3. Mean clutch size differed among years and colonies. However, there was no trend for decreasing mean clutch size with increasing density in any of the colonies. Hatching success did not decrease with increasing density in the largest colony. 4. The production of fledged young per breeding pair declined drastically in the largest colony as numbers of breeding pairs rose. This decline was mainly caused by an increasing proportion of the breeding pairs failing to produce any fledged young at all. 5. The relative contribution of the smaller colonies to the total production of fledged young in the Baltic area increased considerably over the study years. In 1993, colony 2 hosted only about 13% of the number of breeding pairs in colonies 1 and 2 combined, but it produced about 38% of the fledged young. 6. Our results point out the need to study populations of colonially nesting geese on a colony by colony basis in order to detect density-dependent effects on reproduction.
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