| 1. |
- Allander, Klas, et al.
(författare)
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Temporal variation and reliability of blood parasite levels in captive Yellowhammer males Emberiza citrinella
- 1997
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Ingår i: Journal of Avian Biology. - : JSTOR. - 0908-8857 .- 1600-048X. ; 28:4, s. 325-330
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Tidskriftsartikel (refereegranskat)abstract
- The temporal variation of blood parasites in captive Yellowhammer males was studied in order to investigate possible costs of parasites. Birds were caught in the wild in early April and kept in aviaries during the study period. Blood samples were taken, body mass measured, and moult was scored twelve times for the same individuals from April to October. Blood parasites were detectable in smears during the whole study period with an intensity peak coinciding with breeding in the wild. Young birds had more parasites and a consistently higher body mass than older birds. There was no relationship between parasite intensity and mass in older birds but possibly one in young birds. Parasites did not seem to affect moult in either age class. Repeatability of parasite counts of smears from the same individual was very high and smears are therefore a reliable method for estimating parasite intensity. We conclude that blood parasites are probably most severe during, but occur in their hosts long after, the breeding season. Possible costs of parasites outside the breeding season require further study.
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| 2. |
- Ericson, Per G P, 1956-
(författare)
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The skeletal evidence for a sister-group relationship of anseriform and galliform birds - A critical evaluation
- 1996
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Ingår i: Journal of Avian Biology. - : JSTOR. - 0908-8857 .- 1600-048X. ; 27:3, s. 195-202
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Tidskriftsartikel (refereegranskat)abstract
- The osteological basis for the proposed close phylogenetical relationship of anseriform and galliform birds is evaluated and found to be very weak. Out of eleven postulated synapomorphies in cranial morphology (Cracraft 1988), three must be excluded since they express variation that is already covered by any of the other eleven characters. Another six of the postulated synapomorhies either cannot be verified to occur in most anseriforms and galliforms, or have a wide distribution outside this group. A re-analysis of the combined morphological and biochemical data set of Cracraft and Mindell (1989) with the questionable osteological characters excluded, does not corroborate an anseriform-galliform sister-group relationship, but leaves the Neognathae unresolved.
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| 3. |
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| 4. |
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| 5. |
- Bensch, Staffan
(författare)
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The cost of polygyny - definitions and applications
- 1997
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Ingår i: Journal of Avian Biology. - 0908-8857. ; 28:4, s. 345-352
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Tidskriftsartikel (refereegranskat)abstract
- The polygyny threshold model was introduced in the 1960s in order to explain why females in some species choose to mate vith already mated males. Since then, a number of complementary or alternative hypotheses have been suggested. By using a hierarchical testing approach Searcy and Yasukawa (1989) organised the models that proposed to explain the maintenance of territorial polygyny. Here, I point out that there is no true way to organise the models, and that the organisation itself may influence which explanation the observations mill support. In particular, I discuss Searcy and Yasukawa's distinction between cost and no-cost models. As an alternative to the hierarchical approach I suggest careful comparisons of those variables that inflict costs of sharing with those that provide compensation. While the hierarchical approach may put very similar systems in different model families, a cost and benefit evaluation might instead show that the difference is quantitative rather than qualitative. Also, an identical cost of polygyny can arise from several different combinations of costs of sharing and benefits of sharing. Hence, the hierarchical approach may put systems with different mechanisms behind polygyny into the same model family.
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| 6. |
- Dufva, R
(författare)
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Blood parasites, health, reproductive success, and egg volume in female Great Tits Parus major
- 1996
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Ingår i: JOURNAL OF AVIAN BIOLOGY. - : MUNKSGAARD INT PUBL LTD. - 0908-8857. ; 27:1, s. 83-87
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The effect of different genera of blood parasites on female Great Tits Parus major was studied in central Sweden. Haemoproteus, Leucocytozoon, Hepatozoon, Plasmodium and Trypanosoma were found, but only the last mentioned had any measurable effect on the
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| 7. |
- Hoglund, J, et al.
(författare)
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A non-lekking population of black grouse Tetrao tetrix
- 1997
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Ingår i: JOURNAL OF AVIAN BIOLOGY. - : MUNKSGAARD INT PUBL LTD. - 0908-8857. ; 28:2, s. 184-187
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In a two-year study of an area in central Sweden a population of Black Grouse Tetrao tetrix was found in which displaying males were not clustered on leks. The study area which covered approximately 44 km(2) contained 19 and 30-35 displaying males in 1995
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| 8. |
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| 9. |
- Langefors, Åsa, et al.
(författare)
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Extra-pair fertilizations in the Sedge Warbler
- 1998
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Ingår i: Journal of Avian Biology. - 0908-8857. ; 29:2, s. 134-144
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Tidskriftsartikel (refereegranskat)abstract
- Parentage of 201 young (from 44 broods) in a population of Sedge Warblers Acrocephalus schoenobaenus in South Central Sweden, 1990-1992, was determined by using multilocus DNA fingerprinting. The frequency of extra-pair young (EPY) was 7.5% and they occurred in 23% of the broods. For 11 out of 15 extra-pair young we could identify the true father; in all of the cases he was a close neighbour. Among ten broods with extra-pair young, nine contained only one extra-pair sire and the remaining brood two extra-pair sires. The frequency of EPF varied among years (1.8-11.8%). The seasonal timing of broods with and without extra-pair young did not differ, and the occurrence of extra-pair fertilizations (EPF) was not related to the length of the pair male's mate-guarding period. EPF were not related to breeding synchrony (estimated as the mean number of fertile females per day during a female's fertile period). Pairs whose nests contained extra-pair young had more territories within 100 m of their nest than pairs without extra-pair young. Females that engaged in EPF had fewer attractive (i.e. singing) males to choose among the day before and at the day they formed their pair bend. Moreover, in all but one case the extra-pair male was not singing (i.e. not available as pair mate) the day the EPF-female settled. Males that fertilized extra-pair young tended to arrive earlier and to have higher pairing success than both males that were cuckolded and other males. Hence, female Sedge Warblers engaged in extra-pair fertilizations with attractive male neighbours. These results are consistent with the hypotheses that females participating in EPF are seeking genetic benefits to their offspring, but we cannot exclude the alternative explanation that attractive males are more efficient in forcing females to accept EPF.
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