All breeding individuals of a socially polygynous population of great reed warblers at Lake Kvismaren, southern Central Sweden have been monitored since 1983. Based on a comprehensive data set of traits and fates of each territorial male and breeding female, we are able to study what determines breeding success in the population. This includes studying female mate choice, causes of and responses to nest predation, and phenotypic variation that affect breeding success. Since 1987, we have collected blood samples from all adults and chicks in the area that now are used for genetic analyses. Based on this extensive genetic material from the population, we are able to determine the genetic parentage of chicks allowing us to build a very good pedigree as well as identify extra-pair young and determine their true parents.
Song is a key factor to understand the behaviours and life histories of passerine birds. Research over the last 20-30 years have shown that song produced by male birds is important both in male-male competition over territories and for female attraction. We have been studying song in great reed warblers since 1985. In Kvismaren, great reed warbler males spend the entire daylight period producing song until pairing with a female. We have found that male song repertoire size (i.e. number of different sounds a male sings) is an important trait predicting his harem size (number of breeding females on his territory) and his extra-pair fertilization success. Male song repertoire size increases with age and is higher among males hatched in our study area. It also seems to reflect genetic qualities because males with larger song repertoire sizes produce offspring with higher post fledging survival.
We are presently exploring the song of the great reed warbler further by setting up a semi-automated way to measure song complexity of individual birds. Also, we use pedigree-based analyses to understand sex-specific selection and heritability of polygyny.
Hansson B, Bensch S, Hasselquist D (2000) Patterns of nest predation contribute to polygyny in the great reed warbler. Ecology, 81, 319-328.
Hansson B, Bensch S, Hasselquist D (2004) Do female great reed warblers seek extra-pair fertilizations to avoid inbreeding? Proceedings of the Royal Society, London, Series B (Suppl.), B 271, S290-S292.
Hasselquist D (1998) Polygyny in the great reed warbler: a long-term study of factors contributing to male fitness. Ecology, 79, 2376-2390.