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Why are there so many empty lakes?: food limits survival of mallard ducklings
Kristianstad University, Department of Mathematics and Science. (Akvatisk biologi och kemi)ORCID iD: 0000-0003-2345-3953
Kristianstad University, Department of Mathematics and Science. (Akvatisk biologi och kemi)
Department of Animal Ecology, Swedish University of Agricultural Sciences, Umeå.
Finnish Game and Fisheries Research Institute, Joensuu Game and Fisheries Research.
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2004 (English)In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 82, no 11, p. 1698-1703Article in journal (Refereed) Published
Abstract [en]

Food is an important factor affecting survival in many bird species, but this relationship has rarely been explored experimentally with respect to reproductive output of precocial birds. In a field experiment we tested the hypothesis that food abundance limits reproductive output in breeding dabbling ducks. Onto 10 oligotrophic lakes in northern Sweden we introduced one wing-clipped female mallard (Anas platyrhynchos L., 1758) and a brood of 10 newly hatched ducklings, and survival was monitored for 24 days. Food was added ad libitum at five of the lakes, but not at the other five. Duckling survival was best modelled to include a treatment effect, with higher survival on lakes with food added, and a negative effect of harsh weather. As expected, duckling survival increased nonlinearly with age. Only one female remained on control lakes after 24 days, whereas four remained on lakes with food added. This is the first experimental demonstration that food may limit survival and reproductive output in breeding precocial birds. We argue that food limitation may be one reason why duckling mortality is high and why many lakes throughout the Holarctic have no breeding dabbling ducks.

Place, publisher, year, edition, pages
2004. Vol. 82, no 11, p. 1698-1703
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:hkr:diva-713DOI: 10.1139/z04-153ISI: 000227497100003OAI: oai:DiVA.org:hkr-713DiVA, id: diva2:210568
Available from: 2009-04-08 Created: 2009-04-02 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Survival patterns and density-dependent processes in breeding mallards Anas platyrhynchos
Open this publication in new window or tab >>Survival patterns and density-dependent processes in breeding mallards Anas platyrhynchos
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Measuring and assessing vital rates such as births and deaths are prerequisites for understanding population dynamics. Vital rates may be affected by the density of individuals, even though the importance of density dependence on population dynamics has been debated for a long time. The mallard Anas platyrhynchos is one of the foremost game species in the Holarctic, with millions of birds in hunters’ bags annually. Still, basic knowledge about regulation of mallards’ vital rates is poor, and experimental studies on this topic are rare.

In this thesis I have studied survival patterns and density dependence in mallards breeding in Sweden and Finland. Long-term ringing data from both countries were analysed for mortality patterns and causation, as well as for e.g. survival rate estimation. Most of the studies were, though, experiments run over two years involving manipulations of the density of nests, broods and/or adults, in southern and northern Sweden, comprising different biotic regions. Common response variables were survival of nests, ducklings and hens, mainly analysed with program MARK.

About 90% of the recovered mallards in Finland and Sweden were hunting kills. However, survival rates were high, ranging from 0.66 to 0.81 for most groups (sex*age). The generality of density dependence was evident since such processes were detected in all studies. Consequently, depredation rate was higher in high nest density compared to low nest density. Survival of ducklings was density-dependent in both boreal and nemoral biotic regions, with food limitation being evident in the former region but not in the latter. In spite of their generality, density-dependent patterns varied within as well between years, and for nest predation rates also between landscape types.

The findings about density dependence in breeding mallards in this thesis are novel since they are based on experiments. They are potentially of general interest for management because they embrace a variety of lakes in two geographically distant areas, each being representative for large temperate areas in the northern hemisphere. Detection of density dependence at the local scale may be important at larger scales, too, following the principle of ‘ideal preemptive distribution’ in a source-sink dynamic system.

Place, publisher, year, edition, pages
Umeå: Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, 2007. p. 39
Series
Acta Universitatis agriculturae Sueciae, ISSN 1652-6880 ; 2007:12
Keywords
broods, dabbling ducks, density dependence, ducklings, experiments, models, mortality, nest predation, regulation, survival
National Category
Ecology
Identifiers
urn:nbn:se:hkr:diva-6782 (URN)978-91-576-7311-4 (ISBN)
Public defence
2007-03-23, Sveriges Lantbruksuniversitet, Alnarp, 09:00 (English)
Opponent
Supervisors
Available from: 2010-08-24 Created: 2010-06-28 Last updated: 2014-06-05Bibliographically approved

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Gunnarsson, GunnarElmberg, Johan

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