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Survival patterns and density-dependent processes in breeding mallards Anas platyrhynchos
Kristianstad University, Department of Mathematics and Science. (Akvatisk biologi och kemi)ORCID iD: 0000-0003-2345-3953
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. , 39 p.
Series
Acta Universitatis agriculturae Sueciae, ISSN 1652-6880 ; 2007:12
Keyword [en]
broods, dabbling ducks, density dependence, ducklings, experiments, models, mortality, nest predation, regulation, survival
National Category
Ecology
Identifiers
URN: urn:nbn:se:hkr:diva-6782ISBN: 978-91-576-7311-4 (print)OAI: oai:DiVA.org:hkr-6782DiVA: diva2:327098
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
List of papers
1. Manipulated density of adult mallards affects nest survival differently in different landscapes
Open this publication in new window or tab >>Manipulated density of adult mallards affects nest survival differently in different landscapes
2007 (English)In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 85, no 5, 589-595 p.Article in journal (Refereed) Published
Abstract [en]

Breeding success in many birds including wildfowl is mainly determined by nest predation. Few studies address cues used by predators to find duck nests, and the same is true for spacing patterns that ducks might use to reduce predation. We designed a crossover experiment in agricultural and forested settings to test the assumption that nest predation rate is related to density of adult birds on a lake. We used introduced wing-clipped mallards (Anas platyrhynchos L., 1758) to increase local pair density and semi-natural nests to assess predation rate. Depredation patterns were analyzed by model fitting in program MARK, using introduction and landscape type as main effects and abundance of avian predators and wild waterbirds as covariates. Depredation was higher at agricultural lakes than at forest lakes. Nest survival decreased with increasing abundance of wild waterfowl, whereas it tended to increase with the abundance of "other waterbirds". There was a landscape-dependent effect of increased mallard pair density: positive at agricultural lakes and negative at forest lakes. Avian predators found 91% of depredated "known-predator" nests at agricultural lakes and 25% at forest lakes; mammals found 9% at agricultural lakes and 75% at forest lakes. The landscape-dependent density effect may in part be due to different predator communities in these landscape types.

Keyword
ARTIFICIAL DUCK NESTS, PREDATION RISK, HABITAT SELECTION, TEMPORAL, PATTERNS, WATERFOWL NESTS, CROW PREDATION, REAL NESTS, SUCCESS, PARASITISM, DYNAMICS
National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-196 (URN)10.1139/Z07-038 (DOI)000248223600001 ()0008-4301 (ISBN)
Available from: 2009-02-18 Created: 2009-02-11 Last updated: 2014-06-05Bibliographically approved
2. Within-season sequential density dependence regulates breeding success in mallards (Anas platyrhynchos)
Open this publication in new window or tab >>Within-season sequential density dependence regulates breeding success in mallards (Anas platyrhynchos)
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2005 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 108, no 3, 582-590 p.Article in journal (Refereed) Published
Abstract [en]

Density dependence in vital rates is a key issue in population ecology but remains largely unexplored experimentally. We studied breeding success, lake use, and prey availability in wild mallards Anas platyrhynchos on small nemoral lakes in a replicated, two-year cross-over experiment in which pair density was increased. The number of wild mallards that settled on lakes prior to introductions of extra pairs did not differ between control and introduction years. Introductions led to a lake-level reduction in the number of broods observed. However, the number of stage 2+ (almost fledged) ducklings did not differ between treatments, nor did lake utilization by nonbreeding adults, broods and ducklings. Prey resource availability differed greatly among lakes, but it did not correlate with breeding success. Partialling out the possible effect of food competition from wild adult nonbreeding mallards did not change this conclusion. Our study demonstrates sequential density dependence in breeding success; introductions caused a decrease in brood number, but despite fewer broods a similar number of nearly fledged ducklings were produced. We suggest that predation and/or lake change of broods soon after hatching created these patterns. We conclude that using a single and late measure of breeding success such as fledged birds can mask regulatory processes. Implications of density dependence and its relation to individual reproductive success are understood better if breeding success is decomposed into nest success, duckling survival and fledgling survival.

National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-710 (URN)10.1111/j.0030-1299.2005.13618.x (DOI)000226898200016 ()
Available from: 2009-04-02 Created: 2009-04-02 Last updated: 2014-06-05Bibliographically approved
3. Experimental evidence for density-dependent survival in mallard Anas platyrhynchos ducklings
Open this publication in new window or tab >>Experimental evidence for density-dependent survival in mallard Anas platyrhynchos ducklings
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2006 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 149, no 2, 203-213 p.Article in journal (Refereed) Published
Abstract [en]

It is unresolved to what extent waterfowl populations are regulated by density-dependent processes. By doing a 2-year crossover perturbation experiment on ten oligotrophic boreal lakes we addressed the hypothesis that breeding output is density dependent. Wing-clipped mallard (Anas platyrhynchos) hens were introduced with their own brood and then monitored for 24 days. Predicted responses were that per capita duckling and hen survival would be lower in high-density than in low-density treatments. Survival was evaluated by model fitting in program MARK. Density, year, and lake were used as main effects, while day after introduction, a weather harshness index, and presence of hens were covariates. Daily survival in ducklings was lower in the high-density treatment, but this effect was year dependent. The highest-ranking model for duckling survival also included a positive effect of duckling age and presence of hens, and a negative effect of harsh weather. Density did not affect female survival although there was a prominent year effect. The highest-ranking model for female survival also included negative effects of day after introduction and harsh weather. This is the first study to report density-dependent survival in experimentally introduced ducklings in a natural setting. Implications for population dynamics and management of harvested populations are far-reaching if such regulation occurs in some years, but not in others.

Keyword
Dabbling ducks, Duckling, Model, Population regulation, Waterfowl
National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-708 (URN)10.1007/s00442-006-0446-8 (DOI)000239735300003 ()16736185 (PubMedID)
Available from: 2009-04-02 Created: 2009-04-02 Last updated: 2014-08-01Bibliographically approved
4. Density-dependent nest predation: an experiment with simulated Mallard nests in contrasting landscapes
Open this publication in new window or tab >>Density-dependent nest predation: an experiment with simulated Mallard nests in contrasting landscapes
2008 (English)In: Ibis, ISSN 0019-1019, E-ISSN 1474-919X, Vol. 150, no 2, 259-269 p.Article in journal (Refereed) Published
Abstract [en]

Breeding success is a key element of animal population dynamics. In many taxa including birds, nest success, or the proportion of laid clutches that actually hatch, is mainly determined by predation. Previous research gives an inconsistent picture of the prevalence of density-dependent nest predation and one reason for this is the general lack of well-designed replicated experiments. Using simulated Mallard Anas platyrhynchos nests and a crossover design for 20 lakes in the nemoral and boreal biotic zones, we tested the predictions that nest survival is negatively density-dependent and that nest predation is higher in agricultural than in forested landscapes. Study day and daily abundance of waterfowl, other waterbirds, as well as avian predators were included as covariates in the analysis. Model fitting in program mark revealed a general negative effect of nest density on nest survival. In addition, nest survival rate was higher at forest lakes than at lakes in agricultural landscapes, irrespective of nest density. The only covariate producing model improvement was study day; older nests had higher survival rates than recently initiated ones. This is the first replicated lake-level experimental study showing that nest predation is density-dependent in waterfowl. The pattern was consistent between landscape types, implying that density-dependent nest predation may affect habitat choice and population dynamics over large parts of the Mallard's range.

Keyword
Fnctional response, nest age, nest survival rate, numerical response
National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-36 (URN)10.1111/j.1474-919X.2007.00772.x (DOI)000254414800005 ()
Available from: 2008-12-22 Created: 2008-12-22 Last updated: 2014-06-05Bibliographically approved
5. Survival estimates, mortality patterns, and population growth of Fennoscandian mallards Anas platyrhynchos
Open this publication in new window or tab >>Survival estimates, mortality patterns, and population growth of Fennoscandian mallards Anas platyrhynchos
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2008 (English)In: Annales Zoologici Fennici, ISSN 0003-455X, Vol. 45, no 6, 483-495 p.Article in journal (Refereed) Published
Abstract [en]

Long-term mallard capture-recapture data from Sweden and Finland were analyzed to describe temporal mortality patterns and reasons. We used program MARK and Seber models to estimate annual survival (S) and recovery (r) rates. Survival rates were used in a Monte Carlo simulation to evaluate the correspondence between observed and predicted annual population sizes of a Finnish sub-population. About 90% of recovered birds died from hunting. Most recoveries were from the hunting season, and more males than females were shot. Predation was the most common cause of natural mortality. Finnish capture-recapture data fitted best the global model in which survival and recovery vary with age and sex. Annual survival and recovery rates for adult and juvenile males and females were overlapping, ranging from 0.46 to 0.90 (survival) and 0.07 to 0.17 (recovery), whereas pulli had lower survival rates (0.21-0.42). Pulli that were successfully sexed at the time of ringing had higher recovery rates (female pulli: 0.23; male pulli: 0.32) than juveniles and adults. Density-dependent fledgling production was detected in the Finnish sub-population and was accounted for in the Monte Carlo simulation, which estimated predicted breeding population size quite well, although one of the observed annual values (2003) fell outside the 95% confidence limits.

National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-642 (URN)000262882600003 ()
Available from: 2009-03-18 Created: 2009-03-18 Last updated: 2016-04-01Bibliographically approved
6. Why are there so many empty lakes?: food limits survival of mallard ducklings
Open this publication in new window or tab >>Why are there so many empty lakes?: food limits survival of mallard ducklings
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2004 (English)In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 82, no 11, 1698-1703 p.Article 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.

National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-713 (URN)10.1139/z04-153 (DOI)000227497100003 ()
Available from: 2009-04-08 Created: 2009-04-02 Last updated: 2014-06-05Bibliographically approved
7. Ecological basis of sustainable harvesting: is the prevailing paradigm of compensatory mortality still valid?
Open this publication in new window or tab >>Ecological basis of sustainable harvesting: is the prevailing paradigm of compensatory mortality still valid?
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2004 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 104, no 3, 612-615 p.Article in journal (Refereed) Published
National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-714 (URN)10.1111/j.0030-1299.2004.12788.x (DOI)000189023900021 ()
Available from: 2009-04-02 Created: 2009-04-02 Last updated: 2014-06-05Bibliographically approved

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