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| 2. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Gräsandens liv och död
- 2008
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Ingår i: Svensk Jakt. ; :10, s. 82-84
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 3. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Manipulated density of adult mallards affects nest survival differently in different landscapes
- 2007
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Ingår i: Canadian Journal of Zoology. - 0008-4301 .- 1480-3283. - 0008-4301 ; 85:5, s. 589-595
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Putting density dependence in perspective : nest density, nesting phenology, and biome, all matter to survival of simulated mallard Anas platyrhynchos nests
- 2009
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Ingår i: Journal of Avian Biology. - 0908-8857 .- 1600-048X. - 0908-8857 ; 40:3, s. 317-326
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Tidskriftsartikel (refereegranskat)abstract
- Breeding success in ground-nesting birds is primarily determined by nest survival, which may be density-dependent, but the generality of this pattern remains untested. In a replicated crossover experiment conducted on 30 wetlands, survival of simulated mallard nests was related to "biome" (n=14 mediterranean and 16 boreal wetlands), breeding "phenology" (early vs late nests), and "density" (2 vs 8 nests per 225 m shoreline). Local abundances of "waterfowl", "other waterbirds", and "avian predators" were used as covariates. We used an information-theoretic approach and Program MARK to select among competing models. Nest survival was lower in late nests compared with early ones, and it was lower in the mediterranean than in the boreal study region. High-density treatment nests suffered higher depredation rates than low-density nests during days 1-4 of each experimental period. Nest survival was negatively associated with local abundance of "waterfowl" in the boreal but not in the mediterranean biome. Effect estimates from the highest-ranked model showed that nest "density" (d 1-4) had the strongest impact on model fit; i.e. three times that of "biome" and 1.5 times that of "phenology". The latter's effect, in turn, was twice that of "biome". We argue that our study supports the idea that density-dependent nest predation may be temporally and spatially widespread in waterfowl. We also see an urgent need for research of how waterfowl nesting phenology is matched to that of prey and vegetation.
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| 5. |
- Gunnarsson, Gunnar, 1976-, et al.
(författare)
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Density-dependent nest predation : an experiment with simulated Mallard nests in contrasting landscapes
- 2008
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Ingår i: Ibis. - 0019-1019 .- 1474-919X. ; 150:2, s. 259-269
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
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| 7. |
- Gunnarsson, Gunnar, 1976-, et al.
(författare)
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Survival estimates, mortality patterns, and population growth of Fennoscandian mallards Anas platyrhynchos
- 2008
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Ingår i: Annales Zoologici Fennici. - 0003-455X .- 1797-2450. ; 45:6, s. 483-495
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Gunnarsson, Gunnar, 1976-, et al.
(författare)
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Why are there so many empty lakes? : food limits survival of mallard ducklings
- 2004
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Ingår i: Canadian Journal of Zoology. - 0008-4301 .- 1480-3283. ; 82:11, s. 1698-1703
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Gunnarsson, Gunnar, 1976-, et al.
(författare)
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Änderna, influensan och jakten
- 2010
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Ingår i: Svensk jakt: Svenska jägareförbundets tidskrift. - 0039-6583. ; :6, s. 74-75
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 10. |
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