Experimental evidence for density-dependent survival in mallard (Anas platyrhynchos) ducklings

Abstract

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.

Born to cope with climate change? Experimentally manipulated hatching time does not affect duckling survival in the mallard Anas platyrhynchos

“…For overall breeding success, though, it is final duckling production that is the most relevant aspect to study in a 'mismatch' context as driven by climate change, since, e.g. weather and food conditions are crucial for the survival of young ducklings in particular (Cox et al 1998;Gunnarsson et al 2004Gunnarsson et al , 2006Koskimies and Lahti 1964;Nummi et al 2000;Sjöberg et al 2000; see also further discussion below).…”

“…Previous experimental studies involving pairs, hens and broods show that it is suited for manipulation, in captivity as well as under field conditions (e.g. Cunningham and Russell 2000;Elmberg et al 2005a;Gunnarsson et al 2006;Pöysä et al 1998;Rhymer 1988;Sjöberg et al 2000). In addition, the relationship between hatching date and survival in mallard ducklings has been addressed in numerous descriptive studies, and the results are contradicting (see Table 1).…”

Presence of fish affects lake use and breeding success in ducks

“…This pattern makes it difficult to evaluate the relative importance of competition versus predation for fish-bird interactions. We do indeed know that pike predation on waterfowl occurs in our study system (Gunnarsson et al, 2006), but its significance in terms of fitness consequences in relation to other factors remains to be established (cf. Lagler, 1956).…”

First videotaped infanticide in the common pochard Aythya ferina

“…Considering that density of common pochard was not high at least in comparison with other reports from the observed area (A. Trnka, unpublished data), the space limit seems not to be the main driver of the infanticide. One alternative explanation, that is not mutually exclusive with the resource competition hypothesis, can be that lower number of ducklings on the pond decreases vulnerability of predation (Gunnarsson et al 2006). This means that the benefit from infanticide would be a lower rate of attraction of predators like marsh harrier Circus aeruginosus (L., 1758), herons, weasels and others.…”