Abstract

Ducks breeding in Fennoscandia represent a large part of the total population in Europe, and variations in reproductive success can affect continental population trajectories. It is therefore essential to understand processes affecting breeding success. In this thesis I have looked at temporal and spatial food abundance patterns and how these influence breeding ducks. Egg laying and hatching are often assumed to coincide with peaks in available food. No such peak in food abundance was evident in a boreal catchment based on six years of data. Even without clear food abundance peaks, changes in spring arrival can still lead to suboptimal breeding. I have investigated the importance of spring arrival and its effect on spring phenology and breeding success in two dabbling ducks (teal and mallard). Both species can change breeding time in response to variations in spring arrival; however, early springs have a negative effect on teal. Total food abundance is also important, and fish are known to reduce invertebrates, thus potentially affecting survival of ducklings. In a descriptive study I was able to illustrate that fish reduce the availability of invertebrate prey. Fish also reduce the number of breeding ducks, which is probably a result of competition although pike predation on ducklings can also be of importance. To investigate the effects of pike predation, I introduced adult pike to two lakes that were previously fishless. The number of pairs that settled was not affected by pike, but the subsequent breeding success was reduced significantly. The negative impact of pike on breeding ducks is likely to favour adaptations of anti-predator behaviour. In experimental trials, naïve ducklings recognised and responded to calls from predatory birds. They did not, however, avoid pike, although they displayed a very strong response to simulated pike attacks. They ran on the water, scattered and reassemble far from the initial attack. The lack of identification appears to be compensated by the ability to respond instantly to threat and thus reduce losses.