Through the eyes of a woodpecker: Understanding habitat selection, territory quality and reproductive decisions from individual behaviour

In this thesis I present some connections between foraging behaviour and reproductive success, time budget, tree species use, and habitat selection. The thesis is based upon both theoretical and empirical work. All empirical studies concern a south Swedish population of lesser spotted woodpeckers Dendrocopos minor, studied between 1990 and 1996.

The foraging behaviour of the lesser spotted woodpeckers was in agreement with a Bayesian patch leaving model. This was shown by a positive correlation between the giving-up density, GUD, and patch residence time, PRT, in natural patches exploited by the woodpeckers. Theoretical analyses furthermore revealed that the relationships between fitness, average GUD, and average PRT, should indicate which type of ecological factor was responsible for the differences in fitness and behaviour between individuals. Empirical data suggested that differences in food availability, mainly in terms of prey density in dead wood prior to breeding, was the factor most strongly influencing the date of egg-laying, and thereby reproductive success. Birds with high average GUD, i.e. high food availability, also spent less time foraging actively, probably in order to lower the predation risk. Most of the time thus relieved was spent either excavating nests, or perching. Such alternative activities was mainly engaged in mornings, when average GUD was higher than in afternoons.

The foraging preferences for the four most used tree species were positively related to the prey density available in the species, both between and within years. Foraging preferences, therefore, may serve as an indication to patch type value which may vary in both space and time. The preferences for two of the most used tree species were furthermore related to subsequent reproductive success. The preference for a common, but unprofitable tree species, was lower in the mornings, implying that both energy gain and predation risk change over the day. Lastly, the annual tree species preferences in an area could be predicted using a small set of variables. These predicted preferences could be used to predict habitat use within the territory. Thus, food availability determines reproduction, time budget and habitat use across several spatial scales.

There may be more information at the conservation ecology home page