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Abstract

The Ideal Free Distribution was developed to predict the distribution of organisms at a habitat level. The theory of the Ideal Free Distribution assumes that travel between resource sites has a negligible affect on the distribution of organisms. In this experiment we tested whether the Ideal Free Distribution, and in particular its prediction of habitat matching, is robust to violations of this assumption. In an experiment with free-living ducks we manipulated the distance between two food sites. We used two conditions, one with 16 m between the two food sites and another with 45 m between the resource sites. We found that the distribution of organisms became less extreme with increased travel distance. This result is probably due to two effects: that travel distance caused a decrease in the ducks' ability to discriminate between the sites' profitabilities and by a decrease in the number of ducks travelling between the resource sites with increased distance. The decreased number of ducks travelling alone can explain only a relatively small amount of the change in the distribution. The decrease in discriminability may be due to either (or both) the increased distance causing a decrease in the foragers' ability to visually judge the relative profitabilities of the sites or by a decrease in switching rate associated with travel distance (if physical sampling of a site is needed to gather information). Because even a minor change in travel distance can cause a significant change in the distribution of foraging organisms, caution is urged about making extrapolations from experiments at a small spatial scale to the habitat level.

In: Behaviour
In: Evolution, Cognition, and the History of Religion: A New Synthesis

New Caledonian crows have demonstrated flexible behaviour when using tools and solving novel problems. However, we do not know whether this flexibility extends to tool manufacture. Here, we show that these crows respond to different tool-using problems by altering the length of the tools that they manufacture; on average, crows made shorter tools for tasks requiring short tools and longer tools for tasks requiring long tools. They continued to do so when they could not simultaneously see the tool-manufacturing material and the apparatus requiring the use of a tool. Despite altering the length of their tools, the crows frequently did not make tools short or long enough to reliably extract the bait, though this may have been due to shortcomings in the task presented to them. Our results demonstrate that these crows have a degree of behavioural flexibility when making tools, which may be used in the wild during foraging.

In: Behaviour

New Caledonian crows craft wooden hook tools and incorporate naturally occurring barbs into the leaf tools that they manufacture. This raises the question as to whether, or to what degree, these birds are sensitive to the hooks on their hooked and barbed tools. Past research in this area has provided equivocal results. We tested whether New Caledonian crows attend to the presence and orientation of barbs on pandanus leaves and tools during tool manufacture and selection tasks. Our results show that New Caledonian crows attend to barb presence during both pandanus tool manufacture and use, but do not attend to barb direction during pandanus tool use. We conclude that task context, the time and energetic costs of attending to barbs, relative foraging efficiency, and different experimental designs may influence whether, and to what degree, NC crows attend to pandanus barbs.

In: Behaviour