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It's summer time and the social life of fish takes Jens Krause to waters old and new, where he never tires of work in the natural lab.

The summer is for me - as it is for most academics, I guess - a time to return to research questions and for my annual trip to Trinidad where much of the fieldwork of my research group takes place.

We are interested in the evolution of social behaviour, and study animal social networks that have evolved under different ecological constraints. Trinidad has become internationally established as a good place for such evolutionary studies over the past 50 or so years because it has a river system in which different fish populations have undergone short-term and long-term adaptations to a variety of ecological conditions - a natural laboratory so to speak.

Trinidad also offers some wonderful opportunities for other activities and I usually try to stay around for a few days to see other parts of the island that are not directly related to my research. The summer is a fantastic time to see the leatherback turtles laying eggs on the beaches and there are some deep caves with literally millions of bats and colonies of oil birds (a species capable of determining the position of objects by measuring the time taken for an echo to return from them). Some old papers and local folklore also mentioned a mysterious "luminous" lizard. When we finally caught one, it turned out to have some beautiful bright spots but, as we expected, no bioluminescence.

My other trip this summer took me to Alaska because of a conference in Anchorage on fish behaviour and evolution. The timing (mid to late July) turned out to be perfect to see grizzly bears fishing for salmon at some of the local rivers and lakes. To fly by floatplane to one of these isolated locations where the bears are found in large numbers is an adventure in itself, and to live with my students in tents more or less among the bears for a few days was a really spectacular experience and a great opportunity to take pictures that might be useful for my animal behaviour lectures at Leeds University. One of the most entertaining sights was to visit a place close to Anchorage where a particularly rich salmon run temporarily brought bears and local anglers into such close contact that they were almost elbow-to-elbow, fishing for the same prey but with different methods. It seemed that both bears and humans were so entirely focused on the short-term exploitation of this particular resource that they hardly noticed one another.

Jens Krause is professor of behavioural ecology in the ecology and evolution research group at the Institute of Integrative and Comparative Biology, Leeds University.

Next week: Dinah Crystal