Curious Naturalists

Tinbergen argues that the study of animal behavior is best pursued through patient, ingenious field observation and simple experiments conducted in the animals' own environments, rather than in laboratories. The book defends field natural history as a rigorous scientific method, not an antiquated hobby. Tinbergen describes his own research and that of collaborators over twenty-five years, from digger wasps' homing behavior to butterfly courtship and gull social systems, showing how homemade models and careful observation can uncover the sign stimuli and adaptive logic governing behavior. He explicitly addresses the skepticism of laboratory-minded colleagues, insisting that the field provides opportunities for controlled experimentation that no artificial setting can replicate.

The book covers a wide range of field studies. The opening chapters describe Tinbergen's early work on the digger wasp Philanthus, showing how the wasp locates its burrow using landmarks and how it recognizes prey. Later chapters detail the remarkable memory of sand wasps, the biological value of camouflage and warning coloration in caterpillars, the courtship of the Grayling butterfly, and a voyage to Greenland to study snow buntings and phalaropes. Tinbergen also recounts his collaborative work on gull reproductive behavior and the ontogeny of behavior in hobbies. Each study illustrates his core method: observe carefully, form a hypothesis about the sign stimulus or function involved, and test it with simple field experiments.

Reviews were overwhelmingly positive. The journal Nature described it as “cleverly written” and praised its “superb photographs and quaint line-drawings,” predicting it “should be much read” . British Birds called it “one of the best possible advertisements for the general interest and scientific value of natural history,” noting that Tinbergen's book would “secure many valuable recruits to its pursuit” . The reviewer particularly appreciated how Tinbergen made complex ethological concepts—sign stimuli, supernormal stimuli, and the evolution of display—accessible without sacrificing scientific rigor. Some reviewers noted that the book omitted Tinbergen's important laboratory work on stickleback reproductive behavior, but this was seen as a minor limitation in an otherwise exemplary work of popular science.

Curious Naturalists shows Tinbergen's distinct methodological style within the collaboration. While Lorenz supplied much of the theoretical apparatus—innate releasing mechanisms, fixed action patterns—Tinbergen contributed the experimental rigor that tested these concepts in the field. British Birds noted that Lorenz and Tinbergen together “initiated comparative ethology as a new branch of biological science” by showing how displays originated from intention movements and became genetically ritualized . However, the book also reveals Tinbergen's growing interest in questions of function and survival value, concerns that would later crystallize into his four-questions framework. Unlike Lorenz, who tended to defend innate mechanisms against evidence of learning, Tinbergen's field experiments frequently revealed the flexibility and environmental sensitivity of behavior.

Tinbergen repeatedly defends the pursuit of “useless” knowledge against the practical skepticism of laypeople and the suspicion of laboratory scientists. He argues that field natural history is not a lesser form of science but a method that can answer questions inaccessible to laboratory work. His experiments with dummy eggs, models of sticklebacks, and artificial landmarks demonstrate that field conditions permit controlled manipulation of variables. He also addresses the misconception that naturalists merely watch animals without systematic inquiry, showing through detailed examples how observation generates testable hypotheses. As he wrote, curiosity about nature is not a trivial pursuit but what “he got his brains for” .

The book prefigures the framework Tinbergen formalized in his 1963 paper “On aims and methods of ethology,” where he identified four major problems: causation, survival value, evolution, and ontogeny . In Curious Naturalists, Tinbergen addresses all four questions through concrete examples. The digger wasp studies focus on causation (what stimuli elicit homing behavior?), the camouflage work on survival value (how does coloration affect predation?), the comparative gull studies on evolution (how do displays differ across related species?), and the hobby observations on ontogeny (how does hunting behavior develop?). The book thus serves as an accessible demonstration of the integrated approach Tinbergen later prescribed for ethology as a whole.