Wednesday, February 6, 2013

Niko Tinbergen revisited

posted by Machteld

Niko Tinbergen is arguably the most famous Dutch biologist, having won a Nobel prize for his work on Animal Behaviour. As a Dutch student of animal behaviour, I have 'grown up' with his work, and  his work was taught even in my secondary school biology classes.  

He became a professor of biology at Leiden university after WWII, although he left for Oxford not long afterwards. By that point, he had already done some of his most famous work, including the study on instinct in herring gull chick, a study that he would write about quite a few times during his career, and is now a text book example of how certain stimuli can elicit 'instinctive behaviour' (as it was called at the time), and how some exaggerated stimuli elicit greater response than the natural stimuli do, a phenomenon well known as supernormal stimuli. Thus, this study has become very iconic in the field of behavioural biology.

Last week we discussed some occasions when iconic studies in biology were repeated, sometimes finding that the results are similar, but sometimes not. What does this mean for a particular field, when concepts have been built off of the results of such studies? 
This made me think of two papers that my PhD advisor, Carel ten Cate, wrote about the herring gull chick study of Tinbergen. Apparently, when Tinbergen left Leiden, he left behind some of his old field notes and material, including the original data sheets and the models he used in his experiments. I am not sure how they ended up in the hands of Carel, since the building we worked in was not build until after Tinbergen left Leiden, but I suspect that, thrifty as the university is/was, one particular piece of furniture, a set of drawers that was in Niko's office, was passed used in the then new building, and ended up in Carel's. But maybe I remember this wrong. In any case, Carel was of course very interested in these ‘artifacts’. After a while though, he started to investigate some of these findings more closely, and discovered some discrepancies between the original data sheets and the data that Tinbergen published.
Carel thought about what to do with this knowledge for a while, but over time, he decided it was important to publish this. He also started to incorporate some of these findings in his lectures. One year, some of his course students suggested that why not repeat the experiments with the original materials, and test if the ideas proposed by Tinbergen were true, even if the original data did not convincingly show this?
This resulted in two papers, which I suggest we read for next weeks’ lab meeting. The abstracts and links to the full papers you can find below. I think these two papers will supply us with some food for thought about scientific traditions, scientific conduct and the repeatability of experiments. In addition, I will also supply us with some actual food, for fika. 

Niko Tinbergen and the red patch on the herring gull's beak

One of the classic studies in animal behaviour is that by Niko Tinbergen on the stimuli that elicit begging behaviour in young herring gull, Larus argentatus, chicks. Tinbergen examined which features of the beak induced chicks to peck by using various cardboard models of herring gull heads in different shapes and colours. Leiden University, home university to Tinbergen at the time, still has a summarizing overview of the data of the initial experiment of the study. In that experiment, models with a yellow beak with patches in various colours and different positions were presented to young chicks. In this essay, I relate those earliest data to the various publications in which Tinbergen discussed them over the years. Subsequent publications became more and more detached from the original data, resulting in sizeable discrepancies between the original study and later descriptions of when and how the experiment was done and its outcome. I first sketch the scientific context of the herring gull study. Next I present the original data and document the subsequent changes. I discuss what might have led Tinbergen to modify his account of the study over the years, relating it both to its historical context and to the issue of ‘expectancy biases’.

Tinbergen revisited: a replication and extension of experiments on the beak colour preferences of herring gull chicks

Animal Behaviour Volume 77, Issue 4, April 2009, Pages 795–802

Young herring gull, Larus argentatus, chicks peck at the red patch on the lower mandible of their parent's yellow beak. In a famous study on the ‘instinctive behaviour’ of herring gull chicks, Tinbergen examined whether the presence, colour and position of the patch affected the pecking of the chicks. While this experiment is often cited as demonstrating a preference for a red patch, the original data showed that chicks pecked more at a black-patched model (Tinbergen 1948, De Levende Natuur51, 49–56). Tinbergen later ascribed this unexpected outcome to a methodological error in his experiment: the red-patched model was presented more frequently than all the others, which made him adjust his data later on. We repeated Tinbergen's experiment (experiment 1), using replicas of the original models. We also did the experiment as Tinbergen described it later on (but which he never carried out), presenting all models equally often (experiment 2). Our results confirm that red is not the most preferred colour when it is presented more often than other colours. In experiment 2 the relative ranking of all models was the same as in experiment 1, with the exception of the red-patched one, which was now preferred most, as expected by Tinbergen. Our findings also confirm that the more frequent exposure to the red model in experiment 1 resulted in a disproportionate decline in interest for this model. So, although he never did the actual experiment, Tinbergen's intuition and corrected data show a reasonable match to the results of our experiment.

No comments:

Post a Comment