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Methods

Diagram showing test setup. First cohort tested at age 2 weeks with judgement bias test and at age 8 weeks with eyespot test. Second cohort tested with both tests first at age 2 weeks, then at age 4 weeks

Red junglefowl (Gallus gallus) chicks from two cohorts were tested with both judgement bias test and eyespot test in two versions differing in the number of test cues: original and simplified version. The first cohort was tested once with both the judgement bias test and eyespot test, while this procedure was repeated twice for the second cohort.

Training cues for judgement bias test are white and black squares. Test cues are light grey, middle grey and dark grey. Control cue for the eyespot test is a squared background pattern. Eyespot cues consist in dots in the center of the background pattern
Eyespot cues 1 and 2 are putatively ambiguous eyespot cues (mildly aversive) and eyespot cues 3 and 4 are putatively full eyespot cues (aversive). The cues used in the simplified version of the two tests were the ones causing responses that correlated with each other in the original version: the ambiguous middle grey cue and the eyespot cue 3.

Judgement bias test

After training chicks to discriminate a positive and a negative cue, the latency to approach ambiguous cues was measured and compared to responses to learnt cues. A response closer to responses to the positive cue was assumed to indicate a better state.

Rectangular arena with a food bowl and a cue on one side, and the starting position of the chick on the opposite side

Eyespot test

In the eyespot test, after chicks learnt to associate a position (control cue) with a reward, the latency to approach and distance from an eyespot cue in the same position were measured and compared to responses to the control cue. A response closer to responses to control cue putatively indicated a better state.

The arena used in the original version (left) differed from the arena used in the simplified version (right)

On the left, an arena with a division barrier in the middle for testing two birds simultaneously. The eyespot cue is on one end of the arena, and the starting position on the opposite side. On the right, an arena with the same setup, but with no barrier.

Data analyses

  • I controlled for differences in locomotory activity in all tests for all measurements.
  • I ran Spearman rank correlations to compare measurements from the judgement bias test and the eyespot test.
  • I pooled data if Spearman’s Rho > +0.3 or < -0.3 in just one sex or treatment.
  • I controlled for effects of learning that the ambiguous cue was unrewarded due to repeated exposures in the judgement bias test (loss of ambiguity).
  • I detected outliers using boxplots.


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Last updated: 05/15/21