The temporal dependence of exploration on neotic style in birds

Exploration (interacting with objects to gain information) and neophobia (avoiding novelty) are considered independent traits shaped by the socio-ecology of a given species. However, in the literature it is often assumed that neophobia inhibits exploration. Here, we investigate how different approaches to novelty (fast or slow) determine the time at which exploration is likely to occur across a number of species. We presented four corvid and five parrot species with a touchscreen discrimination task in which novel stimuli were occasionally interspersed within the familiar training stimuli. We investigated the likelihood that an animal would choose novelty at different stages of its training and found evidence for a shift in the pattern of exploration, depending on neotic style. The findings suggest that faster approaching individuals explored earlier, whilst animals with long initial approach latencies showed similar amounts of exploration but did so later in training. Age rather than species might have influenced the amount of total exploration, with juveniles exploring more than adults. Neotic style varied consistently only for one species and seems to involve a strong individual component, rather than being a purely species-specific trait. This suggests that variation in behavioural phenotypes within a species may be adaptive.

. Boxplots of corrected novelty responses for all species; bold horizontal lines indicate median values, boxes span the first to third quartiles and whiskers represent 95% confidence intervals; horizontal lines indicate age group comparisons; Significance codes: '***' for p < 0.001, '**' for p < 0.01, '*' for p < 0.05, 't' for p < 0.1 (alpha adjusted for multiple comparisons; see Table S1 for detailed test statistics). Table S1. Multiple comparisons of means for novelty responses, corrected for association strength in each session, of all species. P values are adjusted for multiple comparisons.

Stimulus Generation
For this study a total of 48 stimuli were generated and divided into 12 simple habituation stimuli, 18 straight line stimuli, 18 curved stimuli (see Fig. S6 for examples). For the discrimination task each individual was randomly assigned a specific baseline pair of a positive (rewarded) and negative (non rewarded) stimulus. The baseline pairs contained one straight lined and one curved stimulus.
Additionally, for each positive Stimulus 16 similar stimuli were created (differing slightly in colour and shape from the original positive stimulus). The colours of the stimuli were assigned randomly from a scale, differing in their RGB-scale by 20 steps from one colour to the next, but not in brightness. First the positive stimulus was randomly assigned to a colour, saving five colours above and below on the scale for the similar stimuli. Then the negative stimulus was assigned the most distant colour from the positive stimulus colour, excluding the six colours above and below the negative one. The remaining colours were then randomly assigned to the remaining stimuli.

Pre-training
In order to pre-train the animals to use the touchscreen computer they were presented with a simple geometric figure (circle, triangle, square or star) that was centred on the screen. Individuals were shaped to reliably touched the stimulus and received the reward by moving the mouse cursor around the stimulus or in case of limited approach the screen was introduced in a group setting.
After this initial phase and once the stimulus was touched reliably by the animals, the stimulus was then presented in a random position. This phase consisted of two sessions with 35 trials each. Intertrial-intervals (ITI) were set to one second, during this time the screen was blank.

Discrimination training
In this phase, each individual was given one additional stimulus, which was not rewarded when responded to. Additionally, a correction inter-trial-interval (CITI) of 1.3 seconds was introduced. The two stimuli were presented next to each other, with the rewarded stimulus (S 0 +) displayed randomly on either the right or left side on a horizontal axis on the screen. The height of the stimuli was adapted for each species to ensure the stimuli would appear at head height. If the subjects pecked the unrewarded stimulus (S 0 -) the birds received a correction trial (CT), which was repeated until the S 0 + was selected. Pecking a stimulus resulted in differential acoustic feedback being played (depending on the stimulus that was being pecked).
Discrimination training consisted of two sessions with 16 trials each. The computer program recorded the retention latency (latency from onset of the trial until a peck occurred), correct first choices and number of correction trials, as well as pecks on the screen in other locations than where the stimuli were. Figure S6. Examples of generated stimuli used throughout the task. Habituation stimuli were used during habituating birds to the setup, Discrimination pair exemplifies stimuli used for the main discrimination task, Novelty stimuli were used during novelty test trials with the rewarded stimulus remaining the same as in the basic discrimination task (identical) or being slightly altered in colour and shape (similar); S+ indicates the rewarded stimuli, S-lists the unrewarded stimuli. Figure S7. The relationship of novelty responses in 'Identical' and 'Similar' trials; blue line indicates assumed linear fit; grey area denotes 95% confidence interval.