Scratching under positive and negative arousal in common marmosets (Callithrix jacchus)

Area of Science:

• Primate behavior
• Animal welfare science
• Ethology

Background:

• Scratching is often used as an indicator of anxiety in primates.
• Previous research has primarily focused on negative arousal, with some studies showing no change in scratching.
• Anxiety and excitement share physiological and behavioral similarities, yet positive arousal's effect on scratching is understudied.

Purpose of the Study:

• To investigate the relationship between scratching behavior and both negative and positive arousal in common marmosets.
• To challenge the assumption that scratching is a reliable indicator of anxiety in captive primates.

Main Methods:

• Observed scratching instances in 11 captive common marmosets (Callithrix jacchus).
• Exposed marmosets to three negatively arousing and three positively arousing contexts.
• Scored scratching rates during baseline, manipulation, and post-induction periods for each context.

Main Results:

• Scratching rates significantly decreased during negative arousal contexts compared to baseline and post-induction periods.
• Positive arousal contexts showed varied scratching patterns: play increased scratching, foraging decreased it, and food anticipation had no effect.
• Findings contradict the simple anxiety-scratching link and highlight context-dependent variations.

Conclusions:

• The relationship between scratching and arousal (both negative and positive) in common marmosets is complex and not a straightforward indicator of anxiety.
• The uncritical use of scratching as a measure of anxiety in captive primates may be problematic.
• Results have implications for assessing and managing the welfare of captive non-human primates.