Behavioral effects of progesterone on pair bonding and partner preference in the female zebra finch (Taeniopygia guttata)

Progesterone is a sex steroid known to be involved in reproduction, but its role in pair relationships is not well understood. This study explored the effects of exogenous progesterone (P4) on courtship and pairing behaviors in female zebra finches (Taeniopygia guttata) in two separate experiments: the first focused on courtship and initial pair formation and the second examined the effects on pair maintenance. In these experiments, we tested the hypothesis that P4 increases pairing behaviors and consequently influences their partner preference. In Experiment 1, animals engaged in significantly more pairing behaviors when they were treated with P4 than when they received the vehicle. However, this effect was not partner-specific, since the association index (a marker for female partner preference) did not differ between treatment conditions. In Experiment 2, females were given two weeks to form a pair and then injected with P4 or vehicle. Pairs were observed that day and the subsequent day to determine if P4 caused a decrease in mate-directed behavior and an increase in extra pair behavior. P4 did not affect the quality of the pair relationship and did not increase extra pair behavior. These results suggest that P4 influences the overall quantity of initial pairing behaviors and may slightly increase the likelihood of partner preference formation over short time courses. However, P4 does not alter a previously established bond, suggesting there are likely separate mechanisms for initial pairing behaviors and pair maintenance.