BEHAVIORAL BUILDING BLOCKS: THE HORMONAL MECHANISMS BEHIND COOPERATION, PARENTAL CARE, AND PAIR BONDS IN BIRDS

Abstract

Complex social behaviors have evolved multiple times independently across the vertebrates. An integrative approach to understanding how behavior evolves requires studying the underlying mechanisms. Across many species, cooperative breeding, parental care, and pair bonds share similar affiliative behaviors and likely share hormonal mechanisms but has yet to be determined in many species. I set out to study the proximate mechanisms of cooperative breeding, parental care, and pair bonding in three bird species, the cooperatively breeding Mexican jay (Aphelocoma wollweberi), the pair breeding Woodhouse’s scrub jay (A. woodhouseii) and the pair breeding zebra finch (Taeniopygia guttata). To determine if corticosterone concentrations correlate with cooperative breeding, I measured corticosterone in wild Mexican jays and Woodhouse’s scrub jay across the breeding season. Corticosterone concentrations did not differ between Mexican jay helpers and breeders and were also not correlated with age and sex. Corticosterone did significantly increase with body mass in Mexican jays but there was no sex by body mass interaction. Corticosterone levels also did not differ between Mexican jays and Woodhouse’s scrub jay. However, for both species, corticosterone significantly declined throughout the breeding season, with highest levels occurring in March and lowest levels during May and June. I also measured the effects of experience and nonapeptides on both parental behaviors and pair maintenance behaviors by injecting a short-acting oxytocin receptor antagonist (OTA) or a saline control into breeding pairs of inexperienced or experienced zebra finches and experienced pair bonded zebra finches. For both the parental care and pair study, birds were injected over multiple days and then video taped to measure the effects of the injections on specific behaviors. For the parental care study, I also measured daily chick mass and chick mortality. I found that neither OTA nor parental experience affected time spent in the nest or nest maintenance. However, experience and OTA did affect time spent nest guarding, with inexperienced birds receiving the antagonist performing more nest guarding than inexperienced control and experienced antagonist birds. I also found that OTA significantly negatively affect chick growth rates and OTA and experience increased chick mortality, with experienced antagonist and inexperienced control birds having higher mortality than experienced control birds. For the pair maintenance study, I found the OTA reduced follow bouts in both sexes, allopreening in females, and song in males. The OTA did not affect clumping or pecking for either sex. Overall, this research sheds light on a the regulation and evolution of a number of complex social behaviors in birds.