Vocal output predicts territory quality in a Neotropical songbird

• Females may choose highly ornamented males to access territorial resources.
• Resources may result in improved offspring survival.
• We tested the relation between ornaments and resources in a tropical passerine.
• We found a positive relation between song output and seed density.
• Static ornaments (i.e., plumage attributes) were not indicative of seed density.

Females who choose highly ornamented mates may gain resources that improve offspring production and survival. Studies have focused on the relationship between male quality and the complexity of sexual ornaments; however, less is known of the communicative content of courtship displays, and whether they indicate the quality of resources males can provide to mates. Here, we used blue-black grassquits (Volatinia jacarina) to test the relationship between male display attributes and territory quality, measured as food availability. Our main hypothesis was that territory quality would be better predicted by dynamic displays than by static ornaments. During four breeding seasons in central Brazil, we quantified display song attributes (output and consistency) and the timing of nuptial molt. We measured territorial seed density, body condition, and ectoparasite infestation. We found a positive relationship between song output and territory seed density, suggesting this attribute provides a reliable indicator of territory quality. However, the timing of molt was unrelated to territory quality. Additionally, no other male attribute was associated with seed density. The link between song output and territory quality might reflect variation in male condition in response to territorial resources, or extra time males on higher quality territories have to invest in territorial defense.This article is part of a Special Issue entitled: Neotropical Behaviour.