Do social factors explain seasonal variation in dawn song characteristics of paired male Cerulean Warblers (Setophaga cerulea)?

Territorial male birds of many north temperate species sing prolifically before sunrise in a behaviour known as ‘dawn song,’ after which males sing at lower rates, use different song types, or cease singing altogether. From May to July 2017 in southern Indiana, we recorded 100 dawn song performances from 12 paired male Cerulean Warblers (Setophaga cerulea) and we quantified the relative influences of social (breeding stage of the focal pair) and abiotic factors (Julian date and weather) on six characteristics of dawn song. We found that dawn song was influenced by both biotic and abiotic factors, but weather had the most model support. Males were more likely to sing dawn song early in the season, and most males nesting late in the season ceased dawn song altogether. Dawn song start times (in relation to sunrise) varied little over the season, but males ended dawn song earlier, and sang at lower peak rates, as the season progressed. Additionally, males initiated and ended dawn song later on windy and rainy mornings. Multiple factors apparently influence dawn singing behaviour in paired male Cerulean Warblers, yet weather may have a greater effect on dawn song than do Julian date or social behaviour.