Unusual northern cardinal nest: Cooperative breeding or nest sharing?

Abstract

On 1 July 2008, I found a Northern Cardinal (Cardinalis cardinalis) nest in a residential neighborhood of Stillwater, Payen County, Oklahoma, that was used by 2 adult females and 2 adult males. During the period of observation, females incubated individually and often while the other female roosted on the rim of the nest cup. Males were observed feeding the females and hatchlings. No intra- or intersexual agnostic behavior was noted among the adult cardinals. The nest was lost to a predator on 11 July 2008. Evidence suggests this was a case of shared nesting rather than cooperative breeding.