Diurnal parental care in the sexually dichromatic Chestnut-backed Sparrow-Lark Eremopterix leucotis (Alaudidae)

Abstract

Parental investment strategies are often predicted by sexual dimorphism, with dichromatic species expected to exhibit skewed parental roles due to sexual selection and extra-pair paternity. We investigated the division of diurnal labour (i.e. incubation, brooding, provisioning) in the sexually dichromatic Chestnut-backed Sparrow- Lark Eremopterix leucotis within the phase-specific framework of Wang et al. (2023). We used video to monitor 51 nests in a semi-arid South African savanna, and quantified nest attendance and provisioning dynamics from incubation to the late nestling stage. Our results reveal an exceptionally high degree of biparental coordination during incubation, with males and females each providing ∼44% of diurnal attendance. This egalitarian sharing of duties in a dichromatic species challenges traditional Parental Investment Theory, which typically predicts reduced male care in dimorphic systems. As the nesting cycle progressed, nest attendance declined to 14.0%, while food provisioning rates tripled. This transition was defined by a rapid ‘granivore shift’, as the proportion of invertebrates in the diet dropped from 45.6% at hatching to just 12.5% by the late nestling stage. Crucially, as high-protein items became less frequent, males emerged as ‘dietary specialists’, providing significantly more medium and large invertebrates than females. To underscore the significance of these findings, we compared the species’ strategy with published information on parental care in the monomorphic biparental breeder, the Pink-billed Lark Spizocorys conirostris at the same site. We argue that dichromatism is not inherently associated with paternal investment, but that risk mitigation and dietary transitions are more closely correlated with avian parental strategies than sexual dimorphism alone.