Secondary sexual characters may provide information about individual quality to a partner, which may use it during parental care to strategically allocate resources to the current breeding attempt (Differential Allocation Hypothesis). Differential allocation by females has been demonstrated for a number of species, while male differential allocation based on female secondary sexual traits has received less attention. Yet females of many species, among birds in particular, are ornamented. We performed a test of male differential allocation based on a female ornament in the rock sparrow (Petronia petronia), a monomorphic species in which both sexes have a yellow breast patch, the size of which correlates with individual reproductive quality. We reduced the breast patch in a sample of females and compared the parental care of their partners (chick feeding and nest defence) with the parental care of males paired to sham-manipulated controls. Nest defence was assessed by placing a dummy predator on the nest box. Males of ornament-reduced females defended the nest less but did not feed the chicks less than males paired to control females. Our results only partially support male differential allocation and are in agreement with previous tests of male differential allocation in rock sparrows.