Researchers often use nasal saddles or discs to identify individuals in studies of waterfowl ecology, but previous studies showed that these markers may have detrimental effects on reproductive behavior and success of Ruddy Ducks (Oxyura jamaicensis). To our knowledge, a non-intrusive, external marker that is easy to observe does not exist for breeding Ruddy Ducks. We evaluated effects of a modified nasal marker on behavior of female Ruddy Ducks during pre-laying, laying, and brood rearing. There was no evidence that nasal markers had an adverse influence on nesting patterns of pre-laying and laying females. During brood rearing, however, nasal-marked individuals spent more time scratching their bills and less time alert than unmarked controls. Although bill scratching was more frequent, nasal markers did not appear to influence overall reproductive behavior during nesting and or brood rearing, but we do not know whether reduced vigilance behavior affected survival of young during brood rearing. This nasal marker is a relatively non-intrusive and visible alternative for studying the short-term reproductive ecology of female Ruddy Ducks and possibly other Oxyurinae or anatids not commonly studied because of unique nasal morphologies (i.e., partially divided nasal septa and small nasal openings) which make them difficult to mark. Additionally, this marker may have application for species wintering in colder regions where nasal markers are at risk of icing. Nevertheless, we strongly suggest that researchers evaluate possible effects of these markers as part and parcel of future studies.