Dominance Relations, Resource Use, and Pairing Chronology of Gadwalls in Winter

Abstract I studied pairing chronology and agonistic displays of Gadwalls (Anas strepera) and spatial associations among Gadwalls and other Anatinae in the coastal marshes of southwestern Louisiana from October 1977 through April 1978. Gadwalls began arriving in Louisiana in late September, but by mid-October 45% of females were paired and by late November 81% were paired. The percentage of paired females increased slowly to 90% in April. Bill threats were the predominant agonistic display of Gadwalls, accounting for 89% of all observations, while chasing (5.8%) and biting (5.2%) accounted for the remainder. Nearly all (91.1%) conflicts involved birds that had been feeding before the dispute. On average, Gadwalls spent 0.4% of their time in agonistic activities. Gadwalls preferred to associate with individuals of similar pair status. Paired Gadwalls were more likely to threaten other paired birds, and unpaired Gadwalls other unpaired birds, than they would individuals of the other pair status. Only 14% of disputes involving Gadwalls were with other Anatinae. Pairs were considered dominant over unpaired birds, as pairs won 81% (P < 0.001) of contests with unpaired birds. This study suggested that paired birds, because of their dominance, probably had greater access to preferred food resources and were more successful in meeting nutrient requirements than were unpaired birds. It also suggested that pairing chronology in Anatinae may be related to food choice and foraging strategies, those species feeding on poorer-quality foods forming pairs earlier, as individuals attempt to optimize their allocation of time for feeding and other activities.