Mallard (Anas platyrhynchos) summer diet in Central Portugal rice fields

Rice fields are preferred feeding areas of mallard, Anas platyrhynchos, in Central Portugal. Rice consumption by mallards prior to crop harvest causes conflicts between farmers and waterfowl managers. We analysed the food habits of mallards collected in rice-fields and quantified the impact that mallards had on rice production. Oesophagi, including proventriculi (n=52), were obtained from hunter-shot mallards, from 15 August to late September 1993-1995, on a 600-ha farm included in the main feeding area of the lower Mondego population. Point counts were performed to estimate the numbers of mallards using the area. The diet included rice seeds (51.2% dry matter), weed seeds of rice fields (23.6% dry matter), and animal matter (25.1% dry matter). By means of the diet composition, we calculated that each mallard needed to ingest 93.4 g (dry matter) of food daily, including 47.8 g ogf rice, to meet its energy requirements. The estimated mallarg population using the area was 1600 ducks. They consumed approximately 0.2% of the 4,000 kg/ha minimum rice production. Therefore the decrease in rice production caused by mallargd was insignificant, which suggests that the existence of mallards on rice fields is compatible with rice productio