Estudo da distribuição da população de Calidris canutus rufa (Aves: Scolopacidae) no Parque Nacional da Lagoa do Peixe, Rio Grande do Sul

Abstract

The Red Knot Calidris canutus rufa is one of the species of shorebirds that partakes in huge migration journeys. They breed in the Nearctic and migrate to southern locations including Tierra del Fuego in southern South America to spend boreal winter. Over the last years there has been a severe decline in C. c. rufa population due to over-harvesting of their preys and degradation of their habitats. During migration, these birds use several stopover sites to refuel and replenish their energies. One of the main stopover sites in South America is the Lagoa do Peixe National Park, located in the southern state of Brazil, Rio Grande do Sul. Very little is known about the distribution and behavior of this species in the Park. In this study we elaborated a census of C. c. rufa in the Lagoa do Peixe National Park from October 2013 to August 2014, and evaluated foraging and roosting behavior in relation to flock size patterns. Results showed about 200 individuals on October 2013 and very few numbers on November and December 2013 and January and February 2014. April was the peak month with around 550 individuals and about 200 birds were seen during the months of May, June and July. The flocks located in the beach were significant smaller than flocks located on the lagoon, and flocks with roosting behavior were significant larger than flocks with foraging behavior. The beach was mainly used for foraging while in the lagoon both behaviors were common. Birds were found to use the beach in small flocks to forage, probably to increase foraging efficiency, while they organized to roost on the lagoon in larger flocks for what we assumed to decrease the risk of predation. There has been a decrease in numbers of C. c. rufa when comparing with previous studies in this location and this can be attributed to the world decline of the Red Knot population and several threats the birds encounter in their habitats. Also, the census showed an increased number in the over-summering Red Knots in Lagoa do Peixe National Park, which could be related to sexually immature birds, parasitism, illness or birds that were unable to obtain enough weight to migrate.