RESUMO: A migração é um evento observado em vários animais, como as aves limícolas que se deslocam entre os hemisférios norte e sul, durante os intervalos de reprodução e invernada. Adaptações morfofisiológicas são necessárias para permitir a manutenção dos ciclos migratórios e, portanto, estudos com esse enfoque podem ajudar a esclarecer aspectos biológicos relacionados à migração. Analisamos a variação morfológica nos músculos peitorais e mucosa intestinal de Calidris pusilla, durante diferentes fases do período de invernada no litoral brasileiro. Fragmentos de músculos peitorais e duodenais foram coletados, fixados e processados para histologia de acordo com o procedimento padrão, a partir de espécimes capturados na localidade da costa brasileira. O dinamismo estrutural registrado caracteriza o crescimento da musculatura de vôo e as alterações intestinais relacionadas à nutrição. As mudanças nos parâmetros medidos entre as três fases do inverno, chegada ao Brasil (outubro, meio período), janeiro e saída para o Hemisfério Norte. Tais mudanças ocorrem temporariamente devido às atividades de preparação e migração entre os hemisférios norte e sul.

ABSTRACT: Migration is an event observed in several animals, such as shorebirds moving between the northern and southern hemispheres, during breeding and wintering intervals. Morphophysiological adaptations are necessary to allow the maintenance of migratory cycles and, therefore, studies with this focus can help clarify biological aspects related to migration. We analyzed the morphology variation in pectoral muscles and intestinal mucosa of Calidris pusilla, during different phases of the wintering period on the coast of Brazil. Fragments of pectoral muscles and duodenal were collected, fixed and processed for histology according to standard procedure, from specimens captured in a locality on the Brazilian coast. Modifications were found in the measured parameters among the three phases of wintering, arrival in Brazil (October, mid-period), January and departure to the Northern Hemisphere - May. The registered structural dynamism characterizes the growth of flight musculature and intestinal changes related to nutrition. Such changes occur temporarily due to the activities of preparation and migration between the northern and southern hemispheres.

Every year, Brazil receives large flocks of nearly 40 migratory shorebirds species. The accumulation of body fat and nutrients during the summer is necessary for the long return flights of these birds and is fundamental for feather moulting and the change of their plumage. We present here an examination of the relationship between body mass and plumage change in Arenaria interpres (Linnaeus, 1758), one of those birds, over time during its wintering period on the Brazilian coast. We analyzed information collected at five traditional stopover sites along the Brazilian coast, between 1997 and 2007. During the month of September, individuals with intermediate or breeding plumage had smaller body masses as compared to other months. From October to December, adult individuals were only observed with eclipse plumage and had average body masses of approximately 100 g. In March, individuals with intermediate, eclipse and breeding plumages were recorded, but their average body mass remained at approximately 100 g. In April and May the numbers of individuals with breeding or intermediate plumage increased, and they showed significant increases in body mass at a rate of approximately 1.5 and 2.3 g per day, in the north-northeastern and south coast, respectively, leading to an average mass of 124 and 143g in these months. That is suggested to be the departure mass of A. interpres in the Brazilian north-northeastern and south coast, respectively, when starting the migration to the breeding sites.