Body mass and acquisition of breeding plumage of wintering Calidris pusilla (Linnaeus) (Aves, Scolopacidae) in the coast of Pernambuco, north-eastern Brazil

Annually, large flocks of semipalmated sandpiper Calidris pusilla (Linnaeus, 1766) winter along South America coast, between September-April. They store fats in order to moult and return to their breeding grounds. Here, was examined body masses and plumage of adults Semipalmated Sandpipers during the departure month to evaluate the relationship between body mass and plumage. Fieldwork was conducted at Coroa do Avião (7º40'S, 34º50'W), Pernambuco. Birds were trapped in mist-nets between April 1990 and 1997. They were weighed, and aged according to plumage. Adult plumage may be (1) non-breeding, (2) pre-breeding, and (3) breeding. A total of 213 birds were weighed and examined, so that 8.0% (17) presented non-breeding plumage, 54.0% (115) pre-breeding, and 38.0% (81) breeding plumage. As in Semipalmated Sandpiper, 25g is the minimum body mass required to migrate, birds with breeding plumage and most with pre-breeding, were potentially apt to migrate. Non-breeding plumage birds presented smaller body mass. Apparently physiological problems and infestation may be important factors to explain over-summering, i.e., individuals remaining in the wintering grounds during the boreal summer.Anualmente grandes bandos de Calidris pusilla (Linnaeus, 1766) invernam ao longo da costa da América do Sul, entre setembro e abril. Estas aves acumulam gordura para realizar mudas e retornar aos seus locais de reprodução. Neste estudo foram examinadas a massa corpórea e a plumagem de C. pusilla adultos durante o mês de retorno aos sítios reprodutivos, de forma a avaliar sua relação. A amostragem foi conduzida na Coroa do Avião (7º40'S, 34º50'W), Pernambuco. As aves foram capturadas com redes de neblina entre abril de 1990 e 1997. Os adultos e os jovens foram diferenciados através da análise de plumagem. A plumagem dos adultos foi classificada em: (1) não-reprodutiva, (2) pré-reprodutiva e (3) reprodutiva. Um total de 213 aves foi examinado e sua massa corpórea mensurada. Destas, 8.0% (17) apresentaram plumagem não-reprodutiva, 54.0% (115) pré-reprodutiva e 38.0% (81) reprodutiva. Sendo 25 g a massa corpórea mínima necessária para a migração em C. pusilla, as aves em plumagem reprodutiva e a maior parte daquelas com plumagem pré-reprodutiva estavam potencialmente aptas a migrar. As aves em plumagem não-reprodutiva apresentaram as menores massas corpóreas. Aparentemente, problemas fisiológicos e parasitários podem ser importantes fatores para explicar a permanência de adultos nos locais de invernada durante o verão boreal

Temporal variations of body mass and plumage in Arenaria interpres (Aves: Scolopacidae) along the Brazilian coast

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