We review existing data on the distribution of the Least Tern, Sternula antillarum along the Brazilian coast, based on the literature and museum specimens, and present results of a year-long study (October 2008 to September 2009) on the seasonal abundance of this species on a large tidal flat area, Cajuais Bank, in the State of Ceará, north-eastern Brazil. We evaluate whether the observed variation in the abundance of terns is due to the occurrence of an undocumented breeding colony, or alternatively, whether it results from an influx of migrants from the Northern Hemisphere. The recovery of historical data revealed that all literature references on the distribution of birds in the Americas, published up to the late 1990s include Brazil in the non-breeding range of the Least Tern. This inclusion is based on a few, old (late 19th and early 20th centuries) museum specimens, all of which have been collected on the northern and north-eastern coasts of this country'. From the late 1980s, birds continued to be occasionally recorded along the coastline, running from the State of Amapá (01°N) up to the State of Bahia (10°S), with records of single individuals in south-eastern and southern Brazil. An alleged record from Rocas Atoll, 260 km off the Brazilian mainland, might tentatively refer to the Old World Little Tern S. albifrons. At Cajuais Bank, Least Terns occurred from October 2008 to April 2009, and in September 2009. The highest numbers (> 800 individuals) were recorded in January-February (Southern Hemisphere's summer). The species was observed in rather small numbers (< 30) in March-April (early-mid Southern Hemisphere fall) and in September (early Southern Hemisphere spring), being absent from the area in May-August (Southern Hemisphere's fall and winter). In October-December 2008 (Southern Hemisphere's spring), and September 2009 (early Southern Hemisphere's summer), no birds were in breeding plumage. In January, about 32% of the birds were in breeding plumage, while from February-April (Southern Hemisphere's summer to mid fall) all were in breeding plumage. This pattern is consistent with what would be expected for migratory birds. The Cajuais Bank itself (and adjacent beaches and inland environments) holds the largest numbers of Least Terns recorded in Brazil, thus being one of the most significant sites along the migratory route of the species.

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.

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.