First record of Grey Gull Leucophaeus modestus in Brazil

We report the first record of Grey Gull (Leucophaeus modestus) in Brazil. On 21 April 2019 at 08:31 h, the secondcycle bird was photographed walking near a small stream that flows into the sea on Ilha Comprida, state of São Paulo, southeastern coast of Brazil. The occurrence of a single individual on the Atlantic coast of the South American continent lead us to propose that the species is a vagrant in Brazil.

on 21 April 2019 at 08:31 h. It was observed walking on the beach at the northern portion of Ilha Comprida (24 o 42'27.8''S; 47 o 28'16.8''W), on the southern coast of the state of São Paulo, southeastern Brazil (Fig. 1). Faced with the researchers' approach, the bird had difficulties to fly, trying to run away. The bird was detected during three other consecutive days, moving to the south (5 km away from the first location).
This is a second-cycle bird, since it was gray with brownish shades (Figs. 2A & B), differing from adults with grayish plumage, whose head is whitish during the reproductive period (Harrison 1983). Another characteristic that proves this bird to be second-cycle is the end of the secondary feathers presenting a white band (Harrison 1983). Other diagnostic characteristics contributed to the species identification, such as the beak, feet, tarsus and black end of wings contrasting with gray plumage, as well as the previously mentioned white band at the end of the secondary feathers, which is absent in young birds (Harrison 1983, Erize et al. 2006Fig. 2C).
The occurrence of Grey Gull in the Brazilian coast can be interpreted as an occasional event, due to the absence of previous records and the fact that the species is typical of the western part of the continent, occurring mainly in Chile, Peru and Ecuador (BirdLife International 2019). The bird observed probably hit the Atlantic coastline in one of two main ways: moving inland though the continent, or bordering the coast.
The first hypothesis is supported by the fact that the species reproduces in desert areas in the interior of Chile  to do this, the bird would cross the Andes. Goodall & Johnsons (1945) report Grey Gull nesting in altitudes of up to 2335 m and the recent record for Argentina in Salta also supports that the bird can fly up to 4300 m (Carillo 2015). This suggests that the species could fly in high altitudes and consequently surpass the mountain range in its lowest sectors.
The second possible route would be flying along the coast from the south. This is also supported by literature, since Carrillo (2015) cites two records of the species on the Falkland Islands. Thus, the individual may have crossed from the Pacific to the Atlantic Ocean in the southernmost portion of the continent through Argentina and then moved up along the coast to São Paulo.
We report a relevant record for Brazilian avifauna, since the occurrence of Grey Gull draws attention to the fact that the species has moved quite a lot from where it naturally occurs. Vagrancy in birds is commonly explained by the presence of species in population expansion (Veit 2000, Lees & Gilroy 2009), pursuit of resources (Berthold 1993, Lees & Gilroy 2009 and disorientation caused by natural or anthropogenic events (Patten & Marantz 1996, Gilroy & Lees 2003, Pfeifer et al. 2007. With regard to the climatic interference in the life cycle of Grey Gull, Aguilar et al. (2016) cites that the reproductive season of 2014-2015 was influenced by the climatic phenomenon El Niño, which caused a reduction in the availability of resources and led the species to reproduce in areas closer to the coast. Thus, in the present case, we can speculate that its occurrence in southeastern Brazil may have been influenced by some climatic weather that could have disoriented the bird, which could explain the fact that it took the bird some time to fly away after the approach of the team. Another possibility is simply that the bird dispersed from its original area of occurrence searching for food. Thus, both cases reinforce the fact that the species is considered vagrant.