Enormous Concentration of Martins (Progne spp.) in Iquitos, Peru

Martins (Progne spp.) are known for their tendency to flock in enormous concentrations, a phenomenon that is well documented for the Purple Martin (P.subis; Allen and Nice 1952), and the Brown-chested Martin (I' .tnpera; Meyer de Schauensee and Phelps 1978).I give here the first such report for wintering Southern Martins (I' .modesta), which have recently begun to roost in a concentration of up to 250,060 individuals in the Peruvian Amazon town of Iquitos.This flock includes Purple Martins, constituting approximately 5% of the total.This is the first record of the Purple Martin in Peru.During a visit (13-16 September 1978), I collected seven specimens (deposited at the Museu Goeldi in Be&m, Brazil) and investigated the history of both species in the Iquitos region.The birds roost in the Plaza de Armas, an isolated patch of grass and eugenia trees (Eugenia malaccensis, Myrtaceae) at one edge of the commercial district of the city, one block from the Rio Amazonas.Other species of swallows frequently choose small woods near water for roosting (Skutch 1960), and this site agrees with the usual preferred roosts of the family.The larger Plaza 28 de Julio, approximately 2 km from the Plaza de Armas, and 1 km from the river, is ignored by the birds.The daily arrival of the birds in the evening is spectacular.The following is taken from my field notebook: 14 September 1978 "17:35 Approximately 500 martins catching insects in the air between the plaza and the middle of the river.Another 109 roosting on the facade of a six-story building at the northeastern side of the plaza.This report was made possible through the cooperation