During April, May and June, half a million brown-chested martins (Progne tapera fusca) flock from southern Argentina to the city of Guayana on the banks of the lower Orinoco River in northeastern Venezuela, where they set up their “headquarters” in 18 ceiba trees in the downtown square known as Plaza de las Ciencias. "It still hasn’t been determined why these birds choose to spend the summer in this city 5,000 kilometers from their home, or what exact route they follow,” Josefa León, an environmental sciences specialist at the National Experimental University of Guayana, told Tierramérica.

"Hundreds of fork-tailed flycatchers (Tyrannus sabana) do the same, and we are developing programs for observation, tagging and monitoring,” she added.

Neighboring residents and business owners complain about the smell and dust created by the bird droppings and feathers, while local secondary school students have recommended that the authorities collect the guano for use as fertilizer.