Geographic and Ecological Invasion of the Cattle Egret (Bubulcus I. Ibis) In The Americas and Its Current Seasonal Patterns

Abstract The Cattle Egret (Bubulcus ibis) is a native species of the tropical and subtropical regions of Africa, Asia, and the Iberian Peninsula. This species is mainly sedentary but includes migratory populations and inhabits diverse vegetation types including perturbed areas, which probably has facilitated its dispersion. In this study, we describe the geographic patterns during its invasion process in the Americas, characterize the environmental conditions that could favor this process and identify the areas of migration in North America. We obtained the occurrence records in chronological order from its arrival to the Americas to the present, and we made a climatic profile of the occurrence records. Then, we identified and characterized seasonally the environments associated with America's migration areas using temperature and precipitation variables. Starting in 1937 from Guiana, the species colonized the continent via three fronts: 1) through the Antilles until it reached Florida (United States); 2) towards South America until Patagonia; and 3) through Central America to Mexico, the central and western United States (US), and southern Canada. Since its arrival, the species continuously colonized America's new geographic and climatic conditions. However, in the 1970s, it seems to have reached its environmental limits in the northern extreme of its distribution (southern Canada and the US), where the minimum temperatures in winter (-25°C) apparently determine their physiological tolerance limits. Therefore, migrate from those regions to the south to search for more favorable climatic conditions. Currently, the Cattle Egret ranges from southern Canada to Patagonia (Argentina).